González-Márquez H, Perrin C, Bracquart P, Guimont C, Linden G. A 16 kDa protein family overexpressed by Streptococcus thermophilus PB18 in acid environments.
MICROBIOLOGY (READING, ENGLAND) 1997;
143 ( Pt 5):1587-1594. [PMID:
9168610 DOI:
10.1099/00221287-143-5-1587]
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Abstract
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.
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