σ54-Dependent Response to Nitrogen Limitation and Virulence in Burkholderia cenocepacia Strain H111

Members of the genus Burkholderia are versatile bacteria capable of colonizing highly diverse environmental niches. In this study, we investigated the global response of the opportunistic pathogen Burkholderia cenocepacia H111 to nitrogen limitation at the transcript and protein expression levels. In addition to a classical response to nitrogen starvation, including the activation of glutamine synthetase, PII proteins, and the two-component regulatory system NtrBC, B. cenocepacia H111 also upregulated polyhydroxybutyrate (PHB) accumulation and exopolysaccharide (EPS) production in response to nitrogen shortage. A search for consensus sequences in promoter regions of nitrogen-responsive genes identified a σ54 consensus sequence. The mapping of the σ54 regulon as well as the characterization of a σ54 mutant suggests an important role of σ54 not only in control of nitrogen metabolism but also in the virulence of this organism.