Bicarbonate and unsaturated fatty acids enhance capsular polysaccharide synthesis gene expression in oral...

We recently reported on the capsular polysaccharide (CP) synthesis (cps) genes of the oral streptococci, Streptococcus anginosus. In this study, we investigate the effects of carbon dioxide (CO₂), bicarbonate (HCO₃^-) and unsaturated fatty acids (UFAs) on CP synthesis of S. anginosus. We found that CP production increased when bacteria were exposed to high concentrations of CO₂. This increase was similarly observed in the presence of sodium bicarbonate (NaHCO₃₎ under atmospheric condition. Since ectopic expression of carbonic anhydrase, which converts CO₂ to HCO₃^-, eliminated the requirement for CO₂ in CP production and growth of S. anginosus lacking this enzyme, it seemed that HCO₃^- is an essential factor for CP production. Furthermore, UFAs also stimulated the CP production. Promoter-reporter assay and quantitative reverse transcription polymerase chain reaction (RT-qPCR) analysis confirmed that stimulation of CP production occurs at the transcription level. The results of the promoter assays suggest that the expression and stimulation of cps genes by HCO₃^- or UFAs require the cpsA gene, which is located in the first position of the cps operon. With respect to the relationship between HCO₃^-and UFAs, HCO₃^- may stimulate UFA synthesis pathway at transcription level. Therefore, it is possible that UFAs are definitive signals for the CP production in S. anginosus.