The rbmBCDEF gene cluster modulates development of rugose colony morphology and biofilm formation in Vibrio cholerae

Vibrio cholerae, the causative agent of cholera, can undergo phenotypic variation generating rugose and smooth variants. The rugose variant forms corrugated colonies and well-developed biofilms and exhibits increased levels of resistance to several environmental stresses. Many of these phenotypes are mediated in part by increased expression of the vps genes, which are organized into vps-I and vps-II coding regions, separated by an intergenic region. In this study, we generated in-frame deletions of the five genes located in the vps intergenic region, termed rbmB to -F (rugosity and biofilm structure modulators B to F) in the rugose genetic background, and characterized the mutants for rugose colony development and biofillm formation. Deletion of rbmB, which encodes a protein with low sequence similarity to pollysaccharide hydrolases, resulted in an increase in colony corrugation and accumulation of exopollysaccharides relative to the rugose variant. RbmC and its homolog Bap1 are predicted to encode proteins with carbohydrate-binding domains. The colonies of the rbmC bap1 double deletion mutant and bap1 single deletion mutant exhibited a decrease in colony corrugation. Furthermore, the rbmC bap1 double deletion mutant was unable to form biofilms at the air-liquid interface after 2 days, while the biofilms formed on solid surfaces detached readily. Although the colony morphology of rbmDEF mutants was similar to that of the rugose variant, their biofilm structure and cell aggregation phenotypes were different than those of the rugose variant. Taken together, these results indicate that vps intergenic region genes encode proteins that are involved in biofilm matrix production and maintenance of biofilm structure and stability.