Identification of saliva-regulated genes of Streptococcus gordonii DL1 by differential display using random arbitrarily primed PCR.

Attachment of Streptococcus gordonii to the acquired pellicle of the tooth surface involves specific interactions between bacterial adhesins and adsorbed salivary components. To study saliva-regulated gene expression in S. gordonii, we used random arbitrarily primed PCR (RAP-PCR). Bacteria were incubated in either brain heart infusion medium or saliva. Total RNA from both conditions was purified and RAP fingerprinted and then PCR amplified with an arbitrary primer. The differentially displayed DNA fragments were cloned, sequenced, and analyzed using the BLAST search network service. Three DNA products were up-regulated. One was identified as that of the sspA and -B genes, which encode the salivary agglutinin glycoprotein-binding proteins SspA and SspB of S. gordonii; another had 79% identity with the Lactococcus lactis clpE gene, encoding a member of the Clp protease family; and the third product showed no significant homology to known genes. Five down-regulated genes were identified which encode proteins involved in bacterial metabolism. We have shown, for the first time, direct induction of sspA and -B in S. gordonii by human saliva.