Manganese uptake, mediated by SloABC and MntH, is essential for the fitness ofStreptococcus mutans

Early epidemiological studies implicated manganese (Mn) as a possible caries-promoting agent while laboratory studies have indicated that manganese stimulates the expression of virulence-related factors in the dental pathogenStreptococcus mutans. To better understand the importance of manganese homeostasis toS. mutanspathophysiology, we first used RNA sequencing to obtain the global transcriptional profile ofS. mutansUA159 grown under Mn-restricted conditions. Among the most highly expressed genes were the entiresloABCoperon, encoding a dual iron/manganese transporter, and an uncharacterized gene, hereinmntH, that codes for a protein bearing strong similarity to Nramp-type transporters. While inactivation ofsloC, which encodes the lipoprotein receptor of the SloABC system, ormntHalone had no major consequence on the overall fitness ofS. mutans, simultaneous inactivation ofsloCandmntH(ΔsloCΔmntH) impaired growth and survival under Mn-restricted conditions, including in human saliva or in the presence of calprotectin. Further, disruption of Mn transport resulted in diminished stress tolerance and reduced biofilm formation in the presence of sucrose. These phenotypes were markedly improved when cells were provided with excess Mn. Metal quantifications revealed that the single mutant strains contain similar intracellular levels of Mn as the parent strain, whereas Mn was nearly undetectable in the ΔsloCΔmntHstrain. Collectively, these results reveal that SloABC and MntH work independently and cooperatively to promote cell growth under Mn-restricted conditions, and that mauitanence of Mn homeostasis is essential for the expression of major virulence attributes inS. mutans.IMPORTANCEAs trace biometals such as manganese (Mn) are important for all forms of life, the ability to regulate biometals availability during infection is an essential trait of successful bacterial pathogens. Here, we showed that the caries pathogenStreptococcus mutansutilizes two Mn transport systems, namely SloABC and MntH, to acquire Mn from the environment, and that the ability to maintain the cellular levels of Mn is important for the manifestation of characteristics that associateS. mutanswith dental caries. Our results indicate that the development of strategies to depriveS. mutansof Mn hold promise in the combat against this important bacterial pathogen.