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About half of all bacteria carry genes for CRISPR-Cas adaptive immune systems.sup.1, which provide immunological memory by inserting short DNA sequences from phage and other parasitic DNA elements into CRISPR loci on the host genome.sup.2. Whereas CRISPR loci evolve rapidly in natural environments.sup.3,4, bacterial species typically evolve phage resistance by the mutation or loss of phage receptors under laboratory conditions.sup.5,6. Here we report how this discrepancy may in part be explained by differences in the biotic complexity of in vitro and natural environments.sup.7,8. Specifically, by using the opportunistic pathogen Pseudomonas aeruginosa and its phage DMS3vir, we show that coexistence with other human pathogens amplifies the fitness trade-offs associated with the mutation of phage receptors, and therefore tips the balance in favour of the evolution of CRISPR-based resistance. We also demonstrate that this has important knock-on effects for the virulence of P. aeruginosa, which became attenuated only if the bacteria evolved surface-based resistance. Our data reveal that the biotic complexity of microbial communities in natural environments is an important driver of the evolution of CRISPR-Cas adaptive immunity, with key implications for bacterial fitness and virulence. The biotic environment can fundamentally alter bacteria and phage interactions, and influence the evolution of resistance mechanisms., Author(s): Ellinor O. Alseth [sup.1] , Elizabeth Pursey [sup.1] , Adela M. Luján [sup.2] , Isobel McLeod [sup.1] , Clare Rollie [sup.1] , Edze R. Westra [sup.1] Author Affiliations: (1) [...]

Spatial resource heterogeneity is expected to be a key driver for the evolution of diversity. However, direct empirical support for this prediction is limited to studies carried out in simplified laboratory environments. Here, we investigate how altering spatial heterogeneity of potting compost—by the addition of water and mixing—affects the evolutionary diversification of a bacterial species, Pseudomonas fluorescens, that is naturally found in the environment. There was a greater propensity of resource specialists to evolve in the unmanipulated compost, while more generalist phenotypes dominated the compost–water mix. Genomic data were consistent with these phenotypic findings. Competition experiments strongly suggest these results are due to diversifying selection as a result of resource heterogeneity, as opposed to other covariables. Overall, our findings corroborate theoretical and in vitro findings, but in semi‐natural, more realistic conditions. [ABSTRACT FROM AUTHOR]

DNA damage‐induced mutagenesis is a process governed by the SOS system that requires the activity of specialized DNA polymerases. These polymerases, which are devoid of proof‐reading activity, serve to increase the probability of survival under stressful conditions in exchange for an error‐prone DNA synthesis. As an opportunistic pathogen of humans, Pseudomonas aeruginosa employs adaptive responses that originally evolved for survival in many diverse and often stressful environmental conditions, where the action of error‐prone DNA polymerases may be crucial. In this study, we have investigated the role of the polymerases ImuB and ImuC in P. aeruginosa DNA‐damage induced mutagenesis. UV irradiation of imuB‐ and imuC‐deletion mutants showed that both genes contribute to UV‐induced mutagenesis in this bacterium. Furthermore, we confirmed that UV treatment significantly increase the expression levels of the imuB and imuC genes and that they are co‐transcribed as a single transcriptional unit under the control of LexA as part of the SOS regulon in P. aeruginosa. Environ. Mol. Mutagen. 2019. © 2019 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The article presents a study regarding the emergence of Quorum-sensing-deficient mutants at high frequency from a Pseudomonas aeruginosa mutS strain. To determine the factors that control the morphotypical variants mS2 emergence, the researchers performed a diversification experiment to confirm the reproducibility and to obtain a frequency of mS2 emergence.

Evolution can occur over ecological timescales, suggesting a potentially important role for rapid evolution in shaping community trait distributions. However, evidence of concordant eco-evolutionary dynamics often comes from in vitro studies of highly simplified communities, and measures of ecological and evolutionary dynamics are rarely directly comparable. Here, we quantified how ecological species sorting and rapid evolution simultaneously shape community trait distributions by tracking within- and between-species changes in a key trait in a complex bacterial community. We focused on the production of siderophores; bacteria use these costly secreted metabolites to scavenge poorly soluble iron and to detoxify environments polluted with toxic nonferrous metals. We found that responses to copper-imposed selection within and between species were ultimately the same-intermediate siderophore levels were favored-and occurred over similar timescales. Despite being a social trait, this level of siderophore production was selected regardless of whether species evolved in isolation or in a community context. Our study suggests that evolutionary selection can play a pivotal role in shaping community trait distributions within natural, highly complex, bacterial communities. Furthermore, trait evolution may not always be qualitatively affected by interactions with other community members., Competing Interests: Competing interests statement:The authors declare no competing interest.

Spatial resource heterogeneity is expected to be a key driver for the evolution of diversity. However, direct empirical support for this prediction is limited to studies carried out in simplified laboratory environments. Here, we investigate how altering spatial heterogeneity of potting compost-by the addition of water and mixing-affects the evolutionary diversification of a bacterial species, Pseudomonas fluorescens, that is naturally found in the environment. There was a greater propensity of resource specialists to evolve in the unmanipulated compost, while more generalist phenotypes dominated the compost-water mix. Genomic data were consistent with these phenotypic findings. Competition experiments strongly suggest these results are due to diversifying selection as a result of resource heterogeneity, as opposed to other covariables. Overall, our findings corroborate theoretical and in vitro findings, but in semi-natural, more realistic conditions., (© 2020 The Authors. Journal of Evolutionary Biology published by John Wiley & Sons Ltd on behalf of European Society for Evolutionary Biology.)