Adaptive response to cold temperatures and characterization of cspA in Salmonella typhimurium LT2

Salmonella typhimurium is a major foodborne microbial pathogen which primarily contaminates poultry products causing salmonellosis in humans. S. typhimurium LT2 cultures, when transferred from 37 degrees C to 5 degrees C or 10 degrees C, showed an initial lag period in growth with an approximate generation time of 10-25 h. Western blot assay using E. coli CS7.4 antibody and analysis of radiolabeled total cellular proteins from S. typhimurium cultures after exposure to 10 degrees C or 5 degrees C showed elevated expression of a major cold shock protein, CS7.4. Identification of a decreased level of CS7.4 at 37 degrees C suggests that the expression of this protein may require a large temperature downshift. Putative regulatory protein binding segment on the 5'-untranslated region referred as 'Fragment 7' in S. typhimurium exhibited a 90.6% and a 56.25% nucleotide sequence identity when compared with the Fragment 7 of E. coli and S. enteritidis, respectively. The differences in the nucleotide sequence within the Fragment 7 between S. typhimurium and S. enteritidis may explain the differential expression of CspA at 37 degrees C. The nucleotide sequence of the open reading frame of S. typhimurium cspA gene showed a single base difference at 816 bp position from a G to a C which altered the amino acid residue from a glycine to an alanine. In addition to CspA, an elevated expression of a 105 kDa, and decreased expression of 6 proteins were evidenced when cultures of S. typhimurium were exposed to 10 degrees C or 5 degrees C. Differential expression of the CspA and other proteins in S. typhimurium following exposure to cold temperatures suggest that adaptation and continued growth and survival at cold temperatures in this pathogen may be aided by these cold-responsive proteins.