Candida albicans receptors for Streptococcus gordonii in mixed species communities

Streptococcus bacteria are initial colonizers of oral cavity surfaces and are integral components of complex biofilm communities. Candida albicans is a fungus carried by 20-60% of human populations, colonizing mucosal and dental surfaces in conjunction with many species of bacteria. Streptococcus gordonii is one of several species of oral bacteria that attaches to C. albicans and influences development of Candida biofilms. Objectives: to identify C. albicans cell surface receptors for S. gordonii. Methods: C. albicans mutants, defective in glycosylation and generated by targeted mutagenesis, were analyzed by fluorescence microscopy for interactions with S. gordonii DL1 in planktonic or biofilm conditions. Antigenic receptors present within the C. albicans cell wall were identified by Western immunoblot analysis. Results: S. gordonii cells adhered to all morphological forms of C. albicans, but mainly to hyphae. Glycosylation-deficient C. albicans mutants in MNN4, OCH1 or MNT2 showed no apparent differences in their binding interactions with S. gordonii. However, mutation in MNT1, encoding a mannosyltransferase involved in O-linked glycosylation, led to abrogation of adherence of S. gordonii to C. albicans in planktonic phase. All C. albicans mutants showed various deficiencies in biofilm formation, affecting biomass and architecture. However, the inhibitory effect of MNT1 mutation on S. gordonii binding to C. albicans was less pronounced in mixed species biofilms. Glycosylation defects were associated with differences in antigenic composition of the C. albicans cell wall. Conclusions: These results show that cell wall biogenesis and glycosylation defects in C. albicans modulate their interactions with streptococci in mixed-species communities. Supported by NIDCR (5R01DE016690).