Streptococcus gordonii glucosyltransferase promotes biofilm interactions with Candida albicans

Abstract

BackgroundCandida albicans co-aggregates with Streptococcus gordonii to form biofilms and their interactions in mucosal biofilms may lead to pathogenic synergy. Although the functions of glucosyltransferases (Gtf) of Mutans streptococci have been well characterized, the biological roles of these enzymes in commensal oral streptococci, such as S. gordonii, in oral biofilm communities are less clear.ObjectiveThe objective of this work was to explore the role of GtfG, the single Gtf enzyme of S. gordonii, in biofilm interactions with C. albicans.DesignBiofilms were grown under salivary flow in flow cells in vitro, or under static conditions in 96 well plates. A panel of isogenic S. gordonii CH1 gtfG mutants and complemented strains were co-inoculated with C. albicans strain SC5314 to form mixed biofilms. Biofilm accretion and binding interactions between the two organisms were tested. Biofilms were quantified using confocal microscopy or the crystal violet assay.ResultsThe presence of GtfG enhanced dual biofilm accretion, and sucrose supplementation further augmented dual biofilm formation, pointing to a role of newly synthesized glucans. GtfG also promoted binding to C. albicans preformed biofilms. Soluble α-1,6-glucans played a role in these interactions since: 1) a strain producing only soluble glucans (CH107) formed robust dual biofilms under conditions of salivary flow; and 2) the dual biofilm was susceptible to enzymatic breakdown by dextranase which specifically degrades soluble α-1,6-glucans.ConclusionOur work identified a novel molecular mechanism for C. albicans and S. gordonii biofilm interactions, mediated by GtfG. This protein promotes early biofilm binding of S. gordonii to C. albicans which leads to increased accretion of streptococcal cells in mixed biofilms. We also showed that soluble glucans, with α-1,6-linkages, promoted inter-generic adhesive interactions.

Symbiotic Relationship between Streptococcus mutans and Candida albicans Synergizes Virulence of Plaque Biofilms In Vivo

“…A similar mechanism may also enhance C. albicans and S. gordonii biofilm formation in vitro (73). Altogether, we demonstrate the importance of Gtfs in mediating the cooperativity between C. albicans and S. mutans.…”

Streptococcus gordonii comCDE (competence) operon modulates biofilm formation with Candida albicans

“…sucrose) or trisaccharides and transfer the appropriate monosaccharide to form a-linked polymers. Since we utilized a monosaccharide as carbon and energy source in our studies, no glucans would be produced (Ricker et al, 2014). It has been suggested that release of eDNA by streptococcal cells during early stages of biofilm formation could involve a specialized active release mechanism (Xu & Kreth, 2013) via lysis-independent membrane vesicles (Liao et al, 2014).…”

Biology of Oral Streptococci

“…A Gtf-negative mutant of S. gordonii showed diminished persistence on the teeth of sucrose fed rats, although initial colonization was not affected (79). In addition, deletion of the single gtf gene of S. gordonii , gtfG , impacted its ability to form mixed biofilms with Candida albicans (80). Streptococcus sanguinis also produces water soluble glucans from sucrose through a Gtf enzyme called GtfP.…”