Host-associated bacteria, whether pathogenic or beneficial, survive in an environment determined by the host and its associated microbial community. Host-associated bacteria use sensory networks to regulate the expression of secondary metabolites needed to establish and maintain host associations. Phenazines are secondary metabolites important in plant disease control by Pseudomonas aureofaciens and also in virulence by the human pathogen P. aeruginosa. In both bacteria, phenazines are regulated, in part, by a two-component quorum sensing (QS) system (e.g. phenazines are expressed only after bacterial populations reach a sufficient density or quorum). A novel two-component regulatory system (RpeA/RpeB) was identified in both bacteria that, when mutated, removed the requirement for QS and resulted in overproduction of phenazines. This finding is particularly interesting because mutations in the (RpeA/RpeB) system, which bypasses QS control, could severely limit the effectiveness of new antibiotic therapies aimed at reducing bacterial virulence and infection by interfering with QS regulation. This proposal outlines a systematic approach to characterize the novel negative two component regulatory system (RpeA/RpeB) and its linkage to nutritional sensing and QS. The linkage between these two sensory systems will be determined in both P. aureofaciens and P. aeruginosa using global gene expression analysis. The effect of loss of this two-component system on the ecological fitness of the bacteria when associated with hosts also will be determined. Understanding how loss of this two-component system bypasses QS regulation will provide insights into strategies for enhancing secondary metabolite production essential for successful plant disease control or for blocking secondary metabolite production required for human disease establishment. The multidisciplinary nature of the proposed research will i) provide training opportunities for undergraduate and graduate students and integration of information and technologies into lectures, laboratory exercises and existing undergraduate and graduate research opportunities, ii) outreach via the American Phytopathological Society Education Center.
