Expression of DnaK, HtpG, GroEL and Tf chaperones and the corresponding encoding genes during growth of Salmonella Thompson in presence of thymol alone or in combination with salt and cold stress

The expression of four different proteins (DnaK, HtpG, GroEL and Trigger factor Tf) commonly involved in stress response, and the corresponding encoding genes, was studied in Salmonella enterica serovar Thompson. The growth of S. Thompson MCV1 was monitored in the presence of sublethal concentrations of thymol (0.1%) alone or in combination with salt stress (NaCl 0.7%) or cold stress (15 °C). Salmonella growth was also monitored in the presence of salt stress (NaCl 0.7%) and also in the presence of cold stress (15 °C) alone. During the different growth phases (lag, exponential and early stationary) the expression of dnaK, htpG, groEL and tig genes was studied by quantitative reverse transcription-PCR (qRT-PCR), while the regulation of the corresponding proteins was monitored by 2D-PAGE analysis. Thymol increased the expression of chaperone proteins in all cases except when salt stress was also present. The cold stress increased the levels of expression of the chaperones and this was further enhanced by the presence of thymol. Each stress alone induced a variation in the chaperone regulation and the combination of different stresses together did not always lead to a cumulative response. Our evidence suggests that the response to thymol, salt and cold involves the regulation of all the studied chaperones. This process starts in the lag phase but the chaperones keep working in the further growth phases in order to help Salmonella cells to face the adverse conditions. Our study suggests that adaptation to stress conditions related to food storage takes place through a global response where DnaK, HtpG, GroEL and TF are only part of the protein network that gives support to the adaptation.