1
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Herbst K, Wang T, Forchielli EJ, Thommes M, Paschalidis IC, Segrè D. Multi-Attribute Subset Selection enables prediction of representative phenotypes across microbial populations. Commun Biol 2024; 7:407. [PMID: 38570615 PMCID: PMC10991586 DOI: 10.1038/s42003-024-06093-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2022] [Accepted: 03/22/2024] [Indexed: 04/05/2024] Open
Abstract
The interpretation of complex biological datasets requires the identification of representative variables that describe the data without critical information loss. This is particularly important in the analysis of large phenotypic datasets (phenomics). Here we introduce Multi-Attribute Subset Selection (MASS), an algorithm which separates a matrix of phenotypes (e.g., yield across microbial species and environmental conditions) into predictor and response sets of conditions. Using mixed integer linear programming, MASS expresses the response conditions as a linear combination of the predictor conditions, while simultaneously searching for the optimally descriptive set of predictors. We apply the algorithm to three microbial datasets and identify environmental conditions that predict phenotypes under other conditions, providing biologically interpretable axes for strain discrimination. MASS could be used to reduce the number of experiments needed to identify species or to map their metabolic capabilities. The generality of the algorithm allows addressing subset selection problems in areas beyond biology.
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Affiliation(s)
- Konrad Herbst
- Bioinformatics Program, Boston University, Boston, MA, USA
- Biological Design Center, Boston University, Boston, MA, USA
| | - Taiyao Wang
- Division of Systems Engineering, Boston University, Boston, MA, USA
| | - Elena J Forchielli
- Biological Design Center, Boston University, Boston, MA, USA
- Department of Biology, Boston University, Boston, MA, USA
| | - Meghan Thommes
- Biological Design Center, Boston University, Boston, MA, USA
- Department of Biomedical Engineering, Boston University, Boston, MA, USA
| | - Ioannis Ch Paschalidis
- Division of Systems Engineering, Boston University, Boston, MA, USA.
- Department of Biomedical Engineering, Boston University, Boston, MA, USA.
- Faculty of Computing and Data Science, Boston University, Boston, MA, USA.
- Department of Electrical and Computer Engineering, Boston University, Boston, MA, USA.
| | - Daniel Segrè
- Bioinformatics Program, Boston University, Boston, MA, USA.
- Biological Design Center, Boston University, Boston, MA, USA.
- Department of Biology, Boston University, Boston, MA, USA.
- Department of Biomedical Engineering, Boston University, Boston, MA, USA.
- Faculty of Computing and Data Science, Boston University, Boston, MA, USA.
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2
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Horton JS, Taylor TB. Mutation bias and adaptation in bacteria. MICROBIOLOGY (READING, ENGLAND) 2023; 169. [PMID: 37943288 DOI: 10.1099/mic.0.001404] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2023]
Abstract
Genetic mutation, which provides the raw material for evolutionary adaptation, is largely a stochastic force. However, there is ample evidence showing that mutations can also exhibit strong biases, with some mutation types and certain genomic positions mutating more often than others. It is becoming increasingly clear that mutational bias can play a role in determining adaptive outcomes in bacteria in both the laboratory and the clinic. As such, understanding the causes and consequences of mutation bias can help microbiologists to anticipate and predict adaptive outcomes. In this review, we provide an overview of the mechanisms and features of the bacterial genome that cause mutational biases to occur. We then describe the environmental triggers that drive these mechanisms to be more potent and outline the adaptive scenarios where mutation bias can synergize with natural selection to define evolutionary outcomes. We conclude by describing how understanding mutagenic genomic features can help microbiologists predict areas sensitive to mutational bias, and finish by outlining future work that will help us achieve more accurate evolutionary forecasts.
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Affiliation(s)
- James S Horton
- Milner Centre for Evolution, Department of Life Sciences, University of Bath, BA2 7AY, UK
| | - Tiffany B Taylor
- Milner Centre for Evolution, Department of Life Sciences, University of Bath, BA2 7AY, UK
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3
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Robinson D, Vanacloig-Pedros E, Cai R, Place M, Hose J, Gasch AP. Gene-by-environment interactions influence the fitness cost of gene copy-number variation in yeast. G3 (BETHESDA, MD.) 2023; 13:jkad159. [PMID: 37481264 PMCID: PMC10542507 DOI: 10.1093/g3journal/jkad159] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2023] [Revised: 05/11/2023] [Accepted: 07/12/2023] [Indexed: 07/24/2023]
Abstract
Variation in gene copy number can alter gene expression and influence downstream phenotypes; thus copy-number variation provides a route for rapid evolution if the benefits outweigh the cost. We recently showed that genetic background significantly influences how yeast cells respond to gene overexpression, revealing that the fitness costs of copy-number variation can vary substantially with genetic background in a common-garden environment. But the interplay between copy-number variation tolerance and environment remains unexplored on a genomic scale. Here, we measured the tolerance to gene overexpression in four genetically distinct Saccharomyces cerevisiae strains grown under sodium chloride stress. Overexpressed genes that are commonly deleterious during sodium chloride stress recapitulated those commonly deleterious under standard conditions. However, sodium chloride stress uncovered novel differences in strain responses to gene overexpression. West African strain NCYC3290 and North American oak isolate YPS128 are more sensitive to sodium chloride stress than vineyard BC187 and laboratory strain BY4743. Consistently, NCYC3290 and YPS128 showed the greatest sensitivities to overexpression of specific genes. Although most genes were deleterious, hundreds were beneficial when overexpressed-remarkably, most of these effects were strain specific. Few beneficial genes were shared between the sodium chloride-sensitive isolates, implicating mechanistic differences behind their sodium chloride sensitivity. Transcriptomic analysis suggested underlying vulnerabilities and tolerances across strains, and pointed to natural copy-number variation of a sodium export pump that likely contributes to strain-specific responses to overexpression of other genes. Our results reveal extensive strain-by-environment interactions in the response to gene copy-number variation, raising important implications for the accessibility of copy-number variation-dependent evolutionary routes under times of stress.
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Affiliation(s)
- DeElegant Robinson
- Center for Genomic Science Innovation, University of Wisconsin-Madison, Madison, WI 53704, USA
| | - Elena Vanacloig-Pedros
- Center for Genomic Science Innovation, University of Wisconsin-Madison, Madison, WI 53704, USA
- Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI 53704, USA
| | - Ruoyi Cai
- Center for Genomic Science Innovation, University of Wisconsin-Madison, Madison, WI 53704, USA
| | - Michael Place
- Center for Genomic Science Innovation, University of Wisconsin-Madison, Madison, WI 53704, USA
- Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI 53704, USA
| | - James Hose
- Center for Genomic Science Innovation, University of Wisconsin-Madison, Madison, WI 53704, USA
| | - Audrey P Gasch
- Center for Genomic Science Innovation, University of Wisconsin-Madison, Madison, WI 53704, USA
- Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI 53704, USA
- Department of Medical Genetics, University of Wisconsin-Madison, Madison, WI 53704, USA
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4
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Bhatia RP, Kirit HA, Lewis CM, Sankaranarayanan K, Bollback JP. Evolutionary barriers to horizontal gene transfer in macrophage-associated Salmonella. Evol Lett 2023; 7:227-239. [PMID: 37475746 PMCID: PMC10355182 DOI: 10.1093/evlett/qrad020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2022] [Revised: 04/06/2023] [Accepted: 04/20/2023] [Indexed: 07/22/2023] Open
Abstract
Horizontal gene transfer (HGT) is a powerful evolutionary force facilitating bacterial adaptation and emergence of novel phenotypes. Several factors, including environmental ones, are predicted to restrict HGT, but we lack systematic and experimental data supporting these predictions. Here, we address this gap by measuring the relative fitness of 44 genes horizontally transferred from Escherichia coli to Salmonella enterica in infection-relevant environments. We estimated the distribution of fitness effects in each environment and identified that dosage-dependent effects across different environments are a significant barrier to HGT. The majority of genes were found to be deleterious. We also found longer genes had stronger negative fitness consequences than shorter ones, showing that gene length was negatively associated with HGT. Furthermore, fitness effects of transferred genes were found to be environmentally dependent. In summary, a substantial fraction of transferred genes had a significant fitness cost on the recipient, with both gene characteristics and the environment acting as evolutionary barriers to HGT.
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Affiliation(s)
- Rama P Bhatia
- Institute of Infection, Veterinary, and Ecological Sciences, Department of Evolution, Ecology, and Behaviour, University of Liverpool, Liverpool, United Kingdom
| | - Hande Acar Kirit
- Institute of Infection, Veterinary, and Ecological Sciences, Department of Evolution, Ecology, and Behaviour, University of Liverpool, Liverpool, United Kingdom
- Laboratories of Molecular Anthropology and Microbiome Research (LMAMR), University of Oklahoma, Norman, OK, United States
| | - Cecil M Lewis
- Laboratories of Molecular Anthropology and Microbiome Research (LMAMR), University of Oklahoma, Norman, OK, United States
- Department of Anthropology, University of Oklahoma, Norman, OK, United States
| | - Krithivasan Sankaranarayanan
- Laboratories of Molecular Anthropology and Microbiome Research (LMAMR), University of Oklahoma, Norman, OK, United States
- Department of Microbiology and Plant Biology, University of Oklahoma, Norman, OK, United States
| | - Jonathan P Bollback
- Corresponding author: Institute of Infection, Veterinary, and Ecological Sciences, Department of Evolution, Ecology, and Behaviour, University of Liverpool, Crown Street, Liverpool, L69 7ZB, United Kingdom.
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5
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Robinson D, Vanacloig-Pedros E, Cai R, Place M, Hose J, Gasch AP. Gene-by-environment interactions influence the fitness cost of gene copy-number variation in yeast. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.05.11.540375. [PMID: 37503218 PMCID: PMC10369901 DOI: 10.1101/2023.05.11.540375] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/29/2023]
Abstract
Variation in gene copy number can alter gene expression and influence downstream phenotypes; thus copy-number variation (CNV) provides a route for rapid evolution if the benefits outweigh the cost. We recently showed that genetic background significantly influences how yeast cells respond to gene over-expression (OE), revealing that the fitness costs of CNV can vary substantially with genetic background in a common-garden environment. But the interplay between CNV tolerance and environment remains unexplored on a genomic scale. Here we measured the tolerance to gene OE in four genetically distinct Saccharomyces cerevisiae strains grown under sodium chloride (NaCl) stress. OE genes that are commonly deleterious during NaCl stress recapitulated those commonly deleterious under standard conditions. However, NaCl stress uncovered novel differences in strain responses to gene OE. West African strain NCYC3290 and North American oak isolate YPS128 are more sensitive to NaCl stress than vineyard BC187 and laboratory strain BY4743. Consistently, NCYC3290 and YPS128 showed the greatest sensitivities to gene OE. Although most genes were deleterious, hundreds were beneficial when overexpressed - remarkably, most of these effects were strain specific. Few beneficial genes were shared between the NaCl-sensitive isolates, implicating mechanistic differences behind their NaCl sensitivity. Transcriptomic analysis suggested underlying vulnerabilities and tolerances across strains, and pointed to natural CNV of a sodium export pump that likely contributes to strain-specific responses to OE of other genes. Our results reveal extensive strain-by-environment interaction in the response to gene CNV, raising important implications for the accessibility of CNV-dependent evolutionary routes under times of stress.
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Affiliation(s)
- DeElegant Robinson
- Center for Genomic Science Innovation, University of Wisconsin-Madison, Madison WI 53704
| | - Elena Vanacloig-Pedros
- Center for Genomic Science Innovation, University of Wisconsin-Madison, Madison WI 53704
- Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison WI 53704
| | - Ruoyi Cai
- Center for Genomic Science Innovation, University of Wisconsin-Madison, Madison WI 53704
| | - Michael Place
- Center for Genomic Science Innovation, University of Wisconsin-Madison, Madison WI 53704
- Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison WI 53704
| | - James Hose
- Center for Genomic Science Innovation, University of Wisconsin-Madison, Madison WI 53704
| | - Audrey P Gasch
- Center for Genomic Science Innovation, University of Wisconsin-Madison, Madison WI 53704
- Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison WI 53704
- Department of Medical Genetics, University of Wisconsin-Madison, Madison WI 53704
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6
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Burny C, Nolte V, Dolezal M, Schlötterer C. Genome-wide selection signatures reveal widespread synergistic effects of two different stressors in Drosophila melanogaster. Proc Biol Sci 2022; 289:20221857. [PMID: 36259211 PMCID: PMC9579754 DOI: 10.1098/rspb.2022.1857] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Experimental evolution combined with whole-genome sequencing (evolve and resequence (E&R)) is a powerful approach to study the adaptive architecture of selected traits. Nevertheless, so far the focus has been on the selective response triggered by a single stressor. Building on the highly parallel selection response of founder populations with reduced variation, we evaluated how the presence of a second stressor affects the genomic selection response. After 20 generations of adaptation to laboratory conditions at either 18°C or 29°C, strong genome-wide selection signatures were observed. Only 38% of the selection signatures can be attributed to laboratory adaptation (no difference between temperature regimes). The remaining selection responses are either caused by temperature-specific effects, or reflect the joint effects of temperature and laboratory adaptation (same direction, but the magnitude differs between temperatures). The allele frequency changes resulting from the combined effects of temperature and laboratory adaptation were more extreme in the hot environment for 83% of the affected genomic regions-indicating widespread synergistic effects of the two stressors. We conclude that E&R with reduced genetic variation is a powerful approach to study genome-wide fitness consequences driven by the combined effects of multiple environmental factors.
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Affiliation(s)
- Claire Burny
- Institut für Populationsgenetik, Vetmeduni Vienna, Veterinärplatz 1, Vienna 1210, Austria.,Vienna Graduate School of Population Genetics, Vetmeduni Vienna, Vienna 1210, Austria
| | - Viola Nolte
- Institut für Populationsgenetik, Vetmeduni Vienna, Veterinärplatz 1, Vienna 1210, Austria
| | - Marlies Dolezal
- Plattform Bioinformatik und Biostatistik, Vetmeduni Vienna, Vienna 1210, Austria
| | - Christian Schlötterer
- Institut für Populationsgenetik, Vetmeduni Vienna, Veterinärplatz 1, Vienna 1210, Austria
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7
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Angermayr SA, Pang TY, Chevereau G, Mitosch K, Lercher MJ, Bollenbach T. Growth-mediated negative feedback shapes quantitative antibiotic response. Mol Syst Biol 2022; 18:e10490. [PMID: 36124745 PMCID: PMC9486506 DOI: 10.15252/msb.202110490] [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: 06/04/2021] [Revised: 08/19/2022] [Accepted: 08/26/2022] [Indexed: 11/15/2022] Open
Abstract
Dose–response relationships are a general concept for quantitatively describing biological systems across multiple scales, from the molecular to the whole‐cell level. A clinically relevant example is the bacterial growth response to antibiotics, which is routinely characterized by dose–response curves. The shape of the dose–response curve varies drastically between antibiotics and plays a key role in treatment, drug interactions, and resistance evolution. However, the mechanisms shaping the dose–response curve remain largely unclear. Here, we show in Escherichia coli that the distinctively shallow dose–response curve of the antibiotic trimethoprim is caused by a negative growth‐mediated feedback loop: Trimethoprim slows growth, which in turn weakens the effect of this antibiotic. At the molecular level, this feedback is caused by the upregulation of the drug target dihydrofolate reductase (FolA/DHFR). We show that this upregulation is not a specific response to trimethoprim but follows a universal trend line that depends primarily on the growth rate, irrespective of its cause. Rewiring the feedback loop alters the dose–response curve in a predictable manner, which we corroborate using a mathematical model of cellular resource allocation and growth. Our results indicate that growth‐mediated feedback loops may shape drug responses more generally and could be exploited to design evolutionary traps that enable selection against drug resistance.
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Affiliation(s)
- S Andreas Angermayr
- Institute for Biological Physics, University of Cologne, Cologne, Germany.,Institute of Science and Technology Austria, Klosterneuburg, Austria
| | - Tin Yau Pang
- Institute for Computer Science, Heinrich Heine University Düsseldorf, Düsseldorf, Germany.,Department of Biology, Heinrich Heine University Düsseldorf, Düsseldorf, Germany
| | | | - Karin Mitosch
- Institute of Science and Technology Austria, Klosterneuburg, Austria.,Genome Biology Unit, European Molecular Biology Laboratory (EMBL), Heidelberg, Germany
| | - Martin J Lercher
- Institute for Computer Science, Heinrich Heine University Düsseldorf, Düsseldorf, Germany.,Department of Biology, Heinrich Heine University Düsseldorf, Düsseldorf, Germany
| | - Tobias Bollenbach
- Institute for Biological Physics, University of Cologne, Cologne, Germany.,Center for Data and Simulation Science, University of Cologne, Cologne, Germany
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8
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Lee YCG. Synergistic epistasis of the deleterious effects of transposable elements. Genetics 2021; 220:6458331. [PMID: 34888644 DOI: 10.1093/genetics/iyab211] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2021] [Accepted: 11/10/2021] [Indexed: 11/12/2022] Open
Abstract
The replicative nature and generally deleterious effects of transposable elements (TEs) raise an outstanding question about how TE copy number is stably contained in host populations. Classic theoretical analyses predict that, when the decline in fitness due to each additional TE insertion is greater than linear, or when there is synergistic epistasis, selection against TEs can result in a stable equilibrium of TE copy number. While several mechanisms are predicted to yield synergistic deleterious effects of TEs, we lack empirical investigations of the presence of such epistatic interactions. Purifying selection with synergistic epistasis generates repulsion linkage between deleterious alleles. We investigated this population genetic signal in the likely ancestral Drosophila melanogaster population and found evidence supporting the presence of synergistic epistasis among TE insertions, especially TEs expected to exert large fitness impacts. Even though synergistic epistasis of TEs has been predicted to arise through ectopic recombination and TE-mediated epigenetic silencing mechanisms, we only found mixed support for the associated predictions. We observed signals of synergistic epistasis for a large number of TE families, which is consistent with the expectation that such epistatic interaction mainly happens among copies of the same family. Curiously, significant repulsion linkage was also found among TE insertions from different families, suggesting the possibility that synergism of TEs' deleterious fitness effects could arise above the family level and through mechanisms similar to those of simple mutations. Our findings set the stage for investigating the prevalence and importance of epistatic interactions in the evolutionary dynamics of TEs.
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Affiliation(s)
- Yuh Chwen G Lee
- Department of Ecology and Evolutionary Biology, University of California, Irvine, Irvine, CA 92697, USA
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9
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Lalanne J, Parker DJ, Li G. Spurious regulatory connections dictate the expression-fitness landscape of translation factors. Mol Syst Biol 2021; 17:e10302. [PMID: 33900014 PMCID: PMC8073009 DOI: 10.15252/msb.202110302] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2021] [Revised: 03/12/2021] [Accepted: 03/16/2021] [Indexed: 12/21/2022] Open
Abstract
During steady-state cell growth, individual enzymatic fluxes can be directly inferred from growth rate by mass conservation, but the inverse problem remains unsolved. Perturbing the flux and expression of a single enzyme could have pleiotropic effects that may or may not dominate the impact on cell fitness. Here, we quantitatively dissect the molecular and global responses to varied expression of translation termination factors (peptide release factors, RFs) in the bacterium Bacillus subtilis. While endogenous RF expression maximizes proliferation, deviations in expression lead to unexpected distal regulatory responses that dictate fitness reduction. Molecularly, RF depletion causes expression imbalance at specific operons, which activates master regulators and detrimentally overrides the transcriptome. Through these spurious connections, RF abundances are thus entrenched by focal points within the regulatory network, in one case located at a single stop codon. Such regulatory entrenchment suggests that predictive bottom-up models of expression-fitness landscapes will require near-exhaustive characterization of parts.
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Affiliation(s)
- Jean‐Benoît Lalanne
- Department of BiologyMassachusetts Institute of TechnologyCambridgeMAUSA
- Department of PhysicsMassachusetts Institute of TechnologyCambridgeMAUSA
- Present address:
Department of Genome SciencesUniversity of WashingtonSeattleWAUSA
| | - Darren J Parker
- Department of BiologyMassachusetts Institute of TechnologyCambridgeMAUSA
- Present address:
Biosciences DivisionOak Ridge National LaboratoryOak RidgeTNUSA
| | - Gene‐Wei Li
- Department of BiologyMassachusetts Institute of TechnologyCambridgeMAUSA
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10
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Souque C, Escudero JA, MacLean RC. Integron activity accelerates the evolution of antibiotic resistance. eLife 2021; 10:62474. [PMID: 33634790 PMCID: PMC8024014 DOI: 10.7554/elife.62474] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2020] [Accepted: 02/23/2021] [Indexed: 11/13/2022] Open
Abstract
Mobile integrons are widespread genetic platforms that allow bacteria to modulate the expression of antibiotic resistance cassettes by shuffling their position from a common promoter. Antibiotic stress induces the expression of an integrase that excises and integrates cassettes, and this unique recombination and expression system is thought to allow bacteria to 'evolve on demand' in response to antibiotic pressure. To test this hypothesis, we inserted a custom three-cassette integron into Pseudomonas aeruginosa and used experimental evolution to measure the impact of integrase activity on adaptation to gentamicin. Crucially, integrase activity accelerated evolution by increasing the expression of a gentamicin resistance cassette through duplications and by eliminating redundant cassettes. Importantly, we found no evidence of deleterious off-target effects of integrase activity. In summary, integrons accelerate resistance evolution by rapidly generating combinatorial variation in cassette composition while maintaining genomic integrity.
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Affiliation(s)
- Célia Souque
- University of Oxford, Department of Zoology, Oxford, United Kingdom
| | - José Antonio Escudero
- University of Oxford, Department of Zoology, Oxford, United Kingdom.,Universidad Complutense de Madrid, Departamento de Sanidad Animal and VISAVET, Madrid, Spain
| | - R Craig MacLean
- University of Oxford, Department of Zoology, Oxford, United Kingdom
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11
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Wytock TP, Zhang M, Jinich A, Fiebig A, Crosson S, Motter AE. Extreme Antagonism Arising from Gene-Environment Interactions. Biophys J 2020; 119:2074-2086. [PMID: 33068537 DOI: 10.1016/j.bpj.2020.09.038] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2020] [Revised: 08/27/2020] [Accepted: 09/21/2020] [Indexed: 01/06/2023] Open
Abstract
Antagonistic interactions in biological systems, which occur when one perturbation blunts the effect of another, are typically interpreted as evidence that the two perturbations impact the same cellular pathway or function. Yet, this interpretation ignores extreme antagonistic interactions wherein an otherwise deleterious perturbation compensates for the function lost because of a prior perturbation. Here, we report on gene-environment interactions involving genetic mutations that are deleterious in a permissive environment but beneficial in a specific environment that restricts growth. These extreme antagonistic interactions constitute gene-environment analogs of synthetic rescues previously observed for gene-gene interactions. Our approach uses two independent adaptive evolution steps to address the lack of experimental methods to systematically identify such extreme interactions. We apply the approach to Escherichia coli by successively adapting it to defined glucose media without and with the antibiotic rifampicin. The approach identified multiple mutations that are beneficial in the presence of rifampicin and deleterious in its absence. The analysis of transcription shows that the antagonistic adaptive mutations repress a stringent response-like transcriptional program, whereas nonantagonistic mutations have an opposite transcriptional profile. Our approach represents a step toward the systematic characterization of extreme antagonistic gene-drug interactions, which can be used to identify targets to select against antibiotic resistance.
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Affiliation(s)
- Thomas P Wytock
- Department of Physics and Astronomy, Northwestern University, Evanston, Illinois
| | - Manjing Zhang
- The Committee on Microbiology, University of Chicago, Chicago, Illinois
| | - Adrian Jinich
- Division of Infectious Diseases, Weill Department of Medicine, Weill-Cornell Medical College, New York, New York
| | - Aretha Fiebig
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan
| | - Sean Crosson
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan
| | - Adilson E Motter
- Department of Physics and Astronomy, Northwestern University, Evanston, Illinois; Chemistry of Life Processes Institute, Northwestern University, Evanston, Illinois; Northwestern Institute on Complex Systems, Northwestern University, Evanston, Illinois.
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12
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Kavčič B, Tkačik G, Bollenbach T. Mechanisms of drug interactions between translation-inhibiting antibiotics. Nat Commun 2020; 11:4013. [PMID: 32782250 PMCID: PMC7421507 DOI: 10.1038/s41467-020-17734-z] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2019] [Accepted: 07/14/2020] [Indexed: 02/03/2023] Open
Abstract
Antibiotics that interfere with translation, when combined, interact in diverse and difficult-to-predict ways. Here, we explain these interactions by "translation bottlenecks": points in the translation cycle where antibiotics block ribosomal progression. To elucidate the underlying mechanisms of drug interactions between translation inhibitors, we generate translation bottlenecks genetically using inducible control of translation factors that regulate well-defined translation cycle steps. These perturbations accurately mimic antibiotic action and drug interactions, supporting that the interplay of different translation bottlenecks causes these interactions. We further show that growth laws, combined with drug uptake and binding kinetics, enable the direct prediction of a large fraction of observed interactions, yet fail to predict suppression. However, varying two translation bottlenecks simultaneously supports that dense traffic of ribosomes and competition for translation factors account for the previously unexplained suppression. These results highlight the importance of "continuous epistasis" in bacterial physiology.
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Affiliation(s)
- Bor Kavčič
- Institute of Science and Technology Austria, Am Campus 1, A-3400, Klosterneuburg, Austria
| | - Gašper Tkačik
- Institute of Science and Technology Austria, Am Campus 1, A-3400, Klosterneuburg, Austria
| | - Tobias Bollenbach
- Institute for Biological Physics, University of Cologne, Zülpicher Str. 77, D-50937, Cologne, Germany.
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13
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Ramiro RS, Durão P, Bank C, Gordo I. Low mutational load and high mutation rate variation in gut commensal bacteria. PLoS Biol 2020; 18:e3000617. [PMID: 32155146 PMCID: PMC7064181 DOI: 10.1371/journal.pbio.3000617] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2019] [Accepted: 02/05/2020] [Indexed: 12/14/2022] Open
Abstract
Bacteria generally live in species-rich communities, such as the gut microbiota. Yet little is known about bacterial evolution in natural ecosystems. Here, we followed the long-term evolution of commensal Escherichia coli in the mouse gut. We observe the emergence of mutation rate polymorphism, ranging from wild-type levels to 1,000-fold higher. By combining experiments, whole-genome sequencing, and in silico simulations, we identify the molecular causes and explore the evolutionary conditions allowing these hypermutators to emerge and coexist within the microbiota. The hypermutator phenotype is caused by mutations in DNA polymerase III proofreading and catalytic subunits, which increase mutation rate by approximately 1,000-fold and stabilise hypermutator fitness, respectively. Strong mutation rate variation persists for >1,000 generations, with coexistence between lineages carrying 4 to >600 mutations. The in vivo molecular evolution pattern is consistent with fitness effects of deleterious mutations sd ≤ 10−4/generation, assuming a constant effect or exponentially distributed effects with a constant mean. Such effects are lower than typical in vitro estimates, leading to a low mutational load, an inference that is observed in in vivo and in vitro competitions. Despite large numbers of deleterious mutations, we identify multiple beneficial mutations that do not reach fixation over long periods of time. This indicates that the dynamics of beneficial mutations are not shaped by constant positive Darwinian selection but could be explained by other evolutionary mechanisms that maintain genetic diversity. Thus, microbial evolution in the gut is likely characterised by partial sweeps of beneficial mutations combined with hitchhiking of slightly deleterious mutations, which take a long time to be purged because they impose a low mutational load. The combination of these two processes could allow for the long-term maintenance of intraspecies genetic diversity, including mutation rate polymorphism. These results are consistent with the pattern of genetic polymorphism that is emerging from metagenomics studies of the human gut microbiota, suggesting that we have identified key evolutionary processes shaping the genetic composition of this community. Weak-effect deleterious mutations and negative frequency–dependent selection, acting on beneficial mutations, shape the dynamics of molecular evolution within the mouse gut microbiota.
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Affiliation(s)
- Ricardo S. Ramiro
- Instituto Gulbenkian de Ciência, Oeiras, Portugal
- * E-mail: (RSR); (IG)
| | - Paulo Durão
- Instituto Gulbenkian de Ciência, Oeiras, Portugal
| | - Claudia Bank
- Instituto Gulbenkian de Ciência, Oeiras, Portugal
| | - Isabel Gordo
- Instituto Gulbenkian de Ciência, Oeiras, Portugal
- * E-mail: (RSR); (IG)
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14
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Wu F, Tan C. Dead bacterial absorption of antimicrobial peptides underlies collective tolerance. J R Soc Interface 2020; 16:20180701. [PMID: 30958185 DOI: 10.1098/rsif.2018.0701] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The collective tolerance towards antimicrobial peptides (APs) is thought to occur primarily through mechanisms associated with live bacterial cells. In contrast to the focus on live cells, we discover that the LL37 antimicrobial peptide kills a subpopulation of Escherichia coli, forming dead cells that absorb the remaining LL37 from the environment. Combining mathematical modelling with population and single-cell experiments, we show that bacteria absorb LL37 at a timing that coincides with the permeabilization of their cytoplasmic membranes. Furthermore, we show that one bacterial strain can absorb LL37 and protect another strain from killing by LL37. Finally, we demonstrate that the absorption of LL37 by dead bacteria can be reduced using a peptide adjuvant. In contrast to the known collective tolerance mechanisms, we show that the absorption of APs by dead bacteria is a dynamic process that leads to emergent population behaviour.
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Affiliation(s)
- Fan Wu
- Department of Biomedical Engineering, University of California Davis , Davis, CA 95616 , USA
| | - Cheemeng Tan
- Department of Biomedical Engineering, University of California Davis , Davis, CA 95616 , USA
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15
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Gomes MGM, King JG, Nunes A, Colegrave N, Hoffmann AA. The effects of individual nonheritable variation on fitness estimation and coexistence. Ecol Evol 2019; 9:8995-9004. [PMID: 31462998 PMCID: PMC6706197 DOI: 10.1002/ece3.5437] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2019] [Accepted: 06/18/2019] [Indexed: 12/17/2022] Open
Abstract
Demographic theory and data have emphasized that nonheritable variation in individual frailty enables selection within cohorts, affecting the dynamics of a population while being invisible to its evolution. Here, we include the component of individual variation in longevity or viability which is nonheritable in simple bacterial growth models and explore its ecological and evolutionary impacts. First, we find that this variation produces consistent trends in longevity differences between bacterial genotypes when measured across stress gradients. Given that direct measurements of longevity are inevitably biased due to the presence of this variation and ongoing selection, we propose the use of the trend itself for obtaining more exact inferences of genotypic fitness. Second, we show how species or strain coexistence can be enabled by nonheritable variation in longevity or viability. These general conclusions are likely to extend beyond bacterial systems.
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Affiliation(s)
- M. Gabriela M. Gomes
- Liverpool School of Tropical MedicineLiverpoolUK
- CIBIO‐InBIO, Centro de Investigação em Biodiversidade e Recursos GenéticosCMUP, Centro de Matemática da Universidade do PortoPortoPortugal
| | - Jessica G. King
- School of Biological Sciences, Institute of Evolutionary BiologyUniversity of EdinburghEdinburghUK
| | - Ana Nunes
- Departamento de Física, Faculdade de CiênciasBioISI – Biosystems and Integrative Sciences Institute, Universidade de LisboaLisboaPortugal
| | - Nick Colegrave
- School of Biological Sciences, Institute of Evolutionary BiologyUniversity of EdinburghEdinburghUK
| | - Ary A. Hoffmann
- School of BioSciencesBio21 Institute, University of MelbourneMelbourneVic.Australia
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16
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Wei X, Zhang J. Patterns and Mechanisms of Diminishing Returns from Beneficial Mutations. Mol Biol Evol 2019; 36:1008-1021. [PMID: 30903691 DOI: 10.1093/molbev/msz035] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Diminishing returns epistasis causes the benefit of the same advantageous mutation smaller in fitter genotypes and is frequently observed in experimental evolution. However, its occurrence in other contexts, environment dependence, and mechanistic basis are unclear. Here, we address these questions using 1,005 sequenced segregants generated from a yeast cross. Under each of 47 examined environments, 66-92% of tested polymorphisms exhibit diminishing returns epistasis. Surprisingly, improving environment quality also reduces the benefits of advantageous mutations even when fitness is controlled for, indicating the necessity to revise the global epistasis hypothesis. We propose that diminishing returns originates from the modular organization of life where the contribution of each functional module to fitness is determined jointly by the genotype and environment and has an upper limit, and demonstrate that our model predictions match empirical observations. These findings broaden the concept of diminishing returns epistasis, reveal its generality and potential cause, and have important evolutionary implications.
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Affiliation(s)
- Xinzhu Wei
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI
| | - Jianzhi Zhang
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI
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17
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Mauri M, Vecchione S, Fritz G. Deconvolution of Luminescence Cross-Talk in High-Throughput Gene Expression Profiling. ACS Synth Biol 2019; 8:1361-1370. [PMID: 31095908 DOI: 10.1021/acssynbio.9b00032] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Luciferase reporters have become standard genetic tools to monitor gene expression in real time and in high-throughput using microplate readers. Compared to reporter gene assays based on fluorescence proteins, luciferase reporters have a superior signal-to-noise ratio, since they do not suffer from the high autofluorescence background of the bacterial cell. However, at the same time luciferase reporters have the drawback of constant light emission, which leads to undesired cross-talk between neighboring wells on a microplate. To overcome this limitation, we developed a computational method to correct for luminescence bleed-through and to estimate the "true" luminescence activity for each well of a microplate. As the sole input our algorithm uses the signals measured from a calibration plate, in which the light emitted from a single luminescent well serves as an estimate for the "light-spread function". We show that this light-spread function can be used to deconvolve any other measurement obtained under the same technical conditions. Our analysis demonstrates that the correction preserves low-level signals close to the background and shows that it is universally applicable to different kinds of microplate readers and plate types.
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Affiliation(s)
- Marco Mauri
- LOEWE Center for Synthetic Microbiology and Department of Physics, Philipps-Universität Marburg, 35032 Marburg, Germany
| | - Stefano Vecchione
- LOEWE Center for Synthetic Microbiology and Department of Physics, Philipps-Universität Marburg, 35032 Marburg, Germany
| | - Georg Fritz
- LOEWE Center for Synthetic Microbiology and Department of Physics, Philipps-Universität Marburg, 35032 Marburg, Germany
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18
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Palmer AC, Chait R, Kishony R. Nonoptimal Gene Expression Creates Latent Potential for Antibiotic Resistance. Mol Biol Evol 2019; 35:2669-2684. [PMID: 30169679 PMCID: PMC6231494 DOI: 10.1093/molbev/msy163] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Bacteria regulate genes to survive antibiotic stress, but regulation can be far from perfect. When regulation is not optimal, mutations that change gene expression can contribute to antibiotic resistance. It is not systematically understood to what extent natural gene regulation is or is not optimal for distinct antibiotics, and how changes in expression of specific genes quantitatively affect antibiotic resistance. Here we discover a simple quantitative relation between fitness, gene expression, and antibiotic potency, which rationalizes our observation that a multitude of genes and even innate antibiotic defense mechanisms have expression that is critically nonoptimal under antibiotic treatment. First, we developed a pooled-strain drug-diffusion assay and screened Escherichia coli overexpression and knockout libraries, finding that resistance to a range of 31 antibiotics could result from changing expression of a large and functionally diverse set of genes, in a primarily but not exclusively drug-specific manner. Second, by synthetically controlling the expression of single-drug and multidrug resistance genes, we observed that their fitness–expression functions changed dramatically under antibiotic treatment in accordance with a log-sensitivity relation. Thus, because many genes are nonoptimally expressed under antibiotic treatment, many regulatory mutations can contribute to resistance by altering expression and by activating latent defenses.
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Affiliation(s)
- Adam C Palmer
- Department of Systems Biology, Harvard Medical School, Boston, MA.,Laboratory of Systems Pharmacology, Harvard Medical School, Boston, MA
| | - Remy Chait
- Department of Systems Biology, Harvard Medical School, Boston, MA.,Institute of Science and Technology Austria, Klosterneuburg, Austria
| | - Roy Kishony
- Department of Systems Biology, Harvard Medical School, Boston, MA.,Departments of Biology and Computer Science, Technion-Israel Institute of Technology, Haifa, Israel
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19
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Gurry T, Gibbons SM, Nguyen LTT, Kearney SM, Ananthakrishnan A, Jiang X, Duvallet C, Kassam Z, Alm EJ. Predictability and persistence of prebiotic dietary supplementation in a healthy human cohort. Sci Rep 2018; 8:12699. [PMID: 30139999 PMCID: PMC6107591 DOI: 10.1038/s41598-018-30783-1] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2018] [Accepted: 07/26/2018] [Indexed: 01/05/2023] Open
Abstract
Dietary interventions to manipulate the human gut microbiome for improved health have received increasing attention. However, their design has been limited by a lack of understanding of the quantitative impact of diet on a host’s microbiota. We present a highly controlled diet perturbation experiment in a healthy, human cohort in which individual micronutrients are spiked in against a standardized background. We identify strong and predictable responses of specific microbes across participants consuming prebiotic spike-ins, at the level of both strains and functional genes, suggesting fine-scale resource partitioning in the human gut. No predictable responses to non-prebiotic micronutrients were found. Surprisingly, we did not observe decreases in day-to-day variability of the microbiota compared to a complex, varying diet, and instead found evidence of diet-induced stress and an associated loss of biodiversity. Our data offer insights into the effect of a low complexity diet on the gut microbiome, and suggest that effective personalized dietary interventions will rely on functional, strain-level characterization of a patient’s microbiota.
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Affiliation(s)
- Thomas Gurry
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.,Center for Microbiome Informatics and Therapeutics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.,The Broad Institute of MIT and Harvard, Cambridge, MA, 02142, USA
| | | | - Sean M Gibbons
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.,Center for Microbiome Informatics and Therapeutics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.,The Broad Institute of MIT and Harvard, Cambridge, MA, 02142, USA
| | - Le Thanh Tu Nguyen
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.,Center for Microbiome Informatics and Therapeutics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Sean M Kearney
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.,Center for Microbiome Informatics and Therapeutics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Ashwin Ananthakrishnan
- Division of Gastroenterology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, 02114, USA
| | - Xiaofang Jiang
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.,Center for Microbiome Informatics and Therapeutics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.,The Broad Institute of MIT and Harvard, Cambridge, MA, 02142, USA
| | - Claire Duvallet
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.,Center for Microbiome Informatics and Therapeutics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Zain Kassam
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.,OpenBiome, Somerville, MA, 02143, USA
| | - Eric J Alm
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA. .,Center for Microbiome Informatics and Therapeutics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA. .,The Broad Institute of MIT and Harvard, Cambridge, MA, 02142, USA.
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20
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Ho EKH, Agrawal AF. Mutation accumulation in selfing populations under fluctuating selection. Evolution 2018; 72:1759-1772. [DOI: 10.1111/evo.13553] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2018] [Revised: 06/26/2018] [Accepted: 07/01/2018] [Indexed: 12/13/2022]
Affiliation(s)
- Eddie K. H. Ho
- Department of Ecology and Evolutionary Biology University of Toronto 25 Willcocks Street Toronto ON M5S 3B2 Canada
| | - Aneil F. Agrawal
- Department of Ecology and Evolutionary Biology University of Toronto 25 Willcocks Street Toronto ON M5S 3B2 Canada
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21
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Arbuthnott D, Whitlock MC. Environmental stress does not increase the mean strength of selection. J Evol Biol 2018; 31:1599-1606. [PMID: 29978525 DOI: 10.1111/jeb.13351] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2018] [Revised: 06/06/2018] [Accepted: 06/23/2018] [Indexed: 11/28/2022]
Abstract
A common intuition among evolutionary biologists and ecologists is that environmental stress will increase the strength of selection against deleterious alleles and among alternate genotypes. However, the strength of selection is determined by the relative fitness differences among genotypes, and there is no theoretical reason why these differences should be exaggerated as mean fitness decreases. We update a recent review of the empirical results pertaining to environmental stress and the strength of selection and find that there is no overall trend towards increased selection under stress, in agreement with other recent analyses of existing data. The majority of past studies measure the strength of selection by quantifying the decrease in fitness imposed by single or multiple mutations in different environments. However, selection rarely acts on one locus independently, and the strength of selection will be determined by variation across the whole genome. We used 20 inbred lines of Drosophila melanogaster to make repeated fitness measurements of the same genotypes in four different environments. This framework allowed us to determine the variation in fitness attributable to genotype across stressful environments and to calculate the opportunity for selection among these genotypes in each stress. Although we found significant decreases in mean fitness in our stressful environments, we did not find any significant differences in the strength of selection among any of the four measured environments. Therefore, in agreement with our updated review, we find no evidence for the oft-cited verbal model that stress increases the strength of selection.
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Affiliation(s)
- Devin Arbuthnott
- Department of Zoology, University of British Columbia, Vancouver, BC, Canada
| | - Michael C Whitlock
- Department of Zoology, University of British Columbia, Vancouver, BC, Canada
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22
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Pilizota T, Yang YT. "Do It Yourself" Microbial Cultivation Techniques for Synthetic and Systems Biology: Cheap, Fun, and Flexible. Front Microbiol 2018; 9:1666. [PMID: 30105008 PMCID: PMC6077191 DOI: 10.3389/fmicb.2018.01666] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2018] [Accepted: 07/04/2018] [Indexed: 12/14/2022] Open
Abstract
With the emergence of inexpensive 3D printing technology, open-source platforms for electronic prototyping and single-board computers, "Do it Yourself" (DIY) approaches to the cultivation of microbial cultures are becoming more feasible, user-friendly, and thus wider spread. In this perspective, we survey some of these approaches, as well as add-on solutions to commercial instruments for synthetic and system biology applications. We discuss different cultivation designs, including capabilities and limitations. Our intention is to encourage the reader to consider the DIY solutions. Overall, custom cultivation devices offer controlled growth environments with in-line monitoring of, for example, optical density, fluorescence, pH, and dissolved oxygen, all at affordable prices. Moreover, they offer a great degree of flexibility for different applications and requirements and are fun to design and construct. We include several illustrative examples, such as gaining optogenetic control and adaptive laboratory evolution experiments.
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Affiliation(s)
- Teuta Pilizota
- Centre for Synthetic and Systems Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Ya-Tang Yang
- Department of Electrical Engineering, National Tsing Hua University, Hsinchu, Taiwan
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23
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Effects of mutation and selection on plasticity of a promoter activity in Saccharomyces cerevisiae. Proc Natl Acad Sci U S A 2017; 114:E11218-E11227. [PMID: 29259117 DOI: 10.1073/pnas.1713960115] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Phenotypic plasticity is an evolvable property of biological systems that can arise from environment-specific regulation of gene expression. To better understand the evolutionary and molecular mechanisms that give rise to plasticity in gene expression, we quantified the effects of 235 single-nucleotide mutations in the Saccharomyces cerevisiae TDH3 promoter (PTDH3 ) on the activity of this promoter in media containing glucose, galactose, or glycerol as a carbon source. We found that the distributions of mutational effects differed among environments because many mutations altered the plastic response exhibited by the wild-type allele. Comparing the effects of these mutations with the effects of 30 PTDH3 polymorphisms on expression plasticity in the same environments provided evidence of natural selection acting to prevent the plastic response in PTDH3 activity between glucose and galactose from becoming larger. The largest changes in expression plasticity were observed between fermentable (glucose or galactose) and nonfermentable (glycerol) carbon sources and were caused by mutations located in the RAP1 and GCR1 transcription factor binding sites. Mutations altered expression plasticity most frequently between the two fermentable environments, with mutations causing significant changes in plasticity between glucose and galactose distributed throughout the promoter, suggesting they might affect chromatin structure. Taken together, these results provide insight into the molecular mechanisms underlying gene-by-environment interactions affecting gene expression as well as the evolutionary dynamics affecting natural variation in plasticity of gene expression.
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24
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The Bacillus BioBrick Box 2.0: expanding the genetic toolbox for the standardized work with Bacillus subtilis. Sci Rep 2017; 7:15058. [PMID: 29118374 PMCID: PMC5678133 DOI: 10.1038/s41598-017-15107-z] [Citation(s) in RCA: 67] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2017] [Accepted: 10/20/2017] [Indexed: 12/03/2022] Open
Abstract
Standardized and well-characterized genetic building blocks allow the convenient assembly of novel genetic modules and devices, ensuring reusability of parts and reproducibility of experiments. In the first Bacillus subtilis-specific toolbox using the BioBrick standard, we presented integrative vectors, promoters, reporter genes and epitope tags for this Gram-positive model bacterium. With the Bacillus BioBrick Box 2.0, we significantly expand the range of our toolbox by providing new integrative vectors, introducing novel tools for fine-tuning protein expression, and carefully evaluating codon-adapted fluorescence proteins in B. subtilis, which cover the whole spectrum of visible light. Moreover, we developed new reporter systems to allow evaluating the strength of promoters and ribosome binding sites. This well-evaluated extension of our BioBrick-based toolbox increases the accessibility of B. subtilis and will therefore promote the use of this model bacterium and biotechnological workhorse as a host for fundamental and applied Synthetic Biology projects.
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25
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Kraemer SA, Böndel KB, Ness RW, Keightley PD, Colegrave N. Fitness change in relation to mutation number in spontaneous mutation accumulation lines of Chlamydomonas reinhardtii. Evolution 2017; 71:2918-2929. [PMID: 28884790 PMCID: PMC5765464 DOI: 10.1111/evo.13360] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2017] [Revised: 09/01/2017] [Accepted: 09/05/2017] [Indexed: 01/08/2023]
Abstract
Although all genetic variation ultimately stems from mutations, their properties are difficult to study directly. Here, we used multiple mutation accumulation (MA) lines derived from five genetic backgrounds of the green algae Chlamydomonas reinhardtii that have been previously subjected to whole genome sequencing to investigate the relationship between the number of spontaneous mutations and change in fitness from a nonevolved ancestor. MA lines were on average less fit than their ancestors and we detected a significantly negative correlation between the change in fitness and the total number of accumulated mutations in the genome. Likewise, the number of mutations located within coding regions significantly and negatively impacted MA line fitness. We used the fitness data to parameterize a maximum likelihood model to estimate discrete categories of mutational effects, and found that models containing one to two mutational effect categories (one neutral and one deleterious category) fitted the data best. However, the best‐fitting mutational effects models were highly dependent on the genetic background of the ancestral strain.
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Affiliation(s)
- Susanne A Kraemer
- Institute of Evolutionary Biology, Ashworth Laboratories, University of Edinburgh, Edinburgh EH93FL, United Kingdom
| | - Katharina B Böndel
- Institute of Evolutionary Biology, Ashworth Laboratories, University of Edinburgh, Edinburgh EH93FL, United Kingdom
| | - Robert W Ness
- Department of Biology, William G. Davis Building, University of Toronto, Mississuaga L5L1C6, Canada
| | - Peter D Keightley
- Institute of Evolutionary Biology, Ashworth Laboratories, University of Edinburgh, Edinburgh EH93FL, United Kingdom
| | - Nick Colegrave
- Institute of Evolutionary Biology, Ashworth Laboratories, University of Edinburgh, Edinburgh EH93FL, United Kingdom
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26
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Rutter MT, Wieckowski YM, Murren CJ, Strand AE. Fitness effects of mutation: testing genetic redundancy in Arabidopsis thaliana. J Evol Biol 2017; 30:1124-1135. [PMID: 28387971 DOI: 10.1111/jeb.13081] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2015] [Accepted: 03/09/2017] [Indexed: 01/05/2023]
Abstract
Screens of organisms with disruptive mutations in a single gene often fail to detect phenotypic consequences for the majority of mutants. One explanation for this phenomenon is that the presence of paralogous loci provides genetic redundancy. However, it is also possible that the assayed traits are affected by few loci, that effects could be subtle or that phenotypic effects are restricted to certain environments. We assayed a set of T-DNA insertion mutant lines of Arabidopsis thaliana to determine the frequency with which mutation affected fitness-related phenotypes. We found that between 8% and 42% of the assayed lines had altered fitness from the wild type. Furthermore, many of these lines exhibited fitness greater than the wild type. In a second experiment, we grew a subset of the lines in multiple environments and found whether a T-DNA insert increased or decreased fitness traits depended on the assay environment. Overall, our evidence contradicts the hypothesis that genetic redundancy is a common phenomenon in A. thaliana for fitness traits. Evidence for redundancy from prior screens of knockout mutants may often be an artefact of the design of the phenotypic assays which have focused on less complex phenotypes than fitness and have used single environments. Finally, our study adds to evidence that beneficial mutations may represent a significant component of the mutational spectrum of A. thaliana.
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Affiliation(s)
- M T Rutter
- Department of Biology, College of Charleston, Charleston, SC, USA
| | - Y M Wieckowski
- Department of Biology, College of Charleston, Charleston, SC, USA
| | - C J Murren
- Department of Biology, College of Charleston, Charleston, SC, USA
| | - A E Strand
- Department of Biology, College of Charleston, Charleston, SC, USA
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27
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Weinstein ZB, Zaman MH. Quantitative bioassay to identify antimicrobial drugs through drug interaction fingerprint analysis. Sci Rep 2017; 7:42644. [PMID: 28205640 PMCID: PMC5311984 DOI: 10.1038/srep42644] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2016] [Accepted: 01/09/2017] [Indexed: 02/08/2023] Open
Abstract
Drug interaction analysis, which reports the extent to which the presence of one drug affects the efficacy of another, is a powerful tool to select potent combinatorial therapies and predict connectivity between cellular components. Combinatorial effects of drug pairs often vary even for drugs with similar mechanism of actions. Therefore, drug interaction fingerprinting may be harnessed to differentiate drug identities. We developed a method to analyze drug interactions for the application of identifying active pharmaceutical ingredients, an essential step to assess drug quality. We developed a novel approach towards the identification of active pharmaceutical ingredients by comparing drug interaction fingerprint similarity metrics such as correlation and Euclidean distance. To expedite this method, we used bioluminescent E. coli in a simplified checkerboard assay to generate unique drug interaction fingerprints of antimicrobial drugs. Of 30 antibiotics studied, 29 could be identified based on their drug interaction fingerprints. We present drug interaction fingerprint analysis as a cheap, sensitive and quantitative method towards substandard and counterfeit drug detection.
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Affiliation(s)
- Zohar B Weinstein
- Department of Pharmacology and Experimental Therapeutics, Boston University School of Medicine, Boston, MA 02118, USA
| | - Muhammad H Zaman
- Howard Hughes Medical Institute, Boston University, Boston, MA 02215, USA.,Department of Biomedical Engineering, Boston University, Boston, MA 02215, USA
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28
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Ono J, Gerstein AC, Otto SP. Widespread Genetic Incompatibilities between First-Step Mutations during Parallel Adaptation of Saccharomyces cerevisiae to a Common Environment. PLoS Biol 2017; 15:e1002591. [PMID: 28114370 PMCID: PMC5256870 DOI: 10.1371/journal.pbio.1002591] [Citation(s) in RCA: 58] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2016] [Accepted: 12/16/2016] [Indexed: 11/18/2022] Open
Abstract
Independently evolving populations may adapt to similar selection pressures via different genetic changes. The interactions between such changes, such as in a hybrid individual, can inform us about what course adaptation may follow and allow us to determine whether gene flow would be facilitated or hampered following secondary contact. We used Saccharomyces cerevisiae to measure the genetic interactions between first-step mutations that independently evolved in the same biosynthetic pathway following exposure to the fungicide nystatin. We found that genetic interactions are prevalent and predominantly negative, with the majority of mutations causing lower growth when combined in a double mutant than when alone as a single mutant (sign epistasis). The prevalence of sign epistasis is surprising given the small number of mutations tested and runs counter to expectations for mutations arising in a single biosynthetic pathway in the face of a simple selective pressure. Furthermore, in one third of pairwise interactions, the double mutant grew less well than either single mutant (reciprocal sign epistasis). The observation of reciprocal sign epistasis among these first adaptive mutations arising in the same genetic background indicates that partial postzygotic reproductive isolation could evolve rapidly between populations under similar selective pressures, even with only a single genetic change in each. The nature of the epistatic relationships was sensitive, however, to the level of drug stress in the assay conditions, as many double mutants became fitter than the single mutants at higher concentrations of nystatin. We discuss the implications of these results both for our understanding of epistatic interactions among beneficial mutations in the same biochemical pathway and for speciation.
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Affiliation(s)
- Jasmine Ono
- Department of Zoology & Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, Canada
| | - Aleeza C. Gerstein
- Department of Zoology & Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, Canada
| | - Sarah P. Otto
- Department of Zoology & Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, Canada
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29
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Fitness Effects of Spontaneous Mutations in Picoeukaryotic Marine Green Algae. G3-GENES GENOMES GENETICS 2016; 6:2063-71. [PMID: 27175016 PMCID: PMC4938659 DOI: 10.1534/g3.116.029769] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Estimates of the fitness effects of spontaneous mutations are important for understanding the adaptive potential of species. Here, we present the results of mutation accumulation experiments over 265–512 sequential generations in four species of marine unicellular green algae, Ostreococcus tauri RCC4221, Ostreococcus mediterraneus RCC2590, Micromonas pusilla RCC299, and Bathycoccus prasinos RCC1105. Cell division rates, taken as a proxy for fitness, systematically decline over the course of the experiment in O. tauri, but not in the three other species where the MA experiments were carried out over a smaller number of generations. However, evidence of mutation accumulation in 24 MA lines arises when they are exposed to stressful conditions, such as changes in osmolarity or exposure to herbicides. The selection coefficients, estimated from the number of cell divisions/day, varies significantly between the different environmental conditions tested in MA lines, providing evidence for advantageous and deleterious effects of spontaneous mutations. This suggests a common environmental dependence of the fitness effects of mutations and allows the minimum mutation/genome/generation rates to be inferred at 0.0037 in these species.
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30
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Laugier GJM, Le Moguédec G, Su W, Tayeh A, Soldati L, Serrate B, Estoup A, Facon B. Reduced population size can induce quick evolution of inbreeding depression in the invasive ladybird Harmonia axyridis. Biol Invasions 2016. [DOI: 10.1007/s10530-016-1179-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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31
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Roles AJ, Rutter MT, Dworkin I, Fenster CB, Conner JK. Field measurements of genotype by environment interaction for fitness caused by spontaneous mutations in Arabidopsis thaliana. Evolution 2016; 70:1039-50. [PMID: 27061194 DOI: 10.1111/evo.12913] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2015] [Accepted: 03/24/2016] [Indexed: 12/24/2022]
Abstract
As the ultimate source of genetic diversity, spontaneous mutation is critical to the evolutionary process. The fitness effects of spontaneous mutations are almost always studied under controlled laboratory conditions rather than under the evolutionarily relevant conditions of the field. Of particular interest is the conditionality of new mutations-that is, is a new mutation harmful regardless of the environment in which it is found? In other words, what is the extent of genotype-environment interaction for spontaneous mutations? We studied the fitness effects of 25 generations of accumulated spontaneous mutations in Arabidopsis thaliana in two geographically widely separated field environments, in Michigan and Virginia. At both sites, mean total fitness of mutation accumulation lines exceeded that of the ancestors, contrary to the expected decrease in the mean due to new mutations but in accord with prior work on these MA lines. We observed genotype-environment interactions in the fitness effects of new mutations, such that the effects of mutations in Michigan were a poor predictor of their effects in Virginia and vice versa. In particular, mutational variance for fitness was much larger in Virginia compared to Michigan. This strong genotype-environment interaction would increase the amount of genetic variation maintained by mutation-selection balance.
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Affiliation(s)
- Angela J Roles
- Biology Department, Oberlin College, Oberlin, Ohio, 44074. .,Kellogg Biological Station, Michigan State University, East Lansing, Michigan, 48824. .,Department of Integrative Biology, Michigan State University, East Lansing, Michigan, 48824.
| | - Matthew T Rutter
- Department of Biology, College of Charleston, Charleston, South Carolina, 29401.,Department of Biology, University of Maryland, College Park, Maryland, 20742
| | - Ian Dworkin
- Department of Integrative Biology, Michigan State University, East Lansing, Michigan, 48824.,Department of Biology, McMaster University, Hamilton, Ontario, L8S 4L8, Canada
| | - Charles B Fenster
- Department of Biology, University of Maryland, College Park, Maryland, 20742
| | - Jeffrey K Conner
- Kellogg Biological Station, Michigan State University, East Lansing, Michigan, 48824.,Department of Plant Biology, Michigan State University, East Lansing, Michigan, 48824
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32
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Chait R, Palmer AC, Yelin I, Kishony R. Pervasive selection for and against antibiotic resistance in inhomogeneous multistress environments. Nat Commun 2016; 7:10333. [PMID: 26787239 PMCID: PMC4735756 DOI: 10.1038/ncomms10333] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2015] [Accepted: 12/01/2015] [Indexed: 11/30/2022] Open
Abstract
Antibiotic-sensitive and -resistant bacteria coexist in natural environments with low, if detectable, antibiotic concentrations. Except possibly around localized antibiotic sources, where resistance can provide a strong advantage, bacterial fitness is dominated by stresses unaffected by resistance to the antibiotic. How do such mixed and heterogeneous conditions influence the selective advantage or disadvantage of antibiotic resistance? Here we find that sub-inhibitory levels of tetracyclines potentiate selection for or against tetracycline resistance around localized sources of almost any toxin or stress. Furthermore, certain stresses generate alternating rings of selection for and against resistance around a localized source of the antibiotic. In these conditions, localized antibiotic sources, even at high strengths, can actually produce a net selection against resistance to the antibiotic. Our results show that interactions between the effects of an antibiotic and other stresses in inhomogeneous environments can generate pervasive, complex patterns of selection both for and against antibiotic resistance. Antibiotic concentrations are low in most natural environments, except around localized antibiotic sources. Here, Chait et al. show that sub-inhibitory antibiotic levels can interact with many other stresses to generate complex patterns of selection for and against resistance to the antibiotic.
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Affiliation(s)
- Remy Chait
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.,Institute of Science and Technology, Klosterneuburg 3400, Austria
| | - Adam C Palmer
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts 02115, USA
| | - Idan Yelin
- Faculty of Biology, Technion, Israel Institute of Technology, Haifa 3200003, Israel
| | - Roy Kishony
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.,Faculty of Biology, Technion, Israel Institute of Technology, Haifa 3200003, Israel
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33
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Kraemer SA, Morgan AD, Ness RW, Keightley PD, Colegrave N. Fitness effects of new mutations in Chlamydomonas reinhardtii across two stress gradients. J Evol Biol 2016; 29:583-93. [PMID: 26663473 PMCID: PMC4982031 DOI: 10.1111/jeb.12807] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2015] [Revised: 10/22/2015] [Accepted: 12/02/2015] [Indexed: 11/29/2022]
Abstract
Most spontaneous mutations affecting fitness are likely to be deleterious, but the strength of selection acting on them might be impacted by environmental stress. Such stress‐dependent selection could expose hidden genetic variation, which in turn might increase the adaptive potential of stressed populations. On the other hand, this variation might represent a genetic load and thus lead to population extinction under stress. Previous studies to determine the link between stress and mutational effects on fitness, however, have produced inconsistent results. Here, we determined the net change in fitness in 29 genotypes of the green algae Chlamydomonas reinhardtii that accumulated mutations in the near absence of selection for approximately 1000 generations across two stress gradients, increasing NaCl and decreasing phosphate. We found mutational effects to be magnified under extremely stressful conditions, but such effects were specific both to the type of stress and to the genetic background. The detection of stress‐dependent fitness effects of mutations depended on accurately scaling relative fitness measures by generation times, thus offering an explanation for the inconsistencies among previous studies.
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Affiliation(s)
- S A Kraemer
- Ashworth Laboratories, University of Edinburgh, Edinburgh, UK
| | - A D Morgan
- Ashworth Laboratories, University of Edinburgh, Edinburgh, UK
| | - R W Ness
- Ashworth Laboratories, University of Edinburgh, Edinburgh, UK
| | - P D Keightley
- Ashworth Laboratories, University of Edinburgh, Edinburgh, UK
| | - N Colegrave
- Ashworth Laboratories, University of Edinburgh, Edinburgh, UK
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34
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Chevereau G, Dravecká M, Batur T, Guvenek A, Ayhan DH, Toprak E, Bollenbach T. Quantifying the Determinants of Evolutionary Dynamics Leading to Drug Resistance. PLoS Biol 2015; 13:e1002299. [PMID: 26581035 PMCID: PMC4651364 DOI: 10.1371/journal.pbio.1002299] [Citation(s) in RCA: 67] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2015] [Accepted: 10/14/2015] [Indexed: 01/01/2023] Open
Abstract
The emergence of drug resistant pathogens is a serious public health problem. It is a long-standing goal to predict rates of resistance evolution and design optimal treatment strategies accordingly. To this end, it is crucial to reveal the underlying causes of drug-specific differences in the evolutionary dynamics leading to resistance. However, it remains largely unknown why the rates of resistance evolution via spontaneous mutations and the diversity of mutational paths vary substantially between drugs. Here we comprehensively quantify the distribution of fitness effects (DFE) of mutations, a key determinant of evolutionary dynamics, in the presence of eight antibiotics representing the main modes of action. Using precise high-throughput fitness measurements for genome-wide Escherichia coli gene deletion strains, we find that the width of the DFE varies dramatically between antibiotics and, contrary to conventional wisdom, for some drugs the DFE width is lower than in the absence of stress. We show that this previously underappreciated divergence in DFE width among antibiotics is largely caused by their distinct drug-specific dose-response characteristics. Unlike the DFE, the magnitude of the changes in tolerated drug concentration resulting from genome-wide mutations is similar for most drugs but exceptionally small for the antibiotic nitrofurantoin, i.e., mutations generally have considerably smaller resistance effects for nitrofurantoin than for other drugs. A population genetics model predicts that resistance evolution for drugs with this property is severely limited and confined to reproducible mutational paths. We tested this prediction in laboratory evolution experiments using the "morbidostat", a device for evolving bacteria in well-controlled drug environments. Nitrofurantoin resistance indeed evolved extremely slowly via reproducible mutations-an almost paradoxical behavior since this drug causes DNA damage and increases the mutation rate. Overall, we identified novel quantitative characteristics of the evolutionary landscape that provide the conceptual foundation for predicting the dynamics of drug resistance evolution.
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Affiliation(s)
| | | | - Tugce Batur
- Faculty of Engineering and Natural Sciences, Sabanci University, Istanbul, Turkey
| | - Aysegul Guvenek
- Faculty of Engineering and Natural Sciences, Sabanci University, Istanbul, Turkey
| | - Dilay Hazal Ayhan
- Faculty of Engineering and Natural Sciences, Sabanci University, Istanbul, Turkey
| | - Erdal Toprak
- Faculty of Engineering and Natural Sciences, Sabanci University, Istanbul, Turkey
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35
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Lehtinen S, Bähler J, Orengo C. Co-Expression Network Models Suggest that Stress Increases Tolerance to Mutations. Sci Rep 2015; 5:16726. [PMID: 26568486 PMCID: PMC4644955 DOI: 10.1038/srep16726] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Accepted: 10/19/2015] [Indexed: 11/09/2022] Open
Abstract
Network models are a well established tool for studying the robustness of complex systems, including modelling the effect of loss of function mutations in protein interaction networks. Past work has concentrated on average damage caused by random node removal, with little attention to the shape of the damage distribution. In this work, we use fission yeast co-expression networks before and after exposure to stress to model the effect of stress on mutational robustness. We find that exposure to stress decreases the average damage from node removal, suggesting stress induces greater tolerance to loss of function mutations. The shape of the damage distribution is also changed upon stress, with a greater incidence of extreme damage after exposure to stress. We demonstrate that the change in shape of the damage distribution can have considerable functional consequences, highlighting the need to consider the damage distribution in addition to average behaviour.
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Affiliation(s)
- Sonja Lehtinen
- Department of Infectious Disease Epidemiology, Imperial College, St Mary’s Campus, Norfolk Place, London W2 1PG, UK
- University College London, ISMB, London, WC1E 6BT, UK
| | - Jürg Bähler
- University College London, GEE, London, WC1E 6BT, UK
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36
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Abiotic stress does not magnify the deleterious effects of spontaneous mutations. Heredity (Edinb) 2015; 115:503-8. [PMID: 26103946 DOI: 10.1038/hdy.2015.51] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2014] [Revised: 04/30/2015] [Accepted: 05/06/2015] [Indexed: 01/10/2023] Open
Abstract
Although the effects of deleterious alleles often are predicted to be greater in stressful environments, there is no theoretical basis for this prediction and the empirical evidence is mixed. Here we characterized the effects of three types of abiotic stress (thermal, oxidative and hyperosmotic) on two sets of nematode (Caenorhabditis elegans) mutation accumulation (MA) lines that differ by threefold in fitness. We compared the survival and egg-to-adult viability between environments (benign and stressful) and between fitness categories (high-fitness MA, low-fitness MA). If the environment and mutation load have synergistic effects on trait means, then the difference between the high and low-fitness MA lines should be larger in stressful environments. Although the stress treatments consistently decreased survival and/or viability, we did not detect significant interactions between fitness categories and environment types. In contrast, we did find consistent evidence for synergistic effects on (micro)environmental variation. The lack of signal in trait means likely reflects the very low starting fitness of some low-fitness MA lines, the potential for cross-stress responses and the context dependence of mutational effects. In addition, the large increases in the environmental variance in the stressful environments may have masked small changes in trait means. These results do not provide evidence for synergism between mutation and stress.
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37
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Barker B, Xu L, Gu Z. Dynamic epistasis under varying environmental perturbations. PLoS One 2015; 10:e0114911. [PMID: 25625594 PMCID: PMC4308068 DOI: 10.1371/journal.pone.0114911] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2013] [Accepted: 11/15/2014] [Indexed: 01/17/2023] Open
Abstract
Epistasis describes the phenomenon that mutations at different loci do not have independent effects with regard to certain phenotypes. Understanding the global epistatic landscape is vital for many genetic and evolutionary theories. Current knowledge for epistatic dynamics under multiple conditions is limited by the technological difficulties in experimentally screening epistatic relations among genes. We explored this issue by applying flux balance analysis to simulate epistatic landscapes under various environmental perturbations. Specifically, we looked at gene-gene epistatic interactions, where the mutations were assumed to occur in different genes. We predicted that epistasis tends to become more positive from glucose-abundant to nutrient-limiting conditions, indicating that selection might be less effective in removing deleterious mutations in the latter. We also observed a stable core of epistatic interactions in all tested conditions, as well as many epistatic interactions unique to each condition. Interestingly, genes in the stable epistatic interaction network are directly linked to most other genes whereas genes with condition-specific epistasis form a scale-free network. Furthermore, genes with stable epistasis tend to have similar evolutionary rates, whereas this co-evolving relationship does not hold for genes with condition-specific epistasis. Our findings provide a novel genome-wide picture about epistatic dynamics under environmental perturbations.
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Affiliation(s)
- Brandon Barker
- Center for Advanced Computing, Cornell University, Ithaca, New York, United States of America
| | - Lin Xu
- Division of Hematology/Oncology, Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Zhenglong Gu
- Division of Nutritional Sciences, Cornell University, Ithaca, New York, United States of America
- Tri-Institutional Training Program in Computational Biology and Medicine, New York, New York, United States of America
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38
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Ishizawa Y, Ying BW, Tsuru S, Yomo T. Nutrient-dependent growth defects and mutability of mutators in Escherichia coli. Genes Cells 2014; 20:68-76. [PMID: 25378049 DOI: 10.1111/gtc.12199] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2014] [Accepted: 10/04/2014] [Indexed: 11/28/2022]
Abstract
So-called mutators emerge when mismatch repair and proofreading mechanisms are defective. Mutators not only accelerate the accumulation of mutations that are beneficial for adaptation but also cause a large number of deleterious mutations that are disadvantageous for cell growth. However, such growth defects may be compensated by nutrient availability. How the growth burden is associated with high mutability in relation to nutritional variation is an intriguing question. To address this question, we constructed a variety of Escherichia coli mutator strains through combinatorial deletions of mismatch repair and proofreading genes and quantitatively evaluated their growth and mutation rates under different nutritional conditions. Growth defects caused by high mutation rates were commonly observed in all mutators, and these defects were alleviated by nutrient supplementation in most mutators. In addition, the mutation rates of the mutators fluctuated greatly in response to nutritional conditions, in contrast to the nearly constant mutation rate of the wild-type strain under varying nutritional conditions. The results showed conditional growth defects and nutrition-sensitive mutability as general features of mutators. This study indicates the importance of modulating mutability in response to changing nutrient conditions to minimize the risk of extinction due to genetic load.
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Affiliation(s)
- Yuuka Ishizawa
- Graduate School of Information Science and Technology, Osaka University, 1-5 Yamadaoka, Suita, Osaka, 565-0871, Japan
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39
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Dougherty K, Smith BA, Moore AF, Maitland S, Fanger C, Murillo R, Baltrus DA. Multiple phenotypic changes associated with large-scale horizontal gene transfer. PLoS One 2014; 9:e102170. [PMID: 25048697 PMCID: PMC4105467 DOI: 10.1371/journal.pone.0102170] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2014] [Accepted: 06/16/2014] [Indexed: 12/22/2022] Open
Abstract
Horizontal gene transfer often leads to phenotypic changes within recipient organisms independent of any immediate evolutionary benefits. While secondary phenotypic effects of horizontal transfer (i.e., changes in growth rates) have been demonstrated and studied across a variety of systems using relatively small plasmids and phage, little is known about the magnitude or number of such costs after the transfer of larger regions. Here we describe numerous phenotypic changes that occur after a large-scale horizontal transfer event (∼1 Mb megaplasmid) within Pseudomonas stutzeri including sensitization to various stresses as well as changes in bacterial behavior. These results highlight the power of horizontal transfer to shift pleiotropic relationships and cellular networks within bacterial genomes. They also provide an important context for how secondary effects of transfer can bias evolutionary trajectories and interactions between species. Lastly, these results and system provide a foundation to investigate evolutionary consequences in real time as newly acquired regions are ameliorated and integrated into new genomic contexts.
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Affiliation(s)
- Kevin Dougherty
- School of Plant Sciences, University of Arizona, Tucson, Arizona, United States of America
| | - Brian A. Smith
- School of Plant Sciences, University of Arizona, Tucson, Arizona, United States of America
| | - Autumn F. Moore
- School of Plant Sciences, University of Arizona, Tucson, Arizona, United States of America
| | - Shannon Maitland
- School of Plant Sciences, University of Arizona, Tucson, Arizona, United States of America
| | - Chris Fanger
- School of Plant Sciences, University of Arizona, Tucson, Arizona, United States of America
| | - Rachel Murillo
- School of Plant Sciences, University of Arizona, Tucson, Arizona, United States of America
| | - David A. Baltrus
- School of Plant Sciences, University of Arizona, Tucson, Arizona, United States of America
- * E-mail:
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40
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Opposing effects of target overexpression reveal drug mechanisms. Nat Commun 2014; 5:4296. [PMID: 24980690 DOI: 10.1038/ncomms5296] [Citation(s) in RCA: 92] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2013] [Accepted: 06/03/2014] [Indexed: 12/15/2022] Open
Abstract
Overexpression of a drug's molecular target often increases drug resistance, offering a pathway for adaptive evolution and a tool for target identification. It is unclear though why this phenomenon applies to some drugs but not others. Here we gradually overexpressed antibiotic targets in Escherichia coli and found that drug resistance can increase, remain unchanged, decrease or even change non-monotonically. Even a single target can produce opposing responses to its different inhibitors. We explain these contradicting effects with quantitative models of enzyme inhibition that account for fitness costs and the biochemical activity or inactivity of drug-enzyme complexes. Thus, target overexpression confers resistance or sensitivity as a predictable property of drug mechanism, explaining its variable presence in nature as a resistance mechanism. Though overexpression screens may fail at identifying unknown targets, overexpressing known or putative targets provides a systematic approach to distinguish between simple inhibition and complex mechanisms of drug action.
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41
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SENSITIVITY OF THE DISTRIBUTION OF MUTATIONAL FITNESS EFFECTS TO ENVIRONMENT, GENETIC BACKGROUND, AND ADAPTEDNESS: A CASE STUDY WITHDROSOPHILA. Evolution 2013; 68:840-53. [DOI: 10.1111/evo.12309] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2013] [Accepted: 10/22/2013] [Indexed: 12/22/2022]
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42
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Belinato TA, Martins AJ, Valle D. Fitness evaluation of two Brazilian Aedes aegypti field populations with distinct levels of resistance to the organophosphate temephos. Mem Inst Oswaldo Cruz 2013; 107:916-22. [PMID: 23147149 DOI: 10.1590/s0074-02762012000700013] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2011] [Accepted: 04/12/2012] [Indexed: 11/22/2022] Open
Abstract
In Brazil, decades of dengue vector control using organophosphates and pyrethroids have led to dissemination of resistance. Although these insecticides have been employed for decades against Aedes aegypti in the country, knowledge of the impact of temephos resistance on vector viability is limited. We evaluated several fitness parameters in two Brazilian Ae. aegypti populations, both classified as deltamethrin resistant but with distinct resistant ratios (RR) for temephos. The insecticide-susceptible Rockefeller strain was used as an experimental control. The population presenting the higher temephos resistance level, Aparecida de Goiânia, state of Goiás (RR(95) of 19.2), exhibited deficiency in the following four parameters: blood meal acceptance, amount of ingested blood, number of eggs and frequency of inseminated females. Mosquitoes from Boa Vista, state of Roraima, the population with lower temephos resistance level (RR(95) of 7.4), presented impairment in only two parameters, blood meal acceptance and frequency of inseminated females. These results indicate that the overall fitness handicap was proportional to temephos resistance levels. However, it is unlikely that these disabilities can be attributed solely to temephos resistance, since both populations are also resistant to deltamethrin and harbour the kdr allele, which indicates resistance to pyrethroids. The effects of reduced fitness in resistant populations are discussed.
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Affiliation(s)
- Thiago Affonso Belinato
- Laboratório de Fisiologia e Controle de Artrópodes Vetores, Instituto Oswaldo Cruz, Fiocruz, Rio de Janeiro, Brasil
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43
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Ketola T, Mikonranta L, Zhang J, Saarinen K, Örmälä AM, Friman VP, Mappes J, Laakso J. FLUCTUATING TEMPERATURE LEADS TO EVOLUTION OF THERMAL GENERALISM AND PREADAPTATION TO NOVEL ENVIRONMENTS. Evolution 2013; 67:2936-44. [DOI: 10.1111/evo.12148] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2012] [Accepted: 04/11/2013] [Indexed: 12/19/2022]
Affiliation(s)
- Tarmo Ketola
- Centre of Excellence in Biological Interactions; Department of Biological and Environmental Science; University of Jyväskylä; P.O. Box 35; Jyväskylä; FI-40014; Finland
| | - Lauri Mikonranta
- Centre of Excellence in Biological Interactions; Department of Biological and Environmental Science; University of Jyväskylä; P.O. Box 35; Jyväskylä; FI-40014; Finland
| | - Ji Zhang
- Centre of Excellence in Biological Interactions; Department of Biological and Environmental Science; University of Jyväskylä; P.O. Box 35; Jyväskylä; FI-40014; Finland
| | - Kati Saarinen
- Centre of Excellence in Biological Interactions; Department of Biological and Environmental Science; University of Jyväskylä; P.O. Box 35; Jyväskylä; FI-40014; Finland
| | | | - Ville-Petri Friman
- Biosciences; University of Exeter; Cornwall Campus; Penryn; TR10 9EZ; United Kingdom
| | - Johanna Mappes
- Centre of Excellence in Biological Interactions; Department of Biological and Environmental Science; University of Jyväskylä; P.O. Box 35; Jyväskylä; FI-40014; Finland
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44
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Flynn KM, Cooper TF, Moore FBG, Cooper VS. The environment affects epistatic interactions to alter the topology of an empirical fitness landscape. PLoS Genet 2013; 9:e1003426. [PMID: 23593024 PMCID: PMC3616912 DOI: 10.1371/journal.pgen.1003426] [Citation(s) in RCA: 70] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2012] [Accepted: 02/14/2013] [Indexed: 11/27/2022] Open
Abstract
The fitness effect of mutations can be influenced by their interactions with the environment, other mutations, or both. Previously, we constructed 32 ( = 25) genotypes that comprise all possible combinations of the first five beneficial mutations to fix in a laboratory-evolved population of Escherichia coli. We found that (i) all five mutations were beneficial for the background on which they occurred; (ii) interactions between mutations drove a diminishing returns type epistasis, whereby epistasis became increasingly antagonistic as the expected fitness of a genotype increased; and (iii) the adaptive landscape revealed by the mutation combinations was smooth, having a single global fitness peak. Here we examine how the environment influences epistasis by determining the interactions between the same mutations in two alternative environments, selected from among 1,920 screened environments, that produced the largest increase or decrease in fitness of the most derived genotype. Some general features of the interactions were consistent: mutations tended to remain beneficial and the overall pattern of epistasis was of diminishing returns. Other features depended on the environment; in particular, several mutations were deleterious when added to specific genotypes, indicating the presence of antagonistic interactions that were absent in the original selection environment. Antagonism was not caused by consistent pleiotropic effects of individual mutations but rather by changing interactions between mutations. Our results demonstrate that understanding adaptation in changing environments will require consideration of the combined effect of epistasis and pleiotropy across environments. The fitness effect of beneficial mutations can depend on how they interact with their genetic and external environment. The form of these interactions is important because it can alter adaptive outcomes, selecting for or against certain combinations of beneficial mutations. Here, we examine how interactions between beneficial mutations favored during adaptation of a lab strain of Escherichia coli to one simple environment are altered when the strain is grown in two novel environments. We found that fitness effects were greatly influenced by both the genetic and external environments. In several instances a change in environment reversed the effect of a mutation from beneficial to deleterious or caused combinations of beneficial mutations to become deleterious. Our results suggest that a complex or fluctuating environment may favor combinations of mutations whose interactions may be less sensitive to external conditions.
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Affiliation(s)
- Kenneth M. Flynn
- Department of Molecular, Cellular, and Biomedical Sciences, University of New Hampshire, Durham, New Hampshire, United States of America
| | - Tim F. Cooper
- Department of Biology and Biochemistry, University of Houston, Houston, Texas, United States of America
| | - Francisco B-G. Moore
- Integrated Bioscience Program, University of Akron, Akron, Ohio, United States of America
| | - Vaughn S. Cooper
- Department of Molecular, Cellular, and Biomedical Sciences, University of New Hampshire, Durham, New Hampshire, United States of America
- * E-mail:
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45
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Long TAF, Rowe L, Agrawal AF. The Effects of Selective History and Environmental Heterogeneity on Inbreeding Depression in Experimental Populations of Drosophila melanogaster. Am Nat 2013; 181:532-44. [DOI: 10.1086/669675] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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46
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MacLean RC, Torres-Barceló C, Moxon R. Evaluating evolutionary models of stress-induced mutagenesis in bacteria. Nat Rev Genet 2013; 14:221-7. [PMID: 23400102 DOI: 10.1038/nrg3415] [Citation(s) in RCA: 91] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Increased mutation rates under stress allow bacterial populations to adapt rapidly to stressors, including antibiotics. Here we evaluate existing models for the evolution of stress-induced mutagenesis and present a new model arguing that it evolves as a result of a complex interplay between direct selection for increased stress tolerance, second-order selection for increased evolvability and genetic drift. Further progress in our understanding of the evolutionary biology of stress and mutagenesis will require a more detailed understanding both of the patterns of stress encountered by bacteria in nature and of the mutations that are produced under stress.
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Affiliation(s)
- R Craig MacLean
- Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK.
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47
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Agrawal AF, Whitlock MC. Mutation Load: The Fitness of Individuals in Populations Where Deleterious Alleles Are Abundant. ANNUAL REVIEW OF ECOLOGY EVOLUTION AND SYSTEMATICS 2012. [DOI: 10.1146/annurev-ecolsys-110411-160257] [Citation(s) in RCA: 137] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Many multicellular eukaryotes have reasonably high per-generation mutation rates. Consequently, most populations harbor an abundance of segregating deleterious alleles. These alleles, most of which are of small effect individually, collectively can reduce substantially the fitness of individuals relative to what it would be otherwise; this is mutation load. Mutation load can be lessened by any factor that causes more mutations to be removed per selective death, such as inbreeding, synergistic epistasis, population structure, or harsh environments. The ecological effects of load are not clear-cut because some conditions (such as selection early in life, sexual selection, reproductive compensation, and intraspecific competition) reduce the effects of load on population size and persistence, but other conditions (such as interspecific competition and load on resource use efficiency) can cause small amounts of load to have strong effects on the population, even extinction. We suggest a series of studies to improve our understanding of the effects of mutation load.
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Affiliation(s)
- Aneil F. Agrawal
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada M5S 3B2
| | - Michael C. Whitlock
- Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4
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Maharjan R, McKenzie C, Yeung A, Ferenci T. The basis of antagonistic pleiotropy in hfq mutations that have opposite effects on fitness at slow and fast growth rates. Heredity (Edinb) 2012; 110:10-8. [PMID: 23169561 DOI: 10.1038/hdy.2012.46] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Mutations beneficial in one environment may cause costs in different environments, resulting in antagonistic pleiotropy. Here, we describe a novel form of antagonistic pleiotropy that operates even within the same environment, where benefits and deleterious effects exhibit themselves at different growth rates. The fitness of hfq mutations in Escherichia coli affecting the RNA chaperone involved in small-RNA regulation is remarkably sensitive to growth rate. E. coli populations evolving in chemostats under nutrient limitation acquired beneficial mutations in hfq during slow growth (0.1 h(-1)) but not in populations growing sixfold faster. Four identified hfq alleles from parallel populations were beneficial at 0.1 h(-1) and deleterious at 0.6 h(-1). The hfq mutations were beneficial, deleterious or neutral at an intermediate growth rate (0.5 h(-1)) and one changed from beneficial to deleterious within a 36 min difference in doubling time. The benefit of hfq mutations was due to the greater transport of limiting nutrient, which diminished at higher growth rates. The deleterious effects of hfq mutations at 0.6 h(-1) were less clear, with decreased viability a contributing factor. The results demonstrate distinct pleiotropy characteristics in the alleles of the same gene, probably because the altered residues in Hfq affected the regulation of expression of different genes in distinct ways. In addition, these results point to a source of variation in experimental measurement of the selective advantage of a mutation; estimates of fitness need to consider variation in growth rate impacting on the magnitude of the benefit of mutations and on their fitness distributions.
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Affiliation(s)
- R Maharjan
- School of Molecular Bioscience, University of Sydney, Sydney, New South Wales, Australia
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Abstract
The role of mutations in evolution depends upon the distribution of their effects on fitness. This distribution is likely to depend on the environment. Indeed genotype-by-environment interactions are key for the process of local adaptation and ecological specialization. An important trait in bacterial evolution is antibiotic resistance, which presents a clear case of change in the direction of selection between environments with and without antibiotics. Here, we study the distribution of fitness effects of mutations, conferring antibiotic resistance to Escherichia coli, in benign and stressful environments without drugs. We interpret the distributions in the light of a fitness landscape model that assumes a single fitness peak. We find that mutation effects (s) are well described by a shifted gamma distribution, with a shift parameter that reflects the distance to the fitness peak and varies across environments. Consistent with the theoretical predictions of Fisher's geometrical model, with a Gaussian relationship between phenotype and fitness, we find that the main effect of stress is to increase the variance in s. Our findings are in agreement with the results of a recent meta-analysis, which suggest that a simple fitness landscape model may capture the variation of mutation effects across species and environments.
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Jacobs C, Segrè D. Organization Principles in Genetic Interaction Networks. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 751:53-78. [DOI: 10.1007/978-1-4614-3567-9_3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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