Host-selected mutations converging on a global regulator drive an adaptive leap towards symbiosis in bacteria

Elife. 2017 Apr 27:6:e24414. doi: 10.7554/eLife.24414.


Host immune and physical barriers protect against pathogens but also impede the establishment of essential symbiotic partnerships. To reveal mechanisms by which beneficial organisms adapt to circumvent host defenses, we experimentally evolved ecologically distinct bioluminescent Vibrio fischeri by colonization and growth within the light organs of the squid Euprymna scolopes. Serial squid passaging of bacteria produced eight distinct mutations in the binK sensor kinase gene, which conferred an exceptional selective advantage that could be demonstrated through both empirical and theoretical analysis. Squid-adaptive binK alleles promoted colonization and immune evasion that were mediated by cell-associated matrices including symbiotic polysaccharide (Syp) and cellulose. binK variation also altered quorum sensing, raising the threshold for luminescence induction. Preexisting coordinated regulation of symbiosis traits by BinK presented an efficient solution where altered BinK function was the key to unlock multiple colonization barriers. These results identify a genetic basis for microbial adaptability and underscore the importance of hosts as selective agents that shape emergent symbiont populations.

Keywords: Euprymna scolopes; Vibrio fischeri; evolutionary biology; experimental evolution; genomics; infectious disease; microbiology.

MeSH terms

  • Adaptation, Biological
  • Aliivibrio fischeri / enzymology
  • Aliivibrio fischeri / genetics*
  • Aliivibrio fischeri / physiology*
  • Animal Structures / microbiology
  • Animals
  • Decapodiformes / microbiology*
  • Decapodiformes / physiology
  • Gene Expression Regulation, Bacterial
  • Immune Evasion
  • Mutation*
  • Protein Kinases / genetics*
  • Quorum Sensing
  • Selection, Genetic*
  • Symbiosis*


  • Protein Kinases

Grants and funding

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.