A single point mutation is sufficient to drive syp-dependent biofilm formation and promote colonization by Vibrio fischeri strain ES114

Biofilms promote attachment of bacteria to each other and to surfaces. For Vibrio fischeri, biofilm formation dependent on the symbiosis polysaccharide (syp) locus promotes colonization of its symbiotic host. Multiple two-component regulators, including the central sensor kinase SypF and nitric oxide/HnoX-controlled sensor kinase HahK, induce SYP production. Here, we identify a C/A change in the hnoX-hahK promoter region that dramatically increases its transcription and syp-dependent biofilm formation. We further determined that HahK signals through both SypF and the luminescence regulator LuxU to promote biofilm formation and host colonization. Our findings thus provide insight into the regulatory crossover between two major pathways, quorum sensing-controlled luminescence and biofilm formation, in V. fischeri.