Candida Albicans Adhesins Modulate Interactions With Streptococcus Mutans in Biofilms

Objectives: The fungal pathogen Candida albicans and the bacterial pathogen Streptococcus mutans are known to synergistically interact with each other in the oral cavity. For example, glucosyltransferase B (GtfB), secreted by S. mutans, can bind to the C. albicans cell surface, promoting dual-species biofilm formation. However, the fungal factors mediating interactions with S. mutans are currently unknown. The C. albicans adhesins Als1, Als3 and Hwp1 are key players in C. albicans single-species biofilm formation, but their roles, if any, in interacting with S. mutans are unknown. Here, we investigated the roles of the C. albicans cell wall adhesins Als1, Als3 and Hwp1 on the formation of dual-species biofilms formed with S. mutans.
Methods: We assessed the abilities of the C. albicans wildtype, als1/als1; als3/als3; als1/als1 als3/als3; and hwp1/hwp1 mutant strains to form dual-species biofilms with S. mutans by measuring biofilm CFUs, biofilm optical densities, XTT reduction during biofilm formation, and biofilm dry weights.
Results: Altogether, our results revealed that C. albicans Als3 is the major player in interacting with S. mutans. Interestingly, the presence of S. mutans in a dual-species biofilm with the C. albicans als3/als3 mutant strain partially complemented the biofilm defect of the als3/als3 mutant strain. However, the als1/als1 als3/als3 double mutant strain was unable to form a dual-species biofilm with S. mutans, indicating that Als1 and Als3 are together critical for interacting with S. mutans.
Conclusions: Overall, our data suggest complementary adhesin functions for C. albicans Als1 and Als3 in modulating interactions with S. mutans.