The PhoB regulatory system modulates biofilm formation and stress response in El Tor biotype Vibrio cholerae

The PhoBR regulatory system is required for the induction of multiple genes under conditions of phosphate limitation. Here, we examine the role of PhoB in biofilm formation and environmental stress response in Vibrio cholerae of the El Tor biotype. Deletion of phoB or hapR enhanced biofilm formation in a phosphate-limited medium. Planktonic and redispersed biofilm cells of the delta phoB mutant did not differ from wild type for the expression of HapR, suggesting that PhoB negatively affects biofilm formation through an HapR-independent pathway. The delta phoB mutant exhibited elevated expression of exopolysaccharide genes vpsA and vpsL compared with the wild type. Deletion of hapR enhanced the expression of the positive regulator vpsT, but had no effect on the expression of vpsR. In contrast, deletion of phoB enhanced the expression of the positive regulator vpsR, but had no effect on the expression of hapR and vpsT. The delta phoB mutant was more sensitive to hydrogen peroxide compared with the wild type and with an isogenic delta rpoS mutant. Conversely, the delta phoB mutant was more resistant to acidic conditions and high osmolarity compared with the wild type and with an isogenic delta rpoS mutant. Taken together, our data suggest that phosphate limitation induces V. cholerae to adopt a free-swimming life style in which PhoB modulates environmental stress response in a manner that differs from the general stress response regulator RpoS.