Dual transcriptome of Streptococcus mutans and Candida albicans interplay in biofilms

Objective To assess the interactions between Streptococcus mutans and Candida albicans during cariogenic biofilm formation. Methods The S. mutans and C. albicans duo-species biofilms were formed in 1% sucrose to mimic the high caries risk challenges. The biofilm structure was assessed using two-photon laser confocal microscopy. The transcriptome of 48h-biofilms was assessed by RNA-Seq. The expression of S. mutans and C. albicans virulence genes was examined via real-time reverse transcription-polymerase chain reaction. Results The morphogenesis of C. albicans-S. mutans duo-species biofilms was significantly altered when comparing to S. mutans or C. albicans single-species biofilm. Duo-species biofilms exhibited unique expression profile with a large number of differentially expressed genes (DEGs), including a higher expression of S. mutans atpD (acid-adaptive), C. albicans CHT2 (fungal cell wall chitin remodeling), and C. albicans SOD3 (cytotoxic oxygen radical destroying) (p < 0.05). KEGG pathway analyses further revealed that the majority of the up-regulated DEGs are related to microbial metabolism. Furthermore, the expressions of S. mutans and C. albicans key virulence genes (gtfB, gtfC, gtfD, ECE1, HWP1, ERG4, CHT2) were associated with sugar availability-related and time-related dynamics. Conclusion Cross-kingdom interactions impact S. mutans-C. albicans biofilm formations and dynamic expressions of virulence genes.