Environmental conditions modulate the expression of the sspA and sspB genes in Streptococcus gordonii

The SspA and SspB surface proteins of Streptococcus gordonii are multifunctional adhesins encoded by tandemly arranged genes. The transcriptional regulation of the sspA and sspB genes was investigated by generating chromosomal promoter- cat gene fusions and measuring CAT enzyme activity. The sspA promoter was found to be three-fold more active than the sspB promoter. In addition, sspA transcriptional activity increased throughout growth, whereas sspB activity decreased in stationary phase. Promoter activity of both sspA and sspB was regulated in response to temperature, pH and osmolarity; however the two promoters showed a different pattern of regulation. Changes in promoter activity were reflected in levels of surface protein and in adherence of S. gordonii to Porphyromonas gingivalis, a phenotypic property dependent on Ssp proteins. The results show that S. gordonii strain DL1 differentially regulates sspA and sspB transcription in response to oral environmental cues, suggesting that the SspA and SspB polypeptides may have distinct functional roles in cell adherence to oral substrates.