1
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Akther S, Mongodin EF, Morgan RD, Di L, Yang X, Golovchenko M, Rudenko N, Margos G, Hepner S, Fingerle V, Kawabata H, Norte AC, de Carvalho IL, Núncio MS, Marques A, Schutzer SE, Fraser CM, Luft BJ, Casjens SR, Qiu W. Natural selection and recombination at host-interacting lipoprotein loci drive genome diversification of Lyme disease and related bacteria. mBio 2024:e0174924. [PMID: 39145656 DOI: 10.1128/mbio.01749-24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2024] [Accepted: 06/28/2024] [Indexed: 08/16/2024] Open
Abstract
Lyme disease, caused by spirochetes in the Borrelia burgdorferi sensu lato clade within the Borrelia genus, is transmitted by Ixodes ticks and is currently the most prevalent and rapidly expanding tick-borne disease in Europe and North America. We report complete genome sequences of 47 isolates that encompass all established species in this clade while highlighting the diversity of the widespread human pathogenic species B. burgdorferi. A similar set of plasmids has been maintained throughout Borrelia divergence, indicating that they are a key adaptive feature of this genus. Phylogenetic reconstruction of all sequenced Borrelia genomes revealed the original divergence of Eurasian and North American lineages and subsequent dispersals that introduced B. garinii, B. bavariensis, B. lusitaniae, B. valaisiana, and B. afzelii from East Asia to Europe and B. burgdorferi and B. finlandensis from North America to Europe. Molecular phylogenies of the universally present core replicons (chromosome and cp26 and lp54 plasmids) are highly consistent, revealing a strong clonal structure. Nonetheless, numerous inconsistencies between the genome and gene phylogenies indicate species dispersal, genetic exchanges, and rapid sequence evolution at plasmid-borne loci, including key host-interacting lipoprotein genes. While localized recombination occurs uniformly on the main chromosome at a rate comparable to mutation, lipoprotein-encoding loci are recombination hotspots on the plasmids, suggesting adaptive maintenance of recombinant alleles at loci directly interacting with the host. We conclude that within- and between-species recombination facilitates adaptive sequence evolution of host-interacting lipoprotein loci and contributes to human virulence despite a genome-wide clonal structure of its natural populations. IMPORTANCE Lyme disease (also called Lyme borreliosis in Europe), a condition caused by spirochete bacteria of the genus Borrelia, transmitted by hard-bodied Ixodes ticks, is currently the most prevalent and rapidly expanding tick-borne disease in the United States and Europe. Borrelia interspecies and intraspecies genome comparisons of Lyme disease-related bacteria are essential to reconstruct their evolutionary origins, track epidemiological spread, identify molecular mechanisms of human pathogenicity, and design molecular and ecological approaches to disease prevention, diagnosis, and treatment. These Lyme disease-associated bacteria harbor complex genomes that encode many genes that do not have homologs in other organisms and are distributed across multiple linear and circular plasmids. The functional significance of most of the plasmid-borne genes and the multipartite genome organization itself remains unknown. Here we sequenced, assembled, and analyzed whole genomes of 47 Borrelia isolates from around the world, including multiple isolates of the human pathogenic species. Our analysis elucidates the evolutionary origins, historical migration, and sources of genomic variability of these clinically important pathogens. We have developed web-based software tools (BorreliaBase.org) to facilitate dissemination and continued comparative analysis of Borrelia genomes to identify determinants of human pathogenicity.
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Affiliation(s)
- Saymon Akther
- Graduate Center and Hunter College, City University of New York, New York, New York, USA
| | | | | | - Lia Di
- Graduate Center and Hunter College, City University of New York, New York, New York, USA
| | - Xiaohua Yang
- Department of Medicine, Renaissance School of Medicine, Stony Brook University (SUNY), Stony Brook, New York, USA
| | - Maryna Golovchenko
- Biology Centre Czech Academy of Sciences, Institute of Parasitology, České Budějovice, Czech Republic
| | - Natalie Rudenko
- Biology Centre Czech Academy of Sciences, Institute of Parasitology, České Budějovice, Czech Republic
| | - Gabriele Margos
- Bavarian Health and Food Safety Authority and German National Reference Centre for Borrelia, Oberschleissheim, Bavaria, Germany
| | - Sabrina Hepner
- Bavarian Health and Food Safety Authority and German National Reference Centre for Borrelia, Oberschleissheim, Bavaria, Germany
| | - Volker Fingerle
- Bavarian Health and Food Safety Authority and German National Reference Centre for Borrelia, Oberschleissheim, Bavaria, Germany
| | | | - Ana Cláudia Norte
- Department of Life Sciences, University of Coimbra, MARE-Marine and Environmental Sciences Centre, Coimbra, Portugal
| | | | - Maria Sofia Núncio
- Centre for Vector and Infectious Diseases Research, Águas de Moura, Portugal
| | - Adriana Marques
- National Institute of Allergy and Infectious Diseases, Bethesda, Maryland, USA
| | | | - Claire M Fraser
- University of Maryland School of Medicine, Baltimore, Maryland, USA
| | - Benjamin J Luft
- Department of Medicine, Renaissance School of Medicine, Stony Brook University (SUNY), Stony Brook, New York, USA
| | - Sherwood R Casjens
- University of Utah School of Medicine and School of Biological Sciences, Salt Lake City, Utah, USA
| | - Weigang Qiu
- Graduate Center and Hunter College, City University of New York, New York, New York, USA
- Weill Cornell Medical College, New York, New York, USA
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2
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Anderson MD, Taylor DL, Olson K, Ruess RW. Composition of soil Frankia assemblages across ecological drivers parallels that of nodule assemblages in Alnus incana ssp. tenuifolia in interior Alaska. Ecol Evol 2024; 14:e11458. [PMID: 38979008 PMCID: PMC11229434 DOI: 10.1002/ece3.11458] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2023] [Revised: 04/26/2024] [Accepted: 05/07/2024] [Indexed: 07/10/2024] Open
Abstract
In root nodule symbioses (RNS) between nitrogen (N)-fixing bacteria and plants, bacterial symbionts cycle between nodule-inhabiting and soil-inhabiting niches that exert differential selection pressures on bacterial traits. Little is known about how the resulting evolutionary tension between host plants and symbiotic bacteria structures naturally occurring bacterial assemblages in soils. We used DNA cloning to examine soil-dwelling assemblages of the actinorhizal symbiont Frankia in sites with long-term stable assemblages in Alnus incana ssp. tenuifolia nodules. We compared: (1) phylogenetic diversity of Frankia in soil versus nodules, (2) change in Frankia assemblages in soil versus nodules in response to environmental variation: both across succession, and in response to long-term fertilization with N and phosphorus, and (3) soil assemblages in the presence and absence of host plants. Phylogenetic diversity was much greater in soil-dwelling than nodule-dwelling assemblages and fell into two large clades not previously observed. The presence of host plants was associated with enhanced representation of genotypes specific to A. tenuifolia, and decreased representation of genotypes specific to a second Alnus species. The relative proportion of symbiotic sequence groups across a primary chronosequence was similar in both soil and nodule assemblages. Contrary to expectations, both N and P enhanced symbiotic genotypes relative to non-symbiotic ones. Our results provide a rare set of field observations against which predictions from theoretical and experimental work in the evolutionary ecology of RNS can be compared.
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Affiliation(s)
- M. D. Anderson
- Biology DepartmentMacalester CollegeSaint PaulMinnesotaUSA
- Institute of Arctic BiologyUniversity of AlaskaFairbanksAlaskaUSA
| | - D. L. Taylor
- Department of BiologyUniversity of New MexicoAlbuquerqueNew MexicoUSA
| | - K. Olson
- Institute of Arctic BiologyUniversity of AlaskaFairbanksAlaskaUSA
| | - R. W. Ruess
- Institute of Arctic BiologyUniversity of AlaskaFairbanksAlaskaUSA
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3
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Curry KD, Yu FB, Vance SE, Segarra S, Bhaya D, Chikhi R, Rocha EPC, Treangen TJ. Reference-free structural variant detection in microbiomes via long-read co-assembly graphs. Bioinformatics 2024; 40:i58-i67. [PMID: 38940156 PMCID: PMC11211843 DOI: 10.1093/bioinformatics/btae224] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/29/2024] Open
Abstract
MOTIVATION The study of bacterial genome dynamics is vital for understanding the mechanisms underlying microbial adaptation, growth, and their impact on host phenotype. Structural variants (SVs), genomic alterations of 50 base pairs or more, play a pivotal role in driving evolutionary processes and maintaining genomic heterogeneity within bacterial populations. While SV detection in isolate genomes is relatively straightforward, metagenomes present broader challenges due to the absence of clear reference genomes and the presence of mixed strains. In response, our proposed method rhea, forgoes reference genomes and metagenome-assembled genomes (MAGs) by encompassing all metagenomic samples in a series (time or other metric) into a single co-assembly graph. The log fold change in graph coverage between successive samples is then calculated to call SVs that are thriving or declining. RESULTS We show rhea to outperform existing methods for SV and horizontal gene transfer (HGT) detection in two simulated mock metagenomes, particularly as the simulated reads diverge from reference genomes and an increase in strain diversity is incorporated. We additionally demonstrate use cases for rhea on series metagenomic data of environmental and fermented food microbiomes to detect specific sequence alterations between successive time and temperature samples, suggesting host advantage. Our approach leverages previous work in assembly graph structural and coverage patterns to provide versatility in studying SVs across diverse and poorly characterized microbial communities for more comprehensive insights into microbial gene flux. AVAILABILITY AND IMPLEMENTATION rhea is open source and available at: https://github.com/treangenlab/rhea.
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Affiliation(s)
- Kristen D Curry
- Department of Computer Science, Rice University, 6100 Main St., Houston, TX 77005, United States
- Department of Genomes and Genetics, Microbial Evolutionary Genomics, Institut Pasteur, Université Paris Cité, CNRS, UMR3525, Paris 75015, France
| | | | - Summer E Vance
- Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA 94720, United States
| | - Santiago Segarra
- Department of Electrical and Computer Engineering, Rice University, Houston, TX 77005, United States
| | - Devaki Bhaya
- Carnegie Institution for Science, Department of Plant Biology, Stanford, CA 94305, United States
| | - Rayan Chikhi
- Department of Computational Biology, Institut Pasteur, Université Paris Cité, Paris 75015, France
| | - Eduardo P C Rocha
- Department of Genomes and Genetics, Microbial Evolutionary Genomics, Institut Pasteur, Université Paris Cité, CNRS, UMR3525, Paris 75015, France
| | - Todd J Treangen
- Department of Computer Science, Rice University, 6100 Main St., Houston, TX 77005, United States
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4
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Mallawaarachchi S, Tonkin-Hill G, Pöntinen A, Calland J, Gladstone R, Arredondo-Alonso S, MacAlasdair N, Thorpe H, Top J, Sheppard S, Balding D, Croucher N, Corander J. Detecting co-selection through excess linkage disequilibrium in bacterial genomes. NAR Genom Bioinform 2024; 6:lqae061. [PMID: 38846349 PMCID: PMC11155488 DOI: 10.1093/nargab/lqae061] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2024] [Revised: 04/15/2024] [Accepted: 05/14/2024] [Indexed: 06/09/2024] Open
Abstract
Population genomics has revolutionized our ability to study bacterial evolution by enabling data-driven discovery of the genetic architecture of trait variation. Genome-wide association studies (GWAS) have more recently become accompanied by genome-wide epistasis and co-selection (GWES) analysis, which offers a phenotype-free approach to generating hypotheses about selective processes that simultaneously impact multiple loci across the genome. However, existing GWES methods only consider associations between distant pairs of loci within the genome due to the strong impact of linkage-disequilibrium (LD) over short distances. Based on the general functional organisation of genomes it is nevertheless expected that majority of co-selection and epistasis will act within relatively short genomic proximity, on co-variation occurring within genes and their promoter regions, and within operons. Here, we introduce LDWeaver, which enables an exhaustive GWES across both short- and long-range LD, to disentangle likely neutral co-variation from selection. We demonstrate the ability of LDWeaver to efficiently generate hypotheses about co-selection using large genomic surveys of multiple major human bacterial pathogen species and validate several findings using functional annotation and phenotypic measurements. Our approach will facilitate the study of bacterial evolution in the light of rapidly expanding population genomic data.
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Affiliation(s)
| | | | - Anna K Pöntinen
- Department of Biostatistics, University of Oslo, Oslo, Norway
- Norwegian National Advisory Unit on Detection of Antimicrobial Resistance, Department of Microbiology and Infection Control, University Hospital of North Norway, Tromsø, Norway
| | - Jessica K Calland
- Oslo Centre for Biostatistics and Epidemiology, Oslo University Hospital, Oslo, Norway
| | | | | | | | - Harry A Thorpe
- Department of Biostatistics, University of Oslo, Oslo, Norway
| | - Janetta Top
- Department of Medical Microbiology, UMC Utrecht, Utrecht, The Netherlands
| | - Samuel K Sheppard
- Ineos Oxford Institute of Antimicrobial Research, Department of Biology, University of Oxford, Oxford, United Kingdom
| | - David Balding
- Melbourne Integrative Genomics, School of BioSciences and School of Mathematics & Statistics, University of Melbourne, Parkville, Victoria, Australia
| | - Nicholas J Croucher
- Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, United Kingdom
- MRC Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, United Kingdom
| | - Jukka Corander
- Department of Biostatistics, University of Oslo, Oslo, Norway
- Parasites and Microbes, Wellcome Sanger Institute, Cambridge, UK
- Helsinki Institute of Information Technology, Department of Mathematics and Statistics, University of Helsinki, Helsinki, Finland
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5
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Torrance EL, Burton C, Diop A, Bobay LM. Evolution of homologous recombination rates across bacteria. Proc Natl Acad Sci U S A 2024; 121:e2316302121. [PMID: 38657048 PMCID: PMC11067023 DOI: 10.1073/pnas.2316302121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2023] [Accepted: 03/08/2024] [Indexed: 04/26/2024] Open
Abstract
Bacteria are nonsexual organisms but are capable of exchanging DNA at diverse degrees through homologous recombination. Intriguingly, the rates of recombination vary immensely across lineages where some species have been described as purely clonal and others as "quasi-sexual." However, estimating recombination rates has proven a difficult endeavor and estimates often vary substantially across studies. It is unclear whether these variations reflect natural variations across populations or are due to differences in methodologies. Consequently, the impact of recombination on bacterial evolution has not been extensively evaluated and the evolution of recombination rate-as a trait-remains to be accurately described. Here, we developed an approach based on Approximate Bayesian Computation that integrates multiple signals of recombination to estimate recombination rates. We inferred the rate of recombination of 162 bacterial species and one archaeon and tested the robustness of our approach. Our results confirm that recombination rates vary drastically across bacteria; however, we found that recombination rate-as a trait-is conserved in several lineages but evolves rapidly in others. Although some traits are thought to be associated with recombination rate (e.g., GC-content), we found no clear association between genomic or phenotypic traits and recombination rate. Overall, our results provide an overview of recombination rate, its evolution, and its impact on bacterial evolution.
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Affiliation(s)
- Ellis L Torrance
- Department of Biology, University of North Carolina, Greensboro, NC 27412
| | - Corey Burton
- Department of Biology, University of North Carolina, Greensboro, NC 27412
| | - Awa Diop
- Department of Biological Sciences, North Carolina State University, Raleigh, NC 27695
| | - Louis-Marie Bobay
- Department of Biology, University of North Carolina, Greensboro, NC 27412
- Department of Biological Sciences, North Carolina State University, Raleigh, NC 27695
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6
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Serra Moncadas L, Hofer C, Bulzu PA, Pernthaler J, Andrei AS. Freshwater genome-reduced bacteria exhibit pervasive episodes of adaptive stasis. Nat Commun 2024; 15:3421. [PMID: 38653968 PMCID: PMC11039613 DOI: 10.1038/s41467-024-47767-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2023] [Accepted: 04/10/2024] [Indexed: 04/25/2024] Open
Abstract
The emergence of bacterial species is rooted in their inherent potential for continuous evolution and adaptation to an ever-changing ecological landscape. The adaptive capacity of most species frequently resides within the repertoire of genes encoding the secreted proteome (SP), as it serves as a primary interface used to regulate survival/reproduction strategies. Here, by applying evolutionary genomics approaches to metagenomics data, we show that abundant freshwater bacteria exhibit biphasic adaptation states linked to the eco-evolutionary processes governing their genome sizes. While species with average to large genomes adhere to the dominant paradigm of evolution through niche adaptation by reducing the evolutionary pressure on their SPs (via the augmentation of functionally redundant genes that buffer mutational fitness loss) and increasing the phylogenetic distance of recombination events, most of the genome-reduced species exhibit a nonconforming state. In contrast, their SPs reflect a combination of low functional redundancy and high selection pressure, resulting in significantly higher levels of conservation and invariance. Our findings indicate that although niche adaptation is the principal mechanism driving speciation, freshwater genome-reduced bacteria often experience extended periods of adaptive stasis. Understanding the adaptive state of microbial species will lead to a better comprehension of their spatiotemporal dynamics, biogeography, and resilience to global change.
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Affiliation(s)
- Lucas Serra Moncadas
- Limnological Station, Department of Plant and Microbial Biology, University of Zurich, Kilchberg, Switzerland
| | - Cyrill Hofer
- Limnological Station, Department of Plant and Microbial Biology, University of Zurich, Kilchberg, Switzerland
| | - Paul-Adrian Bulzu
- Department of Aquatic Microbial Ecology, Institute of Hydrobiology, Biology Centre of the Czech Academy of Sciences, České Budějovice, Czech Republic
| | - Jakob Pernthaler
- Limnological Station, Department of Plant and Microbial Biology, University of Zurich, Kilchberg, Switzerland
| | - Adrian-Stefan Andrei
- Limnological Station, Department of Plant and Microbial Biology, University of Zurich, Kilchberg, Switzerland.
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7
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Garushyants SK, Sane M, Selifanova MV, Agashe D, Bazykin GA, Gelfand MS. Mutational Signatures in Wild Type Escherichia coli Strains Reveal Predominance of DNA Polymerase Errors. Genome Biol Evol 2024; 16:evae035. [PMID: 38401265 PMCID: PMC10995721 DOI: 10.1093/gbe/evae035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2023] [Revised: 02/13/2024] [Accepted: 02/17/2024] [Indexed: 02/26/2024] Open
Abstract
While mutational processes operating in the Escherichia coli genome have been revealed by multiple laboratory experiments, the contribution of these processes to accumulation of bacterial polymorphism and evolution in natural environments is unknown. To address this question, we reconstruct signatures of distinct mutational processes from experimental data on E. coli hypermutators, and ask how these processes contribute to differences between naturally occurring E. coli strains. We show that both mutations accumulated in the course of evolution of wild-type strains in nature and in the lab-grown nonmutator laboratory strains are explained predominantly by the low fidelity of DNA polymerases II and III. By contrast, contributions specific to disruption of DNA repair systems cannot be detected, suggesting that temporary accelerations of mutagenesis associated with such disruptions are unimportant for within-species evolution. These observations demonstrate that accumulation of diversity in bacterial strains in nature is predominantly associated with errors of DNA polymerases.
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Affiliation(s)
- Sofya K Garushyants
- A.A. Kharkevich Institute for Information Transmission Problems, RAS, Moscow, Russia
| | - Mrudula Sane
- National Centre for Biological Sciences, Bengaluru, India
| | - Maria V Selifanova
- Faculty of Bioengineering and Bioinformatics, M.V. Lomonosov Moscow State University, Moscow, Russia
| | - Deepa Agashe
- National Centre for Biological Sciences, Bengaluru, India
| | - Georgii A Bazykin
- A.A. Kharkevich Institute for Information Transmission Problems, RAS, Moscow, Russia
| | - Mikhail S Gelfand
- A.A. Kharkevich Institute for Information Transmission Problems, RAS, Moscow, Russia
- Center for Molecular and Cellular Biology, Skolkovo Institute of Science and Technology (Skoltech), Moscow, Russia
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8
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Douglas GM, Shapiro BJ. Pseudogenes act as a neutral reference for detecting selection in prokaryotic pangenomes. Nat Ecol Evol 2024; 8:304-314. [PMID: 38177690 DOI: 10.1038/s41559-023-02268-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2023] [Accepted: 11/10/2023] [Indexed: 01/06/2024]
Abstract
A long-standing question is to what degree genetic drift and selection drive the divergence in rare accessory gene content between closely related bacteria. Rare genes, including singletons, make up a large proportion of pangenomes (all genes in a set of genomes), but it remains unclear how many such genes are adaptive, deleterious or neutral to their host genome. Estimates of species' effective population sizes (Ne) are positively associated with pangenome size and fluidity, which has independently been interpreted as evidence for both neutral and adaptive pangenome models. We hypothesized that pseudogenes, used as a neutral reference, could be used to distinguish these models. We find that most functional categories are depleted for rare pseudogenes when a genome encodes only a single intact copy of a gene family. In contrast, transposons are enriched in pseudogenes, suggesting they are mostly neutral or deleterious to the host genome. Thus, even if individual rare accessory genes vary in their effects on host fitness, we can confidently reject a model of entirely neutral or deleterious rare genes. We also define the ratio of singleton intact genes to singleton pseudogenes (si/sp) within a pangenome, compare this measure across 668 prokaryotic species and detect a signal consistent with the adaptive value of many rare accessory genes. Taken together, our work demonstrates that comparing with pseudogenes can improve inferences of the evolutionary forces driving pangenome variation.
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Affiliation(s)
- Gavin M Douglas
- Department of Microbiology and Immunology, McGill University, Montréal, Québec, Canada.
- McGill Genome Centre, McGill University, Montréal, Québec, Canada.
| | - B Jesse Shapiro
- Department of Microbiology and Immunology, McGill University, Montréal, Québec, Canada.
- McGill Genome Centre, McGill University, Montréal, Québec, Canada.
- McGill Centre for Microbiome Research, McGill University, Montréal, Québec, Canada.
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9
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Curry KD, Yu FB, Vance SE, Segarra S, Bhaya D, Chikhi R, Rocha EP, Treangen TJ. Reference-free Structural Variant Detection in Microbiomes via Long-read Coassembly Graphs. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.25.577285. [PMID: 38352454 PMCID: PMC10862772 DOI: 10.1101/2024.01.25.577285] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 02/20/2024]
Abstract
Bacterial genome dynamics are vital for understanding the mechanisms underlying microbial adaptation, growth, and their broader impact on host phenotype. Structural variants (SVs), genomic alterations of 10 base pairs or more, play a pivotal role in driving evolutionary processes and maintaining genomic heterogeneity within bacterial populations. While SV detection in isolate genomes is relatively straightforward, metagenomes present broader challenges due to absence of clear reference genomes and presence of mixed strains. In response, our proposed method rhea, forgoes reference genomes and metagenome-assembled genomes (MAGs) by encompassing a single metagenome coassembly graph constructed from all samples in a series. The log fold change in graph coverage between subsequent samples is then calculated to call SVs that are thriving or declining throughout the series. We show rhea to outperform existing methods for SV and horizontal gene transfer (HGT) detection in two simulated mock metagenomes, which is particularly noticeable as the simulated reads diverge from reference genomes and an increase in strain diversity is incorporated. We additionally demonstrate use cases for rhea on series metagenomic data of environmental and fermented food microbiomes to detect specific sequence alterations between subsequent time and temperature samples, suggesting host advantage. Our innovative approach leverages raw read patterns rather than references or MAGs to include all sequencing reads in analysis, and thus provide versatility in studying SVs across diverse and poorly characterized microbial communities for more comprehensive insights into microbial genome dynamics.
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Affiliation(s)
- Kristen D. Curry
- Rice University, Department of Computer Science, Houston, TX 77005, United States
- Institut Pasteur, Université Paris Cité, CNRS, UMR3525, Microbial Evolutionary Genomics, 75015 Paris, France
| | | | - Summer E. Vance
- University of California, Berkeley, Department of Environmental Science, Policy, and Management, Berkeley, CA 94720, United States
| | - Santiago Segarra
- Rice University, Department of Electrical and Computer Engineering, Houston, TX 77005, United States
| | - Devaki Bhaya
- Carnegie Institution for Science, Department of Plant Biology, Stanford, CA 94305, United States
| | - Rayan Chikhi
- Institut Pasteur, Université Paris Cité, Sequence Bioinformatics unit, 75015 Paris, France
| | - Eduardo P.C. Rocha
- Institut Pasteur, Université Paris Cité, CNRS, UMR3525, Microbial Evolutionary Genomics, 75015 Paris, France
| | - Todd J. Treangen
- Rice University, Department of Computer Science, Houston, TX 77005, United States
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10
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Zhu S, Hong J, Wang T. Horizontal gene transfer is predicted to overcome the diversity limit of competing microbial species. Nat Commun 2024; 15:800. [PMID: 38280843 PMCID: PMC10821886 DOI: 10.1038/s41467-024-45154-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2023] [Accepted: 01/17/2024] [Indexed: 01/29/2024] Open
Abstract
Natural microbial ecosystems harbor substantial diversity of competing species. Explaining such diversity is challenging, because in classic theories it is extremely infeasible for a large community of competing species to stably coexist in homogeneous environments. One important aspect mostly overlooked in these theories, however, is that microbes commonly share genetic materials with their neighbors through horizontal gene transfer (HGT), which enables the dynamic change of species growth rates due to the fitness effects of the mobile genetic elements (MGEs). Here, we establish a framework of species competition by accounting for the dynamic gene flow among competing microbes. Combining theoretical derivation and numerical simulations, we show that in many conditions HGT can surprisingly overcome the biodiversity limit predicted by the classic model and allow the coexistence of many competitors, by enabling dynamic neutrality of competing species. In contrast with the static neutrality proposed by previous theories, the diversity maintained by HGT is highly stable against random perturbations of microbial fitness. Our work highlights the importance of considering gene flow when addressing fundamental ecological questions in the world of microbes and has broad implications for the design and engineering of complex microbial consortia.
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Affiliation(s)
- Shiben Zhu
- Key Laboratory of Quantitative Synthetic Biology, Shenzhen Institute of Synthetic Biology, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China
| | - Juken Hong
- Key Laboratory of Quantitative Synthetic Biology, Shenzhen Institute of Synthetic Biology, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China
| | - Teng Wang
- Key Laboratory of Quantitative Synthetic Biology, Shenzhen Institute of Synthetic Biology, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China.
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11
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Garber ME, Frank V, Kazakov AE, Incha MR, Nava AA, Zhang H, Valencia LE, Keasling JD, Rajeev L, Mukhopadhyay A. REC protein family expansion by the emergence of a new signaling pathway. mBio 2023; 14:e0262223. [PMID: 37991384 PMCID: PMC10746176 DOI: 10.1128/mbio.02622-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2023] [Accepted: 10/20/2023] [Indexed: 11/23/2023] Open
Abstract
IMPORTANCE We explore when and why large classes of proteins expand into new sequence space. We used an unsupervised machine learning approach to observe the sequence landscape of REC domains of bacterial response regulator proteins. We find that within-gene recombination can switch effector domains and, consequently, change the regulatory context of the duplicated protein.
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Affiliation(s)
- Megan E. Garber
- Department of Comparative Biochemistry, University of California, Berkeley, California, USA
- Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
| | - Vered Frank
- Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
| | - Alexey E. Kazakov
- Environmental Genomics and Systems Biology Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
| | - Matthew R. Incha
- Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
- Department of Plant and Microbial Biology, University of California, Berkeley, California, USA
| | - Alberto A. Nava
- Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
- Department of Chemical and Biomolecular Engineering, University of California, Berkeley, California, USA
| | - Hanqiao Zhang
- Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
- Department of Bioengineering, University of California, Berkeley, California, USA
| | - Luis E. Valencia
- Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
- Department of Bioengineering, University of California, Berkeley, California, USA
| | - Jay D. Keasling
- Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
- Department of Plant and Microbial Biology, University of California, Berkeley, California, USA
- Department of Chemical and Biomolecular Engineering, University of California, Berkeley, California, USA
- Department of Bioengineering, University of California, Berkeley, California, USA
- Center for Biosustainability, Danish Technical University, Lyngby, Denmark
- Center for Synthetic Biochemistry, Shenzhen Institutes for Advanced Technologies, Shenzhen, China
| | - Lara Rajeev
- Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
| | - Aindrila Mukhopadhyay
- Department of Comparative Biochemistry, University of California, Berkeley, California, USA
- Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
- Environmental Genomics and Systems Biology Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
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12
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Abstract
A massive number of microorganisms, belonging to different species, continuously divide inside the guts of animals and humans. The large size of these communities and their rapid division times imply that we should be able to watch microbial evolution in the gut in real time, in a similar manner to what has been done in vitro. Here, we review recent findings on how natural selection shapes intrahost evolution (also known as within-host evolution), with a focus on the intestines of mice and humans. The microbiota of a healthy host is not as static as initially thought from the information measured at only one genomic marker. Rather, the genomes of each gut-colonizing species can be highly dynamic, and such dynamism seems to be related to the microbiota species diversity. Genetic and bioinformatic tools, and analysis of time series data, allow quantification of the selection strength on emerging mutations and horizontal transfer events in gut ecosystems. The drivers and functional consequences of gut evolution can now begin to be grasped. The rules of this intrahost microbiota evolution, and how they depend on the biology of each species, need to be understood for more effective development of microbiota therapies to help maintain or restore host health.
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Affiliation(s)
| | - Isabel Gordo
- Instituto Gulbenkian de Ciência, Oeiras, Portugal.
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13
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Vigué L, Tenaillon O. Predicting the effect of mutations to investigate recent events of selection across 60,472 Escherichia coli strains. Proc Natl Acad Sci U S A 2023; 120:e2304177120. [PMID: 37487088 PMCID: PMC10401003 DOI: 10.1073/pnas.2304177120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2023] [Accepted: 05/25/2023] [Indexed: 07/26/2023] Open
Abstract
Microbial genomics studies focusing on the dynamics of selection have often used a small number of distant genomes. As a result, they could only analyze mutations that had become fixed during the divergence between species. However, thousands of genomes of some species are now available in public databases, thanks to high-throughput sequencing. These data provide a more complete picture of the polymorphisms segregating within a species, offering a unique insight into the processes that shape the recent evolution of a species. In this study, we present GLASS (Gene-Level Amino-acid Score Shift), a selection test that is based on the predicted effects of amino acid changes. By comparing the distribution of effects of mutations observed in a gene to the expectation in the absence of selection, GLASS can quantify the intensity of selection. We applied GLASS to a dataset of 60,472 Escherichia coli strains and used this to reexamine the longstanding debate about the role of essentiality versus expression level in the rate of protein evolution. We found that selection has contrasting short-term and long-term dynamics, with essential genes being subject to strong purifying selection in the short term, while expression level determines the rate of gene evolution in the long term. GLASS also found an overrepresentation of inactivating mutations in specific transcription factors, such as efflux pump repressors, which is consistent with selection for antibiotic resistance. These gene-inactivating polymorphisms do not reach fixation, suggesting another contrast between short-term fitness gains and long-term counterselection.
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Affiliation(s)
- Lucile Vigué
- Université Paris Cité and Université Sorbonne Paris Nord, Inserm, Infection, Antimicrobials, Modelling, Evolution, F-75018Paris, France
| | - Olivier Tenaillon
- Université Paris Cité and Université Sorbonne Paris Nord, Inserm, Infection, Antimicrobials, Modelling, Evolution, F-75018Paris, France
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14
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Birzu G, Muralidharan HS, Goudeau D, Malmstrom RR, Fisher DS, Bhaya D. Hybridization breaks species barriers in long-term coevolution of a cyanobacterial population. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.06.543983. [PMID: 37333348 PMCID: PMC10274767 DOI: 10.1101/2023.06.06.543983] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/20/2023]
Abstract
Bacterial species often undergo rampant recombination yet maintain cohesive genomic identity. Ecological differences can generate recombination barriers between species and sustain genomic clusters in the short term. But can these forces prevent genomic mixing during long-term coevolution? Cyanobacteria in Yellowstone hot springs comprise several diverse species that have coevolved for hundreds of thousands of years, providing a rare natural experiment. By analyzing more than 300 single-cell genomes, we show that despite each species forming a distinct genomic cluster, much of the diversity within species is the result of hybridization driven by selection, which has mixed their ancestral genotypes. This widespread mixing is contrary to the prevailing view that ecological barriers can maintain cohesive bacterial species and highlights the importance of hybridization as a source of genomic diversity.
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Affiliation(s)
- Gabriel Birzu
- Department of Applied Physics, Stanford University, Stanford, CA 94305, USA
| | | | - Danielle Goudeau
- DOE Joint Genome Institute, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Rex R. Malmstrom
- DOE Joint Genome Institute, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Daniel S. Fisher
- Department of Applied Physics, Stanford University, Stanford, CA 94305, USA
| | - Devaki Bhaya
- Department of Plant Biology, Carnegie Institution for Science, Stanford, CA 94305, USA
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15
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Barona-Gómez F, Chevrette MG, Hoskisson PA. On the evolution of natural product biosynthesis. Adv Microb Physiol 2023; 83:309-349. [PMID: 37507161 DOI: 10.1016/bs.ampbs.2023.05.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/30/2023]
Abstract
Natural products are the raw material for drug discovery programmes. Bioactive natural products are used extensively in medicine and agriculture and have found utility as antibiotics, immunosuppressives, anti-cancer drugs and anthelminthics. Remarkably, the natural role and what mechanisms drive evolution of these molecules is relatively poorly understood. The exponential increase in genome and chemical data in recent years, coupled with technical advances in bioinformatics and genetics have enabled progress to be made in understanding the evolution of biosynthetic gene clusters and the products of their enzymatic machinery. Here we discuss the diversity of natural products, incorporating the mechanisms that govern evolution of metabolic pathways and how this can be applied to biosynthetic gene clusters. We build on the nomenclature of natural products in terms of primary, integrated, secondary and specialised metabolism and place this within an ecology-evolutionary-developmental biology framework. This eco-evo-devo framework we believe will help to clarify the nature and use of the term specialised metabolites in the future.
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Affiliation(s)
| | - Marc G Chevrette
- Department of Microbiology and Cell Sciences, University of Florida, Museum Drive, Gainesville, FL, United States; University of Florida Genetics Institute, University of Florida, Mowry Road, Gainesville, FL, United States
| | - Paul A Hoskisson
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Cathedral Street, Glasgow, United Kingdom.
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16
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Papudeshi B, Rusch DB, VanInsberghe D, Lively CM, Edwards RA, Bashey F. Host Association and Spatial Proximity Shape but Do Not Constrain Population Structure in the Mutualistic Symbiont Xenorhabdus bovienii. mBio 2023:e0043423. [PMID: 37154562 DOI: 10.1128/mbio.00434-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/10/2023] Open
Abstract
To what extent are generalist species cohesive evolutionary units rather than a compilation of recently diverged lineages? We examine this question in the context of host specificity and geographic structure in the insect pathogen and nematode mutualist Xenorhabdus bovienii. This bacterial species partners with multiple nematode species across two clades in the genus Steinernema. We sequenced the genomes of 42 X. bovienii strains isolated from four different nematode species and three field sites within a 240-km2 region and compared them to globally available reference genomes. We hypothesized that X. bovienii would comprise several host-specific lineages, such that bacterial and nematode phylogenies would be largely congruent. Alternatively, we hypothesized that spatial proximity might be a dominant signal, as increasing geographic distance might lower shared selective pressures and opportunities for gene flow. We found partial support for both hypotheses. Isolates clustered largely by nematode host species but did not strictly match the nematode phylogeny, indicating that shifts in symbiont associations across nematode species and clades have occurred. Furthermore, both genetic similarity and gene flow decreased with geographic distance across nematode species, suggesting differentiation and constraints on gene flow across both factors, although no absolute barriers to gene flow were observed across the regional isolates. Several genes associated with biotic interactions were found to be undergoing selective sweeps within this regional population. The interactions included several insect toxins and genes implicated in microbial competition. Thus, gene flow maintains cohesiveness across host associations in this symbiont and may facilitate adaptive responses to a multipartite selective environment. IMPORTANCE Microbial populations and species are notoriously hard to delineate. We used a population genomics approach to examine the population structure and the spatial scale of gene flow in Xenorhabdus bovienii, an intriguing species that is both a specialized mutualistic symbiont of nematodes and a broadly virulent insect pathogen. We found a strong signature of nematode host association, as well as evidence for gene flow connecting isolates associated with different nematode host species and collected from distinct study sites. Furthermore, we saw signatures of selective sweeps for genes involved with nematode host associations, insect pathogenicity, and microbial competition. Thus, X. bovienii exemplifies the growing consensus that recombination not only maintains cohesion but can also allow the spread of niche-beneficial alleles.
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Affiliation(s)
- Bhavya Papudeshi
- Flinders Accelerator for Microbiome Exploration, Flinders University, Adelaide, Australia
- National Centre for Genome Analysis Support, Pervasive Institute of Technology, Indiana University, Bloomington, Indiana, USA
| | - Douglas B Rusch
- Center for Genomics and Bioinformatics, Indiana University, Bloomington, Indiana, USA
| | | | - Curtis M Lively
- Department of Biology, Indiana University, Bloomington, Indiana, USA
| | - Robert A Edwards
- Flinders Accelerator for Microbiome Exploration, Flinders University, Adelaide, Australia
| | - Farrah Bashey
- Department of Biology, Indiana University, Bloomington, Indiana, USA
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17
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Dong X, Peng Y, Wang M, Woods L, Wu W, Wang Y, Xiao X, Li J, Jia K, Greening C, Shao Z, Hubert CRJ. Evolutionary ecology of microbial populations inhabiting deep sea sediments associated with cold seeps. Nat Commun 2023; 14:1127. [PMID: 36854684 PMCID: PMC9974965 DOI: 10.1038/s41467-023-36877-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2022] [Accepted: 02/21/2023] [Indexed: 03/02/2023] Open
Abstract
Deep sea cold seep sediments host abundant and diverse microbial populations that significantly influence biogeochemical cycles. While numerous studies have revealed their community structure and functional capabilities, little is known about genetic heterogeneity within species. Here, we examine intraspecies diversity patterns of 39 abundant species identified in sediment layers down to 430 cm below the sea floor across six cold seep sites. These populations are grouped as aerobic methane-oxidizing bacteria, anaerobic methanotrophic archaea and sulfate-reducing bacteria. Different evolutionary trajectories are observed at the genomic level among these physiologically and phylogenetically diverse populations, with generally low rates of homologous recombination and strong purifying selection. Functional genes related to methane (pmoA and mcrA) and sulfate (dsrA) metabolisms are under strong purifying selection in most species investigated. These genes differ in evolutionary trajectories across phylogenetic clades but are functionally conserved across sites. Intrapopulation diversification of genomes and their mcrA and dsrA genes is depth-dependent and subject to different selection pressure throughout the sediment column redox zones at different sites. These results highlight the interplay between ecological processes and the evolution of key bacteria and archaea in deep sea cold seep extreme environments, shedding light on microbial adaptation in the subseafloor biosphere.
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Affiliation(s)
- Xiyang Dong
- Key Laboratory of Marine Genetic Resources, Third Institute of Oceanography, Ministry of Natural Resources, Xiamen, 361005, China.
- Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, 519000, China.
| | - Yongyi Peng
- Key Laboratory of Marine Genetic Resources, Third Institute of Oceanography, Ministry of Natural Resources, Xiamen, 361005, China
- School of Marine Sciences, Sun Yat-Sen University, Zhuhai, 519082, China
| | - Muhua Wang
- Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, 519000, China
- School of Marine Sciences, Sun Yat-Sen University, Zhuhai, 519082, China
| | - Laura Woods
- Department of Microbiology, Biomedicine Discovery Institute, Monash University, Clayton, VIC, 3800, Australia
| | - Wenxue Wu
- Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, 519000, China
- School of Marine Sciences, Sun Yat-Sen University, Zhuhai, 519082, China
- State Key Laboratory of Marine Resource Utilization in South China Sea, Hainan University, Haikou, 570228, China
| | - Yong Wang
- Institute for Ocean Engineering, Shenzhen International Graduate School, Tsinghua University, Shenzhen, 518055, China
| | - Xi Xiao
- Guangzhou Marine Geological Survey, China Geological Survey, Guangzhou, 510075, China
| | - Jiwei Li
- Institute of Deep-Sea Science and Engineering, Chinese Academy of Sciences, Sanya, 572000, China
| | - Kuntong Jia
- School of Marine Sciences, Sun Yat-Sen University, Zhuhai, 519082, China
| | - Chris Greening
- Department of Microbiology, Biomedicine Discovery Institute, Monash University, Clayton, VIC, 3800, Australia
| | - Zongze Shao
- Key Laboratory of Marine Genetic Resources, Third Institute of Oceanography, Ministry of Natural Resources, Xiamen, 361005, China.
- Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, 519000, China.
| | - Casey R J Hubert
- Department of Biological Sciences, University of Calgary, Calgary, AB, T2N 1N4, Canada
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18
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Teng W, Liao B, Chen M, Shu W. Genomic Legacies of Ancient Adaptation Illuminate GC-Content Evolution in Bacteria. Microbiol Spectr 2023; 11:e0214522. [PMID: 36511682 PMCID: PMC9927291 DOI: 10.1128/spectrum.02145-22] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Bacterial evolution is characterized by strong purifying selection as well as rapid adaptive evolution in changing environments. In this context, the genomic GC content (genomic GC) varies greatly but presents some level of phylogenetic stability, making it challenging to explain based on current hypotheses. To illuminate the evolutionary mechanisms of the genomic GC, we analyzed the base composition and functional inventory of 11,083 representative genomes. A phylogenetically constrained bimodal distribution of the genomic GC, which mainly originated from parallel divergences in the early evolution, was demonstrated. Such variation of the genomic GC can be well explained by DNA replication and repair (DRR), in which multiple pathways correlate with the genomic GC. Furthermore, the biased conservation of various stress-related genes, especially the DRR-related ones, implies distinct adaptive processes in the ancestral lineages of high- or low-GC clades which are likely induced by major environmental changes. Our findings support that the mutational biases resulting from these legacies of ancient adaptation have changed the course of adaptive evolution and generated great variation in the genomic GC. This highlights the importance of indirect effects of natural selection, which indicates a new model for bacterial evolution. IMPORTANCE GC content has been shown to be an important factor in microbial ecology and evolution, and the genomic GC of bacteria can be characterized by great intergenomic heterogeneity, high intragenomic homogeneity, and strong phylogenetic inertia, as well as being associated with the environment. Current hypotheses concerning direct selection or mutational biases cannot well explain these features simultaneously. Our findings of the genomic GC showing that ancient adaptations have transformed the DRR system and that the resulting mutational biases further contributed to a bimodal distribution of it offer a more reasonable scenario for the mechanism. This would imply that, when thinking about the evolution of life, diverse processes of adaptation exist, and combined effects of natural selection should be considered.
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Affiliation(s)
- Wenkai Teng
- School of Life Sciences, Sun Yat-sen University, Guangzhou, Guangdong, China
| | - Bin Liao
- School of Life Sciences, Sun Yat-sen University, Guangzhou, Guangdong, China
| | - Mengyun Chen
- School of Life Sciences, South China Normal University, Guangzhou, Guangdong, China
| | - Wensheng Shu
- School of Life Sciences, South China Normal University, Guangzhou, Guangdong, China
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19
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Abstract
The human microbiome harbours a large capacity for within-person adaptive mutations. Commensal bacterial strains can stably colonize a person for decades, and billions of mutations are generated daily within each person's microbiome. Adaptive mutations emerging during health might be driven by selective forces that vary across individuals, vary within an individual, or are completely novel to the human population. Mutations emerging within individual microbiomes might impact the immune system, the metabolism of nutrients or drugs, and the stability of the community to perturbations. Despite this potential, relatively little attention has been paid to the possibility of adaptive evolution within complex human-associated microbiomes. This review discusses the promise of studying within-microbiome adaptation, the conceptual and technical limitations that may have contributed to an underappreciation of adaptive de novo mutations occurring within microbiomes to date, and methods for detecting recent adaptive evolution. This article is part of a discussion meeting issue 'Genomic population structures of microbial pathogens'.
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Affiliation(s)
- Tami D Lieberman
- Department of Civil and Environmental Engineering, Institute for Medical Engineering and Science,Massachusetts Institute of Technology, Cambridge, MA, USA.,Broad Institute, Cambridge, MA, USA.,Ragon Institute, Cambridge, MA, USA
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20
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Garza DR, von Meijenfeldt FAB, van Dijk B, Boleij A, Huynen MA, Dutilh BE. Nutrition or nature: using elementary flux modes to disentangle the complex forces shaping prokaryote pan-genomes. BMC Ecol Evol 2022; 22:101. [PMID: 35974327 PMCID: PMC9382767 DOI: 10.1186/s12862-022-02052-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2021] [Accepted: 07/22/2022] [Indexed: 11/15/2022] Open
Abstract
Background Microbial pan-genomes are shaped by a complex combination of stochastic and deterministic forces. Even closely related genomes exhibit extensive variation in their gene content. Understanding what drives this variation requires exploring the interactions of gene products with each other and with the organism’s external environment. However, to date, conceptual models of pan-genome dynamics often represent genes as independent units and provide limited information about their mechanistic interactions. Results We simulated the stochastic process of gene-loss using the pooled genome-scale metabolic reaction networks of 46 taxonomically diverse bacterial and archaeal families as proxies for their pan-genomes. The frequency by which reactions are retained in functional networks when stochastic gene loss is simulated in diverse environments allowed us to disentangle the metabolic reactions whose presence depends on the metabolite composition of the external environment (constrained by “nutrition”) from those that are independent of the environment (constrained by “nature”). By comparing the frequency of reactions from the first group with their observed frequencies in bacterial and archaeal families, we predicted the metabolic niches that shaped the genomic composition of these lineages. Moreover, we found that the lineages that were shaped by a more diverse metabolic niche also occur in more diverse biomes as assessed by global environmental sequencing datasets. Conclusion We introduce a computational framework for analyzing and interpreting pan-reactomes that provides novel insights into the ecological and evolutionary drivers of pan-genome dynamics. Supplementary Information The online version contains supplementary material available at 10.1186/s12862-022-02052-3.
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21
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Ohtsuki H, Norimatsu H, Makino T, Urabe J. Invasions of an obligate asexual daphnid species support the nearly neutral theory. Sci Rep 2022; 12:7305. [PMID: 35508526 PMCID: PMC9068809 DOI: 10.1038/s41598-022-11218-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Accepted: 04/20/2022] [Indexed: 11/09/2022] Open
Abstract
To verify the "nearly neutral theory (NNT)," the ratio of nonsynonymous to synonymous substitutions (dN/dS) was compared among populations of different species. To determine the validity of NNT, however, populations that are genetically isolated from each other but share the same selection agents and differ in size should be compared. Genetically different lineages of obligate asexual Daphnia pulex invading Japan from North America are an ideal example as they satisfy these prerequisites. Therefore, we analyzed the whole-genome sequences of 18 genotypes, including those of the two independently invaded D. pulex lineages (JPN1 and JPN2) and compared the dN/dS ratio between the lineages. The base substitution rate of each genotype demonstrated that the JPN1 lineage having a larger distribution range diverged earlier and thus was older than the JPN2 lineage. Comparisons of the genotypes within lineages revealed that changes in dN/dS occurred after the divergence and were larger in the younger lineage, JPN2. These results imply that the JPN1 lineage has been more effectively subjected to purification selections, while slightly deteriorating mutations are less purged in JPN2 with smaller population size. Altogether, the lineage-specific difference in the dN/dS ratio for the obligate asexual D. pulex was well explained by the NNT.
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Affiliation(s)
- Hajime Ohtsuki
- Graduate School of Life Sciences, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai, 980-8578, Japan
| | - Hirotomo Norimatsu
- Graduate School of Life Sciences, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai, 980-8578, Japan
| | - Takashi Makino
- Graduate School of Life Sciences, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai, 980-8578, Japan
| | - Jotaro Urabe
- Graduate School of Life Sciences, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai, 980-8578, Japan.
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22
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Kin selection for cooperation in natural bacterial populations. Proc Natl Acad Sci U S A 2022; 119:2119070119. [PMID: 35193981 PMCID: PMC8892524 DOI: 10.1073/pnas.2119070119] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/06/2021] [Indexed: 01/03/2023] Open
Abstract
Bacteria secrete many molecules outside the cell, where they provide benefits to other cells. One potential reason for producing these “public goods” is that they benefit closely related cells that share the gene for cooperation (kin selection). While many laboratory studies have supported this hypothesis, there is a lack of evidence that kin selection favors cooperation in natural populations. We examined bacterial genomes from the environment and used population genetics theory to analyze the DNA sequences. Our analyses suggest that public goods cooperation has indeed been favored by kin selection in natural populations. Bacteria produce a range of molecules that are secreted from the cell and can provide a benefit to the local population of cells. Laboratory experiments have suggested that these “public goods” molecules represent a form of cooperation, favored because they benefit closely related cells (kin selection). However, there is a relative lack of data demonstrating kin selection for cooperation in natural populations of bacteria. We used molecular population genetics to test for signatures of kin selection at the genomic level in natural populations of the opportunistic pathogen Pseudomonas aeruginosa. We found consistent evidence from multiple traits that genes controlling putatively cooperative traits have higher polymorphism and greater divergence and are more likely to harbor deleterious mutations relative to genes controlling putatively private traits, which are expressed at similar rates. These patterns suggest that cooperative traits are controlled by kin selection, and we estimate that the relatedness for social interactions in P. aeruginosa is r = 0.84. More generally, our results demonstrate how molecular population genetics can be used to study the evolution of cooperation in natural populations.
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23
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Habitat Adaptation Drives Speciation of a Streptomyces Species with Distinct Habitats and Disparate Geographic Origins. mBio 2022; 13:e0278121. [PMID: 35012331 PMCID: PMC8749437 DOI: 10.1128/mbio.02781-21] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Microbial diversification is driven by geographic and ecological factors, but how the relative importance of these factors varies among species, geographic scales, and habitats remains unclear. Streptomyces, a genus of antibiotic-producing, spore-forming, and widespread bacteria, offers a robust model for identifying the processes underlying population differentiation. We examined the population structure of 37 Streptomyces olivaceus strains isolated from various sources, showing that they diverged into two habitat-associated (free-living and insect-associated) and geographically disparate lineages. More frequent gene flow within than between the lineages confirmed genetic isolation in S. olivaceus. Geographic isolation could not explain the genetic isolation; instead, habitat type was a strong predictor of genetic distance when controlling for geographic distance. The identification of habitat-specific genetic variations, including genes involved in regulation, resource use, and secondary metabolism, suggested a significant role of habitat adaptation in the diversification process. Physiological assays revealed fitness trade-offs under different environmental conditions in the two lineages. Notably, insect-associated isolates could outcompete free-living isolates in a free-iron-deficient environment. Furthermore, substrate (e.g., sialic acid and glycogen) utilization but not thermal traits differentiated the two lineages. Overall, our results argue that adaptive processes drove ecological divergence among closely related streptomycetes, eventually leading to dispersal limitation and gene flow barriers between the lineages. S. olivaceus may best be considered a species complex consisting of two cryptic species. IMPORTANCE Both isolation by distance and isolation by environment occur in bacteria, and different diversification patterns may apply to different species. Streptomyces species, typified by producing useful natural products, are widespread in nature and possess high genetic diversity. However, the ecological processes and evolutionary mechanisms that shape their distribution are not well understood. Here, we show that the population structure of a ubiquitous Streptomyces species complex matches its habitat distribution and can be defined by gene flow discontinuities. Using comparative genomics and physiological assays, we reveal that gains and losses of specific genomic traits play a significant role in the transition between free-living and host-associated lifestyles, driving speciation of the species. These results provide new insights into the evolutionary trajectory of Streptomyces and the notion of species.
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24
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Chen Z, Wang X, Song Y, Zeng Q, Zhang Y, Luo H. Prochlorococcus have low global mutation rate and small effective population size. Nat Ecol Evol 2022; 6:183-194. [PMID: 34949817 DOI: 10.1038/s41559-021-01591-0] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2021] [Accepted: 10/14/2021] [Indexed: 12/27/2022]
Abstract
Prochlorococcus are the most abundant free-living photosynthetic carbon-fixing organisms in the ocean. Prochlorococcus show small genome sizes, low genomic G+C content, reduced DNA repair gene pool and fast evolutionary rates, which are typical features of endosymbiotic bacteria. Nevertheless, their evolutionary mechanisms are believed to be different. Evolution of endosymbiotic bacteria is dominated by genetic drift owing to repeated population bottlenecks, whereas Prochlorococcus are postulated to have extremely large effective population sizes (Ne) and thus drift has rarely been considered. However, accurately extrapolating Ne requires measuring an unbiased global mutation rate through mutation accumulation, which is challenging for Prochlorococcus. Here, we managed this experiment over 1,065 days using Prochlorococcus marinus AS9601, sequenced genomes of 141 mutant lines and determined its mutation rate to be 3.50 × 10-10 per site per generation. Extrapolating Ne additionally requires identifying population boundaries, which we defined using PopCOGenT and over 400 genomes related to AS9601. Accordingly, we calculated its Ne to be 1.68 × 107, which is only reasonably greater than that of endosymbiotic bacteria but surprisingly smaller than that of many free-living bacteria extrapolated using the same approach. Our results therefore suggest that genetic drift is a key driver of Prochlorococcus evolution.
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Affiliation(s)
- Zhuoyu Chen
- State Key Laboratory of Marine Environmental Science and College of Ocean and Earth Sciences, Xiamen University, Xiamen, China
| | - Xiaojun Wang
- Simon F. S. Li Marine Science Laboratory, School of Life Sciences and State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Shatin, Hong Kong SAR.,Shenzhen Research Institute, The Chinese University of Hong Kong, Shenzhen, China
| | - Yu Song
- State Key Laboratory of Marine Environmental Science and College of Ocean and Earth Sciences, Xiamen University, Xiamen, China
| | - Qinglu Zeng
- Department of Ocean Science, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong SAR.,Hong Kong Branch of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Clear Water Bay, Hong Kong SAR
| | - Yao Zhang
- State Key Laboratory of Marine Environmental Science and College of Ocean and Earth Sciences, Xiamen University, Xiamen, China.
| | - Haiwei Luo
- Simon F. S. Li Marine Science Laboratory, School of Life Sciences and State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Shatin, Hong Kong SAR. .,Shenzhen Research Institute, The Chinese University of Hong Kong, Shenzhen, China. .,Hong Kong Branch of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Clear Water Bay, Hong Kong SAR.
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25
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Abstract
Naturally occurring plasmids come in different sizes. The smallest are less than a kilobase of DNA, while the largest can be over three orders of magnitude larger. Historically, research has tended to focus on smaller plasmids that are usually easier to isolate, manipulate and sequence, but with improved genome assemblies made possible by long-read sequencing, there is increased appreciation that very large plasmids—known as megaplasmids—are widespread, diverse, complex, and often encode key traits in the biology of their host microorganisms. Why are megaplasmids so big? What other features come with large plasmid size that could affect bacterial ecology and evolution? Are megaplasmids 'just' big plasmids, or do they have distinct characteristics? In this perspective, we reflect on the distribution, diversity, biology, and gene content of megaplasmids, providing an overview to these large, yet often overlooked, mobile genetic elements. This article is part of the theme issue ‘The secret lives of microbial mobile genetic elements’.
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Affiliation(s)
- James P J Hall
- Department of Evolution, Ecology and Behaviour, Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Liverpool, UK
| | - João Botelho
- Antibiotic Resistance Evolution Group, Max Planck Institute for Evolutionary Biology, Plön, Germany.,Department of Evolutionary Ecology and Genetics, Zoological Institute, Christian Albrechts University, Kiel, Germany
| | - Adrian Cazares
- EMBL's European Bioinformatics Institute (EMBL-EBI), Wellcome Genome Campus, Cambridge, UK.,Wellcome Sanger Institute, Wellcome Genome Campus, Cambridge, UK
| | - David A Baltrus
- School of Plant Sciences, University of Arizona, Tucson, AZ, USA
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26
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Lee IPA, Eldakar OT, Gogarten JP, Andam CP. Bacterial cooperation through horizontal gene transfer. Trends Ecol Evol 2021; 37:223-232. [PMID: 34815098 DOI: 10.1016/j.tree.2021.11.006] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2021] [Revised: 10/27/2021] [Accepted: 11/01/2021] [Indexed: 11/16/2022]
Abstract
Cooperation exists across all scales of biological organization, from genetic elements to complex human societies. Bacteria cooperate by secreting molecules that benefit all individuals in the population (i.e., public goods). Genes associated with cooperation can spread among strains through horizontal gene transfer (HGT). We discuss recent findings on how HGT mediated by mobile genetic elements promotes bacterial cooperation, how cooperation in turn can facilitate more frequent HGT, and how the act of HGT itself may be considered as a form of cooperation. We propose that HGT is an important enforcement mechanism in bacterial populations, thus creating a positive feedback loop that further maintains cooperation. To enforce cooperation, HGT serves as a homogenizing force by transferring the cooperative trait, effectively eliminating cheaters.
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Affiliation(s)
- Isaiah Paolo A Lee
- Department of Molecular, Cellular and Biomedical Sciences, University of New Hampshire, Durham, NH 03824, USA
| | - Omar Tonsi Eldakar
- Department of Biological Sciences, Nova Southeastern University, Fort Lauderdale, FL 33314, USA
| | - J Peter Gogarten
- Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269, USA.
| | - Cheryl P Andam
- Department of Biological Sciences, University at Albany, State University of New York, Albany, NY 12222, USA.
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27
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Colquhoun RM, Hall MB, Lima L, Roberts LW, Malone KM, Hunt M, Letcher B, Hawkey J, George S, Pankhurst L, Iqbal Z. Pandora: nucleotide-resolution bacterial pan-genomics with reference graphs. Genome Biol 2021; 22:267. [PMID: 34521456 PMCID: PMC8442373 DOI: 10.1186/s13059-021-02473-1] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2020] [Accepted: 08/19/2021] [Indexed: 12/21/2022] Open
Abstract
We present pandora, a novel pan-genome graph structure and algorithms for identifying variants across the full bacterial pan-genome. As much bacterial adaptability hinges on the accessory genome, methods which analyze SNPs in just the core genome have unsatisfactory limitations. Pandora approximates a sequenced genome as a recombinant of references, detects novel variation and pan-genotypes multiple samples. Using a reference graph of 578 Escherichia coli genomes, we compare 20 diverse isolates. Pandora recovers more rare SNPs than single-reference-based tools, is significantly better than picking the closest RefSeq reference, and provides a stable framework for analyzing diverse samples without reference bias.
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Affiliation(s)
- Rachel M Colquhoun
- European Bioinformatics Institute, Hinxton, Cambridge, CB10 1SD, UK
- Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford, UK
- Institute of Evolutionary Biology, Ashworth Laboratories, University of Edinburgh, Edinburgh, UK
| | - Michael B Hall
- European Bioinformatics Institute, Hinxton, Cambridge, CB10 1SD, UK
| | - Leandro Lima
- European Bioinformatics Institute, Hinxton, Cambridge, CB10 1SD, UK
| | - Leah W Roberts
- European Bioinformatics Institute, Hinxton, Cambridge, CB10 1SD, UK
| | - Kerri M Malone
- European Bioinformatics Institute, Hinxton, Cambridge, CB10 1SD, UK
| | - Martin Hunt
- European Bioinformatics Institute, Hinxton, Cambridge, CB10 1SD, UK
- Nuffield Department of Medicine, University of Oxford, Oxford, UK
| | - Brice Letcher
- European Bioinformatics Institute, Hinxton, Cambridge, CB10 1SD, UK
| | - Jane Hawkey
- Department of Infectious Diseases, Central Clinical School, Monash University, Melbourne, Victoria, 3004, Australia
| | - Sophie George
- Nuffield Department of Medicine, University of Oxford, Oxford, UK
| | - Louise Pankhurst
- Nuffield Department of Medicine, University of Oxford, Oxford, UK
- Department of Zoology, University of Oxford, Mansfield Road, Oxford, UK
| | - Zamin Iqbal
- European Bioinformatics Institute, Hinxton, Cambridge, CB10 1SD, UK.
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28
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Pennycook JH, Scanlan PD. Ecological and Evolutionary responses to Antibiotic Treatment in the Human Gut Microbiota. FEMS Microbiol Rev 2021; 45:fuab018. [PMID: 33822937 PMCID: PMC8498795 DOI: 10.1093/femsre/fuab018] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Accepted: 03/25/2021] [Indexed: 12/16/2022] Open
Abstract
The potential for antibiotics to affect the ecology and evolution of the human gut microbiota is well recognised and has wide-ranging implications for host health. Here, we review the findings of key studies that surveyed the human gut microbiota during antibiotic treatment. We find several broad patterns including the loss of diversity, disturbance of community composition, suppression of bacteria in the Actinobacteria phylum, amplification of bacteria in the Bacteroidetes phylum, and promotion of antibiotic resistance. Such changes to the microbiota were often, but not always, recovered following the end of treatment. However, many studies reported unique and/or contradictory results, which highlights our inability to meaningfully predict or explain the effects of antibiotic treatment on the human gut microbiome. This problem arises from variation between existing studies in three major categories: differences in dose, class and combinations of antibiotic treatments used; differences in demographics, lifestyles, and locations of subjects; and differences in measurements, analyses and reporting styles used by researchers. To overcome this, we suggest two integrated approaches: (i) a top-down approach focused on building predictive models through large sample sizes, deep metagenomic sequencing, and effective collaboration; and (ii) a bottom-up reductionist approach focused on testing hypotheses using model systems.
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Affiliation(s)
- Joseph Hugh Pennycook
- APC Microbiome Ireland, Biosciences Institute, University College Cork, College Road, Cork, T12 YT20, Ireland
- School of Mirobiology, Food Science & Technology Building, University College Cork, College Road, Cork, T12 K8AF, Ireland
| | - Pauline Deirdre Scanlan
- APC Microbiome Ireland, Biosciences Institute, University College Cork, College Road, Cork, T12 YT20, Ireland
- School of Mirobiology, Food Science & Technology Building, University College Cork, College Road, Cork, T12 K8AF, Ireland
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29
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Traulsen A, Sieber M. Evolutionary ecology theory - microbial population structure. Curr Opin Microbiol 2021; 63:216-220. [PMID: 34428627 DOI: 10.1016/j.mib.2021.08.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2021] [Revised: 07/30/2021] [Accepted: 08/02/2021] [Indexed: 10/20/2022]
Abstract
Microbial populations typically show a large degree of intra-population diversity. This diversity is intertwined with the structure of the population. Here, we discuss endogenous and exogenous drivers of population structure in microbes and how the population structure can affect evolutionary dynamics and vice versa. Endogenous structure, which can be genetic or demographic, is driven by the ecology and evolutionary dynamics within the population. Exogenous structure is typically driven by the spatial and temporal properties of the environment. A particular interesting case arises when also this exogenous structure experiences feedbacks from the microbial population.
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Affiliation(s)
- Arne Traulsen
- Max Planck Institute for Evolutionary Biology, D-24306 Plön, Germany.
| | - Michael Sieber
- Max Planck Institute for Evolutionary Biology, D-24306 Plön, Germany
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30
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Menden-Deuer S, Rowlett J, Nursultanov M, Collins S, Rynearson T. Biodiversity of marine microbes is safeguarded by phenotypic heterogeneity in ecological traits. PLoS One 2021; 16:e0254799. [PMID: 34347817 PMCID: PMC8336841 DOI: 10.1371/journal.pone.0254799] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2021] [Accepted: 07/05/2021] [Indexed: 11/18/2022] Open
Abstract
Why, contrary to theoretical predictions, do marine microbe communities harbor tremendous phenotypic heterogeneity? How can so many marine microbe species competing in the same niche coexist? We discovered a unifying explanation for both phenomena by investigating a non-cooperative game that interpolates between individual-level competitions and species-level outcomes. We identified all equilibrium strategies of the game. These strategies represent the probability distribution of competitive abilities (e.g. traits) and are characterized by maximal phenotypic heterogeneity. They are also neutral towards each other in the sense that an unlimited number of species can co-exist while competing according to the equilibrium strategies. Whereas prior theory predicts that natural selection would minimize trait variation around an optimum value, here we obtained a mathematical proof that species with maximally variable traits are those that endure. This discrepancy may reflect a disparity between predictions from models developed for larger organisms in contrast to our microbe-centric model. Rigorous mathematics proves that phenotypic heterogeneity is itself a mechanistic underpinning of microbial diversity. This discovery has fundamental ramifications for microbial ecology and may represent an adaptive reservoir sheltering biodiversity in changing environmental conditions.
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Affiliation(s)
- Susanne Menden-Deuer
- Graduate School of Oceanography, University of Rhode Island, Narragansett Bay Campus, Narragansett, RI, United States of America
| | - Julie Rowlett
- Mathematical Sciences, Chalmers University and the University of Gothenburg, Gothenburg, Sweden
- * E-mail:
| | - Medet Nursultanov
- School of Mathematics and Statistics, University of Sydney, Camperdown, Australia
| | - Sinead Collins
- Biological Sciences, Ashworth Laboratories, University of Edinburgh, Edinburgh, United Kingdom
| | - Tatiana Rynearson
- Graduate School of Oceanography, University of Rhode Island, Narragansett Bay Campus, Narragansett, RI, United States of America
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31
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Menardo F, Gagneux S, Freund F. Multiple Merger Genealogies in Outbreaks of Mycobacterium tuberculosis. Mol Biol Evol 2021; 38:290-306. [PMID: 32667991 PMCID: PMC8480183 DOI: 10.1093/molbev/msaa179] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The Kingman coalescent and its developments are often considered among the most important advances in population genetics of the last decades. Demographic inference based on coalescent theory has been used to reconstruct the population dynamics and evolutionary history of several species, including Mycobacterium tuberculosis (MTB), an important human pathogen causing tuberculosis. One key assumption of the Kingman coalescent is that the number of descendants of different individuals does not vary strongly, and violating this assumption could lead to severe biases caused by model misspecification. Individual lineages of MTB are expected to vary strongly in reproductive success because 1) MTB is potentially under constant selection due to the pressure of the host immune system and of antibiotic treatment, 2) MTB undergoes repeated population bottlenecks when it transmits from one host to the next, and 3) some hosts show much higher transmission rates compared with the average (superspreaders). Here, we used an approximate Bayesian computation approach to test whether multiple-merger coalescents (MMC), a class of models that allow for large variation in reproductive success among lineages, are more appropriate models to study MTB populations. We considered 11 publicly available whole-genome sequence data sets sampled from local MTB populations and outbreaks and found that MMC had a better fit compared with the Kingman coalescent for 10 of the 11 data sets. These results indicate that the null model for analyzing MTB outbreaks should be reassessed and that past findings based on the Kingman coalescent need to be revisited.
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Affiliation(s)
- Fabrizio Menardo
- Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland.,University of Basel, Basel, Switzerland
| | - Sébastien Gagneux
- Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland.,University of Basel, Basel, Switzerland
| | - Fabian Freund
- Department of Plant Biodiversity and Breeding Informatics, Institute of Plant Breeding, Seed Science and Population Genetics, University of Hohenheim, Stuttgart, Germany
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32
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Unexpectedly high mutation rate of a deep-sea hyperthermophilic anaerobic archaeon. THE ISME JOURNAL 2021; 15:1862-1869. [PMID: 33452477 PMCID: PMC8163891 DOI: 10.1038/s41396-020-00888-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2020] [Revised: 12/14/2020] [Accepted: 12/16/2020] [Indexed: 01/29/2023]
Abstract
Deep-sea hydrothermal vents resemble the early Earth, and thus the dominant Thermococcaceae inhabitants, which occupy an evolutionarily basal position of the archaeal tree and take an obligate anaerobic hyperthermophilic free-living lifestyle, are likely excellent models to study the evolution of early life. Here, we determined that unbiased mutation rate of a representative species, Thermococcus eurythermalis, exceeded that of all known free-living prokaryotes by 1-2 orders of magnitude, and thus rejected the long-standing hypothesis that low mutation rates were selectively favored in hyperthermophiles. We further sequenced multiple and diverse isolates of this species and calculated that T. eurythermalis has a lower effective population size than other free-living prokaryotes by 1-2 orders of magnitude. These data collectively indicate that the high mutation rate of this species is not selectively favored but instead driven by random genetic drift. The availability of these unusual data also helps explore mechanisms underlying microbial genome size evolution. We showed that genome size is negatively correlated with mutation rate and positively correlated with effective population size across 30 bacterial and archaeal lineages, suggesting that increased mutation rate and random genetic drift are likely two important mechanisms driving microbial genome reduction. Future determinations of the unbiased mutation rate of more representative lineages with highly reduced genomes such as Prochlorococcus and Pelagibacterales that dominate marine microbial communities are essential to test these hypotheses.
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33
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Carroll LM, Cheng RA, Wiedmann M, Kovac J. Keeping up with the Bacillus cereus group: taxonomy through the genomics era and beyond. Crit Rev Food Sci Nutr 2021; 62:7677-7702. [PMID: 33939559 DOI: 10.1080/10408398.2021.1916735] [Citation(s) in RCA: 39] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The Bacillus cereus group, also known as B. cereus sensu lato (s.l.), is a species complex that contains numerous closely related lineages, which vary in their ability to cause illness in humans and animals. The classification of B. cereus s.l. isolates into species-level taxonomic units is thus essential for informing public health and food safety efforts. However, taxonomic classification of these organisms is challenging. Numerous-often conflicting-taxonomic changes to the group have been proposed over the past two decades, making it difficult to remain up to date. In this review, we discuss the major nomenclatural changes that have accumulated in the B. cereus s.l. taxonomic space prior to 2020, particularly in the genomic sequencing era, and outline the resulting problems. We discuss several contemporary taxonomic frameworks as applied to B. cereus s.l., including (i) phenotypic, (ii) genomic, and (iii) hybrid nomenclatural frameworks, and we discuss the advantages and disadvantages of each. We offer suggestions as to how readers can avoid B. cereus s.l. taxonomic ambiguities, regardless of the nomenclatural framework(s) they choose to employ. Finally, we discuss future directions and open problems in the B. cereus s.l. taxonomic realm, including those that cannot be solved by genomic approaches alone.
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Affiliation(s)
- Laura M Carroll
- Structural and Computational Biology Unit, EMBL, Heidelberg, Germany
| | - Rachel A Cheng
- Department of Food Science, Cornell University, Ithaca, New York, USA
| | - Martin Wiedmann
- Department of Food Science, Cornell University, Ithaca, New York, USA
| | - Jasna Kovac
- Department of Food Science, The Pennsylvania State University, University Park, Pennsylvania, USA
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34
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Harrow GL, Lees JA, Hanage WP, Lipsitch M, Corander J, Colijn C, Croucher NJ. Negative frequency-dependent selection and asymmetrical transformation stabilise multi-strain bacterial population structures. THE ISME JOURNAL 2021; 15:1523-1538. [PMID: 33408365 PMCID: PMC8115253 DOI: 10.1038/s41396-020-00867-w] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Revised: 12/01/2020] [Accepted: 12/03/2020] [Indexed: 02/06/2023]
Abstract
Streptococcus pneumoniae can be divided into many strains, each a distinct set of isolates sharing similar core and accessory genomes, which co-circulate within the same hosts. Previous analyses suggested the short-term vaccine-associated dynamics of S. pneumoniae strains may be mediated through multi-locus negative frequency-dependent selection (NFDS), which maintains accessory loci at equilibrium frequencies. Long-term simulations demonstrated NFDS stabilised clonally-evolving multi-strain populations through preventing the loss of variation through drift, based on polymorphism frequencies, pairwise genetic distances and phylogenies. However, allowing symmetrical recombination between isolates evolving under multi-locus NFDS generated unstructured populations of diverse genotypes. Replication of the observed data improved when multi-locus NFDS was combined with recombination that was instead asymmetrical, favouring deletion of accessory loci over insertion. This combination separated populations into strains through outbreeding depression, resulting from recombinants with reduced accessory genomes having lower fitness than their parental genotypes. Although simplistic modelling of recombination likely limited these simulations' ability to maintain some properties of genomic data as accurately as those lacking recombination, the combination of asymmetrical recombination and multi-locus NFDS could restore multi-strain population structures from randomised initial populations. As many bacteria inhibit insertions into their chromosomes, this combination may commonly underlie the co-existence of strains within a niche.
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Affiliation(s)
- Gabrielle L Harrow
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, Imperial College London, Norfolk Place, London, W2 1PG, UK
| | - John A Lees
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, Imperial College London, Norfolk Place, London, W2 1PG, UK
| | - William P Hanage
- Center for Communicable Disease Dynamics, Department of Epidemiology, Harvard T.H. Chan School of Public Health, 677 Huntington Avenue, Boston, MA, 02115, USA
| | - Marc Lipsitch
- Center for Communicable Disease Dynamics, Department of Epidemiology, Harvard T.H. Chan School of Public Health, 677 Huntington Avenue, Boston, MA, 02115, USA
| | - Jukka Corander
- Department of Biostatistics, University of Oslo, Oslo, Norway
- Helsinki Institute of Information Technology, Department of Mathematics and Statistics, University of Helsinki, Helsinki, Finland
- Parasites & Microbes Programme, Wellcome Sanger Institute, Wellcome Genome Campus, Hinxton, Cambridge, UK
| | - Caroline Colijn
- Parasites & Microbes Programme, Wellcome Sanger Institute, Wellcome Genome Campus, Hinxton, Cambridge, UK
- Department of Mathematics, Simon Fraser University, Burnaby, BC, Canada
| | - Nicholas J Croucher
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, Imperial College London, Norfolk Place, London, W2 1PG, UK.
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35
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Domingo-Sananes MR, McInerney JO. Mechanisms That Shape Microbial Pangenomes. Trends Microbiol 2021; 29:493-503. [PMID: 33423895 DOI: 10.1016/j.tim.2020.12.004] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2020] [Revised: 12/09/2020] [Accepted: 12/10/2020] [Indexed: 01/02/2023]
Abstract
Analyses of multiple whole-genome sequences from the same species have revealed that differences in gene content can be substantial, particularly in prokaryotes. Such variation has led to the recognition of pangenomes, the complete set of genes present in a species - consisting of core genes, present in all individuals, and accessory genes whose presence is variable. Questions now arise about how pangenomes originate and evolve. We describe how gene content variation can arise as a result of the combination of several processes, including random drift, selection, gain/loss balance, and the influence of ecological and epistatic interactions. We believe that identifying the contributions of these processes to pangenomes will need novel theoretical approaches and empirical data.
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Affiliation(s)
- Maria Rosa Domingo-Sananes
- School of Life Sciences, University of Nottingham, Nottingham, UK; School of Science and Technology, Nottingham Trent University, Nottingham, UK.
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36
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Nelson WC, Tully BJ, Mobberley JM. Biases in genome reconstruction from metagenomic data. PeerJ 2020; 8:e10119. [PMID: 33194386 PMCID: PMC7605220 DOI: 10.7717/peerj.10119] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2017] [Accepted: 09/16/2020] [Indexed: 01/24/2023] Open
Abstract
BACKGROUND Advances in sequencing, assembly, and assortment of contigs into species-specific bins has enabled the reconstruction of genomes from metagenomic data (MAGs). Though a powerful technique, it is difficult to determine whether assembly and binning techniques are accurate when applied to environmental metagenomes due to a lack of complete reference genome sequences against which to check the resulting MAGs. METHODS We compared MAGs derived from an enrichment culture containing ~20 organisms to complete genome sequences of 10 organisms isolated from the enrichment culture. Factors commonly considered in binning software-nucleotide composition and sequence repetitiveness-were calculated for both the correctly binned and not-binned regions. This direct comparison revealed biases in sequence characteristics and gene content in the not-binned regions. Additionally, the composition of three public data sets representing MAGs reconstructed from the Tara Oceans metagenomic data was compared to a set of representative genomes available through NCBI RefSeq to verify that the biases identified were observable in more complex data sets and using three contemporary binning software packages. RESULTS Repeat sequences were frequently not binned in the genome reconstruction processes, as were sequence regions with variant nucleotide composition. Genes encoded on the not-binned regions were strongly biased towards ribosomal RNAs, transfer RNAs, mobile element functions and genes of unknown function. Our results support genome reconstruction as a robust process and suggest that reconstructions determined to be >90% complete are likely to effectively represent organismal function; however, population-level genotypic heterogeneity in natural populations, such as uneven distribution of plasmids, can lead to incorrect inferences.
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Affiliation(s)
- William C. Nelson
- Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA, USA
| | - Benjamin J. Tully
- Department of Biological Sciences, Marine Environmental Biology Section, University of Southern California, Los Angeles, CA, USA
- Center for Dark Energy Biosphere Investigations, University of Southern California, Los Angeles, CA, USA
| | - Jennifer M. Mobberley
- Chemical and Biological Signature Science Group, Pacific Northwest National Laboratory, Richland, WA, USA
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37
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Uritskiy G, Munn A, Dailey M, Gelsinger DR, Getsin S, Davila A, McCullough PR, Taylor J, DiRuggiero J. Environmental Factors Driving Spatial Heterogeneity in Desert Halophile Microbial Communities. Front Microbiol 2020; 11:578669. [PMID: 33193201 PMCID: PMC7606970 DOI: 10.3389/fmicb.2020.578669] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Accepted: 09/24/2020] [Indexed: 12/22/2022] Open
Abstract
Spatial heterogeneity in microbial communities is observed in all natural ecosystems and can stem from both adaptations to local environmental conditions as well as stochastic processes. Extremophile microbial communities inhabiting evaporitic halite nodules (salt rocks) in the Atacama Desert, Chile, are a good model ecosystem for investigating factors leading to microbiome heterogeneity, due to their diverse taxonomic composition and the spatial segregation of individual nodules. We investigated the abiotic factors governing microbiome composition across different spatial scales, allowing for insight into the factors that govern halite colonization from regional desert-wide scales to micro-scales within individual nodules. We found that water availability and community drift account for microbiome assembly differently at different distance scales, with higher rates of cell dispersion at the smaller scales resulting in a more homogenous composition. This trend likely applies to other endoliths, and to non-desert communities, where dispersion between communities is limited. At the intra-nodule scales, a light availability gradient was most important in determining the distribution of microbial taxa despite intermixing by water displacement via capillary action.
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Affiliation(s)
- Gherman Uritskiy
- Department of Biology, Johns Hopkins University, Baltimore, MD, United States
| | - Adam Munn
- Department of Biology, Johns Hopkins University, Baltimore, MD, United States
| | - Micah Dailey
- Department of Biology, Johns Hopkins University, Baltimore, MD, United States
| | - Diego R. Gelsinger
- Department of Biology, Johns Hopkins University, Baltimore, MD, United States
| | - Samantha Getsin
- Department of Biology, Johns Hopkins University, Baltimore, MD, United States
| | - Alfonso Davila
- NASA Ames Research Center, Moffett Field, CA, United States
| | - P. R. McCullough
- Department of Physics and Astronomy, Johns Hopkins University, and Space Telescope Science Institute, Baltimore, MD, United States
| | - James Taylor
- Department of Biology, Johns Hopkins University, Baltimore, MD, United States
- Department of Computer Science, Johns Hopkins University, Baltimore, MD, United States
| | - Jocelyne DiRuggiero
- Department of Biology, Johns Hopkins University, Baltimore, MD, United States
- Department of Earth & Planetary Sciences, Johns Hopkins University, Baltimore, MD, United States
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38
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Abstract
As the most abundant bacteria in oceans, the Pelagibacterales order (here SAR11) plays an important role in the global carbon cycle, but the study of the evolutionary forces driving its evolution has lagged considerably due to the inherent difficulty of obtaining pure cultures. Multiple evolutionary models have been proposed to explain the diversification of distinct lineages within a population; however, the identification of many of these patterns in natural populations remains mostly enigmatic. We have used a metagenomic approach to explore microdiversity patterns in their natural habitats. Comparison with a collection of bacterial and archaeal groups from the same environments shows that SAR11 populations have a different evolutionary regime, where multiple genotypes coexist within the same population and remain stable over time. Widespread homologous recombination could be one of the main driving factors of this homogenization. The SAR11 clade of Alphaproteobacteria is the most abundant group of planktonic cells in the near-surface epipelagic waters of the ocean, but the mechanisms underlying its exceptional success have not been fully elucidated. Here, we applied a metagenomic approach to explore microdiversity patterns by measuring the accumulation of synonymous and nonsynonymous mutations as well as homologous recombination in populations of SAR11 from different aquatic habitats (marine epipelagic, bathypelagic, and surface freshwater). The patterns of mutation accumulation and recombination were compared to those of other groups of representative marine microbes with multiple ecological strategies that share the same marine habitat, namely, Cyanobacteria (Prochlorococcus and Synechococcus), Archaea (“Candidatus Nitrosopelagicus” and Marine Group II Thalassoarchaea), and some heterotrophic marine bacteria (Alteromonas and Erythrobacter). SAR11 populations showed widespread recombination among distantly related members, preventing divergence leading to a genetically stable population. Moreover, their high intrapopulation sequence diversity with an enrichment in synonymous replacements supports the idea of a very ancient divergence and the coexistence of multiple different clones. However, other microbes analyzed seem to follow different evolutionary dynamics where processes of diversification driven by geographic and ecological instability produce a higher number of nonsynonymous replacements and lower intrapopulation sequence diversity. Together, these data shed light on some of the evolutionary and ecological processes that lead to the large genomic diversity in SAR11. Furthermore, this approach can be applied to other similar microbes that are difficult to culture in the laboratory, but abundant in nature, to investigate the underlying dynamics of their genomic evolution. IMPORTANCE As the most abundant bacteria in oceans, the Pelagibacterales order (here SAR11) plays an important role in the global carbon cycle, but the study of the evolutionary forces driving its evolution has lagged considerably due to the inherent difficulty of obtaining pure cultures. Multiple evolutionary models have been proposed to explain the diversification of distinct lineages within a population; however, the identification of many of these patterns in natural populations remains mostly enigmatic. We have used a metagenomic approach to explore microdiversity patterns in their natural habitats. Comparison with a collection of bacterial and archaeal groups from the same environments shows that SAR11 populations have a different evolutionary regime, where multiple genotypes coexist within the same population and remain stable over time. Widespread homologous recombination could be one of the main driving factors of this homogenization.
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Carroll LM, Cheng RA, Kovac J. No Assembly Required: Using BTyper3 to Assess the Congruency of a Proposed Taxonomic Framework for the Bacillus cereus Group With Historical Typing Methods. Front Microbiol 2020; 11:580691. [PMID: 33072050 PMCID: PMC7536271 DOI: 10.3389/fmicb.2020.580691] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Accepted: 08/25/2020] [Indexed: 12/19/2022] Open
Abstract
The Bacillus cereus group, also known as B. cereus sensu lato (s.l.), is a species complex comprising numerous closely related lineages, which vary in their ability to cause illness in humans and animals. The classification of B. cereus s.l. isolates into species-level taxonomic units is essential for facilitating communication between and among microbiologists, clinicians, public health officials, and industry professionals, but is not always straightforward. A recently proposed genomospecies-subspecies-biovar taxonomic framework aims to provide a standardized nomenclature for this species complex but relies heavily on whole-genome sequencing (WGS). It thus is unclear whether popular, low-cost typing methods (e.g., single- and multi-locus sequence typing) remain congruent with the proposed taxonomy. Here, we characterize 2,231 B. cereus s.l. genomes using a combination of in silico (i) average-nucleotide identity (ANI)-based genomospecies assignment, (ii) ANI-based subspecies assignment, (iii) seven-gene multi-locus sequence typing (MLST), (iv) single-locus panC group assignment, (v) rpoB allelic typing, and (vi) virulence factor detection. We show that sequence types (STs) assigned using MLST can be used for genomospecies assignment, and we provide a comprehensive list of ST/genomospecies associations. For panC group assignment, we show that an adjusted, eight-group framework is largely, albeit not perfectly, congruent with the proposed eight-genomospecies taxonomy, as panC alone may not distinguish (i) B. luti from Group II B. mosaicus and (ii) B. paramycoides from Group VI B. mycoides. We additionally provide a list of loci that capture the topology of the whole-genome B. cereus s.l. phylogeny that may be used in future sequence typing efforts. For researchers with access to WGS, MLST, and/or panC data, we showcase how our recently released software, BTyper3 (https://github.com/lmc297/BTyper3), can be used to assign B. cereus s.l. isolates to taxonomic units within this proposed framework with little-to-no user intervention or domain-specific knowledge of B. cereus s.l. taxonomy. We additionally outline a novel method for assigning B. cereus s.l. genomes to pseudo-gene flow units within proposed genomospecies. The results presented here highlight the backward-compatibility and accessibility of the recently proposed genomospecies-subspecies-biovar taxonomic framework and illustrate that WGS is not a necessity for microbiologists who want to use the proposed nomenclature effectively.
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Affiliation(s)
- Laura M. Carroll
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Rachel A. Cheng
- Department of Food Science, College of Agriculture and Life Sciences, Cornell University, Ithaca, NY, United States
| | - Jasna Kovac
- Department of Food Science, College of Agricultural Sciences, The Pennsylvania State University, University Park, PA, United States
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Abstract
The genomes of bacteria contain fewer genes and substantially less noncoding DNA than those of eukaryotes, and as a result, they have much less raw material to invent new traits. Yet, bacteria are vastly more taxonomically diverse, numerically abundant, and globally successful in colonizing new habitats compared to eukaryotes. Although bacterial genomes are generally considered to be optimized for efficient growth and rapid adaptation, nonadaptive processes have played a major role in shaping the size, contents, and compact organization of bacterial genomes and have allowed the establishment of deleterious traits that serve as the raw materials for genetic innovation.
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Affiliation(s)
- Paul C Kirchberger
- Department of Integrative Biology, University of Texas at Austin, Texas 78712, USA; ; ;
| | - Marian L Schmidt
- Department of Integrative Biology, University of Texas at Austin, Texas 78712, USA; ; ;
| | - Howard Ochman
- Department of Integrative Biology, University of Texas at Austin, Texas 78712, USA; ; ;
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Bobay LM. CoreSimul: a forward-in-time simulator of genome evolution for prokaryotes modeling homologous recombination. BMC Bioinformatics 2020; 21:264. [PMID: 32580695 PMCID: PMC7315543 DOI: 10.1186/s12859-020-03619-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2020] [Accepted: 06/19/2020] [Indexed: 12/26/2022] Open
Abstract
Background Prokaryotes are asexual, but these organisms frequently engage in homologous recombination, a process that differs from meiotic recombination in sexual organisms. Most tools developed to simulate genome evolution either assume sexual reproduction or the complete absence of DNA flux in the population. As a result, very few simulators are adapted to model prokaryotic genome evolution while accounting for recombination. Moreover, many simulators are based on the coalescent, which assumes a neutral model of genomic evolution, and those are best suited for organisms evolving under weak selective pressures, such as animals and plants. In contrast, prokaryotes are thought to be evolving under much stronger selective pressures, suggesting that forward-in-time simulators are better suited for these organisms. Results Here, I present CoreSimul, a forward-in-time simulator of core genome evolution for prokaryotes modeling homologous recombination. Simulations are guided by a phylogenetic tree and incorporate different substitution models, including models of codon selection. Conclusions CoreSimul is a flexible forward-in-time simulator that constitutes a significant addition to the limited list of available simulators applicable to prokaryote genome evolution.
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Affiliation(s)
- Louis-Marie Bobay
- Department of Biology, University of North Carolina Greensboro, 321 McIver Street, PO Box 26170, Greensboro, NC, 27402, USA.
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42
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VanInsberghe D, Arevalo P, Chien D, Polz MF. How can microbial population genomics inform community ecology? Philos Trans R Soc Lond B Biol Sci 2020; 375:20190253. [PMID: 32200748 PMCID: PMC7133533 DOI: 10.1098/rstb.2019.0253] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/20/2019] [Indexed: 12/22/2022] Open
Abstract
Populations are fundamental units of ecology and evolution, but can we define them for bacteria and archaea in a biologically meaningful way? Here, we review why population structure is difficult to recognize in microbes and how recent advances in measuring contemporary gene flow allow us to identify clearly delineated populations among collections of closely related genomes. Such structure can arise from preferential gene flow caused by coexistence and genetic similarity, defining populations based on biological mechanisms. We show that such gene flow units are sufficiently genetically isolated for specific adaptations to spread, making them also ecological units that are differentially adapted compared to their closest relatives. We discuss the implications of these observations for measuring bacterial and archaeal diversity in the environment. We show that operational taxonomic units defined by 16S rRNA gene sequencing have woefully poor resolution for ecologically defined populations and propose monophyletic clusters of nearly identical ribosomal protein genes as an alternative measure for population mapping in community ecological studies employing metagenomics. These population-based approaches have the potential to provide much-needed clarity in interpreting the vast microbial diversity in human and environmental microbiomes. This article is part of the theme issue 'Conceptual challenges in microbial community ecology'.
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Affiliation(s)
- David VanInsberghe
- Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
- Graduate Program in Microbiology, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Philip Arevalo
- Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
- Graduate Program in Microbiology, Massachusetts Institute of Technology, Cambridge, MA, USA
- Department of Ecology and Evolution, University of Chicago, Chicago, IL, USA
| | - Diana Chien
- Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
- Graduate Program in Microbiology, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Martin F. Polz
- Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
- Department of Microbial Ecology, University of Vienna, Vienna, Austria
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Maistrenko OM, Mende DR, Luetge M, Hildebrand F, Schmidt TSB, Li SS, Rodrigues JFM, von Mering C, Pedro Coelho L, Huerta-Cepas J, Sunagawa S, Bork P. Disentangling the impact of environmental and phylogenetic constraints on prokaryotic within-species diversity. THE ISME JOURNAL 2020; 14:1247-1259. [PMID: 32047279 PMCID: PMC7174425 DOI: 10.1038/s41396-020-0600-z] [Citation(s) in RCA: 54] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/02/2019] [Revised: 01/21/2020] [Accepted: 01/27/2020] [Indexed: 12/04/2022]
Abstract
Microbial organisms inhabit virtually all environments and encompass a vast biological diversity. The pangenome concept aims to facilitate an understanding of diversity within defined phylogenetic groups. Hence, pangenomes are increasingly used to characterize the strain diversity of prokaryotic species. To understand the interdependence of pangenome features (such as the number of core and accessory genes) and to study the impact of environmental and phylogenetic constraints on the evolution of conspecific strains, we computed pangenomes for 155 phylogenetically diverse species (from ten phyla) using 7,000 high-quality genomes to each of which the respective habitats were assigned. Species habitat ubiquity was associated with several pangenome features. In particular, core-genome size was more important for ubiquity than accessory genome size. In general, environmental preferences had a stronger impact on pangenome evolution than phylogenetic inertia. Environmental preferences explained up to 49% of the variance for pangenome features, compared with 18% by phylogenetic inertia. This observation was robust when the dataset was extended to 10,100 species (59 phyla). The importance of environmental preferences was further accentuated by convergent evolution of pangenome features in a given habitat type across different phylogenetic clades. For example, the soil environment promotes expansion of pangenome size, while host-associated habitats lead to its reduction. Taken together, we explored the global principles of pangenome evolution, quantified the influence of habitat, and phylogenetic inertia on the evolution of pangenomes and identified criteria governing species ubiquity and habitat specificity.
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Affiliation(s)
- Oleksandr M Maistrenko
- European Molecular Biology Laboratory, Structural and Computational Biology Unit, 69117, Heidelberg, Germany
| | - Daniel R Mende
- European Molecular Biology Laboratory, Structural and Computational Biology Unit, 69117, Heidelberg, Germany
- Laboratory of Applied Evolutionary Biology, Department of Medical Microbiology, Academic Medical Centre, University of Amsterdam, Amsterdam, 1105 AZ, The Netherlands
| | - Mechthild Luetge
- European Molecular Biology Laboratory, Structural and Computational Biology Unit, 69117, Heidelberg, Germany
- Institute of Immunobiology, Kantonsspital St. Gallen, 9007, St. Gallen, Switzerland
| | - Falk Hildebrand
- European Molecular Biology Laboratory, Structural and Computational Biology Unit, 69117, Heidelberg, Germany
- Gut Microbes and Health, Quadram Institute Bioscience, Norwich, Norfolk, UK
- Digital Biology, Earlham Institute, Norwich, Norfolk, UK
| | - Thomas S B Schmidt
- European Molecular Biology Laboratory, Structural and Computational Biology Unit, 69117, Heidelberg, Germany
| | - Simone S Li
- European Molecular Biology Laboratory, Structural and Computational Biology Unit, 69117, Heidelberg, Germany
- Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, 2800, Kongens Lyngby, Denmark
| | - João F Matias Rodrigues
- Department of Molecular Life Sciences and Swiss Institute of Bioinformatics, University of Zurich, CH-8057, Zurich, Switzerland
| | - Christian von Mering
- Department of Molecular Life Sciences and Swiss Institute of Bioinformatics, University of Zurich, CH-8057, Zurich, Switzerland
| | - Luis Pedro Coelho
- European Molecular Biology Laboratory, Structural and Computational Biology Unit, 69117, Heidelberg, Germany
- Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, Shanghai, 200433, China
| | - Jaime Huerta-Cepas
- European Molecular Biology Laboratory, Structural and Computational Biology Unit, 69117, Heidelberg, Germany
- Centro de Biotecnología y Genómica de Plantas, Universidad Politécnica de Madrid (UPM) - Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), Madrid, Spain
| | - Shinichi Sunagawa
- European Molecular Biology Laboratory, Structural and Computational Biology Unit, 69117, Heidelberg, Germany
- Department of Biology and Swiss Institute of Bioinformatics, ETH Zürich, Vladimir-Prelog-Weg 4, 8093, Zürich, Switzerland
| | - Peer Bork
- European Molecular Biology Laboratory, Structural and Computational Biology Unit, 69117, Heidelberg, Germany.
- Max Delbrück Centre for Molecular Medicine, Berlin, Germany.
- Molecular Medicine Partnership Unit, University of Heidelberg and European Molecular Biology Laboratory, Heidelberg, Germany.
- Department of Bioinformatics, Biocenter, University of Würzburg, Würzburg, Germany.
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Weissman JL, Fagan WF, Johnson PLF. Linking high GC content to the repair of double strand breaks in prokaryotic genomes. PLoS Genet 2019; 15:e1008493. [PMID: 31703064 PMCID: PMC6867656 DOI: 10.1371/journal.pgen.1008493] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2019] [Revised: 11/20/2019] [Accepted: 10/25/2019] [Indexed: 01/21/2023] Open
Abstract
Genomic GC content varies widely among microbes for reasons unknown. While mutation bias partially explains this variation, prokaryotes near-universally have a higher GC content than predicted solely by this bias. Debate surrounds the relative importance of the remaining explanations of selection versus biased gene conversion favoring GC alleles. Some environments (e.g. soils) are associated with a high genomic GC content of their inhabitants, which implies that either high GC content is a selective adaptation to particular habitats, or that certain habitats favor increased rates of gene conversion. Here, we report a novel association between the presence of the non-homologous end joining DNA double-strand break repair pathway and GC content; this observation suggests that DNA damage may be a fundamental driver of GC content, leading in part to the many environmental patterns observed to-date. We discuss potential mechanisms accounting for the observed association, and provide preliminary evidence that sites experiencing higher rates of double-strand breaks are under selection for increased GC content relative to the genomic background. The overall nucleotide composition of an organism’s genome varies greatly between species. Previous work has identified certain environmental factors (e.g., oxygen availability) associated with the relative number of GC bases as opposed to AT bases in the genomes of species. Many of these environments that are associated with high GC content are also associated with relatively high rates of DNA damage. We show that organisms possessing the non-homologous end-joining DNA repair pathway, which is one mechanism to repair DNA double-strand breaks, have an elevated GC content relative to expectation. We also show that certain sites on the genome that are particularly susceptible to double strand breaks have an elevated GC content. This leads us to suggest that an important underlying driver of variability in nucleotide composition across environments is the rate of DNA damage (specifically double-strand breaks) to which an organism living in each environment is exposed.
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Affiliation(s)
- JL Weissman
- Department of Biology, University of Maryland - College Park, College Park, Maryland, United States of America
| | - William F. Fagan
- Department of Biology, University of Maryland - College Park, College Park, Maryland, United States of America
| | - Philip L. F. Johnson
- Department of Biology, University of Maryland - College Park, College Park, Maryland, United States of America
- * E-mail:
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45
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Abstract
Due to the promiscuous exchange of genetic material and asexual reproduction, delineating microbial species (and, by extension, populations) remains challenging. Because of this, the vast majority of microbial studies assessing population structure often compare divergent strains from disparate environments under varied selective pressures. Here, we investigated the population structure within a single bacterial ecotype, a unit equivalent to a eukaryotic species, defined as highly clustered genotypic and phenotypic strains with the same ecological niche. Using a combination of genomic and computational analyses, we assessed the phylogenetic structure, extent of recombination, and flexible gene content of this genomic diversity to infer patterns of gene flow. To our knowledge, this study is the first to do so for a dominant soil bacterium. Our results indicate that bacterial soil populations, similarly to those in other environments, are structured by gene flow discontinuities and exhibit distributional patterns consistent with both isolation by distance and isolation by environment. Thus, both dispersal limitation and local environments contribute to the divergence among closely related soil bacteria as observed in macroorganisms. For free-living bacteria and archaea, the equivalent of the biological species concept does not exist, creating several obstacles to the study of the processes contributing to microbial diversification. These obstacles are particularly high in soil, where high bacterial diversity inhibits the study of closely related genotypes and therefore the factors structuring microbial populations. Here, we isolated strains within a single Curtobacterium ecotype from surface soil (leaf litter) across a regional climate gradient and investigated the phylogenetic structure, recombination, and flexible gene content of this genomic diversity to infer patterns of gene flow. Our results indicate that microbial populations are delineated by gene flow discontinuities, with distinct populations cooccurring at multiple sites. Bacterial population structure was further delineated by genomic features allowing for the identification of candidate genes possibly contributing to local adaptation. These results suggest that the genetic structure within this bacterium is maintained both by ecological specialization in localized microenvironments (isolation by environment) and by dispersal limitation between geographic locations (isolation by distance).
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47
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Delmont TO, Kiefl E, Kilinc O, Esen OC, Uysal I, Rappé MS, Giovannoni S, Eren AM. Single-amino acid variants reveal evolutionary processes that shape the biogeography of a global SAR11 subclade. eLife 2019; 8:46497. [PMID: 31478833 PMCID: PMC6721796 DOI: 10.7554/elife.46497] [Citation(s) in RCA: 60] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2019] [Accepted: 08/13/2019] [Indexed: 12/14/2022] Open
Abstract
Members of the SAR11 order Pelagibacterales dominate the surface oceans. Their extensive diversity challenges emerging operational boundaries defined for microbial 'species' and complicates efforts of population genetics to study their evolution. Here, we employed single-amino acid variants (SAAVs) to investigate ecological and evolutionary forces that maintain the genomic heterogeneity within ubiquitous SAR11 populations we accessed through metagenomic read recruitment using a single isolate genome. Integrating amino acid and protein biochemistry with metagenomics revealed that systematic purifying selection against deleterious variants governs non-synonymous variation among very closely related populations of SAR11. SAAVs partitioned metagenomes into two main groups matching large-scale oceanic current temperatures, and six finer proteotypes that connect distant oceanic regions. These findings suggest that environmentally-mediated selection plays a critical role in the journey of cosmopolitan surface ocean microbial populations, and the idea 'everything is everywhere but the environment selects' has credence even at the finest resolutions.
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Affiliation(s)
- Tom O Delmont
- Department of Medicine, The University of Chicago, Chicago, United States
| | - Evan Kiefl
- Department of Medicine, The University of Chicago, Chicago, United States.,Graduate Program in Biophysical Sciences, University of Chicago, Chicago, United States
| | - Ozsel Kilinc
- Department of Electrical Engineering, University of South Florida, Tampa, United States
| | - Ozcan C Esen
- Department of Medicine, The University of Chicago, Chicago, United States
| | - Ismail Uysal
- Department of Electrical Engineering, University of South Florida, Tampa, United States
| | - Michael S Rappé
- Hawaii Institute of Marine Biology, University of Hawaii at Manoa, Kaneohe, United States
| | - Steven Giovannoni
- Department of Microbiology, Oregon State University, Corvallis, United States
| | - A Murat Eren
- Department of Medicine, The University of Chicago, Chicago, United States.,Marine Biological Laboratory, Woods Hole, United States
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48
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A Reverse Ecology Approach Based on a Biological Definition of Microbial Populations. Cell 2019; 178:820-834.e14. [DOI: 10.1016/j.cell.2019.06.033] [Citation(s) in RCA: 74] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2019] [Revised: 05/28/2019] [Accepted: 06/24/2019] [Indexed: 01/30/2023]
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49
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Remigi P, Masson-Boivin C, Rocha EP. Experimental Evolution as a Tool to Investigate Natural Processes and Molecular Functions. Trends Microbiol 2019; 27:623-634. [DOI: 10.1016/j.tim.2019.02.003] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2018] [Revised: 01/31/2019] [Accepted: 02/05/2019] [Indexed: 12/17/2022]
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50
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Concepts of the last eukaryotic common ancestor. Nat Ecol Evol 2019; 3:338-344. [DOI: 10.1038/s41559-019-0796-3] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2018] [Accepted: 01/03/2019] [Indexed: 12/27/2022]
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