Swarming motility growth favours the emergence of a subpopulation of Pseudomonas aeruginosa quorum-sensing mutants

Environ Microbiol. 2020 Jul;22(7):2892-2906. doi: 10.1111/1462-2920.15042. Epub 2020 Jun 15.

Abstract

Pseudomonas aeruginosa exploits several types of motility behaviours to colonize diverse environments. One of these is swarming motility, a coordinated group movement on a semi-solid surface. This bacterium needs to express a functional flagellum and produce rhamnolipids to display this type of social motility. A ΔhptB mutant, a gene part of the Gac/Rsm signalling pathway, produces rhamnolipids and expresses a functional flagellum but has an important swarming defect. Experimental-directed evolution was performed on this mutant under swarming conditions to obtain compensatory mutations and thus identify genes responsible for its deficient swarming phenotype. Unexpectedly, a gain-of-function subpopulation emerged from this evolution with mutations in lasR, which codes for a key quorum-sensing transcriptional regulator. Furthermore, we found that lasR- mutants even emerge at high frequencies in the wild-type strain when using the same experimental evolution strategy. The resulting evolved population, largely composed of LasR-defective mutants, is fitter than the original strain in swarming motility. We also established that lasR- mutants have a growth advantage under swarming conditions when compared with wild-type. Our results demonstrate that a social phenotype, that is, swarming motility, favours the emergence of mutants deficient in a quorum-sensing regulatory pathway to the benefit of the whole population.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism
  • Gene Expression Regulation, Bacterial
  • Glycolipids
  • Mutation
  • Phenotype
  • Pseudomonas aeruginosa / genetics*
  • Pseudomonas aeruginosa / growth & development*
  • Quorum Sensing / genetics*
  • Signal Transduction
  • Trans-Activators / genetics

Substances

  • Bacterial Proteins
  • Glycolipids
  • LasR protein, Pseudomonas aeruginosa
  • Trans-Activators
  • rhamnolipid