iTRAQ-based global proteomic analysis of Salmonella enterica serovar Typhimurium in response to desiccation, low water activity, and thermal treatment

In this study, the changes in the global proteome of Salmonella in response to desiccation and thermal treatment were investigated by using an iTRAQ multiplex technique. A Salmonella enterica serovar Typhimurium strain was dried, equilibrated at high (1.0) and low (0.11) water activity (a_w), and thermally treated at 75°C. The proteomes were characterized after every treatment. The proteomes of the different treatments differed in the expression of 175 proteins. On the basis of their proteomic expression profiles, the samples were clustered into two major groups, namely, "dry" samples and "moist" samples. The groups had different levels of proteins involved in DNA synthesis and transcription and in metabolic reactions, indicating that cells under either of the a_w conditions need to strictly control energy metabolism, the rate of replication, and protein synthesis. The proteins with higher expression levels in moist samples were flagellar proteins (FlgEFGH), membrane proteins, and export systems (SecF, SecD, the Bam complex), as well as stress response proteins, suggesting that rehydration can trigger stress responses in moist cells. Dry samples had higher levels of ribosomal proteins, indicating that ribosomal proteins might be important for additional regulation of the cellular response, even when the synthesis of proteins is slowed down. At both a_ws, no differences in protein expression were observed between the thermally treated samples and the nonheated cells. In conclusion, our study indicates that the preadaptation to a dry condition was linked to increased thermal tolerance, while reversion from a dry state to a moist state induced a significant change in protein expression, possibly linked to the observed loss of thermal tolerance.