molecular mechanisms of bacterial stress response and pathogenesis

We want to elucidate and understand the relationship between bacterial stress response mechanisms and bacterial pathogenesis. As a model system, we are studying the stress response mechanisms and pathogenesis of Pseudomonas aeruginosa, an important opportunistic bacterial pathogen that is found almost ubiquitously in nature. P. aeruginosa is a highly adaptable pathogen that causes both acute and chronic infections with high mortality rates. Our ultimate goal is to elucidate the stress response mechanisms of this bacterium in order to develop new therapeutic strategies.

Elucidate the physiological function of tmRNA in P. aeruginosaRibosome recycling plays an important role in bioenergetics of all organisms including bacterial pathogens.  The transfer-messenger RNA (tmRNA), encoded by the ssrA gene, is a unique bacterial RNA with a mRNA-like domain (MLD) and a tRNA-like domain (TLD).  The tmRNA catalyzes trans-translation mediated rescuing of stalled ribosomes (both Nonstop and No-Go pathways) and degradation of incomplete polypeptides.  Although tmRNA has been extensively studied at the biochemical level, very little research has been performed on the physiological function or genetic regulation of this unique molecule. Our initial characterization suggests that tmRNA has a global, but subtle effect, on P. aeruginosa stress response and virulence factor production.  The ssrA mutant is hypersensitive to osmotic and heat stress and produces decreased amounts of several P. aeruginosa virulence factors including elastase. The subtle effect is likely due to a redundant function first characterized in Escherichia coli as ArfA (alternative ribosome rescue factor A). We recently identified a putative homologue of ArfA that suppresses the tmRNA mutant phenotype. Our inability to construct a double mutant suggests the importance of ribosome recycling in P. aeruginosa

Another aspect of tmRNA biology that had not been previously addressed is the genetic regulation of the cognate gene, ssrA.  Our recent efforts have revealed a complex regulatory circuit between trans-translation, the general stress response regulator RpoS, cell to cell communication systems LasRI and RhlRI, a global regulator Vfr, sigma factor RpoN, and the major intracellular signaling molecule c-di-GMP.  Uncovering this complex regulatory circuit promises to be very interesting.  We are in the process of taking a proteomic approach to identify proteins whose translation requires tmRNA and/or the ArfA homologue in P. aeruginosa.

Elucidate the role of alternative sigma factors RpoS and AlgT(U) in the anaerobic physiology of P. aeruginosa: In many environments, including in the lungs of Cystic Fibrosis (CF) patients, P. aeruginosa survives and persists via anaerobic metabolism. We want to uncover the contributions of two important alternative sigma factors, RpoS and AlgT, in the ability of P. aeruginosa to survive in anaerobic environment.  Although both of these sigma factors have been characterized for their physiological function during aerobiosis, their role in anaerobic physiology has yet to be determined.

Elucidate the molecular mechanisms of adaptation to the CF lung environment: During establishment of chronic infections in the CF lung, P. aeruginosa acquires various mutations that facilitate its adaptation to that environment. We are interested in understanding the basic metabolic alterations that aid the bacterial survival and persistence in the CF lung.  To achive this goal, we collaborate with Dr. Silo-Suh of Mercer University School of Medicine who has demonstrated alteration(s) in P. aeruginosa metabolism to better utilize available nutrients in the CF lung.  We believe one of these alterations results in the entry of P. aeruginosa into the "persister state" that makes the bacterium more recalcitrant to antibiotics.  We are interested in uncovering the molecular mechanisms that result in the "persister state" in order to better combat P. aeruginosa infections.

  Sang-Jin Suh © Auburn University 2012. All rights reserved