Phenotypic variation in the Pseudomonas fluorescens clinical strain MFN1032.

Pseudomonas fluorescens is a highly heterogeneous species and includes both avirulent strains and clinical strains involved in nosocomial infections. We previously demonstrated that clinical strain MFN1032 has hemolytic activity involving phospholipase C (PlcC) and biosurfactants (BSs), similar to that of the opportunistic pathogen Pseudomonas aeruginosa. When incubated under specific conditions, MFN1032 forms translucent phenotypic variant colonies defective in hemolysis, but not necessarily in PlcC. We analyzed eight variants of the original strain MFN1032 and found that they clustered into two groups. Mutations of genes encoding the two-component regulatory system GacS/GacA are responsible for phenotypic variation in the first group of variants. These group 1 variants did not produce secondary metabolites and had impaired biofilm formation. The second group was composed of hyperflagellated cells with enhanced biofilm capacity: they did not produce BSs and were thus unable to swarm. Artificial reduction of the intracellular level of c-di-GMP restored the ability to form biofilm to levels shown by the wild type, but production of BSs was still repressed. Phenotypic variation might increase the virulence potential of this strain.