Streptococcus Mutans Gcrr Inhibits The Morphological Transition Of Candida Albicans

The extracellular polysaccharides (EPSs) of Streptococcus mutans (S. mutans) and the hyphae of Candida albicans (C.albicans) promote each other, significantly enhancing the cariogenicity of symbiotic biofilms. The response regulator GcrR in S. mutans could inhibit the synthesis of EPSs. The purpose of this project is to investigate the regulatory role of S. mutans GcrR in the morphological transition of C. albicans and cariogenicity of symbiotic biofilm. The biofilm quantity was assessed using the crystal violet assay, and lactic acid production was measured through the lactate dehydrogenase (LDH) assay. The expression of genes involved in the hyphal formation pathway, namely the Ras-cAMP-PKA pathway, was detected using RT-qPCR. Protein expression was analyzed by Western Blot. Animal experiments were conducted to investigate the regulatory role of GcrR in the cariogenicity of symbiotic biofilms. We found the morphological transformation of C. albicans from yeast to hyphal form was inhibited by GcrR. The overexpression of GcrR suppressed dual-species biofilm formation. The response regulator GcrR of S. mutans can reduce the biomass of symbiotic biofilms, decrease lactic acid production, and lower the expression of genes in the Ras-cAMP-PKA pathway. The expression of Ndt80, Hwp1, Als3, Sap1 in C. albicans were downregulated and PKA protein was downregulated. Furthermore, we found GcrR attenuated the virulence of dual-species biofilms. This study suggested that GcrR in S. mutans plays a critical role in modulating the cariogenic potential of bacterial-fungal biofilms.