A Novel dnaJ Family Gene, sflA , Encodes an Inhibitor of Flagellation in Marine Vibrio Species

Abstract

ABSTRACT The marine bacterium Vibrio alginolyticus has a single polar flagellum. Formation of that flagellum is regulated positively and negatively by FlhF and by FlhG, respectively. The Δ flhF mutant makes no flagellum, whereas the Δ flhFG double-deletion mutant usually lacks a flagellum. However, the Δ flhFG mutant occasionally reverts to become motile by forming peritrichous flagella. We have isolated a suppressor pseudorevertant from the Δ flhFG strain (Δ flhFG -sup). The suppressor strain forms peritrichous flagella in the majority of cells. We identified candidate suppressor mutations by comparing the genome sequence of the parental strain, VIO5, with the genome sequences of the suppressor strains. Two mutations were mapped to a gene, named sflA ( s uppressor of Δ fl hFG ), at the VEA003730 locus of the Vibrio sp. strain EX25 genome. This gene is specific for Vibrio species and is predicted to encode a transmembrane protein with a DnaJ domain. When the wild-type gene was introduced into the suppressor strain, motility was impaired. Introducing a mutant version of the sflA gene into the Δ flhFG strain conferred the suppressor phenotype. Thus, we conclude that loss of the sflA gene is responsible for the suppressor phenotype and that the wild-type SflA protein plays a role in preventing polar-type flagella from forming on the lateral cell wall.