Commensal oral Rothia mucilaginosa produces enterobactin - a metal chelating siderophore

Abstract

Next-generation sequencing studies of saliva and dental plaque from subjects in both healthy and diseased states have identified bacteria belonging to the Rothia genus as ubiquitous members of the oral microbiota. To gain a deeper understanding of molecular mechanisms underlying the chemical ecology of this unexplored group, we applied a genome mining approach that targets functionally important biosynthetic gene clusters (BGCs). All 45 genomes that were mined, representing Rothia mucilaginosa, R. dentocariosa and R. aeria, harbored a catechol-siderophore-like BGC. To explore siderophore production further we grew the previously characterized R. mucilaginosa ATCC 25296 in liquid cultures, amended with glycerol, which led to the identification of the archetype siderophore enterobactin by using tandem Liquid Chromatography Mass Spectrometry (LC/MS/MS), High Performance Liquid Chromatography (HPLC), and Nuclear Magnetic Resonance (NMR) spectroscopy. Normally attributed to pathogenic gut bacteria, R. mucilaginosa is the first commensal oral bacterium found to produce enterobactin. Co-cultivation studies including R. mucilaginosa or purified enterobactin revealed that enterobactin reduced growth of certain strains of cariogenic Streptococcus mutans and pathogenic strains of Staphylococcus aureus. Commensal oral bacteria were either unaffected by, reduced in growth, or induced to grow adjacent to enterobactin producing R. mucilaginosa or the pure compound. Taken together with Rothias known capacity to ferment a variety of carbohydrates and amino acids, our findings of enterobactin production adds an additional level of explanation to R. mucilaginosas colonization success of the oral cavity. Enterobactin is the strongest Fe(III)-binding siderophore known, and its role in oral health requires further investigation. ImportanceThe communication language of the human oral microbiota is vastly underexplored. However, a few studies have shown that specialized small molecules encoded by BGCs have critical roles such as in colonization resistance against pathogens and quorum sensing. Here, by using a genome mining approach in combination with compound screening of growth cultures, we identified that the commensal oral community member mucilaginosa harbors a catecholate-siderophore BGC, which is responsible for the biosynthesis of enterobactin. The iron-scavenging role of enterobactin is known to have positive effects on the hosts iron pool and negative effects on host immune function, however its role in oral health remains unexplored. R. mucilaginosa was previously identified as an abundant community member in cystic fibrosis, where bacterial iron cycling plays a major role in virulence development. With respect to irons broad biological importance, iron-chelating enterobactin may explain R. mucilaginosas colonization success in both health and disease.