서강대학교

초록/요약

Vibrio vulnificus, a human pathogen causing fatal septicemia, exhibits an ability to form biofilms and its formation, especially initial attachment and dispersion, is dependent on cellular motility derived from the rotation of a polar flagellum. Thus, the timely and strict regulation of flagellum or flagellum-related protein synthesis during biofilm formation is important to V. vulnificus. The filament of its flagellum is composed of multiple flagellin proteins, FlaA, B, C, and D. The open reading frames putatively encoding flagellin-homologous proteins (FHPs) are also present in V. vulnificus genomes. Although these FHPs do not participate in the filament assembly, they are abundantly transcribed and excreted through the flagellar-specific secretion system. The secreted FHPs are incorporated in the extracellular polymeric matrix (EPM) and strengthen the biofilm structure during maturation by directly interacting with exopolysaccharides produced by V. vulnificus. The synthesis of flagellum is regulated in transcriptional and posttranslational levels. FlaJ (or FliS) is a well-known protein acting as a molecular chaperone for the secretion of flagellin. In preliminary experiment, cytoplasmic flagellins are not detected in the V. vulnificus flaJ strain. This suggested that the unidentified regulatory mechanism in expression of flagellin exists at the posttranslational level. Assessment of motility and cytoplasmic flagellin levels using various protease mutants revealed that the protease DegQ is involved in the biofilm formation. The degQ mutant shows an increased initial attachment and dispersion in biofilm formation due to enhanced motility. Furthermore, an in vitro proteolysis assay using DegQ and flagellins shows that flagellins are proteolyzed differentially by DegQ protease. This suggested that the determinant of flagellin level during biofilm formation is DegQ protease by differentially regulating flagellin stability in V. vulnificus. These results suggested that flagellin-associated proteins, including FHPs and DegQ, have crucial roles in specific biofilm formation stages, these are FHPs in maturation and DegQ in initial attachment and dispersion. Taken together, regulation of flagellin-associated proteins during the formation of biofilm successfully leads to proceeding biofilm formation of V. vulnificus.