Starch and Salivary α-Amylase induce expression of Streptococcus gordonii AbpA

Objective: Streptococcus gordonii is a prevalent oral commensal streptococcus involved in dental plaque biofilm formation. S. gordonii binds salivary amylase through surface exposed amylase-binding protein A (AbpA). Previous studies suggest AbpA as a biofilm determinant of S. gordonii. AbpA has been shown to affect S. gordonii growth with starch as a primary nutrition source when bacteria were pretreated with salivary amylase. We hypothesized that expression of AbpA could be influenced by the presence of starch and amylase in the bacterial milieu.

Method: Culture supernatants were analyzed for the AbpA protein using a ligand-binding assay when S. gordonii was grown in chemically defined medium supplemented with 1% starch, 0.5 mg/ml amylase, starch and amylase together, and various linear maltooligosaccharides. Expression of the abpA gene was also tested by relative qRT-PCR.

Result: AbpA was undetectable in the supernatants of cultures containing starch alone or amylase alone. However, in the presence of both starch and amylase the amount of AbpA protein was notably increased. Transcription analysis of abpA revealed a significant increase in abpA gene expression (p < 0.05) after 40 minutes incubation in chemically defined medium supplemented with starch and amylase. Similar results were obtained in cultures in the presence of several short chain maltooligosaccharides.

Conclusion: These results suggest that the products of starch hydrolysis from the action of salivary α-amylase play a regulatory role in AbpA expression by S. gordonii.