Abstract
Biofilm formation of Vibrio vulnificus is initiated by adherence of flagellated cells to surfaces, and then flagellum-driven motility is not necessary during biofilm maturation. Once matured biofilms are constructed, cells become flagellated and swim to disperse from biofilms. As a consequence, timely regulations of the flagellar components’ expression are crucial to complete a biofilm life-cycle. In this study, we demonstrated that flagellins’ production is regulated in a biofilm stage-specific manner, via activities of a protease DegQ and a chaperone FlaJ. Among four flagellin subunits for V. vulnificus filament, FlaC had the highest affinities to hook-associated proteins, and is critical for maturating flagellum, showed the least susceptibility to DegQ due to the presence of methionine residues in its DegQ-sensitive domains, ND1 and CD0. Therefore, differential regulation by DegQ and FlaJ controls the cytoplasmic stability of flagellins, which further determines the motility-dependent, stage-specific development of biofilms.
Highlights
An opportunistic foodborne pathogen, Vibrio vulnificus, causes high risk of fatal septicemia or gastroenteritis in humans with immunocompromised states, chronic liver disease, hemochromatosis, or diabetes[1]
The initial adherence and final dispersal stages of biofilm formation are highly facilitated if bacteria are able to swim by virtue of cellular motility mediated by bacterial flagellum[8,9]
Western blots showed that the species, which facilitates the export of flagellins to extracellular milieu and prevents their polymerization in the cytoplasm[17]
Summary
Vibrio vulnificus, causes high risk of fatal septicemia or gastroenteritis in humans with immunocompromised states, chronic liver disease, hemochromatosis, or diabetes[1]. The abilities to perform specific activities endowing this pathogen with metabolic and behavioral advantages when interacting with hosts are considered as one of the pathogen’s virulence factors[2,3,4]. One of such abilities is the capacity to efficiently form biofilms, which has been found to be important in the pathogenicity of various bacteria including V. vulnificus[5,6]. The initial adherence and final dispersal stages of biofilm formation are highly facilitated if bacteria are able to swim by virtue of cellular motility mediated by bacterial flagellum[8,9]. Flagellar expression and assembly should be dynamically and tightly regulated in response to biofilm stages during the entire period of the biofilm-forming process
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