Regulation of a quorum sensing system by stationary phase sigma factor RpoS and their co-regulation of target genes in Burkholderia pseudomallei

Burkholderia pseudomallei is the causative agent of a fatal disease, melioidosis. However, the mechanisms of pathogenesis and genes involved in its virulence are not understood. In the current study, whether stationary phase and stress response sigma factor RpoS and BpsI-mediated quorum sensing (QS) system co-regulate its target genes was investigated. Positive regulation of RpoS on bpsI expression and autoinducer production in stationary phase, but not on fliC and ppk expression, was observed. In contrast, expression of rpoS was not affected by deletion of bpsI. The present results also indicate that production of extracellular protease and siderophore, two QS-controlled exo products, is regulated via RpoS supporting the previously known inhibitory role of QS on those two factors. Proteomic analysis revealed that expression of 74 protein spots representing 60 genes is controlled by QS. Of those, 45 genes are co-regulated by both RpoS and QS, and regulation of genes involved in transcription and translation is favored by QS. Taken together, our findings indicate major target genes expression in stationary phase that is influenced by hierarchical control of RpoS over QS. We propose that this regulation may play an important role in the pathogenicity of B. pseudomallei.