Altered protein expression of Streptococcus oralis cultured at low pH revealed by two-dimensional gel electrophoresis

Streptococcus oralis is the predominant aciduric nonmutans streptococcus is olated from the human dentition, but the role of this organism in the initi ation and progression of dental caries has yet to be established. To identi fy proteins that are differentially expressed by S. oralis growing under co nditions of low pH, soluble cellular proteins extracted from bacteria grown in batch culture at pH 5.2 or 7.0 were analyzed by two-dimensional (2-D) g el electrophoresis. Thirty-nine proteins had altered expression at low pH; these were excised, digested with trypsin using an in-gel protocol, and fur ther analyzed by peptide mass fingerprinting using matrix-assisted laser de sorption ionization mass spectrometry. The resulting fingerprints were comp ared with the genomic database for Streptococcus pneumoniae, an organism th at is phylogenetically closely related to S. oralis, and putative functions for the majority of these proteins were determined on the basis of functio nal homology. Twenty-eight proteins were up-regulated following growth at p H 5.2; these included enzymes of the glycolytic pathway (glyceraldehyde-3-p hosphate dehydrogenase and lactate dehydrogenase), the polypeptide chains c omprising ATP synthase, and proteins that are considered to play a role in the general stress response of bacteria, including the 60-kDa chaperone, Hs p33, and superoxide dismutase, and three distinct ABC transporters. These d ata identify, for the first time, gene products that may be important in th e survival and proliferation of nonmutans aciduric S. oralis under conditio ns of low pH that are likely to be encountered by this organism in vivo.