Characterization of the propionate-induced protein Dps and its role in stress resistance in Salmonella Enteritidis

The gastrointestinal pathogen Salmonella enterica sv. Enteritidis (S. Enteritidis) encounters high concentrations of the short chain fatty acid propionate (PA) during its infection cycle. I have demonstrated that in S. Enteritidis, long term exposure to PA dramatically enhances resistance to other commonly encountered stressors, including extreme acidity and oxidative/nitrosative stresses. Using 2D gel electrophoresis, I revealed a distinct difference in the proteomes of PA adapted and unadapted S. Enteritidis. Furthermore, I was able to identify (by mass spectrometry) several proteins over expressed in PA adapted cultures, including the virulence-related protein Dps. (Quantitative real time-PCR analysis revealed upregulation of Dps at the transcriptional level as well.) Subsequent deletion mutant studies showed that S. Enteritidis Delta dps is highly susceptible to the aforementioned stressors and that Dps is crucial for defense against the Fenton-mediated common killing mechanism of bactericidal antibiotics-a mechanism manifested by hydroxyl radical production. The possible regulatory role of Dps in S. Enteritidis was also investigated here for the first time using in depth genetic analysis. Utilizing a microarray screen, I identified over 150 genes that are differentially expressed in cells lacking functional Dps protein and identified three stress-related regulatory elements whose expression is dependent upon Dps in starved S. Enteritidis. This work affirms the contribution of PA in the induction of stress resistance in S. Enteritidis. The crucial role of the PA-induced protein Dps in defense against common in vivo and ex vivo stressors, as well as its regulatory role in starved S. Enteritidis is also demonstrated. The relevance of this work is exemplified by the need for new and increasingly effective therapies to treat S. Enteritidis and other enteropathogens. Understanding the molecular mechanisms of PA-induced stress resistance will help develop methods to combat the phenomenon. Along the same lines, targeting Dps may represent a means to reduce stress resistance and increase the potency of certain therapies, particularly bactericidal antibiotics.