MOLECULAR MECHANISMS OF PATHOGENIC BACTERIA INTERACTIONS WITH PLANT SURFACES AND ENVIRONMENTAL MATRICES
Location: Environmental Microbial and Food Safety Laboratory
Title: Proteomic pleiotropy of OpgGH, an operon necessary for efficient growth of Salmonella enterica serovar Typhimurium under low-osmotic conditions
Submitted to: Journal of Proteome Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 23, 2012
Publication Date: January 23, 2012
Citation: Cooper, B., Chen, R., Garrett, W.M., Chang, C., Tucker, M.L., Bhagwat, A.A. 2012. Proteomic pleiotropy of OpgGH, an operon necessary for efficient growth of Salmonella enterica serovar Typhimurium under low-osmotic conditions. Journal of Proteome Research. 11:1720-1727.
Interpretive Summary: The ability of Salmonella spp. to survive in irrigation or wash waters enables them to enter the food chain. Vegetable wash waters and irrigation waters have been implicated in recent outbreaks of infections caused by Salmonella spp. In this study we analyzed the entire protein components of Salmonella during its growth in low osmotic media similar to irrigation waters. The study identified several cellular proteins which were essential for optimal growth of Salmonella under low osmotic conditions. Characterizing human pathogens grown under conditions mimicking fresh produce handling and washing practices will advance our knowledge of how enteric human pathogens enter the food chain. The research will benefit the fresh produce industry, as well as increasing the microbial food safety of the American food supply.
Salmonella enterica, a bacterial, food-borne pathogen of humans, can contaminate raw fruits and vegetables. Causing much public concern, the bacteria can survive in water used to wash produce. The ability to survive the low-osmolarity of the wash waters is attributed to the OpgGH operon that leads to the production of osmotically-regulated periplasmic glucans. Mutants lacking OpgGH grow slowly under low-osmotic conditions, but there are also unexpected traits such as abnormal flagellar motility and reduced virulence in mice. To get a broader understanding of these pleiotropic effects, we examined the proteome of these mutants using high-throughput mass spectrometry. We identified approximately one third of the proteins encoded by the genome and used label-free spectral counting to determine the relative amounts of proteins in wild-type cultures and mutants. Mutants had reduced amounts of proteins required for osmotic sensing, flagellar motility, purine and pyrimidine metabolism, oxidative energy production and protein translation. By contrast, mutants had greater amounts of ABC transporters needed to balance cellular osmolarity. Hence, the pleiotropic effects of OpgGH reach across the proteome and the data are consistent with the mutant phenotypes. A model that explains reduced virulence is proposed.