The landscape of the bacteriome and mycobiome at different stages of root caries and the cross-kingdom interactions of the core species

Background The unbalanced oral microbiome is considered the key pathogenic agent for root caries, the most common tooth disease in elderly individuals; however, the bacteriome and mycobiome at different stages of root caries, especially from the same individual, are not clear. Results In this study, superficial and deep root caries plaques from thirty patients with different levels of root caries simultaneously in the oral cavity were collected, whereas sound root surface plaques from their healthy teeth served as caries-free controls. The full-length sequencing results of 16S and 18S rDNA analysis via the self-controlled method on the basis of the same patients indicated that the different stages of root caries represented different microbiota, including Streptococcus mutans and Actinomyces sp. HMT448 in superficial root caries and Prevotella sp. in deep root caries. Candida albicans was the most abundant fungal species from all the plaques, while it showed strong interspecies interactions with S. mutans and Actinomyces sp . Their interactions were closely associated with the different stages of root caries. An in vitro model further confirmed that C. albicans was able to increase the growth, biofilm formation and cariogenicity of S. mutans and A. viscosus through the activation of the arginine biosynthesis pathway, indicating its key roles in the development of root caries. Conclusion Our study revealed the first landscape of the microbiome from different stages of root caries and indicated that targeting the interactions of core species may be a practical way to prevent and treat clinical root caries.