1
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Cantin LJ, Dunning Hotopp JC, Foster JM. Improved metagenome assemblies through selective enrichment of bacterial genomic DNA from eukaryotic host genomic DNA using ATAC-seq. Front Microbiol 2024; 15:1352378. [PMID: 38426058 PMCID: PMC10902005 DOI: 10.3389/fmicb.2024.1352378] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2023] [Accepted: 02/05/2024] [Indexed: 03/02/2024] Open
Abstract
Genomics can be used to study the complex relationships between hosts and their microbiota. Many bacteria cannot be cultured in the laboratory, making it difficult to obtain adequate amounts of bacterial DNA and to limit host DNA contamination for the construction of metagenome-assembled genomes (MAGs). For example, Wolbachia is a genus of exclusively obligate intracellular bacteria that live in a wide range of arthropods and some nematodes. While Wolbachia endosymbionts are frequently described as facultative reproductive parasites in arthropods, the bacteria are obligate mutualistic endosymbionts of filarial worms. Here, we achieve 50-fold enrichment of bacterial sequences using ATAC-seq (Assay for Transposase-Accessible Chromatin using sequencing) with Brugia malayi nematodes, containing Wolbachia (wBm). ATAC-seq uses the Tn5 transposase to cut and attach Illumina sequencing adapters to accessible DNA lacking histones, typically thought to be open chromatin. Bacterial and mitochondrial DNA in the lysates are also cut preferentially since they lack histones, leading to the enrichment of these sequences. The benefits of this include minimal tissue input (<1 mg of tissue), a quick protocol (<4 h), low sequencing costs, less bias, correct assembly of lateral gene transfers and no prior sequence knowledge required. We assembled the wBm genome with as few as 1 million Illumina short paired-end reads with >97% coverage of the published genome, compared to only 12% coverage with the standard gDNA libraries. We found significant bacterial sequence enrichment that facilitated genome assembly in previously published ATAC-seq data sets from human cells infected with Mycobacterium tuberculosis and C. elegans contaminated with their food source, the OP50 strain of E. coli. These results demonstrate the feasibility and benefits of using ATAC-seq to easily obtain bacterial genomes to aid in symbiosis, infectious disease, and microbiome research.
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Affiliation(s)
- Lindsey J. Cantin
- Biochemistry and Microbiology Division, New England BioLabs, Ipswich, MA, United States
| | - Julie C. Dunning Hotopp
- Institute for Genome Sciences, University of Maryland School of Medicine, Baltimore, MD, United States
| | - Jeremy M. Foster
- Biochemistry and Microbiology Division, New England BioLabs, Ipswich, MA, United States
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2
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Riley AB, Grillo MA, Epstein B, Tiffin P, Heath KD. Discordant population structure among rhizobium divided genomes and their legume hosts. Mol Ecol 2023; 32:2646-2659. [PMID: 36161739 DOI: 10.1111/mec.16704] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2021] [Revised: 09/15/2022] [Accepted: 09/20/2022] [Indexed: 11/29/2022]
Abstract
Symbiosis often occurs between partners with distinct life history characteristics and dispersal mechanisms. Many bacterial symbionts have genomes comprising multiple replicons with distinct rates of evolution and horizontal transmission. Such differences might drive differences in population structure between hosts and symbionts and among the elements of the divided genomes of bacterial symbionts. These differences might, in turn, shape the evolution of symbiotic interactions and bacterial evolution. Here we use whole genome resequencing of a hierarchically structured sample of 191 strains of Sinorhizobium meliloti collected from 21 locations in southern Europe to characterize population structures of this bacterial symbiont, which forms a root nodule symbiosis with the host plant Medicago truncatula. S. meliloti genomes showed high local (within-site) variation and little isolation by distance. This was particularly true for the two symbiosis elements, pSymA and pSymB, which have population structures that are similar to each other, but distinct from both the bacterial chromosome and the host plant. Given limited recombination on the chromosome, compared to the symbiosis elements, distinct population structures may result from differences in effective gene flow. Alternatively, positive or purifying selection, with little recombination, may explain distinct geographical patterns at the chromosome. Discordant population structure between hosts and symbionts indicates that geographically and genetically distinct host populations in different parts of the range might interact with genetically similar symbionts, potentially minimizing local specialization.
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Affiliation(s)
- Alex B Riley
- Department of Plant Biology, University of Illinois, Urbana, Illinois, USA
| | - Michael A Grillo
- Department of Biology, Loyola University Chicago, Chicago, Illinois, USA
| | - Brendan Epstein
- Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, USA
| | - Peter Tiffin
- Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, USA
| | - Katy D Heath
- Department of Plant Biology, University of Illinois, Urbana, Illinois, USA
- Carl R. Woese Institute for Genomic Biology, University of Illinois, Urbana, Illinois, USA
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3
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Adaptive Evolution of Rhizobial Symbiosis beyond Horizontal Gene Transfer: From Genome Innovation to Regulation Reconstruction. Genes (Basel) 2023; 14:genes14020274. [PMID: 36833201 PMCID: PMC9957244 DOI: 10.3390/genes14020274] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2022] [Revised: 01/17/2023] [Accepted: 01/18/2023] [Indexed: 01/22/2023] Open
Abstract
There are ubiquitous variations in symbiotic performance of different rhizobial strains associated with the same legume host in agricultural practices. This is due to polymorphisms of symbiosis genes and/or largely unexplored variations in integration efficiency of symbiotic function. Here, we reviewed cumulative evidence on integration mechanisms of symbiosis genes. Experimental evolution, in concert with reverse genetic studies based on pangenomics, suggests that gain of the same circuit of key symbiosis genes through horizontal gene transfer is necessary but sometimes insufficient for bacteria to establish an effective symbiosis with legumes. An intact genomic background of the recipient may not support the proper expression or functioning of newly acquired key symbiosis genes. Further adaptive evolution, through genome innovation and reconstruction of regulation networks, may confer the recipient of nascent nodulation and nitrogen fixation ability. Other accessory genes, either co-transferred with key symbiosis genes or stochastically transferred, may provide the recipient with additional adaptability in ever-fluctuating host and soil niches. Successful integrations of these accessory genes with the rewired core network, regarding both symbiotic and edaphic fitness, can optimize symbiotic efficiency in various natural and agricultural ecosystems. This progress also sheds light on the development of elite rhizobial inoculants using synthetic biology procedures.
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4
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Genome-Wide Association Studies across Environmental and Genetic Contexts Reveal Complex Genetic Architecture of Symbiotic Extended Phenotypes. mBio 2022; 13:e0182322. [PMID: 36286519 PMCID: PMC9765617 DOI: 10.1128/mbio.01823-22] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A goal of modern biology is to develop the genotype-phenotype (G→P) map, a predictive understanding of how genomic information generates trait variation that forms the basis of both natural and managed communities. As microbiome research advances, however, it has become clear that many of these traits are symbiotic extended phenotypes, being governed by genetic variation encoded not only by the host's own genome, but also by the genomes of myriad cryptic symbionts. Building a reliable G→P map therefore requires accounting for the multitude of interacting genes and even genomes involved in symbiosis. Here, we use naturally occurring genetic variation in 191 strains of the model microbial symbiont Sinorhizobium meliloti paired with two genotypes of the host Medicago truncatula in four genome-wide association studies (GWAS) to determine the genomic architecture of a key symbiotic extended phenotype-partner quality, or the fitness benefit conferred to a host by a particular symbiont genotype, within and across environmental contexts and host genotypes. We define three novel categories of loci in rhizobium genomes that must be accounted for if we want to build a reliable G→P map of partner quality; namely, (i) loci whose identities depend on the environment, (ii) those that depend on the host genotype with which rhizobia interact, and (iii) universal loci that are likely important in all or most environments. IMPORTANCE Given the rapid rise of research on how microbiomes can be harnessed to improve host health, understanding the contribution of microbial genetic variation to host phenotypic variation is pressing, and will better enable us to predict the evolution of (and select more precisely for) symbiotic extended phenotypes that impact host health. We uncover extensive context-dependency in both the identity and functions of symbiont loci that control host growth, which makes predicting the genes and pathways important for determining symbiotic outcomes under different conditions more challenging. Despite this context-dependency, we also resolve a core set of universal loci that are likely important in all or most environments, and thus, serve as excellent targets both for genetic engineering and future coevolutionary studies of symbiosis.
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5
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Luu TB, Ourth A, Pouzet C, Pauly N, Cullimore J. A newly evolved chimeric lysin motif receptor-like kinase in Medicago truncatula spp. tricycla R108 extends its Rhizobia symbiotic partnership. THE NEW PHYTOLOGIST 2022; 235:1995-2007. [PMID: 35611584 DOI: 10.1111/nph.18270] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2022] [Accepted: 05/11/2022] [Indexed: 06/15/2023]
Abstract
Rhizobial lipochitooligosaccharidic Nod factors (NFs), specified by nod genes, are the primary determinants of host specificity in the legume-Rhizobia symbiosis. We examined the nodulation ability of Medicago truncatula cv Jemalong A17 and M. truncatula ssp. tricycla R108 with the Sinorhizobium meliloti nodF/nodL mutant, which produces modified NFs. We then applied genetic and functional approaches to study the genetic basis and mechanism of nodulation of R108 by this mutant. We show that the nodF/nodL mutant can nodulate R108 but not A17. Using genomics and reverse genetics, we identified a newly evolved, chimeric LysM receptor-like kinase gene in R108, LYK2bis, which is responsible for the phenotype and can allow A17 to gain nodulation with the nodF/nodL mutant. We found that LYK2bis is involved in nodulation by mutants producing nonO-acetylated NFs and interacts with the key receptor protein NFP. Many, but not all, natural S. meliloti and S. medicae strains tested require LYK2bis for efficient nodulation of R108. Our findings reveal that a newly evolved gene in R108, LYK2bis, extends nodulation specificity to mutants producing nonO-acetylated NFs and is important for nodulation by many natural Sinorhizobia. Evolution of this gene may present an adaptive advantage to allow nodulation by a greater variety of strains.
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Affiliation(s)
- Thi-Bich Luu
- Laboratory of Plant-Microbe Interactions and Environment (LIPME), University Toulouse III, INRAE, CNRS, 31326, Castanet-Tolosan Cedex, France
| | - Anna Ourth
- Laboratory of Plant-Microbe Interactions and Environment (LIPME), University Toulouse III, INRAE, CNRS, 31326, Castanet-Tolosan Cedex, France
| | - Cécile Pouzet
- FRAIB-TRI Imaging Platform Facilities, FR AIB, Université de Toulouse, CNRS, 31320, Castanet-Tolosan, France
| | - Nicolas Pauly
- Laboratory of Plant-Microbe Interactions and Environment (LIPME), University Toulouse III, INRAE, CNRS, 31326, Castanet-Tolosan Cedex, France
- Institut Sophia Agrobiotech, Université Côte d'Azur, INRAE, CNRS, 06903, Sophia Antipolis Cedex, France
| | - Julie Cullimore
- Laboratory of Plant-Microbe Interactions and Environment (LIPME), University Toulouse III, INRAE, CNRS, 31326, Castanet-Tolosan Cedex, France
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6
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Epstein B, Burghardt LT, Heath KD, Grillo MA, Kostanecki A, Hämälä T, Young ND, Tiffin P. Combining GWAS and population genomic analyses to characterize coevolution in a legume-rhizobia symbiosis. Mol Ecol 2022. [PMID: 35793264 DOI: 10.1111/mec.16602] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2022] [Revised: 06/03/2022] [Accepted: 07/04/2022] [Indexed: 11/28/2022]
Abstract
The mutualism between legumes and rhizobia is clearly the product of past coevolution. However, the nature of ongoing evolution between these partners is less clear. To characterize the nature of recent coevolution between legumes and rhizobia, we used population genomic analysis to characterize selection on functionally annotated symbiosis genes as well as on symbiosis gene candidates identified through a two-species association analysis. For the association analysis, we inoculated each of 202 accessions of the legume host Medicago truncatula with a community of 88 Sinorhizobia (Ensifer) meliloti strains. Multistrain inoculation, which better reflects the ecological reality of rhizobial selection in nature than single-strain inoculation, allows strains to compete for nodulation opportunities and host resources and for hosts to preferentially form nodules and provide resources to some strains. We found extensive host by symbiont, that is, genotype-by-genotype, effects on rhizobial fitness and some annotated rhizobial genes bear signatures of recent positive selection. However, neither genes responsible for this variation nor annotated host symbiosis genes are enriched for signatures of either positive or balancing selection. This result suggests that stabilizing selection dominates selection acting on symbiotic traits and that variation in these traits is under mutation-selection balance. Consistent with the lack of positive selection acting on host genes, we found that among-host variation in growth was similar whether plants were grown with rhizobia or N-fertilizer, suggesting that the symbiosis may not be a major driver of variation in plant growth in multistrain contexts.
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Affiliation(s)
- Brendan Epstein
- Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, USA
| | - Liana T Burghardt
- Department of Plant Sciences, The University of Pennsylvania, University Park, Pennsylvania, USA
| | - Katy D Heath
- Department of Plant Biology, University of Illinois, Urbana, Illinois, USA.,Carl R. Woese Institute for Genomic Biology, University of Illinois, Urbana, Illinois, USA
| | - Michael A Grillo
- Department of Biology, Loyola University Chicago, Chicago, Illinois, USA
| | - Adam Kostanecki
- Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, USA
| | - Tuomas Hämälä
- Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, USA.,School of Life Sciences, University of Nottingham, Nottingham, UK
| | - Nevin D Young
- Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, USA.,Department of Plant Pathology, University of Minnesota, St. Paul, Minnesota, USA
| | - Peter Tiffin
- Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, USA
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7
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MGEs as the MVPs of Partner Quality Variation in Legume-Rhizobium Symbiosis. mBio 2022; 13:e0088822. [PMID: 35758609 PMCID: PMC9426554 DOI: 10.1128/mbio.00888-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Despite decades of research, we are only just beginning to understand the forces maintaining variation in the nitrogen-fixing symbiosis between rhizobial bacteria and leguminous plants. In their recent work, Alexandra Weisberg and colleagues use genomics to document the breadth of mobile element diversity that carries the symbiosis genes of Bradyrhizobium in natural populations. Studying rhizobia from the perspective of their mobile genetic elements, which have their own transmission modes and fitness interests, reveals novel mechanisms for the generation and maintenance of diversity in natural populations of these ecologically and economically important mutualisms.
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8
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Cangioli L, Vaccaro F, Fini M, Mengoni A, Fagorzi C. Scent of a Symbiont: The Personalized Genetic Relationships of Rhizobium—Plant Interaction. Int J Mol Sci 2022; 23:ijms23063358. [PMID: 35328782 PMCID: PMC8954435 DOI: 10.3390/ijms23063358] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2022] [Revised: 03/17/2022] [Accepted: 03/18/2022] [Indexed: 01/24/2023] Open
Abstract
Many molecular signals are exchanged between rhizobia and host legume plants, some of which are crucial for symbiosis to take place, while others are modifiers of the interaction, which have great importance in the competition with the soil microbiota and in the genotype-specific perception of host plants. Here, we review recent findings on strain-specific and host genotype-specific interactions between rhizobia and legumes, discussing the molecular actors (genes, gene products and metabolites) which play a role in the establishment of symbiosis, and highlighting the need for research including the other components of the soil (micro)biota, which could be crucial in developing rational-based strategies for bioinoculants and synthetic communities’ assemblage.
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9
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Epstein B, Tiffin P. Comparative genomics reveals high rates of horizontal transfer and strong purifying selection on rhizobial symbiosis genes. Proc Biol Sci 2021; 288:20201804. [PMID: 33402066 DOI: 10.1098/rspb.2020.1804] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Horizontal transfer (HT) alters the repertoire of symbiosis genes in rhizobial genomes and may play an important role in the on-going evolution of the rhizobia-legume symbiosis. To gain insight into the extent of HT of symbiosis genes with different functional roles (nodulation, N-fixation, host benefit and rhizobial fitness), we conducted comparative genomic and selection analyses of the full-genome sequences from 27 rhizobial genomes. We find that symbiosis genes experience high rates of HT among rhizobial lineages but also bear signatures of purifying selection (low Ka : Ks). HT and purifying selection appear to be particularly strong in genes involved in initiating the symbiosis (e.g. nodulation) and in genome-wide association candidates for mediating benefits provided to the host. These patterns are consistent with rhizobia adapting to the host environment through the loss and gain of symbiosis genes, but not with host-imposed positive selection driving divergence of symbiosis genes through recurring bouts of positive selection.
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Affiliation(s)
- Brendan Epstein
- Department of Plant and Microbial Biology, University of Minnesota, St Paul, MN, USA
| | - Peter Tiffin
- Department of Plant and Microbial Biology, University of Minnesota, St Paul, MN, USA
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10
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Cavassim MIA, Moeskjær S, Moslemi C, Fields B, Bachmann A, Vilhjálmsson BJ, Schierup MH, W. Young JP, Andersen SU. Symbiosis genes show a unique pattern of introgression and selection within a Rhizobium leguminosarum species complex. Microb Genom 2020; 6:e000351. [PMID: 32176601 PMCID: PMC7276703 DOI: 10.1099/mgen.0.000351] [Citation(s) in RCA: 24] [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: 11/29/2019] [Accepted: 02/17/2020] [Indexed: 12/22/2022] Open
Abstract
Rhizobia supply legumes with fixed nitrogen using a set of symbiosis genes. These can cross rhizobium species boundaries, but it is unclear how many other genes show similar mobility. Here, we investigate inter-species introgression using de novo assembly of 196 Rhizobium leguminosarum sv. trifolii genomes. The 196 strains constituted a five-species complex, and we calculated introgression scores based on gene-tree traversal to identify 171 genes that frequently cross species boundaries. Rather than relying on the gene order of a single reference strain, we clustered the introgressing genes into four blocks based on population structure-corrected linkage disequilibrium patterns. The two largest blocks comprised 125 genes and included the symbiosis genes, a smaller block contained 43 mainly chromosomal genes, and the last block consisted of three genes with variable genomic location. All introgression events were likely mediated by conjugation, but only the genes in the symbiosis linkage blocks displayed overrepresentation of distinct, high-frequency haplotypes. The three genes in the last block were core genes essential for symbiosis that had, in some cases, been mobilized on symbiosis plasmids. Inter-species introgression is thus not limited to symbiosis genes and plasmids, but other cases are infrequent and show distinct selection signatures.
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Affiliation(s)
- Maria Izabel A. Cavassim
- Bioinformatics Research Centre, Aarhus University, Aarhus, Denmark
- Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
| | - Sara Moeskjær
- Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
| | - Camous Moslemi
- Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
| | | | - Asger Bachmann
- Bioinformatics Research Centre, Aarhus University, Aarhus, Denmark
| | | | | | | | - Stig U. Andersen
- Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
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11
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Burghardt LT, Trujillo DI, Epstein B, Tiffin P, Young ND. A Select and Resequence Approach Reveals Strain-Specific Effects of Medicago Nodule-Specific PLAT-Domain Genes. PLANT PHYSIOLOGY 2020; 182:463-471. [PMID: 31653715 PMCID: PMC6945875 DOI: 10.1104/pp.19.00831] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2019] [Accepted: 10/07/2019] [Indexed: 05/23/2023]
Abstract
Genetic studies of legume symbiosis with nitrogen-fixing rhizobial bacteria have traditionally focused on nodule and nitrogen-fixation phenotypes when hosts are inoculated with a single rhizobial strain. These approaches overlook the potential effect of host genes on rhizobial fitness (i.e. how many rhizobia are released from host nodules) and strain-specific effects of host genes (i.e. genome × genome interactions). Using Medicago truncatula mutants in the recently described nodule-specific PLAT domain (NPD) gene family, we show how inoculating plants with a mixed inoculum of 68 rhizobial strains (Ensifer meliloti) via a select-and-resequence approach can be used to efficiently assay host mutants for strain-specific effects of late-acting host genes on interacting bacteria. The deletion of a single NPD gene (npd2) or all five members of the NPD gene family (npd1-5) differentially altered the frequency of rhizobial strains in nodules even though npd2 mutants had no visible nodule morphology or N-fixation phenotype. Also, npd1-5 nodules were less diverse and had larger populations of colony-forming rhizobia despite their smaller size. Lastly, NPD mutations disrupt a positive correlation between strain fitness and wild-type host biomass. These changes indicate that the effects of NPD proteins are strain dependent and that NPD family members are not redundant with regard to their effects on rhizobial strains. Association analyses of the rhizobial strains in the mixed inoculation indicate that rhizobial genes involved in chromosome segregation, cell division, GABA metabolism, efflux systems, and stress tolerance play an important role in the strain-specific effects of NPD genes.
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Affiliation(s)
- Liana T Burghardt
- Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota 55108
| | - Diana I Trujillo
- Department of Plant Pathology, University of Minnesota, St. Paul, Minnesota 55108
| | - Brendan Epstein
- Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota 55108
| | - Peter Tiffin
- Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota 55108
| | - Nevin D Young
- Department of Plant Pathology, University of Minnesota, St. Paul, Minnesota 55108
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12
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Smith BA, Leligdon C, Baltrus DA. Just the Two of Us? A Family of Pseudomonas Megaplasmids Offers a Rare Glimpse into the Evolution of Large Mobile Elements. Genome Biol Evol 2019; 11:1192-1206. [PMID: 30918968 PMCID: PMC6482414 DOI: 10.1093/gbe/evz066] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/26/2019] [Indexed: 02/06/2023] Open
Abstract
Pseudomonads are ubiquitous group of environmental proteobacteria, well known for their roles in biogeochemical cycling, in the breakdown of xenobiotic materials, as plant growth promoters, and as pathogens of a variety of host organisms. We have previously identified a large megaplasmid present within one isolate of the plant pathogen Pseudomonas syringae, and here we report that a second member of this megaplasmid family is found within an environmental Pseudomonad isolate most closely related to Pseudomonas putida. Many of the shared genes are involved in critical cellular processes like replication, transcription, translation, and DNA repair. We argue that presence of these shared pathways sheds new light on discussions about the types of genes that undergo horizontal gene transfer (i.e., the complexity hypothesis) as well as the evolution of pangenomes. Furthermore, although both megaplasmids display a high level of synteny, genes that are shared differ by over 50% on average at the amino acid level. This combination of conservation in gene order despite divergence in gene sequence suggests that this Pseudomonad megaplasmid family is relatively old, that gene order is under strong selection within this family, and that there are likely many more members of this megaplasmid family waiting to be found in nature.
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Affiliation(s)
| | | | - David A Baltrus
- School of Plant Sciences, University of Arizona.,School of Animal and Comparative Biomedical Sciences, University of Arizona
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13
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diCenzo GC, Mengoni A, Perrin E. Chromids Aid Genome Expansion and Functional Diversification in the Family Burkholderiaceae. Mol Biol Evol 2019; 36:562-574. [PMID: 30608550 DOI: 10.1093/molbev/msy248] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Multipartite genomes, containing at least two large replicons, are found in diverse bacteria; however, the advantage of this genome structure remains incompletely understood. Here, we perform comparative genomics of hundreds of finished β-proteobacterial genomes to gain insights into the role and emergence of multipartite genomes. Almost all essential secondary replicons (chromids) of the β-proteobacteria are found in the family Burkholderiaceae. These replicons arose from just two plasmid acquisition events, and they were likely stabilized early in their evolution by the presence of core genes. On average, Burkholderiaceae genera with multipartite genomes had a larger total genome size, but smaller chromosome, than genera without secondary replicons. Pangenome-level functional enrichment analyses suggested that interreplicon functional biases are partially driven by the enrichment of secondary replicons in the accessory pangenome fraction. Nevertheless, the small overlap in orthologous groups present in each replicon's pangenome indicated a clear functional separation of the replicons. Chromids appeared biased to environmental adaptation, as the functional categories enriched on chromids were also overrepresented on the chromosomes of the environmental genera (Paraburkholderia and Cupriavidus) compared with the pathogenic genera (Burkholderia and Ralstonia). Using ancestral state reconstruction, it was predicted that the rate of accumulation of modern-day genes by chromids was more rapid than the rate of gene accumulation by the chromosomes. Overall, the data are consistent with a model where the primary advantage of secondary replicons is in facilitating increased rates of gene acquisition through horizontal gene transfer, consequently resulting in replicons enriched in genes associated with adaptation to novel environments.
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Affiliation(s)
- George C diCenzo
- Department of Biology, University of Florence, Sesto Fiorentino, Florence, Italy
| | - Alessio Mengoni
- Department of Biology, University of Florence, Sesto Fiorentino, Florence, Italy
| | - Elena Perrin
- Department of Biology, University of Florence, Sesto Fiorentino, Florence, Italy
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14
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Gano‐Cohen KA, Wendlandt CE, Stokes PJ, Blanton MA, Quides KW, Zomorrodian A, Adinata ES, Sachs JL. Interspecific conflict and the evolution of ineffective rhizobia. Ecol Lett 2019; 22:914-924. [DOI: 10.1111/ele.13247] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2019] [Accepted: 02/07/2019] [Indexed: 12/25/2022]
Affiliation(s)
- Kelsey A. Gano‐Cohen
- Department of Microbiology and Plant Pathology University of California Riverside CA USA
- Department of Evolution Ecology & Organismal Biology University of California Riverside CA USA
| | - Camille E. Wendlandt
- Department of Evolution Ecology & Organismal Biology University of California Riverside CA USA
- Department of Botany and Plant Sciences University of California Riverside CA USA
| | - Peter J. Stokes
- Department of Evolution Ecology & Organismal Biology University of California Riverside CA USA
| | - Mia A. Blanton
- Department of Evolution Ecology & Organismal Biology University of California Riverside CA USA
| | - Kenjiro W. Quides
- Department of Evolution Ecology & Organismal Biology University of California Riverside CA USA
| | - Avissa Zomorrodian
- Department of Evolution Ecology & Organismal Biology University of California Riverside CA USA
| | - Eunice S. Adinata
- Department of Evolution Ecology & Organismal Biology University of California Riverside CA USA
| | - Joel L. Sachs
- Department of Microbiology and Plant Pathology University of California Riverside CA USA
- Department of Evolution Ecology & Organismal Biology University of California Riverside CA USA
- Department of Botany and Plant Sciences University of California Riverside CA USA
- Institute for Integrative Genome Biology University of California Riverside CA USA
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15
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Kramer EM, Statter SA, Yi HJ, Carlson JW, McClelland DHR. Flowering plant immune repertoires expand under mycorrhizal symbiosis. PLANT DIRECT 2019; 3:e00125. [PMID: 31245768 PMCID: PMC6508770 DOI: 10.1002/pld3.125] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/22/2018] [Revised: 02/13/2019] [Accepted: 02/14/2019] [Indexed: 06/09/2023]
Abstract
Immune perception in flowering plants is mediated by a repertoire of cytoplasmic and cell-surface receptors that detect invading microbes and their effects on cells. Here, we show that several large families of immune receptors exhibit size variations related to a plant's competence to host symbiotic root fungi (mycorrhiza). Plants that do not participate in mycorrhizal associations have significantly smaller immune repertoires, while the most promiscuous symbiotic hosts (ectomycorrhizal plant species) have significantly larger immune repertoires. By contrast, we find no significant increase in immune repertoire size among legumes competent to form a symbiosis with nitrogen-fixing bacteria (rhizobia). To explain these observations, we hypothesize that plant immune repertoire size expands with symbiote species diversity.
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Affiliation(s)
- Eric M. Kramer
- Department of PhysicsBard College at Simon's RockGreat BarringtonMassachusetts
| | - Samantha A. Statter
- Department of PhysicsBard College at Simon's RockGreat BarringtonMassachusetts
| | - Ho Jun Yi
- Department of PhysicsBard College at Simon's RockGreat BarringtonMassachusetts
| | - Joseph W. Carlson
- Lawrence Berkeley National LaboratoryJoint Genome InstituteBerkeleyCalifornia
| | - Donald H. R. McClelland
- Department of Environmental ScienceBard College at Simon's RockGreat BarringtonMassachusetts
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16
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Lassalle F, Planel R, Penel S, Chapulliot D, Barbe V, Dubost A, Calteau A, Vallenet D, Mornico D, Bigot T, Guéguen L, Vial L, Muller D, Daubin V, Nesme X. Ancestral Genome Estimation Reveals the History of Ecological Diversification in Agrobacterium. Genome Biol Evol 2018; 9:3413-3431. [PMID: 29220487 PMCID: PMC5739047 DOI: 10.1093/gbe/evx255] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/01/2017] [Indexed: 12/12/2022] Open
Abstract
Horizontal gene transfer (HGT) is considered as a major source of innovation in bacteria, and as such is expected to drive adaptation to new ecological niches. However, among the many genes acquired through HGT along the diversification history of genomes, only a fraction may have actively contributed to sustained ecological adaptation. We used a phylogenetic approach accounting for the transfer of genes (or groups of genes) to estimate the history of genomes in Agrobacterium biovar 1, a diverse group of soil and plant-dwelling bacterial species. We identified clade-specific blocks of cotransferred genes encoding coherent biochemical pathways that may have contributed to the evolutionary success of key Agrobacterium clades. This pattern of gene coevolution rejects a neutral model of transfer, in which neighboring genes would be transferred independently of their function and rather suggests purifying selection on collectively coded acquired pathways. The acquisition of these synapomorphic blocks of cofunctioning genes probably drove the ecological diversification of Agrobacterium and defined features of ancestral ecological niches, which consistently hint at a strong selective role of host plant rhizospheres.
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Affiliation(s)
- Florent Lassalle
- Ecologie Microbienne, CNRS, INRA, VetAgro Sup, UCBL, Université de Lyon, Villeurbanne, France.,Biométrie et Biologie Evolutive, CNRS, UCBL, Université de Lyon, Villeurbanne, France.,Ecole Normale Supérieure de Lyon, Lyon, France
| | - Rémi Planel
- Biométrie et Biologie Evolutive, CNRS, UCBL, Université de Lyon, Villeurbanne, France
| | - Simon Penel
- Biométrie et Biologie Evolutive, CNRS, UCBL, Université de Lyon, Villeurbanne, France
| | - David Chapulliot
- Ecologie Microbienne, CNRS, INRA, VetAgro Sup, UCBL, Université de Lyon, Villeurbanne, France
| | - Valérie Barbe
- Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA) Direction de la Recherche Fondamentale, Institut de Biologie Francois-Jacob (IBFJ), Genoscope, Evry, France
| | - Audrey Dubost
- Ecologie Microbienne, CNRS, INRA, VetAgro Sup, UCBL, Université de Lyon, Villeurbanne, France
| | - Alexandra Calteau
- Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA) Direction de la Recherche Fondamentale, Institut de Biologie Francois-Jacob (IBFJ), Genoscope, Evry, France.,Laboratoire d'Analyse Bioinformatiques pour la Génomique et le Métabolisme, CNRS, UMR 8030, Evry, France.,UEVE, Université d'Evry Val d'Essonne, France
| | - David Vallenet
- Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA) Direction de la Recherche Fondamentale, Institut de Biologie Francois-Jacob (IBFJ), Genoscope, Evry, France.,Laboratoire d'Analyse Bioinformatiques pour la Génomique et le Métabolisme, CNRS, UMR 8030, Evry, France.,UEVE, Université d'Evry Val d'Essonne, France
| | - Damien Mornico
- Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA) Direction de la Recherche Fondamentale, Institut de Biologie Francois-Jacob (IBFJ), Genoscope, Evry, France.,Laboratoire d'Analyse Bioinformatiques pour la Génomique et le Métabolisme, CNRS, UMR 8030, Evry, France.,UEVE, Université d'Evry Val d'Essonne, France
| | - Thomas Bigot
- Biométrie et Biologie Evolutive, CNRS, UCBL, Université de Lyon, Villeurbanne, France
| | - Laurent Guéguen
- Biométrie et Biologie Evolutive, CNRS, UCBL, Université de Lyon, Villeurbanne, France
| | - Ludovic Vial
- Ecologie Microbienne, CNRS, INRA, VetAgro Sup, UCBL, Université de Lyon, Villeurbanne, France
| | - Daniel Muller
- Ecologie Microbienne, CNRS, INRA, VetAgro Sup, UCBL, Université de Lyon, Villeurbanne, France
| | - Vincent Daubin
- Biométrie et Biologie Evolutive, CNRS, UCBL, Université de Lyon, Villeurbanne, France
| | - Xavier Nesme
- Ecologie Microbienne, CNRS, INRA, VetAgro Sup, UCBL, Université de Lyon, Villeurbanne, France
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17
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Abstract
Genome-wide association studies (GWAS) can identify genetic variants responsible for naturally occurring and quantitative phenotypic variation. Association studies therefore provide a powerful complement to approaches that rely on de novo mutations for characterizing gene function. Although bacteria should be amenable to GWAS, few GWAS have been conducted on bacteria, and the extent to which nonindependence among genomic variants (e.g., linkage disequilibrium [LD]) and the genetic architecture of phenotypic traits will affect GWAS performance is unclear. We apply association analyses to identify candidate genes underlying variation in 20 biochemical, growth, and symbiotic phenotypes among 153 strains of Ensifer meliloti For 11 traits, we find genotype-phenotype associations that are stronger than expected by chance, with the candidates in relatively small linkage groups, indicating that LD does not preclude resolving association candidates to relatively small genomic regions. The significant candidates show an enrichment for nucleotide polymorphisms (SNPs) over gene presence-absence variation (PAV), and for five traits, candidates are enriched in large linkage groups, a possible signature of epistasis. Many of the variants most strongly associated with symbiosis phenotypes were in genes previously identified as being involved in nitrogen fixation or nodulation. For other traits, apparently strong associations were not stronger than the range of associations detected in permuted data. In sum, our data show that GWAS in bacteria may be a powerful tool for characterizing genetic architecture and identifying genes responsible for phenotypic variation. However, careful evaluation of candidates is necessary to avoid false signals of association.IMPORTANCE Genome-wide association analyses are a powerful approach for identifying gene function. These analyses are becoming commonplace in studies of humans, domesticated animals, and crop plants but have rarely been conducted in bacteria. We applied association analyses to 20 traits measured in Ensifer meliloti, an agriculturally and ecologically important bacterium because it fixes nitrogen when in symbiosis with leguminous plants. We identified candidate alleles and gene presence-absence variants underlying variation in symbiosis traits, antibiotic resistance, and use of various carbon sources; some of these candidates are in genes previously known to affect these traits whereas others were in genes that have not been well characterized. Our results point to the potential power of association analyses in bacteria, but also to the need to carefully evaluate the potential for false associations.
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18
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Porter SS, Faber-Hammond J, Montoya AP, Friesen ML, Sackos C. Dynamic genomic architecture of mutualistic cooperation in a wild population of Mesorhizobium. ISME JOURNAL 2018; 13:301-315. [PMID: 30218020 PMCID: PMC6331556 DOI: 10.1038/s41396-018-0266-y] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/29/2018] [Revised: 07/01/2018] [Accepted: 08/04/2018] [Indexed: 12/14/2022]
Abstract
Research on mutualism seeks to explain how cooperation can be maintained when uncooperative mutants co-occur with cooperative kin. Gains and losses of the gene modules required for cooperation punctuate symbiont phylogenies and drive lifestyle transitions between cooperative symbionts and uncooperative free-living lineages over evolutionary time. Yet whether uncooperative symbionts commonly evolve from within cooperative symbiont populations or from within distantly related lineages with antagonistic or free-living lifestyles (i.e., third-party mutualism exploiters or parasites), remains controversial. We use genomic data to show that genotypes that differ in the presence or absence of large islands of symbiosis genes are common within a single wild recombining population of Mesorhizobium symbionts isolated from host tissues and are an important source of standing heritable variation in cooperation in this population. In a focal population of Mesorhizobium, uncooperative variants that lack a symbiosis island segregate at 16% frequency in nodules, and genome size and symbiosis gene number are positively correlated with cooperation. This finding contrasts with the genomic architecture of variation in cooperation in other symbiont populations isolated from host tissues in which the islands of genes underlying cooperation are ubiquitous and variation in cooperation is primarily driven by allelic substitution and individual gene gain and loss events. Our study demonstrates that uncooperative mutants within mutualist populations can comprise a significant component of genetic variation in nature, providing biological rationale for models and experiments that seek to explain the maintenance of mutualism in the face of non-cooperators.
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Affiliation(s)
- Stephanie S Porter
- School of Biological Sciences, Washington State University, Vancouver, WA, 98686, USA.
| | - Joshua Faber-Hammond
- School of Biological Sciences, Washington State University, Vancouver, WA, 98686, USA
| | - Angeliqua P Montoya
- School of Biological Sciences, Washington State University, Vancouver, WA, 98686, USA
| | - Maren L Friesen
- Department of Plant Biology, Michigan State University, East Lansing, MI, 48824, USA.,Department of Plant Pathology, Washington State University, Pullman, WA, 99164, USA.,Department of Crop and Soil Sciences, Washington State University, Pullman, WA, 99164, USA
| | - Cynthia Sackos
- School of Biological Sciences, Washington State University, Vancouver, WA, 98686, USA
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19
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Nelson M, Guhlin J, Epstein B, Tiffin P, Sadowsky MJ. The complete replicons of 16 Ensifer meliloti strains offer insights into intra- and inter-replicon gene transfer, transposon-associated loci, and repeat elements. Microb Genom 2018; 4. [PMID: 29671722 PMCID: PMC5994717 DOI: 10.1099/mgen.0.000174] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Ensifer meliloti (formerly Rhizobium meliloti and Sinorhizobium meliloti) is a model bacterium for understanding legume–rhizobial symbioses. The tripartite genome of E. meliloti consists of a chromosome, pSymA and pSymB, and in some instances strain-specific accessory plasmids. The majority of previous sequencing studies have relied on the use of assemblies generated from short read sequencing, which leads to gaps and assembly errors. Here we used PacBio-based, long-read assemblies and were able to assemble, de novo, complete circular replicons. In this study, we sequenced, de novo-assembled and analysed 10 E. meliloti strains. Sequence comparisons were also done with data from six previously published genomes. We identified genome differences between the replicons, including mol% G+C and gene content, nucleotide repeats, and transposon-associated loci. Additionally, genomic rearrangements both within and between replicons were identified, providing insight into evolutionary processes at the structural level. There were few cases of inter-replicon gene transfer of core genes between the main replicons. Accessory plasmids were more similar to pSymA than to either pSymB or the chromosome, with respect to gene content, transposon content and G+C content. In our population, the accessory plasmids appeared to share an open genome with pSymA, which contains many nodulation- and nitrogen fixation-related genes. This may explain previous observations that horizontal gene transfer has a greater effect on the content of pSymA than pSymB, or the chromosome, and why some rhizobia show unstable nodulation phenotypes on legume hosts.
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Affiliation(s)
- Matthew Nelson
- 1Biotechnology Institute and Department of Soil, Water, and Climate, University of Minnesota, St. Paul, MN 55108, USA
| | - Joseph Guhlin
- 2Department of Plant and Microbial Biology, University of Minnesota, St. Paul, MN 55108, USA
| | - Brendan Epstein
- 2Department of Plant and Microbial Biology, University of Minnesota, St. Paul, MN 55108, USA
| | - Peter Tiffin
- 2Department of Plant and Microbial Biology, University of Minnesota, St. Paul, MN 55108, USA
| | - Michael J Sadowsky
- 1Biotechnology Institute and Department of Soil, Water, and Climate, University of Minnesota, St. Paul, MN 55108, USA
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20
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Toro N, Martínez-Abarca F, Molina-Sánchez MD, García-Rodríguez FM, Nisa-Martínez R. Contribution of Mobile Group II Introns to Sinorhizobium meliloti Genome Evolution. Front Microbiol 2018; 9:627. [PMID: 29670598 PMCID: PMC5894124 DOI: 10.3389/fmicb.2018.00627] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Accepted: 03/19/2018] [Indexed: 12/26/2022] Open
Abstract
Mobile group II introns are ribozymes and retroelements that probably originate from bacteria. Sinorhizobium meliloti, the nitrogen-fixing endosymbiont of legumes of genus Medicago, harbors a large number of these retroelements. One of these elements, RmInt1, has been particularly successful at colonizing this multipartite genome. Many studies have improved our understanding of RmInt1 and phylogenetically related group II introns, their mobility mechanisms, spread and dynamics within S. meliloti and closely related species. Although RmInt1 conserves the ancient retroelement behavior, its evolutionary history suggests that this group II intron has played a role in the short- and long-term evolution of the S. meliloti genome. We will discuss its proposed role in genome evolution by controlling the spread and coexistence of potentially harmful mobile genetic elements, by ectopic transposition to different genetic loci as a source of early genomic variation and by generating sequence variation after a very slow degradation process, through intron remnants that may have continued to evolve, contributing to bacterial speciation.
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Affiliation(s)
- Nicolás Toro
- Structure, Dynamics and Function of Rhizobacterial Genomes (Grupo de Ecología Genética de la Rizosfera), Department of Soil Microbiology and Symbiotic Systems, Consejo Superior de Investigaciones Científicas, Estación Experimental del Zaidín, Granada, Spain
| | - Francisco Martínez-Abarca
- Structure, Dynamics and Function of Rhizobacterial Genomes (Grupo de Ecología Genética de la Rizosfera), Department of Soil Microbiology and Symbiotic Systems, Consejo Superior de Investigaciones Científicas, Estación Experimental del Zaidín, Granada, Spain
| | - María D Molina-Sánchez
- Structure, Dynamics and Function of Rhizobacterial Genomes (Grupo de Ecología Genética de la Rizosfera), Department of Soil Microbiology and Symbiotic Systems, Consejo Superior de Investigaciones Científicas, Estación Experimental del Zaidín, Granada, Spain
| | - Fernando M García-Rodríguez
- Structure, Dynamics and Function of Rhizobacterial Genomes (Grupo de Ecología Genética de la Rizosfera), Department of Soil Microbiology and Symbiotic Systems, Consejo Superior de Investigaciones Científicas, Estación Experimental del Zaidín, Granada, Spain
| | - Rafael Nisa-Martínez
- Structure, Dynamics and Function of Rhizobacterial Genomes (Grupo de Ecología Genética de la Rizosfera), Department of Soil Microbiology and Symbiotic Systems, Consejo Superior de Investigaciones Científicas, Estación Experimental del Zaidín, Granada, Spain
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21
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Abstract
Rhizobia are some of the best-studied plant microbiota. These oligotrophic Alphaproteobacteria or Betaproteobacteria form symbioses with their legume hosts. Rhizobia must exist in soil and compete with other members of the microbiota before infecting legumes and forming N2-fixing bacteroids. These dramatic lifestyle and developmental changes are underpinned by large genomes and even more complex pan-genomes, which encompass the whole population and are subject to rapid genetic exchange. The ability to respond to plant signals and chemoattractants and to colonize nutrient-rich roots are crucial for the competitive success of these bacteria. The availability of a large body of genomic, physiological, biochemical and ecological studies makes rhizobia unique models for investigating community interactions and plant colonization.
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22
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Zhao R, Liu LX, Zhang YZ, Jiao J, Cui WJ, Zhang B, Wang XL, Li ML, Chen Y, Xiong ZQ, Chen WX, Tian CF. Adaptive evolution of rhizobial symbiotic compatibility mediated by co-evolved insertion sequences. THE ISME JOURNAL 2018; 12:101-111. [PMID: 28800133 PMCID: PMC5738999 DOI: 10.1038/ismej.2017.136] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/09/2017] [Revised: 06/22/2017] [Accepted: 07/12/2017] [Indexed: 11/08/2022]
Abstract
Mutualism between bacteria and eukaryotes has essential roles in the history of life, but the evolution of their compatibility is poorly understood. Here we show that different Sinorhizobium strains can form either nitrogen-fixing nodules or uninfected pseudonodules on certain cultivated soybeans, while being all effective microsymbionts of some wild soybeans. However, a few well-infected nodules can be found on a commercial soybean using inocula containing a mixed pool of Tn5 insertion mutants derived from an incompatible strain. Reverse genetics and genome sequencing of compatible mutants demonstrated that inactivation of T3SS (type three secretion system) accounted for this phenotypic change. These mutations in the T3SS gene cluster were dominated by parallel transpositions of insertion sequences (ISs) other than the introduced Tn5. This genetic and phenotypic change can also be achieved in an experimental evolution scenario on a laboratory time scale using incompatible wild-type strains as inocula. The ISs acting in the adaptive evolution of Sinorhizobium strains exhibit broader phyletic and replicon distributions than other ISs, and prefer target sequences of low GC% content, a characteristic feature of symbiosis plasmid where T3SS genes are located. These findings suggest an important role of co-evolved ISs in the adaptive evolution of rhizobial compatibility.
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Affiliation(s)
- Ran Zhao
- State Key Laboratory of Agrobiotechnology, MOA Key Laboratory of Soil Microbiology, Rhizobium Research Center, and College of Biological Sciences, China Agricultural University, Beijing, China
| | - Li Xue Liu
- State Key Laboratory of Agrobiotechnology, MOA Key Laboratory of Soil Microbiology, Rhizobium Research Center, and College of Biological Sciences, China Agricultural University, Beijing, China
| | - Yun Zeng Zhang
- State Key Laboratory of Agrobiotechnology, MOA Key Laboratory of Soil Microbiology, Rhizobium Research Center, and College of Biological Sciences, China Agricultural University, Beijing, China
| | - Jian Jiao
- State Key Laboratory of Agrobiotechnology, MOA Key Laboratory of Soil Microbiology, Rhizobium Research Center, and College of Biological Sciences, China Agricultural University, Beijing, China
| | - Wen Jing Cui
- State Key Laboratory of Agrobiotechnology, MOA Key Laboratory of Soil Microbiology, Rhizobium Research Center, and College of Biological Sciences, China Agricultural University, Beijing, China
| | - Biliang Zhang
- State Key Laboratory of Agrobiotechnology, MOA Key Laboratory of Soil Microbiology, Rhizobium Research Center, and College of Biological Sciences, China Agricultural University, Beijing, China
| | - Xiao Lin Wang
- State Key Laboratory of Agrobiotechnology, MOA Key Laboratory of Soil Microbiology, Rhizobium Research Center, and College of Biological Sciences, China Agricultural University, Beijing, China
| | - Meng Lin Li
- State Key Laboratory of Agrobiotechnology, MOA Key Laboratory of Soil Microbiology, Rhizobium Research Center, and College of Biological Sciences, China Agricultural University, Beijing, China
| | - Yi Chen
- State Key Laboratory of Agrobiotechnology, MOA Key Laboratory of Soil Microbiology, Rhizobium Research Center, and College of Biological Sciences, China Agricultural University, Beijing, China
| | - Zhu Qing Xiong
- State Key Laboratory of Agrobiotechnology, MOA Key Laboratory of Soil Microbiology, Rhizobium Research Center, and College of Biological Sciences, China Agricultural University, Beijing, China
| | - Wen Xin Chen
- State Key Laboratory of Agrobiotechnology, MOA Key Laboratory of Soil Microbiology, Rhizobium Research Center, and College of Biological Sciences, China Agricultural University, Beijing, China
| | - Chang Fu Tian
- State Key Laboratory of Agrobiotechnology, MOA Key Laboratory of Soil Microbiology, Rhizobium Research Center, and College of Biological Sciences, China Agricultural University, Beijing, China
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23
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Liu LX, Li QQ, Zhang YZ, Hu Y, Jiao J, Guo HJ, Zhang XX, Zhang B, Chen WX, Tian CF. The nitrate-reduction gene cluster components exert lineage-dependent contributions to optimization of Sinorhizobium symbiosis with soybeans. Environ Microbiol 2017; 19:4926-4938. [PMID: 28967174 DOI: 10.1111/1462-2920.13948] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2017] [Revised: 09/02/2017] [Accepted: 09/26/2017] [Indexed: 11/28/2022]
Abstract
Receiving nodulation and nitrogen fixation genes does not guarantee rhizobia an effective symbiosis with legumes. Here, variations in gene content were determined for three Sinorhizobium species showing contrasting symbiotic efficiency on soybeans. A nitrate-reduction gene cluster absent in S. sojae was found to be essential for symbiotic adaptations of S. fredii and S. sp. III. In S. fredii, the deletion mutation of the nap (nitrate reductase), instead of nir (nitrite reductase) and nor (nitric oxide reductase), led to defects in nitrogen-fixation (Fix- ). By contrast, none of these core nitrate-reduction genes were required for the symbiosis of S. sp. III. However, within the same gene cluster, the deletion of hemN1 (encoding oxygen-independent coproporphyrinogen III oxidase) in both S. fredii and S. sp. III led to the formation of nitrogen-fixing (Fix+ ) but ineffective (Eff- ) nodules. These Fix+ /Eff- nodules were characterized by significantly lower enzyme activity of glutamine synthetase indicating rhizobial modulation of nitrogen-assimilation by plants. A distant homologue of HemN1 from S. sojae can complement this defect in S. fredii and S. sp. III, but exhibited a more pleotropic role in symbiosis establishment. These findings highlighted the lineage-dependent optimization of symbiotic functions in different rhizobial species associated with the same host.
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Affiliation(s)
- Li Xue Liu
- State Key Laboratory of Agrobiotechnology, Ministry of Agriculture Key Laboratory of Soil Microbiology, Rhizobium Research Center, and College of Biological Sciences, China Agricultural University, Beijing, China
| | - Qin Qin Li
- State Key Laboratory of Agrobiotechnology, Ministry of Agriculture Key Laboratory of Soil Microbiology, Rhizobium Research Center, and College of Biological Sciences, China Agricultural University, Beijing, China
| | - Yun Zeng Zhang
- State Key Laboratory of Agrobiotechnology, Ministry of Agriculture Key Laboratory of Soil Microbiology, Rhizobium Research Center, and College of Biological Sciences, China Agricultural University, Beijing, China
| | - Yue Hu
- State Key Laboratory of Agrobiotechnology, Ministry of Agriculture Key Laboratory of Soil Microbiology, Rhizobium Research Center, and College of Biological Sciences, China Agricultural University, Beijing, China
| | - Jian Jiao
- State Key Laboratory of Agrobiotechnology, Ministry of Agriculture Key Laboratory of Soil Microbiology, Rhizobium Research Center, and College of Biological Sciences, China Agricultural University, Beijing, China
| | - Hui Juan Guo
- State Key Laboratory of Agrobiotechnology, Ministry of Agriculture Key Laboratory of Soil Microbiology, Rhizobium Research Center, and College of Biological Sciences, China Agricultural University, Beijing, China
| | - Xing Xing Zhang
- State Key Laboratory of Agrobiotechnology, Ministry of Agriculture Key Laboratory of Soil Microbiology, Rhizobium Research Center, and College of Biological Sciences, China Agricultural University, Beijing, China
| | - Biliang Zhang
- State Key Laboratory of Agrobiotechnology, Ministry of Agriculture Key Laboratory of Soil Microbiology, Rhizobium Research Center, and College of Biological Sciences, China Agricultural University, Beijing, China
| | - Wen Xin Chen
- State Key Laboratory of Agrobiotechnology, Ministry of Agriculture Key Laboratory of Soil Microbiology, Rhizobium Research Center, and College of Biological Sciences, China Agricultural University, Beijing, China
| | - Chang Fu Tian
- State Key Laboratory of Agrobiotechnology, Ministry of Agriculture Key Laboratory of Soil Microbiology, Rhizobium Research Center, and College of Biological Sciences, China Agricultural University, Beijing, China
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24
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Yoder JB, Tiffin P. Sanctions, Partner Recognition, and Variation in Mutualism. Am Nat 2017; 190:491-505. [DOI: 10.1086/693472] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
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25
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Burghardt LT, Guhlin J, Chun CL, Liu J, Sadowsky MJ, Stupar RM, Young ND, Tiffin P. Transcriptomic basis of genome by genome variation in a legume‐rhizobia mutualism. Mol Ecol 2017; 26:6122-6135. [DOI: 10.1111/mec.14285] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2017] [Accepted: 07/10/2017] [Indexed: 02/01/2023]
Affiliation(s)
- Liana T. Burghardt
- Department of Plant and Microbial Biology University of Minnesota St. Paul MN USA
| | - Joseph Guhlin
- Department of Plant and Microbial Biology University of Minnesota St. Paul MN USA
| | - Chan Lan Chun
- BioTechnology Institute University of Minnesota St. Paul MN USA
| | - Junqi Liu
- Department of Agronomy and Plant Genetics University of Minnesota St. Paul MN USA
| | | | - Robert M. Stupar
- Department of Agronomy and Plant Genetics University of Minnesota St. Paul MN USA
| | - Nevin D. Young
- Department of Plant and Microbial Biology University of Minnesota St. Paul MN USA
- Department of Plant Pathology University of Minnesota St. Paul MN USA
| | - Peter Tiffin
- Department of Plant and Microbial Biology University of Minnesota St. Paul MN USA
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26
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diCenzo GC, Finan TM. The Divided Bacterial Genome: Structure, Function, and Evolution. Microbiol Mol Biol Rev 2017; 81:e00019-17. [PMID: 28794225 PMCID: PMC5584315 DOI: 10.1128/mmbr.00019-17] [Citation(s) in RCA: 135] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Approximately 10% of bacterial genomes are split between two or more large DNA fragments, a genome architecture referred to as a multipartite genome. This multipartite organization is found in many important organisms, including plant symbionts, such as the nitrogen-fixing rhizobia, and plant, animal, and human pathogens, including the genera Brucella, Vibrio, and Burkholderia. The availability of many complete bacterial genome sequences means that we can now examine on a broad scale the characteristics of the different types of DNA molecules in a genome. Recent work has begun to shed light on the unique properties of each class of replicon, the unique functional role of chromosomal and nonchromosomal DNA molecules, and how the exploitation of novel niches may have driven the evolution of the multipartite genome. The aims of this review are to (i) outline the literature regarding bacterial genomes that are divided into multiple fragments, (ii) provide a meta-analysis of completed bacterial genomes from 1,708 species as a way of reviewing the abundant information present in these genome sequences, and (iii) provide an encompassing model to explain the evolution and function of the multipartite genome structure. This review covers, among other topics, salient genome terminology; mechanisms of multipartite genome formation; the phylogenetic distribution of multipartite genomes; how each part of a genome differs with respect to genomic signatures, genetic variability, and gene functional annotation; how each DNA molecule may interact; as well as the costs and benefits of this genome structure.
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Affiliation(s)
- George C diCenzo
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | - Turlough M Finan
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
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27
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Harrison TL, Wood CW, Heath KD, Stinchcombe JR. Geographically structured genetic variation in the
Medicago lupulina
–
Ensifer
mutualism. Evolution 2017; 71:1787-1801. [DOI: 10.1111/evo.13268] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2016] [Revised: 04/08/2017] [Accepted: 04/15/2017] [Indexed: 12/30/2022]
Affiliation(s)
- Tia L. Harrison
- Department of Ecology and Evolutionary BiologyUniversity of Toronto 25 Willcocks Street Toronto Ontario Canada M5S 3B2
| | - Corlett W. Wood
- Department of Ecology and Evolutionary BiologyUniversity of Toronto 25 Willcocks Street Toronto Ontario Canada M5S 3B2
| | - Katy D. Heath
- Department of Plant BiologyUniversity of Illinois 505 S. Goodwin Avenue Urbana Illinois 61801
| | - John R. Stinchcombe
- Department of Ecology and Evolutionary BiologyUniversity of Toronto 25 Willcocks Street Toronto Ontario Canada M5S 3B2
- Centre for Genome Evolution and FunctionUniversity of Toronto 25 Willcocks Street Toronto Ontario Canada M5S 3B2
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28
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Harrison TL, Wood CW, Borges IL, Stinchcombe JR. No evidence for adaptation to local rhizobial mutualists in the legume Medicago lupulina. Ecol Evol 2017; 7:4367-4376. [PMID: 28649348 PMCID: PMC5478075 DOI: 10.1002/ece3.3012] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2016] [Revised: 03/15/2017] [Accepted: 03/27/2017] [Indexed: 12/31/2022] Open
Abstract
Local adaptation is a common but not ubiquitous feature of species interactions, and understanding the circumstances under which it evolves illuminates the factors that influence adaptive population divergence. Antagonistic species interactions dominate the local adaptation literature relative to mutualistic ones, preventing an overall assessment of adaptation within interspecific interactions. Here, we tested whether the legume Medicago lupulina is adapted to the locally abundant species of mutualistic nitrogen-fixing rhizobial bacteria that vary in frequency across its eastern North American range. We reciprocally inoculated northern and southern M. lupulina genotypes with the northern (Ensifer medicae) or southern bacterium (E. meliloti) in a greenhouse experiment. Despite producing different numbers of root nodules (the structures in which the plants house the bacteria), neither northern nor southern plants produced more seeds, flowered earlier, or were more likely to flower when inoculated with their local rhizobia. We then used a pre-existing dataset to perform a genome scan for loci that showed elevated differentiation between field-collected plants that hosted different bacteria. None of the loci we identified belonged to the well-characterized suite of legume-rhizobia symbiosis genes, suggesting that the rhizobia do not drive genetic divergence between M. lupulina populations. Our results demonstrate that symbiont local adaptation has not evolved in this mutualism despite large-scale geographic variation in the identity of the interacting species.
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Affiliation(s)
- Tia L. Harrison
- Department of Ecology and Evolutionary BiologyUniversity of TorontoTorontoONCanada
| | - Corlett W. Wood
- Department of Ecology and Evolutionary BiologyUniversity of TorontoTorontoONCanada
| | - Isabela L. Borges
- Department of Ecology and Evolutionary BiologyUniversity of TorontoTorontoONCanada
| | - John R. Stinchcombe
- Department of Ecology and Evolutionary BiologyUniversity of TorontoTorontoONCanada
- Centre for Genome Evolution and FunctionUniversity of TorontoTorontoONCanada
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Biogeography of a Novel Ensifer meliloti Clade Associated with the Australian Legume Trigonella suavissima. Appl Environ Microbiol 2017; 83:AEM.03446-16. [PMID: 28283520 DOI: 10.1128/aem.03446-16] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Accepted: 03/02/2017] [Indexed: 11/20/2022] Open
Abstract
Here, we describe a novel clade within Ensifer meliloti and consider how geographic and ecological isolation contributed to the limited distribution of this group. Members of the genus Ensifer are best known for their ability to form nitrogen-fixing symbioses with forage legumes of three related genera, Medicago L., Melilotus Mill., and Trigonella L., which are members of the tribe Trifolieae. These legumes have a natural distribution extending from the Mediterranean Basin through western Asia, where there is an unsurpassed number of species belonging to these genera. Trigonella suavissima L. is unusual in that it is the only species in the tribe Trifolieae that is native to Australia. We compared the genetic diversity and taxonomic placement of rhizobia nodulating T. suavissima with those of members of an Ensifer reference collection. Our goal was to determine if the T. suavissima rhizobial strains, like their plant host, are naturally limited to the Australian continent. We used multilocus sequence analysis to estimate the genetic relatedness of 56 T. suavissima symbionts to 28 Ensifer reference strains. Sequence data were partitioned according to the replicons in which the loci are located. The results were used to construct replicon-specific phylogenetic trees. In both the chromosomal and chromid trees, the Australian strains formed a distinct clade within E. meliloti The strains also shared few alleles with Ensifer reference strains from other continents. Carbon source utilization assays revealed that the strains are also unusual in their ability to utilize 2-oxoglutarate as a sole carbon source. A strategy was outlined for locating similar strains elsewhere.IMPORTANCE In this study, we employed a biogeographical approach to investigate the origins of a symbiotic relationship between an Australian legume and its nitrogen-fixing rhizobia. The question of the ancestral origins of these symbionts is based on the observation that the legume host is not closely related to other native Australian legumes. Previous research has shown that the legume host Trigonella suavissima is instead closely related to legumes native to the Mediterranean Basin and western Asia, suggesting that it may have been introduced in Australia from those regions. This led to the question of whether its rhizobia may have been introduced as well. In this study, we were unable to find persuasive evidence supporting this hypothesis. Instead, our results suggest either that the T. suavissima rhizobia are native to Australia or that our methods for locating their close relatives elsewhere are inadequate. A strategy to investigate the latter alternative is proposed.
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The underlying process of early ecological and genetic differentiation in a facultative mutualistic Sinorhizobium meliloti population. Sci Rep 2017; 7:675. [PMID: 28386109 PMCID: PMC5429615 DOI: 10.1038/s41598-017-00730-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2016] [Accepted: 03/10/2017] [Indexed: 11/21/2022] Open
Abstract
The question of how genotypic and ecological units arise and spread in natural microbial populations remains controversial in the field of evolutionary biology. Here, we investigated the early stages of ecological and genetic differentiation in a highly clonal sympatric Sinorhizobium meliloti population. Whole-genome sequencing revealed that a large DNA region of the symbiotic plasmid pSymB was replaced in some isolates with a similar synteny block carrying densely clustered SNPs and displaying gene acquisition and loss. Two different versions of this genomic island of differentiation (GID) generated by multiple genetic exchanges over time appear to have arisen recently, through recombination in a particular clade within this population. In addition, these isolates display resistance to phages from the same geographic region, probably due to the modification of surface components by the acquired genes. Our results suggest that an underlying process of early ecological and genetic differentiation in S. meliloti is primarily triggered by acquisition of genes that confer resistance to soil phages within particular large genomic DNA regions prone to recombination.
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31
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Vinatzer BA, Weisberg AJ, Monteil CL, Elmarakeby HA, Sheppard SK, Heath LS. A Proposal for a Genome Similarity-Based Taxonomy for Plant-Pathogenic Bacteria that Is Sufficiently Precise to Reflect Phylogeny, Host Range, and Outbreak Affiliation Applied to Pseudomonas syringae sensu lato as a Proof of Concept. PHYTOPATHOLOGY 2017; 107:18-28. [PMID: 27552324 DOI: 10.1094/phyto-07-16-0252-r] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Taxonomy of plant pathogenic bacteria is challenging because pathogens of different crops often belong to the same named species but current taxonomy does not provide names for bacteria below the subspecies level. The introduction of the host range-based pathovar system in the 1980s provided a temporary solution to this problem but has many limitations. The affordability of genome sequencing now provides the opportunity for developing a new genome-based taxonomic framework. We already proposed to name individual bacterial isolates based on pairwise genome similarity. Here, we expand on this idea and propose to use genome similarity-based codes, which we now call life identification numbers (LINs), to describe and name bacterial taxa. Using 93 genomes of Pseudomonas syringae sensu lato, LINs were compared with a P. syringae genome tree whereby the assigned LINs were found to be informative of a majority of phylogenetic relationships. LINs also reflected host range and outbreak association for strains of P. syringae pathovar actinidiae, a pathovar for which many genome sequences are available. We conclude that LINs could provide the basis for a new taxonomic framework to address the shortcomings of the current pathovar system and to complement the current taxonomic system of bacteria in general.
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Affiliation(s)
- Boris A Vinatzer
- First, second, and third authors: Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Virginia; second author: Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon; fourth and sixth authors: Department of Computer Science, Virginia Tech, Blacksburg, Virginia; and fifth author: Department of Biology & Biotechnology, University of Bath, Claverton Down, Bath, United Kingdom
| | - Alexandra J Weisberg
- First, second, and third authors: Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Virginia; second author: Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon; fourth and sixth authors: Department of Computer Science, Virginia Tech, Blacksburg, Virginia; and fifth author: Department of Biology & Biotechnology, University of Bath, Claverton Down, Bath, United Kingdom
| | - Caroline L Monteil
- First, second, and third authors: Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Virginia; second author: Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon; fourth and sixth authors: Department of Computer Science, Virginia Tech, Blacksburg, Virginia; and fifth author: Department of Biology & Biotechnology, University of Bath, Claverton Down, Bath, United Kingdom
| | - Haitham A Elmarakeby
- First, second, and third authors: Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Virginia; second author: Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon; fourth and sixth authors: Department of Computer Science, Virginia Tech, Blacksburg, Virginia; and fifth author: Department of Biology & Biotechnology, University of Bath, Claverton Down, Bath, United Kingdom
| | - Samuel K Sheppard
- First, second, and third authors: Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Virginia; second author: Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon; fourth and sixth authors: Department of Computer Science, Virginia Tech, Blacksburg, Virginia; and fifth author: Department of Biology & Biotechnology, University of Bath, Claverton Down, Bath, United Kingdom
| | - Lenwood S Heath
- First, second, and third authors: Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Virginia; second author: Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon; fourth and sixth authors: Department of Computer Science, Virginia Tech, Blacksburg, Virginia; and fifth author: Department of Biology & Biotechnology, University of Bath, Claverton Down, Bath, United Kingdom
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32
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Yoder JB. Understanding the coevolutionary dynamics of mutualism with population genomics. AMERICAN JOURNAL OF BOTANY 2016; 103:1742-1752. [PMID: 27756732 DOI: 10.3732/ajb.1600154] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2016] [Accepted: 09/06/2016] [Indexed: 06/06/2023]
Abstract
Decades of research on the evolution of mutualism has generated a wealth of possible ways whereby mutually beneficial interactions between species persist in spite of the apparent advantages to individuals that accept the benefits of mutualism without reciprocating - but identifying how any particular empirical system is stabilized against cheating remains challenging. Different hypothesized models of mutualism stability predict different forms of coevolutionary selection, and emerging high-throughput sequencing methods allow examination of the selective histories of mutualism genes and, thereby, the form of selection acting on those genes. Here, I review the evolutionary theory of mutualism stability and identify how differing models make contrasting predictions for the population genomic diversity and geographic differentiation of mutualism-related genes. As an example of the possibilities offered by genomic data, I analyze genes with roles in the symbiosis of Medicago truncatula and nitrogen-fixing rhizobial bacteria, the first classic mutualism in which extensive genomic resources have been developed for both partners. Medicago truncatula symbiosis genes, as a group, differ from the rest of the genome, but they vary in the form of selection indicated by their diversity and differentiation - some show signs of selection expected from roles in sanctioning noncooperative symbionts, while others show evidence of balancing selection expected from coevolution with symbiont signaling factors. I then assess the current state of development for similar resources in other mutualistic interactions and look ahead to identify ways in which modern sequencing technology can best inform our understanding of mutualists and mutualism.
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Affiliation(s)
- Jeremy B Yoder
- Department of Forest and Conservation Sciences, University of British Columbia, Vancouver, British Columbia V6T 1Z4 Canada
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33
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Heath KD, Grillo MA. Rhizobia: tractable models for bacterial evolutionary ecology. Environ Microbiol 2016; 18:4307-4311. [DOI: 10.1111/1462-2920.13492] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- Katy D. Heath
- Department of Plant Biology; University of Illinois at Urbana-Champaign; 265 Morrill Hall, 505 S. Goodwin Ave Urbana IL 61801, USA
| | - Michael A. Grillo
- Department of Plant Biology; University of Illinois at Urbana-Champaign; 265 Morrill Hall, 505 S. Goodwin Ave Urbana IL 61801, USA
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34
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Toro N, Martínez-Abarca F, Fernández-López M. The early events underlying genome evolution in a localized Sinorhizobium meliloti population. BMC Genomics 2016; 17:556. [PMID: 27495742 PMCID: PMC4974801 DOI: 10.1186/s12864-016-2878-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2015] [Accepted: 07/05/2016] [Indexed: 11/02/2022] Open
Abstract
BACKGROUND Population genetic analyses based on genome-wide sequencing data have been carried out for Sinorhizobium medicae and S. meliloti, two closely related bacterial species forming nitrogen-fixing symbioses with plants of the genus Medicago. However, genome coverage was low or the isolates had a broad geographic distribution, making it difficult to interpret the estimated diversity and to unravel the early events underlying population genetic variations and ecological differentiation. RESULTS Here, to gain insight into the early genome level variation and diversification within S. meliloti populations, we first used Illumina paired-end reads technology to sequence a new clone of S. meliloti strain GR4, a highly competitive strain for alfalfa nodulation. The Illumina data and the GR4 genome sequence previously obtained with 454 technology were used to generate a high-quality reference genome sequence. We then used Illumina technology to sequence the genomes of 13 S. meliloti isolates representative of the genomic variation within the GR4-type population, obtained from a single field site with a high degree of coverage. The genome sequences obtained were analyzed to determine nucleotide diversity, divergence times, polymorphism and genomic variation. Similar low levels of nucleotide diversity were observed for the chromosome, pSymB and pSymA replicons. The isolates displayed other types of variation, such as indels, recombination events, genomic island excision and the transposition of mobile elements. CONCLUSIONS Our results suggest that the GR4-type population has experienced a process of demographic expansion and behaves as a stable genotypic cluster of genome-wide similarity, with most of the genome following a clonal pattern of evolution. Although some of genetic variation detected within the GR4-type population is probably due to genetic drift, others might be important in diversification and environmental adaptation.
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Affiliation(s)
- Nicolás Toro
- Grupo de Ecología Genética, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Calle Profesor Albareda 1, 18008, Granada, Spain.
| | - Francisco Martínez-Abarca
- Grupo de Ecología Genética, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Calle Profesor Albareda 1, 18008, Granada, Spain
| | - Manuel Fernández-López
- Grupo de Ecología Genética, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Calle Profesor Albareda 1, 18008, Granada, Spain
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35
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Porter SS, Chang PL, Conow CA, Dunham JP, Friesen ML. Association mapping reveals novel serpentine adaptation gene clusters in a population of symbiotic Mesorhizobium. ISME JOURNAL 2016; 11:248-262. [PMID: 27420027 PMCID: PMC5315480 DOI: 10.1038/ismej.2016.88] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/03/2016] [Revised: 05/23/2016] [Accepted: 05/25/2016] [Indexed: 01/18/2023]
Abstract
The genetic variants that underlie microbial environmental adaptation are key components of models of microbial diversification. Characterizing adaptive variants and the pangenomic context in which they evolve remains a frontier in understanding how microbial diversity is generated. The genomics of rhizobium adaptation to contrasting soil environments is ecologically and agriculturally important because these bacteria are responsible for half of all current biologically fixed nitrogen, yet they live the majority of their lives in soil. Our study uses whole-genome sequencing to describe the pan-genome of a focal clade of wild mesorhizobia that show contrasting levels of nickel adaptation despite high relatedness (99.8% identity at 16S). We observe ecotypic specialization within an otherwise genomically cohesive population, rather than finding distinct specialized bacterial lineages in contrasting soil types. This finding supports recent reports that heterogeneous environments impose selection that maintains differentiation only at a small fraction of the genome. Our work further uses a genome-wide association study to propose candidate genes for nickel adaptation. Several candidates show homology to genetic systems involved in nickel tolerance and one cluster of candidates correlates perfectly with soil origin, which validates our approach of ascribing genomic variation to adaptive divergence.
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Affiliation(s)
- Stephanie S Porter
- School of Biological Sciences, Washington State University, Vancouver, WA, USA
| | - Peter L Chang
- Section of Molecular and Computational Biology, Department of Biological Sciences, University of Southern California, Los Angeles, CA, USA.,Department of Plant Pathology and Nematology, University of California, Davis, CA, USA
| | - Christopher A Conow
- Section of Molecular and Computational Biology, Department of Biological Sciences, University of Southern California, Los Angeles, CA, USA
| | - Joseph P Dunham
- Section of Molecular and Computational Biology, Department of Biological Sciences, University of Southern California, Los Angeles, CA, USA
| | - Maren L Friesen
- Department of Plant Biology, Michigan State University, East Lansing, MI, USA
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36
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Pérez Carrascal OM, VanInsberghe D, Juárez S, Polz MF, Vinuesa P, González V. Population genomics of the symbiotic plasmids of sympatric nitrogen-fixing Rhizobium species associated with Phaseolus vulgaris. Environ Microbiol 2016; 18:2660-76. [PMID: 27312778 DOI: 10.1111/1462-2920.13415] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Accepted: 06/13/2016] [Indexed: 11/28/2022]
Abstract
Cultivated common beans are the primary protein source for millions of people around the world who subsist on low-input agriculture, enabled by the symbiotic N2 -fixation these legumes perform in association with rhizobia. Within a single agricultural plot, multiple Rhizobium species can nodulate bean roots, but it is unclear how genetically isolated these species remain in sympatry. To better understand this issue, we sequenced and compared the genomes of 33 strains isolated from the rhizosphere and root nodules of a particular bean variety grown in the same agricultural plot. We found that the Rhizobium species we observed coexist with low genetic recombination across their core genomes. Accessory plasmids thought to be necessary for the saprophytic lifestyle in soil show similar levels of genetic isolation, but with higher rates of recombination than the chromosomes. However, the symbiotic plasmids are extremely similar, with high rates of recombination and do not appear to have co-evolved with the chromosome or accessory plasmids. Therefore, while Rhizobium species are genetically isolated units within the microbial community, a common symbiotic plasmid allows all Rhizobium species to engage in symbiosis with the same host in a single agricultural plot.
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Affiliation(s)
- Olga M Pérez Carrascal
- Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, 62210, México
| | - David VanInsberghe
- Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Soledad Juárez
- Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, 62210, México
| | - Martin F Polz
- Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Pablo Vinuesa
- Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, 62210, México
| | - Víctor González
- Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, 62210, México
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37
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Hollowell AC, Regus JU, Turissini D, Gano-Cohen KA, Bantay R, Bernardo A, Moore D, Pham J, Sachs JL. Metapopulation dominance and genomic-island acquisition of Bradyrhizobium with superior catabolic capabilities. Proc Biol Sci 2016; 283:20160496. [PMID: 27122562 PMCID: PMC4855393 DOI: 10.1098/rspb.2016.0496] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2016] [Accepted: 04/04/2016] [Indexed: 01/05/2023] Open
Abstract
Root nodule-forming rhizobia exhibit a bipartite lifestyle, replicating in soil and also within plant cells where they fix nitrogen for legume hosts. Host control models posit that legume hosts act as a predominant selective force on rhizobia, but few studies have examined rhizobial fitness in natural populations. Here, we genotyped and phenotyped Bradyrhizobium isolates across more than 800 km of the native Acmispon strigosus host range. We sequenced chromosomal genes expressed under free-living conditions and accessory symbiosis loci expressed in planta and encoded on an integrated 'symbiosis island' (SI). We uncovered a massive clonal expansion restricted to the Bradyrhizobium chromosome, with a single chromosomal haplotype dominating populations, ranging more than 700 km, and acquiring 42 divergent SI haplotypes, none of which were spatially widespread. For focal genotypes, we quantified utilization of 190 sole-carbon sources relevant to soil fitness. Chromosomal haplotypes that were both widespread and dominant exhibited superior growth on diverse carbon sources, whereas these patterns were not mirrored among SI haplotypes. Abundance, spatial range and catabolic superiority of chromosomal, but not symbiosis genotypes suggests that fitness in the soil environment, rather than symbiosis with hosts, might be the key driver of Bradyrhizobium dominance.
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Affiliation(s)
- Amanda C Hollowell
- Department of Biology, University of California, Riverside, CA 92521, USA
| | - John U Regus
- Department of Biology, University of California, Riverside, CA 92521, USA
| | - David Turissini
- Department of Biology, University of North Carolina, Chapel Hill, NC 27599, USA
| | | | - Roxanne Bantay
- Department of Biology, University of California, Riverside, CA 92521, USA
| | - Andrew Bernardo
- Department of Biology, University of California, Riverside, CA 92521, USA
| | - Devora Moore
- Department of Biology, University of California, Riverside, CA 92521, USA
| | - Jonathan Pham
- Department of Biology, University of California, Riverside, CA 92521, USA
| | - Joel L Sachs
- Department of Biology, University of California, Riverside, CA 92521, USA Institute for Integrative Genome Biology, University of California, Riverside, CA 92521, USA
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38
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Gordon BR, Klinger CR, Weese DJ, Lau JA, Burke PV, Dentinger BTM, Heath KD. Decoupled genomic elements and the evolution of partner quality in nitrogen-fixing rhizobia. Ecol Evol 2016; 6:1317-27. [PMID: 27087920 PMCID: PMC4775534 DOI: 10.1002/ece3.1953] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2015] [Revised: 12/14/2015] [Accepted: 12/15/2015] [Indexed: 01/24/2023] Open
Abstract
Understanding how mutualisms evolve in response to a changing environment will be critical for predicting the long-term impacts of global changes, such as increased N (nitrogen) deposition. Bacterial mutualists in particular might evolve quickly, thanks to short generation times and the potential for independent evolution of plasmids through recombination and/or HGT (horizontal gene transfer). In a previous work using the legume/rhizobia mutualism, we demonstrated that long-term nitrogen fertilization caused the evolution of less-mutualistic rhizobia. Here, we use our 63 previously isolated rhizobium strains in comparative phylogenetic and quantitative genetic analyses to determine the degree to which variation in partner quality is attributable to phylogenetic relationships among strains versus recent genetic changes in response to N fertilization. We find evidence of distinct evolutionary relationships between chromosomal and pSym genes, and broad similarity between pSym genes. We also find that nifD has a unique evolutionary history that explains much of the variation in partner quality, and suggest MoFe subunit interaction sites in the evolution of less-mutualistic rhizobia. These results provide insight into the mechanisms behind the evolutionary response of rhizobia to long-term N fertilization, and we discuss the implications of our results for the evolution of the mutualism.
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Affiliation(s)
- Benjamin R. Gordon
- Department of Plant BiologyUniversity of Illinois Urbana‐Champaign505 S. Goodwin Ave.UrbanaIllinois61801
| | - Christie R. Klinger
- Department of Plant BiologyUniversity of Illinois Urbana‐Champaign505 S. Goodwin Ave.UrbanaIllinois61801
| | - Dylan J. Weese
- Department of BiologySt. Ambrose University518 West Locust StDavenportIowa52803
| | - Jennifer A. Lau
- Kellogg Biological Station and Department of Plant BiologyMichigan State University3700 E. Gull Lake DriveHickory CornersMichigan49060
| | - Patricia V. Burke
- Department of Plant BiologyUniversity of Illinois Urbana‐Champaign505 S. Goodwin Ave.UrbanaIllinois61801
| | | | - Katy D. Heath
- Department of Plant BiologyUniversity of Illinois Urbana‐Champaign505 S. Goodwin Ave.UrbanaIllinois61801
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39
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diCenzo GC, Zamani M, Milunovic B, Finan TM. Genomic resources for identification of the minimal N2 -fixing symbiotic genome. Environ Microbiol 2016; 18:2534-47. [PMID: 26768651 DOI: 10.1111/1462-2920.13221] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Revised: 12/17/2015] [Accepted: 01/09/2016] [Indexed: 12/11/2022]
Abstract
The lack of an appropriate genomic platform has precluded the use of gain-of-function approaches to study the rhizobium-legume symbiosis, preventing the establishment of the genes necessary and sufficient for symbiotic nitrogen fixation (SNF) and potentially hindering synthetic biology approaches aimed at engineering this process. Here, we describe the development of an appropriate system by reverse engineering Sinorhizobium meliloti. Using a novel in vivo cloning procedure, the engA-tRNA-rmlC (ETR) region, essential for cell viability and symbiosis, was transferred from Sinorhizobium fredii to the ancestral location on the S. meliloti chromosome, rendering the ETR region on pSymB redundant. A derivative of this strain lacking both the large symbiotic replicons (pSymA and pSymB) was constructed. Transfer of pSymA and pSymB back into this strain restored symbiotic capabilities with alfalfa. To delineate the location of the single-copy genes essential for SNF on these replicons, we screened a S. meliloti deletion library, representing > 95% of the 2900 genes of the symbiotic replicons, for their phenotypes with alfalfa. Only four loci, accounting for < 12% of pSymA and pSymB, were essential for SNF. These regions will serve as our preliminary target of the minimal set of horizontally acquired genes necessary and sufficient for SNF.
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Affiliation(s)
- George C diCenzo
- Department of Biology, McMaster University, 1280 Main St. W., Hamilton, Ontario, Canada, L8S 4K1
| | - Maryam Zamani
- Department of Biology, McMaster University, 1280 Main St. W., Hamilton, Ontario, Canada, L8S 4K1
| | - Branislava Milunovic
- Department of Biology, McMaster University, 1280 Main St. W., Hamilton, Ontario, Canada, L8S 4K1
| | - Turlough M Finan
- Department of Biology, McMaster University, 1280 Main St. W., Hamilton, Ontario, Canada, L8S 4K1
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Ardley J, Tian R, O'Hara G, Seshadri R, Reddy TBK, Pati A, Woyke T, Markowitz V, Ivanova N, Kyrpides N, Howieson J, Reeve W. High-quality permanent draft genome sequence of Ensifer medicae strain WSM244, a microsymbiont isolated from Medicago polymorpha growing in alkaline soil. Stand Genomic Sci 2015; 10:126. [PMID: 26664655 PMCID: PMC4674904 DOI: 10.1186/s40793-015-0119-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2015] [Accepted: 11/03/2015] [Indexed: 11/12/2022] Open
Abstract
Ensifer medicae WSM244 is an aerobic, motile, Gram-negative, non-spore-forming rod that can exist as a soil saprophyte or as a legume microsymbiont of Medicago species. WSM244 was isolated in 1979 from a nodule recovered from the roots of the annual Medicago polymorpha L. growing in alkaline soil (pH 8.0) in Tel Afer, Iraq. WSM244 is the only acid-sensitive E. medicae strain that has been sequenced to date. It is effective at fixing nitrogen with M. polymorpha L., as well as with more alkaline-adapted Medicago spp. such as M. littoralis Loisel., M. scutellata (L.) Mill., M. tornata (L.) Mill. and M. truncatula Gaertn. This strain is also effective with the perennial M. sativa L. Here we describe the features of E. medicae WSM244, together with genome sequence information and its annotation. The 6,650,282 bp high-quality permanent draft genome is arranged into 91 scaffolds of 91 contigs containing 6,427 protein-coding genes and 68 RNA-only encoding genes, and is one of the rhizobial genomes sequenced as part of the DOE Joint Genome Institute 2010 Genomic Encyclopedia for Bacteria and Archaea-Root Nodule Bacteria (GEBA-RNB) project proposal.
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Affiliation(s)
- Julie Ardley
- Centre for Rhizobium Studies, Murdoch University, Murdoch, Australia
| | - Rui Tian
- Centre for Rhizobium Studies, Murdoch University, Murdoch, Australia
| | - Graham O'Hara
- Centre for Rhizobium Studies, Murdoch University, Murdoch, Australia
| | | | - T B K Reddy
- DOE Joint Genome Institute, Walnut Creek, CA USA
| | - Amrita Pati
- DOE Joint Genome Institute, Walnut Creek, CA USA
| | - Tanja Woyke
- DOE Joint Genome Institute, Walnut Creek, CA USA
| | - Victor Markowitz
- Biological Data Management and Technology Center, Lawrence Berkeley National Laboratory, Berkeley, CA USA
| | | | - Nikos Kyrpides
- DOE Joint Genome Institute, Walnut Creek, CA USA ; Department of Biological Sciences, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia
| | - John Howieson
- Centre for Rhizobium Studies, Murdoch University, Murdoch, Australia
| | - Wayne Reeve
- Centre for Rhizobium Studies, Murdoch University, Murdoch, Australia
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Remigi P, Zhu J, Young JPW, Masson-Boivin C. Symbiosis within Symbiosis: Evolving Nitrogen-Fixing Legume Symbionts. Trends Microbiol 2015; 24:63-75. [PMID: 26612499 DOI: 10.1016/j.tim.2015.10.007] [Citation(s) in RCA: 143] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2015] [Revised: 10/08/2015] [Accepted: 10/22/2015] [Indexed: 10/22/2022]
Abstract
Bacterial accessory genes are genomic symbionts with an evolutionary history and future that is different from that of their hosts. Packages of accessory genes move from strain to strain and confer important adaptations, such as interaction with eukaryotes. The ability to fix nitrogen with legumes is a remarkable example of a complex trait spread by horizontal transfer of a few key symbiotic genes, converting soil bacteria into legume symbionts. Rhizobia belong to hundreds of species restricted to a dozen genera of the Alphaproteobacteria and Betaproteobacteria, suggesting infrequent successful transfer between genera but frequent successful transfer within genera. Here we review the genetic and environmental conditions and selective forces that have shaped evolution of this complex symbiotic trait.
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Affiliation(s)
- Philippe Remigi
- INRA, Laboratoire des Interactions Plantes-Microorganismes (LIPM), UMR441, Castanet-Tolosan, France; CNRS, Laboratoire des Interactions Plantes-Microorganismes (LIPM), UMR2594, Castanet-Tolosan, France; New Zealand Institute for Advanced Study, Massey University, Auckland, New Zealand
| | - Jun Zhu
- Department of Microbiology, Nanjing Agricultural University, Nanjing, China; Department of Microbiology, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - J Peter W Young
- Department of Biology, University of York, York YO10 5DD, UK
| | - Catherine Masson-Boivin
- INRA, Laboratoire des Interactions Plantes-Microorganismes (LIPM), UMR441, Castanet-Tolosan, France; CNRS, Laboratoire des Interactions Plantes-Microorganismes (LIPM), UMR2594, Castanet-Tolosan, France.
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Kumar N, Lad G, Giuntini E, Kaye ME, Udomwong P, Shamsani NJ, Young JPW, Bailly X. Bacterial genospecies that are not ecologically coherent: population genomics of Rhizobium leguminosarum. Open Biol 2015; 5:140133. [PMID: 25589577 PMCID: PMC4313370 DOI: 10.1098/rsob.140133] [Citation(s) in RCA: 105] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Biological species may remain distinct because of genetic isolation or ecological adaptation, but these two aspects do not always coincide. To establish the nature of the species boundary within a local bacterial population, we characterized a sympatric population of the bacterium Rhizobium leguminosarum by genomic sequencing of 72 isolates. Although all strains have 16S rRNA typical of R. leguminosarum, they fall into five genospecies by the criterion of average nucleotide identity (ANI). Many genes, on plasmids as well as the chromosome, support this division: recombination of core genes has been largely within genospecies. Nevertheless, variation in ecological properties, including symbiotic host range and carbon-source utilization, cuts across these genospecies, so that none of these phenotypes is diagnostic of genospecies. This phenotypic variation is conferred by mobile genes. The genospecies meet the Mayr criteria for biological species in respect of their core genes, but do not correspond to coherent ecological groups, so periodic selection may not be effective in purging variation within them. The population structure is incompatible with traditional ‘polyphasic taxonomy′ that requires bacterial species to have both phylogenetic coherence and distinctive phenotypes. More generally, genomics has revealed that many bacterial species share adaptive modules by horizontal gene transfer, and we envisage a more consistent taxonomic framework that explicitly recognizes this. Significant phenotypes should be recognized as ‘biovars' within species that are defined by core gene phylogeny.
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Affiliation(s)
- Nitin Kumar
- Department of Biology, University of York, York YO10 5DD, UK
| | - Ganesh Lad
- Department of Biology, University of York, York YO10 5DD, UK
| | - Elisa Giuntini
- Department of Biology, University of York, York YO10 5DD, UK
| | - Maria E Kaye
- Department of Biology, University of York, York YO10 5DD, UK
| | | | | | - J Peter W Young
- Department of Biology, University of York, York YO10 5DD, UK
| | - Xavier Bailly
- Department of Biology, University of York, York YO10 5DD, UK
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43
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Molina-Sánchez MD, López-Contreras JA, Toro N, Fernández-López M. Genomic characterization of Sinorhizobium meliloti AK21, a wild isolate from the Aral Sea Region. SPRINGERPLUS 2015; 4:259. [PMID: 26090306 PMCID: PMC4468178 DOI: 10.1186/s40064-015-1062-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/15/2015] [Accepted: 05/26/2015] [Indexed: 11/10/2022]
Abstract
The symbiotic, nitrogen-fixing bacterium Sinorhizobium meliloti has been widely studied due to its ability to improve crop yields through direct interactions with leguminous plants. S. meliloti AK21 is a wild type strain that forms nodules on Medicago plants in saline and drought conditions in the Aral Sea Region. The aim of this work was to establish the genetic similarities and differences between S. meliloti AK21 and the reference strain S. meliloti 1021. Comparative genome hybridization with the model reference strain S. meliloti 1021 yielded 365 variable genes, grouped into 11 regions in the three main replicons in S. meliloti AK21. The most extensive regions of variability were found in the symbiotic plasmid pSymA, which also contained the largest number of orthologous and polymorphic sequences identified by suppression subtractive hybridization. This procedure identified a large number of divergent sequences and others without homology in the databases, the further investigation of which could provide new insight into the alternative metabolic pathways present in S. meliloti AK21. We identified a plasmid replication module from the repABC replicon family, together with plasmid mobilization-related genes (traG and a VirB9-like protein), which suggest that this indigenous isolate harbors an accessory plasmid. Furthermore, the transcriptomic profiles reflected differences in gene content and regulation between S. meliloti AK21 and S. meliloti 1021 (ExpR and PhoB regulons), but provided evidence for an as yet unknown, alternative mechanism involving activation of the cbb3 terminal oxidase. Finally, phenotypic microarrays characterization revealed a greater versatility of substrate use and chemical degradation than for S. meliloti 1021.
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Affiliation(s)
- María Dolores Molina-Sánchez
- Grupo de Ecología Genética, Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, CSIC, Calle Profesor Albareda 1, 18008 Granada, Spain
| | - José Antonio López-Contreras
- Grupo de Ecología Genética, Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, CSIC, Calle Profesor Albareda 1, 18008 Granada, Spain
| | - Nicolás Toro
- Grupo de Ecología Genética, Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, CSIC, Calle Profesor Albareda 1, 18008 Granada, Spain
| | - Manuel Fernández-López
- Grupo de Ecología Genética, Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, CSIC, Calle Profesor Albareda 1, 18008 Granada, Spain
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Zgadzaj R, James EK, Kelly S, Kawaharada Y, de Jonge N, Jensen DB, Madsen LH, Radutoiu S. A legume genetic framework controls infection of nodules by symbiotic and endophytic bacteria. PLoS Genet 2015; 11:e1005280. [PMID: 26042417 PMCID: PMC4456278 DOI: 10.1371/journal.pgen.1005280] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2014] [Accepted: 05/14/2015] [Indexed: 11/18/2022] Open
Abstract
Legumes have an intrinsic capacity to accommodate both symbiotic and endophytic bacteria within root nodules. For the symbionts, a complex genetic mechanism that allows mutual recognition and plant infection has emerged from genetic studies under axenic conditions. In contrast, little is known about the mechanisms controlling the endophytic infection. Here we investigate the contribution of both the host and the symbiotic microbe to endophyte infection and development of mixed colonised nodules in Lotus japonicus. We found that infection threads initiated by Mesorhizobium loti, the natural symbiont of Lotus, can selectively guide endophytic bacteria towards nodule primordia, where competent strains multiply and colonise the nodule together with the nitrogen-fixing symbiotic partner. Further co-inoculation studies with the competent coloniser, Rhizobium mesosinicum strain KAW12, show that endophytic nodule infection depends on functional and efficient M. loti-driven Nod factor signalling. KAW12 exopolysaccharide (EPS) enabled endophyte nodule infection whilst compatible M. loti EPS restricted it. Analysis of plant mutants that control different stages of the symbiotic infection showed that both symbiont and endophyte accommodation within nodules is under host genetic control. This demonstrates that when legume plants are exposed to complex communities they selectively regulate access and accommodation of bacteria occupying this specialized environmental niche, the root nodule. Plants have evolved elaborated mechanisms to monitor microbial presence and to control their infection, therefore only particular microbes, so called “endophytes,” are able to colonise the internal tissues with minimal or no host damage. The legume root nodule is a unique environmental niche induced by symbiotic bacteria, but where multiple species, symbiotic and endophytic co-exist. Genetic studies of the binary interaction legume-symbiont led to the discovery of key components evolved in the two partners allowing mutual recognition and nodule infection. In contrast, there is limited knowledge about the endophytic nodule infection, the role of the legume host, or the symbiont in the process of nodule colonisation by endophytes. Here we focus on the early stages of nodule infection in order to identify which molecular signatures and genetic components favour/allow endophyte accommodation, and multiple species co-existence inside nodules. We found that colonisation of Lotus japonicus nodules by endophytic bacteria is a selective process, that endophyte nodule occupancy is host-controlled, and that exopolysaccharides are key bacterial features for chronic infection of nodules. Our strategy based on model legume genetics and co-inoculation can thus be used for identifying mechanisms operating behind host-microbes compatibility in environments where multiple species co-exist.
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Affiliation(s)
- Rafal Zgadzaj
- Department of Molecular Biology and Genetics, Faculty of Science and Technology, Aarhus University, Aarhus, Denmark
- Carbohydrate Recognition and Signalling (CARB) Centre, Aarhus, Denmark
| | - Euan K. James
- Ecological Sciences, The James Hutton Institute, Invergowrie, Dundee, United Kingdom
| | - Simon Kelly
- Department of Molecular Biology and Genetics, Faculty of Science and Technology, Aarhus University, Aarhus, Denmark
- Carbohydrate Recognition and Signalling (CARB) Centre, Aarhus, Denmark
| | - Yasuyuki Kawaharada
- Department of Molecular Biology and Genetics, Faculty of Science and Technology, Aarhus University, Aarhus, Denmark
- Carbohydrate Recognition and Signalling (CARB) Centre, Aarhus, Denmark
| | - Nadieh de Jonge
- Department of Molecular Biology and Genetics, Faculty of Science and Technology, Aarhus University, Aarhus, Denmark
- Carbohydrate Recognition and Signalling (CARB) Centre, Aarhus, Denmark
| | - Dorthe B. Jensen
- Department of Molecular Biology and Genetics, Faculty of Science and Technology, Aarhus University, Aarhus, Denmark
- Carbohydrate Recognition and Signalling (CARB) Centre, Aarhus, Denmark
| | - Lene H. Madsen
- Department of Molecular Biology and Genetics, Faculty of Science and Technology, Aarhus University, Aarhus, Denmark
- Carbohydrate Recognition and Signalling (CARB) Centre, Aarhus, Denmark
| | - Simona Radutoiu
- Department of Molecular Biology and Genetics, Faculty of Science and Technology, Aarhus University, Aarhus, Denmark
- Carbohydrate Recognition and Signalling (CARB) Centre, Aarhus, Denmark
- * E-mail:
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Gardner SN, Slezak T, Hall BG. kSNP3.0: SNP detection and phylogenetic analysis of genomes without genome alignment or reference genome. Bioinformatics 2015; 31:2877-8. [PMID: 25913206 DOI: 10.1093/bioinformatics/btv271] [Citation(s) in RCA: 405] [Impact Index Per Article: 45.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2015] [Accepted: 04/23/2015] [Indexed: 11/14/2022] Open
Abstract
UNLABELLED We announce the release of kSNP3.0, a program for SNP identification and phylogenetic analysis without genome alignment or the requirement for reference genomes. kSNP3.0 is a significantly improved version of kSNP v2. AVAILABILITY AND IMPLEMENTATION kSNP3.0 is implemented as a package of stand-alone executables for Linux and Mac OS X under the open-source BSD license. The executable packages, source code and a full User Guide are freely available at https://sourceforge.net/projects/ksnp/files/ CONTACT barryghall@gmail.com.
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Affiliation(s)
- Shea N Gardner
- Computations/Global Security, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA and
| | - Tom Slezak
- Computations/Global Security, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA and
| | - Barry G Hall
- Bellingham Research Institute, Bellingham, WA 98229, USA
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Jorrin B, Imperial J. Population Genomics Analysis of Legume Host Preference for Specific Rhizobial Genotypes in the Rhizobium leguminosarum bv. viciae Symbioses. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2015; 28:310-8. [PMID: 25514682 DOI: 10.1094/mpmi-09-14-0296-fi] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Rhizobium leguminosarum bv. viciae establishes root nodule symbioses with several legume genera. Although most isolates are equally effective in establishing symbioses with all host genera, previous evidence suggests that hosts select specific rhizobial genotypes among those present in the soil. We have used population genomics to further investigate this observation. Pisum sativum, Lens culinaris, Vicia sativa, and V. faba plants were used to trap rhizobia from a well-characterized soil, and pooled genomic DNA from 100 isolates from each plant were sequenced. Sequence reads were aligned to the R. leguminosarum bv. viciae 3841 reference genome. High overall conservation of sequences was observed in all subpopulations, although several multigenic regions were absent from the soil population. A large fraction (16 to 22%) of sequence reads could not be recruited to the reference genome, suggesting that they represent sequences specific to that particular soil population. Although highly conserved, the 16S to 23S ribosomal RNA gene region presented single nucleotide polymorphisms (SNP) regarding the reference genome, but no striking differences could be found among plant-selected subpopulations. Plant-specific SNP patterns were, however, clearly observed within the nod gene cluster, supporting the existence of a plant preference for specific rhizobial genotypes. This was also shown after genome-wide analysis of SNP patterns.
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diCenzo GC, Finan TM. Genetic redundancy is prevalent within the 6.7 Mb Sinorhizobium meliloti genome. Mol Genet Genomics 2015; 290:1345-56. [PMID: 25638282 DOI: 10.1007/s00438-015-0998-6] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2014] [Accepted: 01/17/2015] [Indexed: 01/09/2023]
Abstract
Biological pathways are frequently identified via a genetic loss-of-function approach. While this approach has proven to be powerful, it is imperfect as illustrated by well-studied pathways continuing to have missing steps. One potential limiting factor is the masking of phenotypes through genetic redundancy. The prevalence of genetic redundancy in bacterial species has received little attention, although isolated examples of functionally redundant gene pairs exist. Here, we made use of a strain of Sinorhizobium meliloti whose genome was reduced by 45 % through the complete removal of a megaplasmid and a chromid (3 Mb of the 6.7 Mb genome was removed) to begin quantifying the level of genetic redundancy within a large bacterial genome. A mutagenesis of the strain with the reduced genome identified a set of transposon insertions precluding growth of this strain on minimal medium. Transfer of these mutations to the wild-type background revealed that 10-15 % of these chromosomal mutations were located within duplicated genes, as they did not prevent growth of cells with the full genome. The functionally redundant genes were involved in a variety of metabolic pathways, including central carbon metabolism, transport, and amino acid biosynthesis. These results indicate that genetic redundancy may be prevalent within large bacterial genomes. Failing to account for redundantly encoded functions in loss-of-function studies will impair our understanding of a broad range of biological processes and limit our ability to use synthetic biology in the construction of designer cell factories.
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Affiliation(s)
- George C diCenzo
- Department of Biology, McMaster University, 1280 Main St. W., Hamilton, ON, L8S 4K1, Canada
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diCenzo GC, MacLean AM, Milunovic B, Golding GB, Finan TM. Examination of prokaryotic multipartite genome evolution through experimental genome reduction. PLoS Genet 2014; 10:e1004742. [PMID: 25340565 PMCID: PMC4207669 DOI: 10.1371/journal.pgen.1004742] [Citation(s) in RCA: 74] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2014] [Accepted: 09/08/2014] [Indexed: 01/12/2023] Open
Abstract
Many bacteria carry two or more chromosome-like replicons. This occurs in pathogens such as Vibrio cholerea and Brucella abortis as well as in many N2-fixing plant symbionts including all isolates of the alfalfa root-nodule bacteria Sinorhizobium meliloti. Understanding the evolution and role of this multipartite genome organization will provide significant insight into these important organisms; yet this knowledge remains incomplete, in part, because technical challenges of large-scale genome manipulations have limited experimental analyses. The distinct evolutionary histories and characteristics of the three replicons that constitute the S. meliloti genome (the chromosome (3.65 Mb), pSymA megaplasmid (1.35 Mb), and pSymB chromid (1.68 Mb)) makes this a good model to examine this topic. We transferred essential genes from pSymB into the chromosome, and constructed strains that lack pSymB as well as both pSymA and pSymB. This is the largest reduction (45.4%, 3.04 megabases, 2866 genes) of a prokaryotic genome to date and the first removal of an essential chromid. Strikingly, strains lacking pSymA and pSymB (ΔpSymAB) lost the ability to utilize 55 of 74 carbon sources and various sources of nitrogen, phosphorous and sulfur, yet the ΔpSymAB strain grew well in minimal salts media and in sterile soil. This suggests that the core chromosome is sufficient for growth in a bulk soil environment and that the pSymA and pSymB replicons carry genes with more specialized functions such as growth in the rhizosphere and interaction with the plant. These experimental data support a generalized evolutionary model, in which non-chromosomal replicons primarily carry genes with more specialized functions. These large secondary replicons increase the organism's niche range, which offsets their metabolic burden on the cell (e.g. pSymA). Subsequent co-evolution with the chromosome then leads to the formation of a chromid through the acquisition of functions core to all niches (e.g. pSymB). Rhizobia are free-living bacteria of agricultural and environmental importance that form root-nodules on leguminous plants and provide these plants with fixed nitrogen. Many of the rhizobia have a multipartite genome, as do several plant and animal pathogens. All isolates of the alfalfa symbiont, Sinorhizobium meliloti, carry three large replicons, the chromosome (∼3.7 Mb), pSymA megaplasmid (∼1.4 Mb), and pSymB chromid (∼1.7 Mb). To gain insight into the role and evolutionary history of these replicons, we have ‘reversed evolution’ by constructing a S. meliloti strain consisting solely of the chromosome and lacking the pSymB chromid and pSymA megaplasmid. As the resulting strain was viable, we could perform a detailed phenotypic analysis and these data provided significant insight into the biology and metabolism of S. meliloti. The data lend direct experimental evidence in understanding the evolution and role of the multipartite genome. Specifically the large secondary replicons increase the organism's niche range, and this advantage offsets the metabolic burden of these replicons on the cell. Additionally, the single-chromosome strain offers a useful platform to facilitate future forward genetic approaches to understanding and manipulating the symbiosis and plant-microbe interactions.
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Affiliation(s)
- George C. diCenzo
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | | | | | - G. Brian Golding
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | - Turlough M. Finan
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
- * E-mail:
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Donnarumma F, Bazzicalupo M, Blažinkov M, Mengoni A, Sikora S, Babić KH. Biogeography of Sinorhizobium meliloti nodulating alfalfa in different Croatian regions. Res Microbiol 2014; 165:508-16. [DOI: 10.1016/j.resmic.2014.06.001] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2013] [Accepted: 06/11/2014] [Indexed: 11/16/2022]
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50
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Epstein B, Sadowsky MJ, Tiffin P. Selection on horizontally transferred and duplicated genes in sinorhizobium (ensifer), the root-nodule symbionts of medicago. Genome Biol Evol 2014; 6:1199-209. [PMID: 24803571 PMCID: PMC4040998 DOI: 10.1093/gbe/evu090] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Structural variation, including variation in gene copy number and presence or absence of genes, is a widespread and important source of genomic variation. We used whole-genome DNA sequences from 48 strains of Sinorhizobium (recently renamed Ensifer), including 20 strains of Sinorhizobium meliloti and 12 strains of S. medicae that were the focus of the analyses, to study the fitness effects of new structural variants created by duplication and horizontal gene transfer. We find that derived duplicated and horizontally transferred (HT) genes segregate at lower frequency than synonymous and nonsynonymous nucleotide variants in S. meliloti and S. medicae. Furthermore, the relative frequencies of different types of variants are more similar in S. medicae than in S. meliloti, the species with the larger effective population size. These results are consistent with the hypothesis that most duplications and HT genes have deleterious effects. Diversity of duplications, as measured by segregating duplicated genes per gene, is greater than nucleotide diversity, consistent with a high rate of duplication. Our results suggest that the vast majority of structural variants found among closely related bacterial strains are short-lived and unlikely to be involved in species-wide adaptation.
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Affiliation(s)
- Brendan Epstein
- Department of Plant Biology, University of MinnesotaSchool of Biological Sciences, Washington State University
| | - Michael J Sadowsky
- Department of Soil, Water, and Climate, University of MinnesotaBioTechnology Institute, Saint Paul, MN
| | - Peter Tiffin
- Department of Plant Biology, University of Minnesota
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