The influence of a glucosyltransferase, encoded by gtfP, on biofilm formation by Streptococcus sanguinis in a dual‐species model

Streptococcus sanguinis is an early colonizer of tooth surfaces and forms biofilms with other species of microorganisms. In vitro, S. sanguinis produces water-soluble glucans from sucrose and releases them into the culture supernatant; however, the role played by these glucans in biofilm formation is unclear. The present study examined both the effect of glucans on biofilm formation by S. sanguinis and the proportion of this bacterial species within the biofilms. Inactivation of the gtfP gene, annotated as glucosyltransferase in the S. sanguinis genome database, caused a marked reduction in the amount of water-soluble glucans in the culture supernatant, but not in the amount of water-insoluble glucans expressed on the bacterial cell surface. Scanning electron microscopy revealed that wild-type S. sanguinis, but not the gtfP-deficient mutant, produced large amounts of sticky material in the presence of 1% (w/v) sucrose. In addition, biofilm production by wild-type bacteria was greater than that by the mutant strain. By contrast, co-culture of mutant bacteria with Streptococcus mutans, S. sobrinus, S. oralis, S. gordonii, S. anginosus, or S. salivarius showed that inactivating the gtfP gene had little effect on the amount of biofilm produced. Furthermore, inactivating the gtfP gene did not greatly alter the proportion of S. sanguinis in the biofilms formed by the co-cultures. Thus, despite the role of S. sanguinis glucosyltransferase in formation of water-soluble glucans and biofilms in monoculture, the functional gene contributed little to biofilms in co-culture experiments.