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Effects of oxygen on virulence traits of Streptococcus mutans.

ABSTRACT: Oxygen profoundly affects the composition of oral biofilms. Recently, we showed that exposure of Streptococcus mutans to oxygen strongly inhibits biofilm formation and alters cell surface biogenesis. To begin to dissect the underlying mechanisms by which oxygen affects known virulence traits of S. mutans, transcription profiling was used to show that roughly 5% of the genes of this organism are differentially expressed in response to aeration. Among the most profoundly upregulated genes were autolysis-related genes and those that encode bacteriocins, the ClpB protease chaperone subunit, pyruvate dehydrogenase, the tricarboxylic acid cycle enzymes, NADH oxidase enzymes, and certain carbohydrate transporters and catabolic pathways. Consistent with our observation that the ability of S. mutans to form biofilms was severely impaired by oxygen exposure, transcription of the gtfB gene, which encodes one of the primary enzymes involved in the production of water-insoluble, adhesive glucan exopolysaccharides, was down-regulated in cells growing aerobically. Further investigation revealed that transcription of gtfB, but not gtfC, was responsive to oxygen and that aeration causes major changes in the amount and degree of cell association of the Gtf enzymes. Moreover, inactivation of the VicK sensor kinase affected the expression and localization the GtfB and GtfC enzymes. This study provides novel insights into the complex transcriptional and posttranscriptional regulatory networks used by S. mutans to modulate virulence gene expression and exopolysaccharide production in response to changes in oxygen availability.

SUBMITTER: Ahn SJ

PROVIDER: S-EPMC2168947 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Streptococcus mutans is a common constituent of oral biofilms and a primary etiologic agent of human dental caries. The bacteria associated with dental caries have potent abilities to produce organic acids from dietary carbohydrates and to grow and metabolize in acidic conditions. By contrast, many commensal bacteria produce ammonia through the arginine deiminase system (ADS), which moderates the pH of oral biofilms. Arginine metabolism by the ADS is a significant deterrent to the initiation and progression of dental caries. In this study, we observed how exogenously provided l-arginine affects the growth, the virulence properties, and the tolerance of environmental stresses of S. mutans Supplementation with 1.5% arginine (final concentration) had an inhibitory effect on the growth of S. mutans in complex and chemically defined media, particularly when cells were exposed to acid or oxidative stress. The genes encoding virulence factors required for attachment/accumulation (gtfB and spaP), bacteriocins (nlmA, nlmB, nlmD, and cipB), and the sigma factor required for competence development (comX) were downregulated during growth with 1.5% arginine. Deep sequencing of RNA (RNA-Seq) comparing the transcriptomes of S. mutans growing in chemically defined media with and without 1.5% arginine revealed differential expression of genes encoding ATP-binding cassette transporters, metal transporters, and constituents required for survival, metabolism, and biofilm formation. Therefore, the mechanisms of action by which arginine inhibits dental caries include direct adverse effects on multiple virulence-related properties of the most common human dental caries pathogen.IMPORTANCE Metabolism of the amino acid arginine by the arginine deiminase system (ADS) of certain oral bacteria raises the pH of dental plaque and provides a selective advantage to health-associated bacteria, thereby protecting the host from dental caries (cavities). Here, we examine the effects of arginine on the cavity-causing bacterium Streptococcus mutans We find that arginine negatively impacts the growth, the pathogenic potential, and the tolerance of environmental stresses in a way that is likely to compromise the ability of S. mutans to cause disease. Using genetic and genomic techniques, multiple mechanisms by which arginine exerts its influence on virulence-related properties of S. mutans are discovered. This report demonstrates that a primary mechanism of action by which arginine inhibits the initiation and progression of dental caries may be by reducing the pathogenic potential of S. mutans.

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Effects of oxygen on virulence traits of Streptococcus mutans.

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