| Shigella flexneri is a pathogen of global health significance. Many aspects of S. flexneri have been well studied, but little research has thus far been directed toward understanding the role of the lipopolysaccharide (LPS) component of the outer membrane in the pathogenesis of S. flexneri. Recent work has demonstrated that the LPS of Gram-negative bacteria is a highly dynamic structure, and that the intricacies of LPS modification are idiosyncratic to each species. In this work, I have investigated the role genes of the poorly characterized shf-wabB-virK-msbB2 operon in S. flexneri, with a particular focus on virK and msbB2. Each gene product in this operon is either known or predicted to play a role in LPS synthesis or modification. Using biochemistry and molecular biology techniques, I have determined that transcription of the shf-wabB-virK-msbB2 operon is induced in a magnesium dependent manner by the PhoP magnesium starvation response regulator. The genome of S. flexneri is unusual in that it encodes two homologs of MsbB, a myristoyltransferase in the lipid A biosynthesis pathway. Work presented here offers a possible explanation for this duplication of myristoyltransferase-encoding genes. Under certain conditions within the host, possibly associated with magnesium starvation, induction of msbB2 is required for full virulence. I further determined that neither virK, msbB2 nor a double virK msbB2 mutant recapitulates the published effect of a virK::Tn10 insertion on the abundance of the S. flexneri virulence proteins IcsA and IcsP, suggesting that this locus is either not involved in modulating the levels of these proteins or that the mechanism of modulation is more complex than hypothesized in the published literature. |
