The oral cavity is a highly diverse microbial environment, consisting of >2000 bacterial, archaeal, and fungal species most of which have not been functionally characterized. Numerous studies have identified that oral Rothia mucilaginosa, a Gram-positive oral commensal Actinobacteria, is highly abundant in saliva and dental plaque in global human populations, however, its ecological role is unknown. We identified that R. mucilaginosa produced the catechol siderophore enterobactin, the strongest iron-chelating molecule known. We also identified the enterobactin biosynthetic gene cluster (ent-BGC) in global Rothia genomes, which suggests that enterobactin is crucial in Rothia ecology. The purified enterobactin compound impacted growth differentially when amended to cultures of other oral bacterial species. It boosted the growth of commensal Streptococcus salivarius while it reduced the growth of some strains of pathogenic S. mutans. The overarching goal of this study is to determine the role of R. mucilaginosa produced enterobactin in interactions with both the oral microbiota and human oral epithelial cells representing the oral mucosa. We propose an interdisciplinary research approach with two specific aims:
Aim 1 : Characterization of molecular and ecological responses of oral bacteria to R. mucilaginosa produced enterobactin. The activities of enterobactin will be characterized both in highly diverse oral in vitro grown biofilms, and in bacterial monocultures. The capacity to import enterobactin by different bacterial community members will be revealed by amending growth cultures with fluorescently rhodamine- labeled enterobactin, fluorescence-activated cell sorting, and confocal microscopy. Multi-OMICS sequencing will be conducted to characterize functional changes both in biofilm communities as well as in single and dual- species cultures, specifically targeting genes encoding transport proteins and release mechanisms of enterobactin.
Aim 2 : Determine the impact of enterobactin on oral mucosal sentinel cells. Co-cultivation systems including both 2D and 3D models of human oral epithelial cells will be applied to study interactions with the oral microbiota and enterobactin. Outcomes of the interactions will be characterized by using a multipronged approach including a comparative gene transcription approach and a gene reporter system that reveals ROS activation in host cells. Production of extracellular pro- and anti-inflammatory cytokines in cell medium relation to enterobactin and oral bacteria will also be addressed to elucidate interactions of importance. The proposed study provides a unique opportunity to expand our knowledge on enterobactin functional role in the oral microbiota, and in interactions with human oral epithelial cells, which is severely lacking. A deeper knowledge of the role of iron scavenging siderophores in the oral cavity will likely bring about a shift in the research field of oral microbial ecology and shine a new light on the importance of iron metabolism in oral health.
Oral Rothia bacteria are frequently identified in saliva and dental plaque in global human microbiome studies, however, their ecological role in the oral cavity is yet unexplored. We have found that Rothia genomes harbor a catecholate-like siderophore biosynthetic gene cluster (ent-BGC) that encodes enterobactin, the strongest siderophore known thus far. This research will explore the ecological role of R. mucilaginosa produced enterobactin, both in interactions with other bacterial community members and with human oral mucosal cells.
