Biofilm formation and cell-cell signaling in Stenotrophomonas maltophilia

Stenotrophomonas maltophilia strain WR-C (WR-C), an opportunistic human pathogen, was isolated from the clogged zone of a mound-type septic system. Biofilm formation by this microorganism was postulated to be one of the mechanisms that cause clogging. Biofilm formation, surface translocation, and expression of virulence factors are critical for bacterial survival and pathogenesis and may be controlled by cell-cell communication systems mediated by small signal molecules. Little is known about the molecular mechanisms underlying these biological processes by WR-C. The aims of this project are to (1) identify genes that affect biofilm development, surface translocation, and virulence by transposon mutagenesis; (2) identify genes that synthesize and regulate the production of cell-cell communication signals; (3) investigate the potential interactions between genes identified in the first objective and cell-cell signaling. Elucidating these interactions will lead to development of more effective strategies in preventing bofilm formation, clogging of septic tank system, and infections caused by this microorganism.; The lipopolysaccharide/exopolysaccharide-coupled biosynthetic genes rmlA, rmlC, and xanB are necessary for biofilm formation and twitching motility. Mutations in rmlAC and xanB resulted in contrasting biofilm phenotypes on polystyrene and glass and differ in swimming motility.; In searching for potential regulatory systems in biofilm formation, a cell-cell communication system was investigated. S. maltophilia strain WR-C produces cis-Delta2-11-methyl-dodecenoic acid, a diffusible signal factor (DSF) and seven structural derivatives which require RpfF and RpfB for synthesis. The rpf/DSF system did not play role in biofilm formation. Our results demonstrated that DSF and its structural derivatives acted as wetting agents to create a path for a flagella-independent translocation by WR-C.; Acquisition of iron from the environment is important for bacterial growth as well as expression of some virulence genes. We identified a gene that encodes for a ferric citrate receptor, FecA, for transporting a heterologous siderophore, ferric citrate, from the environment into the bacterial periplasm. Our data suggest that the rpf/DSF cell-cell communication system plays a role in ferric citrate uptake. DSF is a signal in regulating fecA at the transcriptional level. Cyclic AMP receptor protein positively regulates the rpf/DSF system, possibly by directly binding regions upstream of rpfF.