Specific strains of bifidobacteria and lactobacilli are widely used as probiotics in different food products.  Often these viable bacterial cells are exposed to several stress conditions during industrial processes and keeping the bacterial cells viable remains as one of the biggest challenges in the use of probiotics.

In this study, the effect of heat shock on protein expression patterns of Bifidobacterium animalis subsp. lactis BB-12 and Lactobacillus rhamnosus GG (ATCC 5103) and their heat tolerant derivatives were examined. The bacteria were exposed to a heat shock treatment, B. animalis subsp. lactis BB-12 and its derivative at 50 °C and the L. rhamnosus GG and its derivative at 60 °C, for 2 and 8 hours. Protein synthesis before and after heat shock was examined using two-dimensional differential in gel electrophoresis coupled to matrix-assisted laser desorption/ionization -time of flight mass spectrometry and gene expression by reverse transcription quantitative PCR.

The analysis revealed that the regulation of seven proteins in both strains and their derivatives was modified during heat treatment. Chaperones, including classic heat-shock proteins, GroEL, GroES and DnaK, were upregulated and proteins involved in microbial metabolism were downregulated, excluding L-lactate dehydrogenase which was upregulated in L. rhamnosus GG strains. The comparison of wild type strains and the heat tolerant derivatives suggest that the acquisition of heat tolerance is due to an increased ability to induce chaperones.