B-268. Proteomics of Salmonella typhimurium LT2 in Response to Cold Stress

J. D. Shah, D. Chen, J. R. Stevens, B. C. Weimer;
Utah State Univ., Logan, UT.

Salmonella, a Gram-negative bacterium, is an important food borne pathogen throughout the world that leads to substantial illness globally, as well as in the U.S. This organism evolved elaborate systems for sensing and responding to stress. Resistance to cold shock and persistent exposure is particularly important for food borne illness. We hypothesized that the cell has differential protein expression that enables survival during cold shock and cold persistence. Using protein expression profiling with LC/MS/MS, we determined the proteins expressed with and without pre-adaptation in Salmonella typhimurium LT2 (ΔrpoS). Proteome changes after pre-adaptation at 10°C for 30 min with subsequent exposure to 5°C were compared to the patterns observed in cold shock given at 5°C for 30 min and subsequent exposure at 5°C; and the control samples incubated at physiological temperature. All experiments were done using a repeated measures statistical model with R in Bioconductor. Statistically significant changes (q <= 0.5) were observed for 341 proteins. The dataset was dominated by proteins in COGs J (translation), K (transcription) and O (post translational modification, protein turnover and chaperones). We observed a significant decline in the expression of all proteins of COG J, as well as many proteins in other COGs, in the control (37°C after 240 h) compared to proteins in all COGs at 5°C after 240 h. Presumably, this caused the control culture to limit growth. However, the opposite result was observed in cold shock and cold persistence, which allowed the culture to continue growth with a small increase in the cell density. We found 304 unique proteins during cold shock. For example, CspB (cold shock protein B) was detected only in cold shocked samples. Many of the proteins in almost all COG categories were present in lower amounts in pre-adapted samples as compared to cold shocked samples. Thus, cells that were pre-adapted before cold storage, exhibit better cryotolerance. Salmonella survived at 5°C, for longer period of time, as compared to 37°C. Pre-adaptation to cold shock further increased the survival that was independent of rpoS.