1
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Lear L, Hesse E, Newsome L, Gaze W, Buckling A, Vos M. The effect of metal remediation on the virulence and antimicrobial resistance of the opportunistic pathogen Pseudomonas aeruginosa. Evol Appl 2023; 16:1377-1389. [PMID: 37492145 PMCID: PMC10363854 DOI: 10.1111/eva.13576] [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: 11/28/2022] [Revised: 05/18/2023] [Accepted: 06/19/2023] [Indexed: 07/27/2023] Open
Abstract
Anthropogenic metal pollution can result in co-selection for antibiotic resistance and potentially select for increased virulence in bacterial pathogens. Metal-polluted environments can select for the increased production of siderophore molecules to detoxify non-ferrous metals. However, these same molecules also aid the uptake of ferric iron, a limiting factor for within-host pathogen growth, and are consequently a virulence factor. Anthropogenic methods to remediate environmental metal contamination commonly involve amendment with lime-containing materials. However, whether this reduces in situ co-selection for antibiotic resistance and siderophore-mediated virulence remains unknown. Here, using microcosms containing non-sterile metal-contaminated river water and sediment, we test whether liming reduces co-selection for these pathogenicity traits in the opportunistic pathogen Pseudomonas aeruginosa. To account for the effect of environmental structure, which is known to impact siderophore production, microcosms were incubated under either static or shaking conditions. Evolved P. aeruginosa populations had greater fitness in the presence of toxic concentrations of copper than the ancestral strain and showed increased resistance to the clinically relevant antibiotics apramycin, cefotaxime and trimethoprim, regardless of lime addition or environmental structure. Although we found virulence to be significantly associated with siderophore production, neither virulence nor siderophore production significantly differed between the four treatments. Furthermore, liming did not mitigate metal-imposed selection for antibiotic resistance or virulence in P. aeruginosa. Consequently, metal-contaminated environments may select for antibiotic resistance and virulence traits even when treated with lime.
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Affiliation(s)
- Luke Lear
- College of Life and Environmental ScienceUniversity of ExeterPenrynUK
| | - Elze Hesse
- College of Life and Environmental ScienceUniversity of ExeterPenrynUK
| | - Laura Newsome
- College of Engineering, Mathematics and Physical SciencesUniversity of ExeterPenrynUK
| | - William Gaze
- European Centre for Environment and Human HealthUniversity of Exeter Medical SchoolPenrynUK
| | - Angus Buckling
- College of Life and Environmental ScienceUniversity of ExeterPenrynUK
| | - Michiel Vos
- European Centre for Environment and Human HealthUniversity of Exeter Medical SchoolPenrynUK
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2
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Dimitriu T, Souissi W, Morwool P, Darby A, Crickmore N, Raymond B. Selecting for infectivity across metapopulations can increase virulence in the social microbe
Bacillus thuringiensis. Evol Appl 2023; 16:705-720. [PMID: 36969139 PMCID: PMC10033855 DOI: 10.1111/eva.13529] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2022] [Accepted: 12/27/2022] [Indexed: 01/18/2023] Open
Abstract
Passage experiments that sequentially infect hosts with parasites have long been used to manipulate virulence. However, for many invertebrate pathogens, passage has been applied naively without a full theoretical understanding of how best to select for increased virulence and this has led to very mixed results. Understanding the evolution of virulence is complex because selection on parasites occurs across multiple spatial scales with potentially different conflicts operating on parasites with different life histories. For example, in social microbes, strong selection on replication rate within hosts can lead to cheating and loss of virulence, because investment in public goods virulence reduces replication rate. In this study, we tested how varying mutation supply and selection for infectivity or pathogen yield (population size in hosts) affected the evolution of virulence against resistant hosts in the specialist insect pathogen Bacillus thuringiensis, aiming to optimize methods for strain improvement against a difficult to kill insect target. We show that selection for infectivity using competition between subpopulations in a metapopulation prevents social cheating, acts to retain key virulence plasmids, and facilitates increased virulence. Increased virulence was associated with reduced efficiency of sporulation, and possible loss of function in putative regulatory genes but not with altered expression of the primary virulence factors. Selection in a metapopulation provides a broadly applicable tool for improving the efficacy of biocontrol agents. Moreover, a structured host population can facilitate artificial selection on infectivity, while selection on life-history traits such as faster replication or larger population sizes can reduce virulence in social microbes.
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Affiliation(s)
- Tatiana Dimitriu
- Centre for Ecology and Conservation University of Exeter Penryn UK
| | - Wided Souissi
- School of Life Sciences University of Sussex Brighton UK
| | - Peter Morwool
- Centre for Ecology and Conservation University of Exeter Penryn UK
| | - Alistair Darby
- Centre for Genomic Research, Institute of Integrative Biology University of Liverpool Liverpool UK
| | - Neil Crickmore
- School of Life Sciences University of Sussex Brighton UK
| | - Ben Raymond
- Centre for Ecology and Conservation University of Exeter Penryn UK
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3
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Bentley MA, Yates CA, Hein J, Preston GM, Foster KR. Pleiotropic constraints promote the evolution of cooperation in cellular groups. PLoS Biol 2022; 20:e3001626. [PMID: 35658016 PMCID: PMC9166655 DOI: 10.1371/journal.pbio.3001626] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2021] [Accepted: 04/11/2022] [Indexed: 12/12/2022] Open
Abstract
The evolution of cooperation in cellular groups is threatened by lineages of cheaters that proliferate at the expense of the group. These cell lineages occur within microbial communities, and multicellular organisms in the form of tumours and cancer. In contrast to an earlier study, here we show how the evolution of pleiotropic genetic architectures-which link the expression of cooperative and private traits-can protect against cheater lineages and allow cooperation to evolve. We develop an age-structured model of cellular groups and show that cooperation breaks down more slowly within groups that tie expression to a private trait than in groups that do not. We then show that this results in group selection for pleiotropy, which strongly promotes cooperation by limiting the emergence of cheater lineages. These results predict that pleiotropy will rapidly evolve, so long as groups persist long enough for cheater lineages to threaten cooperation. Our results hold when pleiotropic links can be undermined by mutations, when pleiotropy is itself costly, and in mixed-genotype groups such as those that occur in microbes. Finally, we consider features of multicellular organisms-a germ line and delayed reproductive maturity-and show that pleiotropy is again predicted to be important for maintaining cooperation. The study of cancer in multicellular organisms provides the best evidence for pleiotropic constraints, where abberant cell proliferation is linked to apoptosis, senescence, and terminal differentiation. Alongside development from a single cell, we propose that the evolution of pleiotropic constraints has been critical for cooperation in many cellular groups.
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Affiliation(s)
- Michael A. Bentley
- Department of Zoology, University of Oxford, Oxford, United Kingdom
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Christian A. Yates
- Department of Mathematical Sciences, University of Bath, Bath, United Kingdom
| | - Jotun Hein
- Department of Statistics, University of Oxford, Oxford, United Kingdom
| | - Gail M. Preston
- Department of Plant Sciences, University of Oxford, Oxford, United Kingdom
| | - Kevin R. Foster
- Department of Zoology, University of Oxford, Oxford, United Kingdom
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
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4
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O'Brien S, Kümmerli R, Paterson S, Winstanley C, Brockhurst MA. Transposable temperate phages promote the evolution of divergent social strategies in Pseudomonas aeruginosa populations. Proc Biol Sci 2019; 286:20191794. [PMID: 31594506 DOI: 10.1098/rspb.2019.1794] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Transposable temperate phages randomly insert into bacterial genomes, providing increased supply and altered spectra of mutations available to selection, thus opening alternative evolutionary trajectories. Transposable phages accelerate bacterial adaptation to new environments, but their effect on adaptation to the social environment is unclear. Using experimental evolution of Pseudomonas aeruginosa in iron-limited and iron-rich environments, where the cost of producing cooperative iron-chelating siderophores is high and low, respectively, we show that transposable phages promote divergence into extreme siderophore production phenotypes. Iron-limited populations with transposable phages evolved siderophore overproducing clones alongside siderophore non-producing cheats. Low siderophore production was associated with parallel mutations in pvd genes, encoding pyoverdine biosynthesis, and pqs genes, encoding quinolone signalling, while high siderophore production was associated with parallel mutations in phenazine-associated gene clusters. Notably, some of these parallel mutations were caused by phage insertional inactivation. These data suggest that transposable phages, which are widespread in microbial communities, can mediate the evolutionary divergence of social strategies.
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Affiliation(s)
- Siobhán O'Brien
- Institute of Integrative Biology, University of Liverpool, Liverpool L69 7ZB, UK
| | - Rolf Kümmerli
- Department of Plant and Microbial Biology, University of Zürich, Switzerland
| | - Steve Paterson
- Institute of Integrative Biology, University of Liverpool, Liverpool L69 7ZB, UK
| | - Craig Winstanley
- Institute of Infection and Global Health, University of Liverpool, Liverpool L69 7BE, UK
| | - Michael A Brockhurst
- Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK
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5
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Enforcement is central to the evolution of cooperation. Nat Ecol Evol 2019; 3:1018-1029. [PMID: 31239554 DOI: 10.1038/s41559-019-0907-1] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2018] [Accepted: 04/26/2019] [Indexed: 01/21/2023]
Abstract
Cooperation occurs at all levels of life, from genomes, complex cells and multicellular organisms to societies and mutualisms between species. A major question for evolutionary biology is what these diverse systems have in common. Here, we review the full breadth of cooperative systems and find that they frequently rely on enforcement mechanisms that suppress selfish behaviour. We discuss many examples, including the suppression of transposable elements, uniparental inheritance of mitochondria and plastids, anti-cancer mechanisms, reciprocation and punishment in humans and other vertebrates, policing in eusocial insects and partner choice in mutualisms between species. To address a lack of accompanying theory, we develop a series of evolutionary models that show that the enforcement of cooperation is widely predicted. We argue that enforcement is an underappreciated, and often critical, ingredient for cooperation across all scales of biological organization.
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6
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Hesse E, Padfield D, Bayer F, van Veen EM, Bryan CG, Buckling A. Anthropogenic remediation of heavy metals selects against natural microbial remediation. Proc Biol Sci 2019; 286:20190804. [PMID: 31213187 PMCID: PMC6599979 DOI: 10.1098/rspb.2019.0804] [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] [Indexed: 12/22/2022] Open
Abstract
In an era of unprecedented environmental change, there have been increasing ecological and global public health concerns associated with exposure to anthropogenic pollutants. While there is a pressing need to remediate polluted ecosystems, human intervention might unwittingly oppose selection for natural detoxification, which is primarily carried out by microbes. We test this possibility in the context of a ubiquitous chemical remediation strategy aimed at targeting metal pollution: the addition of lime-containing materials. Here, we show that raising pH by liming decreased the availability of toxic metals in acidic mine-degraded soils, but as a consequence selected against microbial taxa that naturally remediate soil through the production of metal-binding siderophores. Our results therefore highlight the crucial need to consider the eco-evolutionary consequences of human environmental strategies on microbial ecosystem services and other traits.
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Affiliation(s)
- Elze Hesse
- 1 ESI and CEC, Biosciences, University of Exeter , Penryn Campus, Cornwall TR10 9FE , UK
| | - Daniel Padfield
- 1 ESI and CEC, Biosciences, University of Exeter , Penryn Campus, Cornwall TR10 9FE , UK
| | - Florian Bayer
- 1 ESI and CEC, Biosciences, University of Exeter , Penryn Campus, Cornwall TR10 9FE , UK
| | - Eleanor M van Veen
- 2 Camborne School of Mines, CEMPS, University of Exeter , Penryn Campus, Cornwall TR10 9FE , UK
| | - Christopher G Bryan
- 2 Camborne School of Mines, CEMPS, University of Exeter , Penryn Campus, Cornwall TR10 9FE , UK
| | - Angus Buckling
- 1 ESI and CEC, Biosciences, University of Exeter , Penryn Campus, Cornwall TR10 9FE , UK
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7
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Evans RML. Pay-off scarcity causes evolution of risk-aversion and extreme altruism. Sci Rep 2018; 8:16074. [PMID: 30375455 PMCID: PMC6207719 DOI: 10.1038/s41598-018-34384-w] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2018] [Accepted: 10/08/2018] [Indexed: 01/24/2023] Open
Abstract
All organisms descend from populations with limited resources, so it is clear why evolution should select strategies that win resources at the expense of competitors. Less obvious is how altruistic behaviours evolve, whereby an individual helps others despite expense to itself. Modelling simple agents using evolutionary game theory, it is shown that steady states of extreme altruism can evolve when pay-offs are very rare compared with death. In these states, agents give away most of their wealth. A new theorem for general evolutionary models shows that, when pay-offs are rare, evolution no longer selects strategies to maximize income (average pay-off), but to minimize the risk of missing-out entirely on a rare resource. Principles revealed by the model are widely applicable, where the game represents rare life-changing events: disasters or gluts.
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Affiliation(s)
- R M L Evans
- School of Mathematics, University of Leeds, Leeds, LS2 9JT, UK.
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8
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O'Brien S, Fothergill JL. The role of multispecies social interactions in shaping Pseudomonas aeruginosa pathogenicity in the cystic fibrosis lung. FEMS Microbiol Lett 2018; 364:3958795. [PMID: 28859314 PMCID: PMC5812498 DOI: 10.1093/femsle/fnx128] [Citation(s) in RCA: 85] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2017] [Accepted: 07/11/2017] [Indexed: 02/07/2023] Open
Abstract
Pseudomonas aeruginosa is a major pathogen in the lungs of cystic fibrosis (CF) patients. However, it is now recognised that a diverse microbial community exists in the airways comprising aerobic and anaerobic bacteria as well as fungi and viruses. This rich soup of microorganisms provides ample opportunity for interspecies interactions, particularly when considering secreted compounds. Here, we discuss how P. aeruginosa-secreted products can have community-wide effects, with the potential to ultimately shape microbial community dynamics within the lung. We focus on three well-studied traits associated with worsening clinical outcome in CF: phenazines, siderophores and biofilm formation, and discuss how secretions can shape interactions between P. aeruginosa and other commonly encountered members of the lung microbiome: Staphylococcus aureus, the Burkholderia cepacia complex, Candida albicans and Aspergillus fumigatus. These interactions may shape the evolutionary trajectory of P. aeruginosa while providing new opportunities for therapeutic exploitation of the CF lung microbiome.
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Affiliation(s)
- Siobhán O'Brien
- Center for Adaptation to a Changing Environment (ACE), ETH Zürich, 8092 Zürich, Switzerland.,Department of Biology, University of York, Wentworth Way, York YO10 5DD, UK
| | - Joanne L Fothergill
- Institute of Infection and Global Health, University of Liverpool, 8 West Derby Street, Liverpool L69 7B3, UK
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9
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O'Brien S, Luján AM, Paterson S, Cant MA, Buckling A. Adaptation to public goods cheats in Pseudomonas aeruginosa. Proc Biol Sci 2018; 284:rspb.2017.1089. [PMID: 28747481 PMCID: PMC5543229 DOI: 10.1098/rspb.2017.1089] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Accepted: 06/23/2017] [Indexed: 01/25/2023] Open
Abstract
Cooperation in nature is ubiquitous, but is susceptible to social cheats who pay little or no cost of cooperation yet reap the benefits. The effect such cheats have on reducing population productivity suggests that there is selection for cooperators to mitigate the adverse effects of cheats. While mechanisms have been elucidated for scenarios involving a direct association between producer and cooperative product, it is less clear how cooperators may suppress cheating in an anonymous public goods scenario, where cheats cannot be directly identified. Here, we investigate the real-time evolutionary response of cooperators to cheats when cooperation is mediated by a diffusible public good: the production of iron-scavenging siderophores by Pseudomonas aeruginosa. We find that siderophore producers evolved in the presence of a high frequency of non-producing cheats were fitter in the presence of cheats, at no obvious cost to population productivity. A novel morphotype independently evolved and reached higher frequencies in cheat-adapted versus control populations, exhibiting reduced siderophore production but increased production of pyocyanin—an extracellular toxin that can also increase the availability of soluble iron. This suggests that cooperators may have mitigated the negative effects of cheats by downregulating siderophore production and upregulating an alternative iron-acquisition public good. More generally, the study emphasizes that cooperating organisms can rapidly adapt to the presence of anonymous cheats without necessarily incurring fitness costs in the environment they evolve in.
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Affiliation(s)
- Siobhán O'Brien
- Center for Adaptation to a Changing Environment (ACE), ETH Zürich, 8092 Zürich, Switzerland
| | - Adela M Luján
- Centro de Investigaciones en Química Biológica de Córdoba, CIQUIBIC, CONICET and Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, X5000HUA Córdoba, Argentina
| | - Steve Paterson
- Institute of Integrative Biology, University of Liverpool, Crown Street, Liverpool L69 7ZB, UK
| | - Michael A Cant
- College of Life and Environmental Sciences, University of Exeter, Penryn Campus, Cornwall TR10 9FE, UK
| | - Angus Buckling
- Environment and Sustainability Institute, University of Exeter, Penryn Campus, Cornwall TR10 9FE, UK
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10
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Hesse E, O'Brien S, Tromas N, Bayer F, Luján AM, van Veen EM, Hodgson DJ, Buckling A. Ecological selection of siderophore-producing microbial taxa in response to heavy metal contamination. Ecol Lett 2017; 21:117-127. [PMID: 29161760 PMCID: PMC5765521 DOI: 10.1111/ele.12878] [Citation(s) in RCA: 64] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Revised: 08/23/2017] [Accepted: 10/16/2017] [Indexed: 11/27/2022]
Abstract
Some microbial public goods can provide both individual and community-wide benefits, and are open to exploitation by non-producing species. One such example is the production of metal-detoxifying siderophores. Here, we investigate whether conflicting selection pressures on siderophore production by heavy metals - a detoxifying effect of siderophores, and exploitation of this detoxifying effect - result in a net increase or decrease. We show that the proportion of siderophore-producing taxa increases along a natural heavy metal gradient. A causal link between metal contamination and siderophore production was subsequently demonstrated in a microcosm experiment in compost, in which we observed changes in community composition towards taxa that produce relatively more siderophores following copper contamination. We confirmed the selective benefit of siderophores by showing that taxa producing large amounts of siderophore suffered less growth inhibition in toxic copper. Our results suggest that ecological selection will favour siderophore-mediated decontamination, with important consequences for potential remediation strategies.
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Affiliation(s)
- Elze Hesse
- ESI & CEC, Biosciences, University of Exeter, Penryn Campus, Cornwall, TR10 9FE, UK
| | - Siobhán O'Brien
- ESI & CEC, Biosciences, University of Exeter, Penryn Campus, Cornwall, TR10 9FE, UK.,Institut für Integrative Biologie, ETH Zürich, Universitätstrasse 16, Zürich, 8092, Switzerland
| | - Nicolas Tromas
- Département de Sciences Biologiques, Université de Montréal, 90 Vincent-d'Indy, Montréal, QC, H2V 2S9, Canada
| | - Florian Bayer
- ESI & CEC, Biosciences, University of Exeter, Penryn Campus, Cornwall, TR10 9FE, UK
| | - Adela M Luján
- ESI & CEC, Biosciences, University of Exeter, Penryn Campus, Cornwall, TR10 9FE, UK.,CIQUIBIC, Departamento de Química Biológica, Facultad de Ciencias Químicas, CONICET, Universidad Nacional de Córdoba, Córdoba, X5000HUA, Argentina
| | - Eleanor M van Veen
- Camborne School of Mines, CEMPS, University of Exeter, Penryn Campus, Cornwall, TR10 9FE, UK
| | - Dave J Hodgson
- CEC, University of Exeter, Penryn Campus, Cornwall, TR10 9FE, UK
| | - Angus Buckling
- ESI & CEC, Biosciences, University of Exeter, Penryn Campus, Cornwall, TR10 9FE, UK
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11
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Frénoy A, Taddei F, Misevic D. Second-order cooperation: Cooperative offspring as a living public good arising from second-order selection on non-cooperative individuals. Evolution 2017; 71:1802-1814. [PMID: 28568812 DOI: 10.1111/evo.13279] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2016] [Accepted: 05/02/2017] [Indexed: 11/28/2022]
Abstract
Switching rate between cooperating and non-cooperating genotypes is a crucial social evolution factor, often neglected by game theory-inspired theoretical and experimental frameworks. We show that the evolution of alleles increasing the mutation or phenotypic switching rates toward cooperation is in itself a social dilemma. Although cooperative offspring are often unlikely to reproduce, due to high cost of cooperation, they can be seen both as a living public good and a part of the extended parental phenotype. The competition between individuals that generate cooperators and ones that do not is often more relevant than the competition between cooperators and non-cooperators. The dilemma of second-order cooperation we describe relates directly to eusociality, but can be also interpreted as a division of labor or a soma-germline distinction. The results of our simulations shine a new light on what Darwin had already termed a "special difficulty" of evolutionary theory and describe a novel type of cooperation dynamics.
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Affiliation(s)
- Antoine Frénoy
- Institute for Integrative Biology, ETH Zürich, Switzerland.,INSERM UMR 1001, Université Paris Descartes, Sorbonne Paris Cité, Faculté de Médecine, Paris, France
| | - François Taddei
- INSERM UMR 1001, Université Paris Descartes, Sorbonne Paris Cité, Faculté de Médecine, Paris, France
| | - Dusan Misevic
- INSERM UMR 1001, Université Paris Descartes, Sorbonne Paris Cité, Faculté de Médecine, Paris, France
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12
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Inglis RF, Biernaskie JM, Gardner A, Kümmerli R. Presence of a loner strain maintains cooperation and diversity in well-mixed bacterial communities. Proc Biol Sci 2016; 283:rspb.2015.2682. [PMID: 26763707 PMCID: PMC4721107 DOI: 10.1098/rspb.2015.2682] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Cooperation and diversity abound in nature despite cooperators risking exploitation from defectors and superior competitors displacing weaker ones. Understanding the persistence of cooperation and diversity is therefore a major problem for evolutionary ecology, especially in the context of well-mixed populations, where the potential for exploitation and displacement is greatest. Here, we demonstrate that a ‘loner effect’, described by economic game theorists, can maintain cooperation and diversity in real-world biological settings. We use mathematical models of public-good-producing bacteria to show that the presence of a loner strain, which produces an independent but relatively inefficient good, can lead to rock–paper–scissor dynamics, whereby cooperators outcompete loners, defectors outcompete cooperators and loners outcompete defectors. These model predictions are supported by our observations of evolutionary dynamics in well-mixed experimental communities of the bacterium Pseudomonas aeruginosa. We find that the coexistence of cooperators and defectors that produce and exploit, respectively, the iron-scavenging siderophore pyoverdine, is stabilized by the presence of loners with an independent iron-uptake mechanism. Our results establish the loner effect as a simple and general driver of cooperation and diversity in environments that would otherwise favour defection and the erosion of diversity.
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Affiliation(s)
- R F Inglis
- Environmental Microbiology, Swiss Federal Institute of Aquatic Science and Technology (Eawag), Überlandstrasse 133, 8600 Dübendorf, Switzerland Department of Environmental Systems Science, ETH Zurich, Universitätsstrasse 16, 8092 Zürich, Switzerland
| | - J M Biernaskie
- Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK
| | - A Gardner
- School of Biology, University of St Andrews, Dyers Brae, St Andrews KY16 9TH, UK
| | - R Kümmerli
- Department of Plant and Microbial Biology, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland
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13
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Nutrient reduction induced stringent responses promote bacterial quorum-sensing divergence for population fitness. Sci Rep 2016; 6:34925. [PMID: 27713502 PMCID: PMC5054682 DOI: 10.1038/srep34925] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2016] [Accepted: 09/20/2016] [Indexed: 02/05/2023] Open
Abstract
Bacteria use a cell-cell communication system termed quorum-sensing (QS) to adjust population size by coordinating the costly but beneficial cooperative behaviors. It has long been suggested that bacterial social conflict for expensive extracellular products may drive QS divergence and cause the “tragedy of the commons”. However, the underlying molecular mechanism of social divergence and its evolutionary consequences for the bacterial ecology still remain largely unknown. By using the model bacterium Pseudomonas aeruginosa PAO1, here we show that nutrient reduction can promote QS divergence for population fitness during evolution but requiring adequate cell density. Mechanically, decreased nutrient supplies can induce RpoS-directed stringent response and enhance the selection pressure on lasR gene, and lasR mutants are evolved in association with the DNA mismatch repair “switch-off”. The lasR mutants have higher relative fitness than QS-intact individuals due to their energy-saving characteristic under nutrient decreased condition. Furthermore an optimal incorporation of lasR mutants is capable of maximizing the fitness of entire population during in vitro culture and the colonization in mouse lung. Consequently, rather than worsen the population health, QS-coordinated social divergence is an elaborate evolutionary strategy that renders the entire bacterial population more fit in tough times.
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14
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O'Brien S, Hodgson DJ, Buckling A. Social evolution of toxic metal bioremediation in Pseudomonas aeruginosa. Proc Biol Sci 2015; 281:rspb.2014.0858. [PMID: 24898376 PMCID: PMC4071558 DOI: 10.1098/rspb.2014.0858] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Bacteria are often iron-limited, and hence produce extracellular iron-scavenging siderophores. A crucial feature of siderophore production is that it can be an altruistic behaviour (individually costly but benefitting neighbouring cells), thus siderophore producers can be invaded by non-producing social 'cheats'. Recent studies have shown that siderophores can also bind other heavy metals (such as Cu and Zn), but in this case siderophore chelation actually reduces metal uptake by bacteria. These complexes reduce heavy metal toxicity, hence siderophore production may contribute to toxic metal bioremediation. Here, we show that siderophore production in the context of bioremediation is also an altruistic trait and can be exploited by cheating phenotypes in the opportunistic pathogen Pseudomonas aeruginosa. Specifically, we show that in toxic copper concentrations (i) siderophore non-producers evolve de novo and reach high frequencies, and (ii) producing strains are fitter than isogenic non-producing strains in monoculture, and vice versa in co-culture. Moreover, we show that the evolutionary effect copper has on reducing siderophore production is greater than the reduction observed under iron-limited conditions. We discuss the relevance of these results to the evolution of siderophore production in natural communities and heavy metal bioremediation.
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Affiliation(s)
- Siobhán O'Brien
- Department of Biosciences, University of Exeter, Penryn Campus, Penryn TR10 9FE, UK
| | - David J Hodgson
- Department of Biosciences, University of Exeter, Penryn Campus, Penryn TR10 9FE, UK
| | - Angus Buckling
- Department of Biosciences, University of Exeter, Penryn Campus, Penryn TR10 9FE, UK
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15
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Ohland CL, Jobin C. Microbial activities and intestinal homeostasis: A delicate balance between health and disease. Cell Mol Gastroenterol Hepatol 2014; 1:28-40. [PMID: 25729763 PMCID: PMC4339954 DOI: 10.1016/j.jcmgh.2014.11.004] [Citation(s) in RCA: 107] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The concept that the intestinal microbiota modulates numerous physiological processes including immune development and function, nutrition and metabolism as well as pathogen exclusion is relatively well established in the scientific community. The molecular mechanisms driving these various effects and the events leading to the establishment of a "healthy" microbiome are slowly emerging. The objective of this review is to bring into focus important aspects of microbial/host interactions in the intestine and to discuss key molecular mechanisms controlling health and disease states. We will discuss recent evidence on how microbes interact with the host and one another and their impact on intestinal homeostasis.
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Affiliation(s)
| | - Christian Jobin
- Department of Medicine, University of Florida, Gainesville, Florida
- Department of Infectious Diseases and Pathology, University of Florida, Gainesville, Florida
- Correspondence Address correspondence to: Christian Jobin, PhD, Department of Medicine, University of Florida, 2033 Mowry Road, Office 461, Gainesville, Florida 32610. fax: (352) 392-3944.
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Molina CA, Vilchez S. Cooperation and bacterial pathogenicity: an approach to social evolution. REVISTA CHILENA DE HISTORIA NATURAL 2014. [DOI: 10.1186/s40693-014-0014-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Goldsby HJ, Knoester DB, Ofria C, Kerr B. The evolutionary origin of somatic cells under the dirty work hypothesis. PLoS Biol 2014; 12:e1001858. [PMID: 24823361 PMCID: PMC4019463 DOI: 10.1371/journal.pbio.1001858] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2013] [Accepted: 04/02/2014] [Indexed: 12/28/2022] Open
Abstract
Reproductive division of labor is a hallmark of multicellular organisms. However, the evolutionary pressures that give rise to delineated germ and somatic cells remain unclear. Here we propose a hypothesis that the mutagenic consequences associated with performing metabolic work favor such differentiation. We present evidence in support of this hypothesis gathered using a computational form of experimental evolution. Our digital organisms begin each experiment as undifferentiated multicellular individuals, and can evolve computational functions that improve their rate of reproduction. When such functions are associated with moderate mutagenic effects, we observe the evolution of reproductive division of labor within our multicellular organisms. Specifically, a fraction of the cells remove themselves from consideration as propagules for multicellular offspring, while simultaneously performing a disproportionately large amount of mutagenic work, and are thus classified as soma. As a consequence, other cells are able to take on the role of germ, remaining quiescent and thus protecting their genetic information. We analyze the lineages of multicellular organisms that successfully differentiate and discover that they display unforeseen evolutionary trajectories: cells first exhibit developmental patterns that concentrate metabolic work into a subset of germ cells (which we call "pseudo-somatic cells") and later evolve to eliminate the reproductive potential of these cells and thus convert them to actual soma. We also demonstrate that the evolution of somatic cells enables phenotypic strategies that are otherwise not easily accessible to undifferentiated organisms, though expression of these new phenotypic traits typically includes negative side effects such as aging.
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Affiliation(s)
- Heather J. Goldsby
- BEACON Center for Evolution in Action, Michigan State University, East Lansing, Michigan, United States of America
- Department of Biology, University of Washington, Seattle, Washington, United States of America
| | - David B. Knoester
- BEACON Center for Evolution in Action, Michigan State University, East Lansing, Michigan, United States of America
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, United States of America
| | - Charles Ofria
- BEACON Center for Evolution in Action, Michigan State University, East Lansing, Michigan, United States of America
- Department of Computer Science and Engineering, Michigan State University, East Lansing, Michigan, United States of America
| | - Benjamin Kerr
- BEACON Center for Evolution in Action, Michigan State University, East Lansing, Michigan, United States of America
- Department of Biology, University of Washington, Seattle, Washington, United States of America
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O'Brien S, Rodrigues AMM, Buckling A. The evolution of bacterial mutation rates under simultaneous selection by interspecific and social parasitism. Proc Biol Sci 2013; 280:20131913. [PMID: 24197408 PMCID: PMC3826219 DOI: 10.1098/rspb.2013.1913] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2013] [Accepted: 10/09/2013] [Indexed: 02/05/2023] Open
Abstract
Many bacterial populations harbour substantial numbers of hypermutable bacteria, in spite of hypermutation being associated with deleterious mutations. One reason for the persistence of hypermutators is the provision of novel mutations, enabling rapid adaptation to continually changing environments, for example coevolving virulent parasites. However, hypermutation also increases the rate at which intraspecific parasites (social cheats) are generated. Interspecific and intraspecific parasitism are therefore likely to impose conflicting selection pressure on mutation rate. Here, we combine theory and experiments to investigate how simultaneous selection from inter- and intraspecific parasitism affects the evolution of bacterial mutation rates in the plant-colonizing bacterium Pseudomonas fluorescens. Both our theoretical and experimental results suggest that phage presence increases and selection for public goods cooperation (the production of iron-scavenging siderophores) decreases selection for mutator bacteria. Moreover, phages imposed a much greater growth cost than social cheating, and when both selection pressures were imposed simultaneously, selection for cooperation did not affect mutation rate evolution. Given the ubiquity of infectious phages in the natural environment and clinical infections, our results suggest that phages are likely to be more important than social interactions in determining mutation rate evolution.
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Affiliation(s)
- Siobhán O'Brien
- Department of Biosciences, University of Exeter, Tremough, Penryn, Cornwall TR10 9EZ, UK
| | | | - Angus Buckling
- Department of Biosciences, University of Exeter, Tremough, Penryn, Cornwall TR10 9EZ, UK
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19
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Abstract
Dense and diverse microbial communities are found in many environments. Disentangling the social interactions between strains and species is central to understanding microbes and how they respond to perturbations. However, the study of social evolution in microbes tends to focus on single species. Here, we broaden this perspective and review evolutionary and ecological theory relevant to microbial interactions across all phylogenetic scales. Despite increased complexity, we reduce the theory to a simple null model that we call the genotypic view. This states that cooperation will occur when cells are surrounded by identical genotypes at the loci that drive interactions, with genetic identity coming from recent clonal growth or horizontal gene transfer (HGT). In contrast, because cooperation is only expected to evolve between different genotypes under restrictive ecological conditions, different genotypes will typically compete. Competition between two genotypes includes mutual harm but, importantly, also many interactions that are beneficial to one of the two genotypes, such as predation. The literature offers support for the genotypic view with relatively few examples of cooperation between genotypes. However, the study of microbial interactions is still at an early stage. We outline the logic and methods that help to better evaluate our perspective and move us toward rationally engineering microbial communities to our own advantage.
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Affiliation(s)
- Sara Mitri
- Department of Zoology, University of Oxford, Oxford OX1 3PS, United Kingdom; ,
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20
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Zhang XX, Rainey PB. Exploring the sociobiology of pyoverdin-producing Pseudomonas. Evolution 2013; 67:3161-74. [PMID: 24152000 DOI: 10.1111/evo.12183] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2012] [Accepted: 05/29/2013] [Indexed: 01/19/2023]
Abstract
The idea that bacteria are social is a popular concept with implications for understanding the ecology and evolution of microbes. The view arises predominately from reasoning regarding extracellular products, which, it has been argued, can be considered "public goods." Among the best studied is pyoverdin-a diffusible iron-chelating agent produced by bacteria of the genus Pseudomonas. Here we report the de novo evolution of pyoverdin nonproducing mutants, genetically characterize these types and then test the appropriateness of the sociobiology framework by performing growth and fitness assays in the same environment in which the nonproducing mutants evolved. Our data draw attention to discordance in the fit between social evolution theory and biological reality. We show that pyoverdin-defective genotypes can gain advantage by avoiding the cost of production under conditions where the molecule is not required; in some environments pyoverdin is personalized. By exploring the fitness consequences of nonproducing types under a range of conditions, we show complex genotype-by-environment interactions with outcomes that range from social to asocial. Together these findings give reason to question the generality of the conclusion that pyoverdin is a social trait.
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Affiliation(s)
- Xue-Xian Zhang
- Institute of Natural and Mathematical Sciences, Massey University at Albany, Private Bag 102 904, North Shore Mail Centre, Auckland, New Zealand
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21
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Harrison F. Dynamic social behaviour in a bacterium: pseudomonas aeruginosa partially compensates for siderophore loss to cheats. J Evol Biol 2013; 26:1370-8. [PMID: 23662904 DOI: 10.1111/jeb.12126] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2012] [Revised: 12/20/2012] [Accepted: 01/10/2013] [Indexed: 11/28/2022]
Abstract
Cooperation underlies diverse phenomena including the origins of multicellular life, human behaviour in economic markets and the mechanisms by which pathogenic bacteria cause disease. Experiments with microorganisms have advanced our understanding of how, when and why cooperation evolves, but the extent to which microbial cooperation can recapitulate aspects of animal behaviour is debated. For instance, understanding the evolution of behavioural response rules (how should one individual respond to another's decision to cooperate or defect?) is a key part of social evolution theory, but the possible existence of such rules in social microbes has not been explored. In one specific context (biparental care in animals), cooperation is maintained if individuals respond to a partner's defection by increasing their own investment into cooperation, but not so much that this fully compensates for the defector's lack of investment. This is termed 'partial compensation'. Here, I show that partial compensation for the presence of noncooperating 'cheats' is also observed in a microbial social behaviour: the cooperative production of iron-scavenging siderophores by the bacterium Pseudomonas aeruginosa. A period of evolution in the presence of cheats maintains this response, whereas evolution in the absence of cheats leads to a loss of compensatory behaviour. These results demonstrate (i) the remarkable flexibility of bacterial social behaviour, (ii) the potential generality of partial compensation as a social response rule and (iii) the need for mathematical models to explore the evolution of response rules in multi-player social interactions.
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Affiliation(s)
- F Harrison
- Department of Zoology, University of Oxford, Oxford, United Kingdom.
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22
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Harrison F. Bacterial cooperation in the wild and in the clinic: are pathogen social behaviours relevant outside the laboratory? Bioessays 2012; 35:108-12. [PMID: 23281188 PMCID: PMC4267416 DOI: 10.1002/bies.201200154] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Individual bacterial cells can communicate via quorum sensing, cooperate to harvest nutrients from their environment, form multicellular biofilms, compete over resources and even kill one another. When the environment that bacteria inhabit is an animal host, these social behaviours mediate virulence. Over the last decade, much attention has focussed on the ecology, evolution and pathology of bacterial cooperation, and the possibility that it could be exploited or destabilised to treat infections. But how far can we really extrapolate from theoretical predictions and laboratory experiments to make inferences about ‘cooperative’ behaviours in hosts and reservoirs? To determine the likely importance and evolution of cooperation ‘in the wild’, several questions must be addressed. A recent paper that reports the dynamics of bacterial cooperation and virulence in a field experiment provides an excellent nucleus for bringing together key empirical and theoretical results which help us to frame – if not completely to answer – these questions.
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Affiliation(s)
- Freya Harrison
- School of Molecular Medical Sciences, University of Nottingham, Nottingham, United Kingdom.
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23
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Queller DC, Strassmann JE. Experimental evolution of multicellularity using microbial pseudo-organisms. Biol Lett 2012; 9:20120636. [PMID: 23015456 DOI: 10.1098/rsbl.2012.0636] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
In a major evolutionary transition to a new level of organization, internal conflicts must be controlled before the transition can truly be successful. One such transition is that from single cells to multicellularity. Conflicts among cells in multicellular organisms can be greatly reduced if they consist of genetically identical clones. However, mutations to cheaters that experience one round of within-individual selection could still be a problem, particularly for certain life cycles. We propose an experimental evolution method to investigate this issue, using micro-organisms to construct multicellular pseudo-organisms, which can be evolved under different artificial life cycles. These experiments can be used to test the importance of various life cycle features in maintaining cooperation. They include structured reproduction, in which small propagule size reduces within-individual genetic variation. They also include structured growth, which increases local relatedness within individual bodies. Our method provides a novel way to test how different life cycles favour cooperation, even for life cycles that do not exist.
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Affiliation(s)
- David C Queller
- Department of Biology, Washington University in St. Louis, St. Louis, MO 63130-4899, USA
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24
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Morgan AD, Quigley BJZ, Brown SP, Buckling A. Selection on non-social traits limits the invasion of social cheats. Ecol Lett 2012; 15:841-6. [PMID: 22639835 PMCID: PMC3444687 DOI: 10.1111/j.1461-0248.2012.01805.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2012] [Revised: 04/17/2012] [Accepted: 04/25/2012] [Indexed: 11/29/2022]
Abstract
While the conditions that favour the maintenance of cooperation have been extensively investigated, the significance of non-social selection pressures on social behaviours has received little attention. In the absence of non-social selection pressures, patches of cooperators are vulnerable to invasion by cheats. However, we show both theoretically, and experimentally with the bacterium Pseudomonas fluorescens, that cheats may be unable to invade patches of cooperators under strong non-social selection (both a novel abiotic environment and to a lesser extent, the presence of a virulent parasite). This is because beneficial mutations are most likely to arise in the numerically dominant cooperator population. Given the ubiquity of novel selection pressures on microbes, these results may help to explain why cooperation is the norm in natural populations of microbes.
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25
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Dumas Z, Kümmerli R. Cost of cooperation rules selection for cheats in bacterial metapopulations. J Evol Biol 2011; 25:473-84. [PMID: 22168669 DOI: 10.1111/j.1420-9101.2011.02437.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Bacteria secrete a large variety of beneficial metabolites into the environment, which can be shared as public goods among producing bacteria, but also be exploited by nonproducing cheats. Here, we focus on cooperative production of iron-chelating molecules (siderophores) in the bacterium Pseudomonas aeruginosa to study how relevant ecological factors influence selection for cheating. We designed patch-structured metapopulations that allowed us introducing among-patch ecological variation. We found that cheating readily evolved in uniform iron-limited environments. This finding is explained by severe iron limitation demanding high siderophore-production efforts, which results in high metabolic costs accruing to cooperators, and thereby facilitates the spread of cheats. In contrast, we observed a significant reduction or even negation of selection for cheating in metapopulations where we introduced patches with increased iron availability and/or opportunities to recycle siderophores. These findings are compatible with the view that cheats are less likely to invade in environments that allow bacteria to reduce siderophore-production efforts, as this lowers the overall metabolic costs accruing to cooperators. Because we increased iron availability and siderophore recycling opportunities moderately, and only in some patches, our findings demonstrate that already-small local variations in ecological conditions as occurring in nature can significantly affect selection for public-goods secretion in microbes. In addition, we found that most (84.6%) of the evolved cheats were partially deficient for siderophore production and not loss-of-function mutants. Genetic considerations indicate that mutations leading to partial deficiency occur more frequent than mutations leading to loss of function, but also suggest that partially deficient mutants might often be the more competitive cheats.
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Affiliation(s)
- Z Dumas
- Swiss Federal Institute of Aquatic Science and Technology (Eawag), Environmental Microbiology, Dübendorf, Switzerland
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26
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Conserving antibiotics for the future: new ways to use old and new drugs from a pharmacokinetic and pharmacodynamic perspective. Drug Resist Updat 2011; 14:107-17. [PMID: 21440486 DOI: 10.1016/j.drup.2011.02.005] [Citation(s) in RCA: 156] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2011] [Revised: 02/16/2011] [Accepted: 02/17/2011] [Indexed: 12/13/2022]
Abstract
There is a growing need to optimize the use of old and new antibiotics to treat serious as well as less serious infections. The topic of how to use pharmacokinetic and pharmacodynamic (PK/PD) knowledge to conserve antibiotics for the future was elaborated on in a workshop of the conference (The conference "The Global Need for Effective Antibiotics - moving towards concerted action", ReAct, Uppsala, Sweden, 2010). The optimization of dosing regimens is accomplished by choosing the dose and schedule that results in the antimicrobial exposure that will achieve the microbiological and clinical outcome desired while simultaneously suppressing emergence of resistance. PK/PD of antimicrobial agents describe how the therapeutic drug effect is dependent on the potency of a drug against a microorganism and the exposure (the concentration of antimicrobial available for effect over time). The description and modeling of these relationships quantitatively then allow for a rational approach to dose optimization and several strategies to that purpose are described. These strategies include not only the dosing regimen itself but also the duration of therapy, preventing collateral damage through inappropriate use and the application of PK/PD in drug development. Furthermore, PK/PD relationships of older antibiotics need to be urgently established. The need for global harmonization of breakpoints is also suggested and would add efficacy to antibiotic therapy. For each of the strategies, a number of priority actions are provided.
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27
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Oliver A, Mena A. Bacterial hypermutation in cystic fibrosis, not only for antibiotic resistance. Clin Microbiol Infect 2011; 16:798-808. [PMID: 20880409 DOI: 10.1111/j.1469-0691.2010.03250.x] [Citation(s) in RCA: 147] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Hypermutable or mutator microorganisms are those that have an increased spontaneous mutation rate as a result of defects in DNA repair or error avoidance systems. Over the last two decades, several studies have provided strong evidence for a relevant role of mutators in the evolution of natural bacterial populations, particularly in the field of infectious diseases. Among them, chronic respiratory infection with Pseudomonas aeruginosa in cystic fibrosis (CF) patients was the first natural environment to reveal the high prevalence and important role of mutators. A remarkable positive selection of mutators during the course of the chronic infection has been reported, mainly as a result of the emergence of DNA mismatch repair system (mutS, mutL or mutU)-deficient mutants, although strains defective in the GO system (mutM, mutY and mutT) have also been observed. High frequencies of mutators have also been noted among other pathogens in the CF setting, particularly Staphylococcus aureus and Haemophilus influenzae. Enhanced antimicrobial resistance development is the most thoroughly studied consequence of mutators in CF and other chronic infections, although recent studies show that mutators may additionally have important effects on the evolution of virulence, genetic adaptation to the airways of CF patients, persistence of colonization, transmissibility, and perhaps lung function decline. Further prospective clinical studies are nevertheless still needed for an in-depth evaluation of the impact of mutators on disease progression and outcome.
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Affiliation(s)
- A Oliver
- Servicio de Microbiología and Unidad de Investigación, Hospital Son Dureta, Instituto Universitario de Investigación en Ciencias de la Salud, Palma de Mallorca, Spain.
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28
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Abstract
Organisms from prokaryotes to plants and animals make costly investments in diffusible beneficial external products. While the costs of producing such products are born only by the producer, the benefits may be distributed more widely. How are external goods-producing populations stabilized against invasion by nonproducing variants that receive the benefits without paying the cost? This question parallels the classic question of altruism, but because external goods production need not be altruistic per se, a broader range of conditions may lead to the maintenance of these traits. We start from the physics of diffusion to develop an expression for the conditions that favor the production of diffusible external goods. Important variables in determining the evolutionary outcome include the diffusion coefficient of the good, the distance between individuals, and the uptake rate of the external good. These variables join the coefficient of relatedness and the cost/benefit ratio in an expanded form of Hamilton's rule that includes both selfish and altruistic paths to the evolution of external goods strategies. This expanded framework can be applied to any external goods trait, and is a useful heuristic even when it is difficult to quantify the fitness consequences of producing the good.
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Affiliation(s)
- William W Driscoll
- Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA.
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29
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Wider access to genotypic space facilitates loss of cooperation in a bacterial mutator. PLoS One 2011; 6:e17254. [PMID: 21364773 PMCID: PMC3045467 DOI: 10.1371/journal.pone.0017254] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2010] [Accepted: 01/26/2011] [Indexed: 11/30/2022] Open
Abstract
Understanding the ecological, evolutionary and genetic factors that affect the expression of cooperative behaviours is a topic of wide biological significance. On a practical level, this field of research is useful because many pathogenic microbes rely on the cooperative production of public goods (such as nutrient scavenging molecules, toxins and biofilm matrix components) in order to exploit their hosts. Understanding the evolutionary dynamics of cooperation is particularly relevant when considering long-term, chronic infections where there is significant potential for intra-host evolution. The impact of responses to non-social selection pressures on social evolution is arguably an under-examined area. In this paper, we consider how the evolution of a non-social trait – hypermutability – affects the cooperative production of iron-scavenging siderophores by the opportunistic human pathogen Pseudomonas aeruginosa. We confirm an earlier prediction that hypermutability accelerates the breakdown of cooperation due to increased sampling of genotypic space, allowing mutator lineages to generate non-cooperative genotypes with the ability to persist at high frequency and dominate populations. This may represent a novel cost of hypermutability.
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30
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Jiricny N, Diggle SP, West SA, Evans BA, Ballantyne G, Ross-Gillespie A, Griffin AS. Fitness correlates with the extent of cheating in a bacterium. J Evol Biol 2010; 23:738-47. [PMID: 20210835 DOI: 10.1111/j.1420-9101.2010.01939.x] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
There is growing awareness of the importance of cooperative behaviours in microbial communities. Empirical support for this insight comes from experiments using mutant strains, termed 'cheats', which exploit the cooperative behaviour of wild-type strains. However, little detailed work has gone into characterising the competitive dynamics of cooperative and cheating strains. We test three specific predictions about the fitness consequences of cheating to different extents by examining the production of the iron-scavenging siderophore molecule, pyoverdin, in the bacterium Pseudomonas aeruginosa. We create a collection of mutants that differ in the amount of pyoverdin that they produce (from 1% to 96% of the production of paired wild types) and demonstrate that these production levels correlate with both gene activity and the ability to bind iron. Across these mutants, we found that (1) when grown in a mixed culture with a cooperative wild-type strain, the relative fitness of a mutant is negatively correlated with the amount of pyoverdin that it produces; (2) the absolute and relative fitness of the wild-type strain in the mixed culture is positively correlated with the amount of pyoverdin that the mutant produces; and (3) when grown in a monoculture, the absolute fitness of the mutant is positively correlated with the amount of pyoverdin that it produces. Overall, we demonstrate that cooperative pyoverdin production is exploitable and illustrate how variation in a social behaviour determines fitness differently, depending on the social environment.
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Affiliation(s)
- N Jiricny
- Department of Zoology, Oxford University, Oxford, UK
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31
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Racey D, Inglis RF, Harrison F, Oliver A, Buckling A. THE EFFECT OF ELEVATED MUTATION RATES ON THE EVOLUTION OF COOPERATION AND VIRULENCE OFPSEUDOMONAS AERUGINOSA. Evolution 2010; 64:515-21. [DOI: 10.1111/j.1558-5646.2009.00821.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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32
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Jousset A, Rochat L, Péchy-Tarr M, Keel C, Scheu S, Bonkowski M. Predators promote defence of rhizosphere bacterial populations by selective feeding on non-toxic cheaters. ISME JOURNAL 2009; 3:666-74. [DOI: 10.1038/ismej.2009.26] [Citation(s) in RCA: 101] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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33
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Abstract
Why infer evolution when you can watch it happen in real time? This is the basic premise of using populations of fast-replicating microorganisms in test tubes to study evolution. The approach, known as experimental evolution, has provided a way of testing many of the key hypotheses that arose from the modern evolutionary synthesis. However, details of the unnatural histories of microorganisms in test tubes can be extrapolated only so far. Potential future directions for the approach include studying microbial evolution for its own sake under the most natural conditions possible in the test tube, and testing some qualitative theories of genome evolution.
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34
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Harrison F, Buckling A. Siderophore production and biofilm formation as linked social traits. ISME JOURNAL 2009; 3:632-4. [DOI: 10.1038/ismej.2009.9] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
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35
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Craig Maclean R, Brandon C. Stable public goods cooperation and dynamic social interactions in yeast. J Evol Biol 2008; 21:1836-43. [PMID: 18643862 DOI: 10.1111/j.1420-9101.2008.01579.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Despite long-standing theoretical interest in the evolution of cooperation, empirical data on the evolutionary dynamics of cooperative traits remain limited. Here, we investigate the evolutionary dynamics of a simple public goods cooperative trait, invertase secretion, using a long-term selection experiment in Saccharomyces cerevisiae. We show that average investment in cooperation remains essentially constant over a period of hundreds of generations in viscous populations with high relatedness. Average cooperation remains constant despite transient local selection for high and low levels of cooperation that generate dynamic social interactions. Natural populations of yeast show similar variation in social strategies, which is consistent with the existence of similar selective pressures on public goods cooperation in nature.
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Affiliation(s)
- R Craig Maclean
- NERC Centre for Population Biology, Imperial College London, Silwood Park, Ascot, UK.
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36
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Brockhurst MA, Buckling A, Racey D, Gardner A. Resource supply and the evolution of public-goods cooperation in bacteria. BMC Biol 2008; 6:20. [PMID: 18479522 PMCID: PMC2409295 DOI: 10.1186/1741-7007-6-20] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2007] [Accepted: 05/14/2008] [Indexed: 11/23/2022] Open
Abstract
Background Explaining public-goods cooperation is a challenge for evolutionary biology. However, cooperation is expected to more readily evolve if it imposes a smaller cost. Such costs of cooperation are expected to decline with increasing resource supply, an ecological parameter that varies widely in nature. We experimentally tested the effect of resource supply on the evolution of cooperation using two well-studied bacterial public-good traits: biofilm formation by Pseudomonas fluorescens and siderophore production by Pseudomonas aeruginosa. Results The frequency of cooperative bacteria increased with resource supply in the context of both bacterial public-good traits. In both cases this was due to decreasing costs of investment into public-goods cooperation with increasing resource supply. Conclusion Our empirical tests with bacteria suggest that public-goods cooperation is likely to increase with increasing resource supply due to reduced costs of cooperation, confirming that resource supply is an important factor in the evolution of cooperation.
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Affiliation(s)
- Michael A Brockhurst
- School of Biological Sciences, Biosciences Building, University of Liverpool, Crown Street, Liverpool, L69 7ZB, UK.
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37
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West SA, Diggle SP, Buckling A, Gardner A, Griffin AS. The Social Lives of Microbes. ANNUAL REVIEW OF ECOLOGY EVOLUTION AND SYSTEMATICS 2007. [DOI: 10.1146/annurev.ecolsys.38.091206.095740] [Citation(s) in RCA: 529] [Impact Index Per Article: 29.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Stuart A. West
- Institute of Evolutionary Biology, University of Edinburgh, Edinburgh EH9 3JT, United Kingdom; ,
| | - Stephen P. Diggle
- Institute of Infection, Immunity & Inflammation, Center for Biomolecular Sciences, University of Nottingham, Nottingham NG7 2RD, United Kingdom;
| | - Angus Buckling
- Department of Zoology, Oxford University, Oxford OX1 3PS, United Kingdom;
| | - Andy Gardner
- Institute of Evolutionary Biology, University of Edinburgh, Edinburgh EH9 3JT, United Kingdom; ,
- St. John's College, Oxford University, Oxford OX1 3JP, United Kingdom;
| | - Ashleigh S. Griffin
- Institute of Evolutionary Biology, University of Edinburgh, Edinburgh EH9 3JT, United Kingdom; ,
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Abstract
Understanding the microbial flora of the cystic fibrosis (CF) respiratory tract is of considerable importance, as patient morbidity and death are primarily caused by chronic respiratory infections. However, chronically colonized CF airways represent a surprisingly complex and diverse ecosystem. The precise contributions of different microbes to patient morbidity, and in particular the importance of inter-specific interactions, remain largely unelucidated. The importance of within-species genetic and phenotypic variation has similarly received limited explicit attention. While a host of studies provide data on the microbial species recovered from patients, these are often incomparable due to differences in sampling and data reporting, or do not present the data in a way that aids our understanding of the ecosystem within each patient. This review brings together a cross-section of recent research on the CF airways and the microbes which infect them. The results presented suggest that understanding the CF lung in terms of its community and evolutionary ecology could benefit our understanding of disease progression and influence treatment regimens.
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Affiliation(s)
- Freya Harrison
- Department of Zoology, University of Oxford, Oxford OX1 3PS, UK
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Interspecific competition and siderophore-mediated cooperation in Pseudomonas aeruginosa. ISME JOURNAL 2007; 2:49-55. [DOI: 10.1038/ismej.2007.96] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Buckling A, Harrison F, Vos M, Brockhurst MA, Gardner A, West SA, Griffin A. Siderophore-mediated cooperation and virulence in Pseudomonas aeruginosa. FEMS Microbiol Ecol 2007; 62:135-41. [DOI: 10.1111/j.1574-6941.2007.00388.x] [Citation(s) in RCA: 130] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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41
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Brockhurst MA. Population bottlenecks promote cooperation in bacterial biofilms. PLoS One 2007; 2:e634. [PMID: 17653261 PMCID: PMC1919422 DOI: 10.1371/journal.pone.0000634] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2007] [Accepted: 06/15/2007] [Indexed: 11/18/2022] Open
Abstract
Population bottlenecks are assumed to play a key role in the maintenance of social traits in microbes. Ecological parameters such as colonisation or disturbances can favour cooperation through causing population bottlenecks that enhance genetic structuring (relatedness). However, the size of the population bottleneck is likely to play a crucial role in determining the success of cooperation. Relatedness is likely to increase with decreasing bottleneck size thus favouring the evolution of cooperation. I used an experimental evolution approach to test this prediction with biofilm formation by the bacterium Pseudomonas fluorescens as the cooperative trait. Replicate populations were exposed to disturbance events every four days under one of six population bottleneck treatments (from 103 to 108 bacterial cells). In line with predictions, the frequency of evolved cheats within the populations increased with increasing bottleneck size. This result highlights the importance of ecologically mediated population bottlenecks in the maintenance of social traits in microbes.
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Affiliation(s)
- Michael A Brockhurst
- School of Biological Sciences, University of Liverpool, Liverpool, United Kingdom.
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42
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Harrison F, Buckling A. High relatedness selects against hypermutability in bacterial metapopulations. Proc Biol Sci 2007; 274:1341-7. [PMID: 17374597 PMCID: PMC2176179 DOI: 10.1098/rspb.2006.0408] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Mutation rate and cooperation have important ecological and evolutionary consequences and, moreover, can affect pathogen virulence. While hypermutability accelerates adaptation to novel environments, hypermutable lineages ('mutators') are selected against in well-adapted populations. Using the model organism Pseudomonas aeruginosa, we previously demonstrated a further potential disadvantage to hypermutability, namely, that it can accelerate the breakdown of cooperation. We now investigate how this property of mutators can affect their persistence in metapopulations. Mutator and wild-type bacteria were competed for 250 generations in globally competing metapopulations, imposing conditions of high or low intra-deme relatedness. High relatedness favours cooperating groups, so we predicted that mutators should achieve lower equilibrium frequencies under high relatedness than under low relatedness. This was observed in our study. Consistent with our hypothesis, there was a positive correlation between mean mutator and cheat frequencies. We conclude that when dense population growth requires cooperation, and when cooperation is favoured (high relatedness), demes containing high frequencies of mutators are likely to be selected against because they also contain high frequencies of non-cooperating cheats. We have also identified conditions where mutator lineages are likely to dominate metapopulations; namely, when low relatedness reduces kin selection for cooperation. These results may help to explain clinical distributions of mutator bacteria.
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Affiliation(s)
- Freya Harrison
- Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK.
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Brockhurst MA, Buckling A, Gardner A. Cooperation Peaks at Intermediate Disturbance. Curr Biol 2007; 17:761-5. [PMID: 17379522 DOI: 10.1016/j.cub.2007.02.057] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2007] [Revised: 02/26/2007] [Accepted: 02/26/2007] [Indexed: 11/21/2022]
Abstract
Explaining cooperation is a challenge for evolutionary biology. Surprisingly, the role of extrinsic ecological parameters remains largely unconsidered. Disturbances are widespread in nature and have evolutionary consequences. We develop a mathematical model predicting that cooperative traits most readily evolve at intermediate disturbance. Under infrequent disturbance, cooperation breaks down through the accumulation of evolved cheats. Higher rates of disturbance prevent this because the resulting bottlenecks increase genetic structuring (relatedness) promoting kin selection for cooperation. However, cooperation cannot be sustained under very frequent disturbance if population density remains below the level required for successful cooperation. We tested these predictions by using cooperative biofilm formation by the bacterium Pseudomonas fluorescens. The proportion of biofilm-forming bacteria peaked at intermediate disturbance, in a manner consistent with model predictions. Under infrequent and intermediate disturbance, most bacteria occupied the biofilm, but the proportion of cheats was higher under less frequent disturbance. Under frequent disturbance, many bacteria did not occupy the biofilm, suggesting that biofilm dwelling was not as beneficial under frequent versus intermediate disturbance. Given the ubiquity of disturbances in nature, these results suggest that they may play a major role in the evolution of social traits in microbes.
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Affiliation(s)
- Michael A Brockhurst
- School of Biological Sciences, Biosciences Building, University of Liverpool, Crown Street, Liverpool, L69 7ZB, UK.
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Brockhurst MA, Colegrave N, Hodgson DJ, Buckling A. Niche occupation limits adaptive radiation in experimental microcosms. PLoS One 2007; 2:e193. [PMID: 17285146 PMCID: PMC1781339 DOI: 10.1371/journal.pone.0000193] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2006] [Accepted: 01/13/2007] [Indexed: 11/18/2022] Open
Abstract
Adaptive radiations have played a key role in the evolution of biological diversity. The breadth of adaptive radiation in an invading lineage is likely to be influenced by the availability of ecological niches, which will be determined to some extent by the diversity of the resident community. High resident diversity may result in existing ecological niches being filled, inhibiting subsequent adaptive radiation. Conversely, high resident diversity could result in the creation of novel ecological niches or an increase in within niche competition driving niche partitioning, thus promoting subsequent diversification. We tested the role of resident diversity on adaptive radiations in experimental populations of the bacterium Pseudomonas fluorescens that readily diversify into a range of niche specialists when grown in a heterogeneous environment. We allowed an undiversified strain to invade resident communities that varied in the number of niche specialists. The breadth of adaptive radiation attainable by an invading lineage decreased with increasing niche occupation of the resident community. Our results highlight the importance of niche occupation as a constraint on adaptive radiation.
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Affiliation(s)
- Michael A Brockhurst
- School of Biological Sciences, Biosciences Building, University of Liverpool, Crown Street, Liverpool, United Kingdom.
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45
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Jékely G. Origin of phagotrophic eukaryotes as social cheaters in microbial biofilms. Biol Direct 2007; 2:3. [PMID: 17239231 PMCID: PMC1794243 DOI: 10.1186/1745-6150-2-3] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2007] [Accepted: 01/19/2007] [Indexed: 12/28/2022] Open
Abstract
BACKGROUND The origin of eukaryotic cells was one of the most dramatic evolutionary transitions in the history of life. It is generally assumed that eukaryotes evolved later then prokaryotes by the transformation or fusion of prokaryotic lineages. However, as yet there is no consensus regarding the nature of the prokaryotic group(s) ancestral to eukaryotes. Regardless of this, a hardly debatable fundamental novel characteristic of the last eukaryotic common ancestor was the ability to exploit prokaryotic biomass by the ingestion of entire cells, i.e. phagocytosis. The recent advances in our understanding of the social life of prokaryotes may help to explain the origin of this form of total exploitation. PRESENTATION OF THE HYPOTHESIS Here I propose that eukaryotic cells originated in a social environment, a differentiated microbial mat or biofilm that was maintained by the cooperative action of its members. Cooperation was costly (e.g. the production of developmental signals or an extracellular matrix) but yielded benefits that increased the overall fitness of the social group. I propose that eukaryotes originated as selfish cheaters that enjoyed the benefits of social aggregation but did not contribute to it themselves. The cheaters later evolved into predators that lysed other cells and eventually became professional phagotrophs. During several cycles of social aggregation and dispersal the number of cheaters was contained by a chicken game situation, i.e. reproductive success of cheaters was high when they were in low abundance but was reduced when they were over-represented. Radical changes in cell structure, including the loss of the rigid prokaryotic cell wall and the development of endomembranes, allowed the protoeukaryotes to avoid cheater control and to exploit nutrients more efficiently. Cellular changes were buffered by both the social benefits and the protective physico-chemical milieu of the interior of biofilms. Symbiosis with the mitochondial ancestor evolved after phagotrophy as alphaproteobacterial prey developed post-ingestion defence mechanisms to circumvent digestion in the food vacuole. Mitochondrial symbiosis triggered the origin of the nucleus. Cilia evolved last and allowed eukaryotes to predate also on planktonic prey. I will discuss how this scenario may possibly fit into the contrasting phylogenetic frameworks that have been proposed. TESTING THE HYPOTHESIS Some aspects of the hypothesis can be tested experimentally by studying the level of exploitation cheaters can reach in social microbes. It would be interesting to test whether absorption of nutrients from lysed fellow colony members can happen and if cheaters can evolve into predators that actively digest neighbouring cells. IMPLICATIONS OF THE HYPOTHESIS The hypothesis highlights the importance of social exploitation in cell evolution and how a social environment can buffer drastic cellular transformations that would be lethal for planktonic forms.
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Affiliation(s)
- Gáspár Jékely
- European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany.
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Visca P, Imperi F, Lamont IL. Pyoverdine siderophores: from biogenesis to biosignificance. Trends Microbiol 2007; 15:22-30. [PMID: 17118662 DOI: 10.1016/j.tim.2006.11.004] [Citation(s) in RCA: 365] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2006] [Revised: 09/28/2006] [Accepted: 11/08/2006] [Indexed: 11/23/2022]
Abstract
Pyoverdines are a group of structurally related siderophores produced by fluorescent Pseudomonas species. Recent genomic and biochemical data have shed new light on the complex molecular steps of pyoverdine biogenesis and explained the chemical diversity of these compounds. In the opportunistic pathogen Pseudomonas aeruginosa, pyoverdine is necessary for infection in several different disease models. The occurrence of pyoverdine-defective strains in chronic infections of patients with cystic fibrosis and the extremely high sequence diversity of genes involved in pyoverdine synthesis and uptake indicate that pyoverdine production is subject to high evolutionary pressure. Pyoverdine-dependent iron transport is also crucial for biofilm development, further expanding the importance of these siderophores in Pseudomonas biology.
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Affiliation(s)
- Paolo Visca
- Department of Biology, University Roma Tre, Rome I-00146, Italy
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Brockhurst MA, Hochberg ME, Bell T, Buckling A. Character displacement promotes cooperation in bacterial biofilms. Curr Biol 2006; 16:2030-4. [PMID: 17055982 DOI: 10.1016/j.cub.2006.08.068] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2006] [Revised: 08/09/2006] [Accepted: 08/21/2006] [Indexed: 11/18/2022]
Abstract
Resource competition within a group of cooperators is expected to decrease selection for cooperative behavior but can also result in diversifying selection for the use of different resources, which in turn could retard the breakdown of cooperation. Diverse groups are likely to be less susceptible to invasion by noncooperating social cheats: First, competition repression resulting from character displacement may provide less of a selective advantage to cheating; second, cheats may trade off the ability to exploit cooperators that specialize in one type of resource against cooperators that specialize in another ; third, diverse communities of any kind may have higher invasion resistance because there are fewer resources available for an invader to use . Furthermore, diverse groups are likely to be more productive than clonal groups if a wider range of total resources are being used . We addressed these issues by using the cooperative trait of biofilm formation in Pseudomonas fluorescens. Character displacement through resource competition evolved within biofilms; productivity increased with increasing character displacement, and diverse biofilms were less susceptible to invasion by cheats. These results demonstrate that diversification into different ecological niches can minimize selection against cooperation in the face of local resource competition.
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Affiliation(s)
- Michael A Brockhurst
- School of Biological Sciences, Biosciences Building, University of Liverpool, Crown Street, Liverpool L69 7ZB, United Kingdom.
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Harrison F, Browning LE, Vos M, Buckling A. Cooperation and virulence in acute Pseudomonas aeruginosa infections. BMC Biol 2006; 4:21. [PMID: 16827933 PMCID: PMC1526758 DOI: 10.1186/1741-7007-4-21] [Citation(s) in RCA: 159] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2006] [Accepted: 07/07/2006] [Indexed: 11/17/2022] Open
Abstract
Background Efficient host exploitation by parasites is frequently likely to depend on cooperative behaviour. Under these conditions, mixed-strain infections are predicted to show lower virulence (host mortality) than are single-clone infections, due to competition favouring non-contributing social 'cheats' whose presence will reduce within-host growth. We tested this hypothesis using the cooperative production of iron-scavenging siderophores by the pathogenic bacterium Pseudomonas aeruginosa in an insect host. Results We found that infection by siderophore-producing bacteria (cooperators) results in more rapid host death than does infection by non-producers (cheats), and that mixtures of both result in intermediate levels of virulence. Within-host bacterial growth rates exhibited the same pattern. Crucially, cheats were more successful in mixed infections compared with single-clone infections, while the opposite was true of cooperators. Conclusion These data demonstrate that mixed clone infections can favour the evolution of social cheats, and thus decrease virulence when parasite growth is dependent on cooperative behaviours.
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Affiliation(s)
- Freya Harrison
- Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK
| | - Lucy E Browning
- Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK
- Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK
| | - Michiel Vos
- Max Planck Institute for Developmental Biology, Spemannstrasse 35, 72076 Tuebingen, Germany
| | - Angus Buckling
- Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK
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