Patrice Bracquart

A 16 kDa protein family overexpressed by Streptococcus thermophilus PB18 in acid environments

The one- and two-dimensional protein patterns of Streptococcus thermophilus PB18 in the exponential and stationary phases of growth were analysed. One-dimensional SDS-PAGE showed that a 16 kDa protein was overexpressed in stationary phase as well as 2 h after an acid shock, and that it was not expressed when the bacteria reached the stationary phase in medium with limiting lactose concentrations (5 or 10 g l-1), in which the pH (5.5) was not as acid as in control cultures (pH 4.7, lactose 20 g l-1). The results support the idea that this protein is expressed in response to the acidic environment and not in response to the growth phase. Two-dimensional PAGE showed that nine proteins were expressed only during the exponential phase and ten others only during the stationary phase. The 16 kDa band seen in one-dimensional SDS-PAGE corresponded to a 16 kDa protein family observed on two-dimensional SDS-PAGE/IEF gels, whose expression was increased 8.5-fold when the extracellular pH reached a critical value below 5.0. The N-terminal sequences of proteins from two spots on the two-dimensional gels (members of the 16 kDa family) were determined and found to be identical. The physiological role of this protein family has not yet been elucidated.

Expression of a New Cold Shock Protein of 21.5 kDa and of the Major Cold Shock Protein by Streptococcus thermophilus After Cold Shock

Abstract.Streptococcus thermophilus is widely used in food fermentations; it commonly suffers diverse stress challenges during manufacturing. This study investigated the cold shock response of S. thermophilus when the cell culture temperature shifted from 42°C to 15°C or 20°C. The growth of cells was affected more drastically after cold shock at 15°C than at 20°C. The generation time was increased by a factor of 19 when the temperature was lowered from 42° to 20°C, and by a factor of 72 after a cold shock at 15°C. The two-dimensional electrophoretic protein patterns of S. thermophilus under cold shock conditions were compared with the reference protein pattern when cells were grown at optimal temperature. Two proteins of 21.5 and 7.5 kDa synthesized in response to cold shock were characterized. N-terminal sequencing and sequence homology searches have shown that the 7.5-kDa protein belonged to the family of the major cold shock proteins, while no homology was found for the new cold shock protein of 21.5 kDa.

Reference map of soluble proteins from Streptococcus thermophilus by two-dimensional electrophoresis

Streptococcus thermophilus is a lactic acid bacterium widely used for the production of fermented dairy products. The two‐dimensional electrophoresis (2‐DE) protein profile was obtained from three independent analyses of 2‐DE gels of soluble proteins of the strain PB18. About 270 spots were detected by silver staining and the average molecular weight and isoelectric point of each protein spot were calculated to be 41 600 and 5.2, respectively. Twelve proteins were purified by chromatographic techniques because their concentration was too low for direct sequencing from blots. Eleven were located in the PB18 2‐DE profile after silver staining. These preliminary results contribute to the setting up of a two‐dimensional image (or reference map) of the proteins from S. thermophilus in order to identify and compare strains of various origin or to follow metabolic process such as stress. Bidimensional autoradiographs of two strains (PB18 and ST105) of S. thermophilus grown in exponential phase at 42°C with [35S]methionine were compared with an image analysis system. Among the eleven located proteins in the 2‐DE silver‐stained profile, nine were found in PB18 and eight in ST105 autoradiographs. One protein was specific to PB18. The eight proteins could play the role of internal 2‐D PAGE markers of pI and Mr for S. thermophilus.

Uptake of glutamic acid by Streptococcus salivarius subsp. thermophilus CNRZ 302

Glutamic acid uptake in Streptococcus salivarius subsp. thermophilus was energy dependent, the source of energy and adaptation to sugar being important to efficiency of uptake. The disaccharides, lactose and sucrose, stimulated uptake, but cells grown in glucose were more active. Optimum temperature was approximately 40 degrees C and pH approximately 7.0. NaCl was strongly inhibitory to the uptake of glutamic acid although not to that of isoleucine. High specificity existed because only L-aspartic acid was inhibitory.

Carbon dioxide fixation by cells and cell-free extracts of Streptococcus thermophilus

The present study describes fixation into cellular amino acids of 14 C from NaH 14 CO 3 by growing cells and cell-free extracts of Str. thermophilus, and the enzyme system responsible for fixation. In addition, a comparison was made of the bicarbonate uptake and carboxylase activity of two morphological variants.