Streptococcus mutans regulates ubiquitin modification of Candida albicans in the bacterial-fungal interaction

The ecological interplay between Streptococcus mutans and Candida albicans within dental plaque biofilms is an important factor driving pathogenesis of dental caries. This study aimed to investigate S. mutans regulation of C. albicans growth and virulence through extracellular membrane vesicles (EMVs) and modulation of ubiquitination, a key protein post-translational modification. We established a transwell co-culture model to enable "contact-independent" interactions between S. mutans and C. albicans. S. mutans EMVs were found to directly associate with C. albicans cells and promote biofilm formation and growth. Quantitative ubiquitination profiling revealed S. mutans dramatically alters the ubiquitination landscape in C. albicans. We identified 10,661 ubiquitination sites across the C. albicans proteome and their enrichment in pathways related to translation, metabolism, and stress adaptation. Co-culture with S. mutans led to upregulation of ubiquitination on 398 proteins involved in sugar catabolism and generation of reducing power. S. mutans upregulated ubiquitination of superoxide dismutase-3 of C. albicans, inducing its degradation and heightened reactive oxygen species levels, and concomitantly stimulated C. albicans growth. Our findings elucidate EMVs and ubiquitination modulation as key mechanisms governing the S. mutans-C. albicans interplay and provide new insights into the promotion of a cariogenic oral biofilm environment. This study significantly advances understanding of the complex molecular interactions underlying dental plaque dysbiosis and caries pathogenesis.