Different molecular routes to mat formation in environmental Pseudomonas isolates

Many bacterial species secrete polymers and form mat-like structures. These mats can be useful (e.g., in bioremediation), or problematic (e.g., in hospital settings). The molecular bases of mat formation have been investigated in a number of species, including various pseudomonads. One well-characterized example is the plant symbiont Pseudomonas fluorescens SBW25. Laboratory populations of SBW25 readily acquire mutations in one of three regulatory loci (wsp, aws, mws), leading to the over-production of the secondary messenger cyclic-di-GMP. In turn, this activates the production of a cellulose-like polymer, the major structural component of the SBW25 mat. Here, we dissect and compare the molecular mechanisms of mat formation in two further plant-associated pseudomonads: P. simiae PICF7 and P. fluorescens A506. We find that both PICF7 and A506 are capable of mat formation in the laboratory, by distinct molecular routes. Mat formation in PICF7 involves mutations in wsp, aws, or mws that serve to activate the production of Pel (as opposed to cellulose in SBW25). Contrastingly, A506 mat formation does not require mutation of wsp, aws, or mws (despite their retention in the genome). Instead, our results are consistent with a readily reversible, non-mutational route to polymer production and mat formation in A506. Overall, our results demonstrate the presence of multiple molecular routes to mat formation among environmental, plant-associated pseudomonads.

The presented work has since been published: Mukherjee A, Dechow-Seligmann G, Gallie J. 2022. Molecular Microbiology 117(2): 394-410.