Coincidental loss of bacterial virulence in multi-enemy microbial communities

PLoS One. 2014 Nov 3;9(11):e111871. doi: 10.1371/journal.pone.0111871. eCollection 2014.

Abstract

The coincidental virulence evolution hypothesis suggests that outside-host selection, such as predation, parasitism and resource competition can indirectly affect the virulence of environmentally-growing bacterial pathogens. While there are some examples of coincidental environmental selection for virulence, it is also possible that the resource acquisition and enemy defence is selecting against it. To test these ideas we conducted an evolutionary experiment by exposing the opportunistic pathogen bacterium Serratia marcescens to the particle-feeding ciliate Tetrahymena thermophila, the surface-feeding amoeba Acanthamoeba castellanii, and the lytic bacteriophage Semad11, in all possible combinations in a simulated pond water environment. After 8 weeks the virulence of the 384 evolved clones were quantified with fruit fly Drosophila melanogaster oral infection model, and several other life-history traits were measured. We found that in comparison to ancestor bacteria, evolutionary treatments reduced the virulence in most of the treatments, but this reduction was not clearly related to any changes in other life-history traits. This suggests that virulence traits do not evolve in close relation with these life-history traits, or that different traits might link to virulence in different selective environments, for example via resource allocation trade-offs.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acanthamoeba castellanii* / genetics
  • Acanthamoeba castellanii* / pathogenicity
  • Bacteriophages* / genetics
  • Bacteriophages* / pathogenicity
  • Evolution, Molecular*
  • Microbial Consortia / genetics*
  • Serratia marcescens* / genetics
  • Serratia marcescens* / pathogenicity
  • Virulence Factors / genetics*

Substances

  • Virulence Factors

Grants and funding

This work was supported by the Finnish Academy to JL, 1130724 and 1255572 (URL: www.aka.fi), which had a role in study design, data collection and analysis, decision to publish and preparation of the manuscript. This work was also supported by the CoE in Biological Interactions to JM, 252411 (URL: https://www.jyu.fi/bioenv/en/divisions/coe-interactions), which had a role in study design, data collection and analysis, decision to publish and preparation of the manuscript. This work was also supported by the Finnish Cultural Foundation to JZ (URL: www.skr.fi), which had a role in data collection and analysis, decision to publish and preparation of the manuscript. This work was also supported by the Ellen and Artturi Nyyssö nen Foundation to JZ (URL: www.eans.fi), which had a role in study design, data collection and analysis.