FliI Role in Flagellar Assembly of Salmonella ΔfliI Mutant Strain Determines Motility and Biofilm Formation

Biofilms formation is a serious problem in both clinical and environmental settings. Various gram negative bacteria exhibit biofilm formation mediated by flagellum-mediated motility. Type III protein secretion systems of several gram-negative bacterial pathogens use flagella to invade foreign surfaces, host tissues and substrates. Flagellar biosynthesis and function in Salmonella typhimurium is regulated by >50 genes. Bioinformatics analysis of flagellar assembly in S. typhimurium identified several conserved structural elements. In this study, FliI a flagellar protein required for flagellar assembly and involved in a specialized protein export pathway was cloned and overexpressed. Delta fliI mutant Salmonella strain was used to transform fliI overproducing plasmid pTrc99A by electroporation. Using vital dyes (Alexaflour 488), visualization of motility was observed in wild type, Delta fliI mutant and fliI complemented strain which was further assessed by biofilm formation ability. Swimming, swarming motility alongwith significantly reduced biofilm formation was observed in Delta fliI mutant compared to wild type and fliI complemented strains. This study will extend initial evidence that FliI plays important role in flagellar export system and flagellum-mediated rotation is critical for swimming, swarming motility and biofilm formation. The flagellar basal body has an ancient and evolutionarily conserved macromolecular assembly and known architecture making it an ideal drug target. The knowledge obtained will help to elucidate mechanism and design principles necessary to understand protein secretion systems.