The Role of in Histophilus somni Virulence and Biofilm Formation.

-Ribosylhomocysteinase (LuxS) is required for the synthesis of the autoinducer-2 (AI-2) quorum-sensing signaling molecule in many Gram-negative bacteria. The bovine (and ovine) opportunistic pathogen contains and forms a biofilm containing an exopolysaccharide (EPS) in the matrix. Since biofilm formation is regulated by quorum sensing in many bacteria, the roles of in virulence and biofilm formation were investigated. Although culture supernatants from were ineffective at inducing bioluminescence in the reporter strain BB170, complemented the biosynthesis of AI-2 in the -deficient strain DH5α. strain 2336 was inactivated by transposon mutagenesis. RNA expression profiles revealed that many genes were significantly differentially expressed in the mutant compared to that in the wild-type, whether the bacteria were grown planktonically or in a biofilm. Furthermore, the mutant had a truncated and asialylated lipooligosaccharide (LOS) and was substantially more serum sensitive than the wild-type. Not surprisingly, the mutant was attenuated in a mouse model for virulence, and some of the altered phenotypes were partially restored after the mutation was complemented with a functional However, no major differences were observed between the wild-type and the mutant in regard to outer membrane protein profiles, biofilm formation, EPS production, or intracellular survival. These results indicate that plays a role in virulence in the context of LOS biosynthesis but not biofilm formation or other phenotypic properties examined.