Role of Glucosyltransferase B in Interactions of Candida albicans with Streptococcus mutans and with an Experimental Pellicle on Hydroxyapatite Surfaces

Abstract

Candida albicans and mutans streptococci are frequently detected in dental plaque biofilms from toddlers afflicted with early childhood caries. Glucosyltransferases (Gtfs) secreted by Streptococcus mutans bind to saliva-coated apatite (sHA) and to bacterial surfaces, synthesizing exopolymers in situ, which promote cell clustering and adherence to tooth enamel. We investigated the potential role Gtfs may play in mediating the interactions between C. albicans SC5314 and S. mutans UA159, both with each other and with the sHA surface. GtfB adhered effectively to the C. albicans yeast cell surface in an enzymatically active form, as determined by scintillation spectroscopy and fluorescence imaging. The glucans formed on the yeast cell surface were more susceptible to dextranase than those synthesized in solution or on sHA and bacterial cell surfaces (P < 0.05), indicating an elevated ␣-1,6-linked glucose content. Fluorescence imaging revealed that larger numbers of S. mutans cells bound to C. albicans cells with glucans present on their surface than to yeast cells without surface glucans (uncoated). The glucans formed in situ also enhanced C. albicans interactions with sHA, as determined by a novel single-cell micromechanical method. Furthermore, the presence of glucan-coated yeast cells significantly increased the accumulation of S. mutans on the sHA surface (versus S. mutans incubated alone or mixed with uncoated C. albicans; P < 0.05). These data reveal a novel cross-kingdom interaction that is mediated by bacterial GtfB, which readily attaches to the yeast cell surface. Surface-bound GtfB promotes the formation of a glucan-rich matrix in situ and may enhance the accumulation of S. mutans on the tooth enamel surface, thereby modulating the development of virulent biofilms.

Cross-feeding and interkingdom communication in dual-species biofilms of Streptococcus mutans and Candida albicans

“…The half-life of most proteins is in the range of 24 h, whereas that of mRNA is around 5 min (Moran et al, 2013). Excreted glucosyltransferases have been shown to be active on Candida surfaces (Gregoire et al, 2011) and thus are likely to have been operating although their transcription was rapidly downregulated.…”

“…A tight co-aggregation between C. albicans and streptococci has been observed (Jenkinson et al, 1990;Metwalli et al, 2013) and could be owing to specific adhesins similar to those found in S. gordonii (Silverman et al, 2010) or to a glucan layer formed on the Candida cells by the glucosyltransferase B (GtfB) exoenzyme (Gregoire et al, 2011). Interaction between C. albicans and streptococci can contribute to enhanced biofilm formation.…”

Fungi at the Scene of the Crime: Innocent Bystanders or Accomplices in Oral Infections?

“…The exoenzyme glucosyltransferases (Gtfs) are predominantly responsible for the production of α-glucans from dietary sugar, and it is known that these extracellular polysaccharides are the key mediators of these dual-species cariogenic biofilms. In the absence of sucrose, C. albicans demonstrates a weak co-aggregation with S. mutans; however, secreted Gtfs from S. mutans establishes a co-aggregation between these two organisms, binding with high affinity [61,62]. The increased ECM biovolume within the dual-species biofilm actively contributes to the pathogenicity of disease, with increased levels of infection and carious lesions observed in vivo [60].…”

Glycosyltransferase-mediated Sweet Modification in Oral Streptococci

“…In addition to synthesizing different glucans, GtfBCD also have distinct roles in the building of dental plaque. GtfC is absorbed to enamel, GtfB binds to bacteria or fungi and enhances adhesion to plaque, and GtfD catalyzes the biosynthesis of a soluble polysaccharide, which acts as a primer for GtfB (Bowen and Koo 2011;Gregoire et al 2011). Since the diverse glycosyl linkage products are determined by limited differences in the conserved catalytic domain, the distinct roles in the formation of dental plaque can be attributed to low homology among putative glucan binding modules found in each GTF.…”