Conservative Sex and the Benefits of Transformation in Streptococcus pneumoniae

PLoS Pathogens

Ian Donaldson¹  Daniel J. P. Engelmoer²  Daniel E. Rozen² 

[1] Department of Animal Ecology, Faculty of Earth and Life Sciences,Vrije Universiteit Amsterdam, Amsterdam, The Netherlands;Faculty of Life Science, University of Manchester, Manchester, United Kingdom

关键词: Pneumococcus;    Bacterial evolution;    Genome evolution;    Evolutionary adaptation;    Mutation;    Substitution mutation;    Microbial evolution;    Deletion mutation;   

DOI  :  10.1371/journal.ppat.1003758

学科分类：生物科学（综合）

来源: Public Library of Science

【 摘 要 】

Natural transformation has significant effects on bacterial genome evolution, but the evolutionary factors maintaining this mode of bacterial sex remain uncertain. Transformation is hypothesized to have both positive and negative evolutionary effects on bacteria. It can facilitate adaptation by combining beneficial mutations into a single individual, or reduce the mutational load by exposing deleterious alleles to natural selection. Alternatively, it may expose transformed cells to damaged or otherwise mutated environmental DNA and is energetically expensive. Here, we examine the long-term effects of transformation in the naturally competent species Streptococcus pneumoniae by evolving populations of wild-type and competence-deficient strains in chemostats for 1000 generations. Half of these populations were exposed to periodic mild stress to examine context-dependent benefits of transformation. We find that competence reduces fitness gain under benign conditions; however, these costs are reduced in the presence of periodic stress. Using whole genome re-sequencing, we show that competent populations fix fewer new mutations and that competence prevents the emergence of mutators. Our results show that during evolution in benign conditions competence helps maintain genome stability but is evolutionary costly; however, during periods of stress this same conservativism enables cells to retain fitness in the face of new mutations, showing for the first time that the benefits of transformation are context dependent.

【 授权许可】

CC BY