Comparative study of the protein composition of three strains of Streptococcus thermophilus grown either in M17 medium or in milk

摘要

Streptococcus thermophilus is a lactic acid bacterium widely used for manufacturing milk products. The protein composition of three strains of S. thermophilus grown in either M17 medium or milk was investigated. These conditions were chosen on the basis of the observed technological differences between these strains. Protein extracts prepared from cells harvested at the same pH (5.2 +/- 0.1), were analyzed by two-dimensional gel electrophoresis. Gel comparison revealed qualitative and quantitative differences between the two growth media and between the strains. Some proteins with quantitative variation were partially identified. The most significant medium-related differences concerned the number of spots detected and the heat shock protein (GroEL, HSP70) levels which were higher in milk than in M17. On the contrary, the levels of enzymes ( proton translocating ATPase, pyruvate kinase, tributyrin esterase, phospho-glycerate kinase, glyceraldehyde-3-phosphate dehydrogenase, fructose diphosphate aldolase, superoxide dismutase) and of a putative penicillin binding protein were lower in milk than in M17. Strain-related differences were accentuated in milk for heat shock proteins, tributryrine esterase and dinitrogenase reductase.