Glycerol metabolism contributes to competition by oral streptococci through production of hydrogen peroxide

• Published in: Journal of bacteriology 2024-09, Vol.206 (9), p.e0022724
• Main Authors: Taylor, Zachary A, Chen, Ping, Noeparvar, Payam, Pham, Danniel N, Walker, Alejandro R, Kitten, Todd, Zeng, Lin
• Format: Article
• Language: English
• Subjects: Assaying; Bacteria; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacteriology; Biofilms; Biofilms - growth & development; Carbohydrate metabolism; Carbohydrates; Catabolism; Catabolite repression; Competition; Dental caries; Gene deletion; Gene Expression Regulation, Bacterial; Genetic analysis; Glucose metabolism; Glycerol; Glycerol - metabolism; Homeostasis; Humans; Hydrogen peroxide; Hydrogen Peroxide - metabolism; Hydrogen production; Metabolic pathways; Metabolism; Microorganisms; Mouth - microbiology; Oral cavity; Pyruvate oxidase; Pyruvic acid; Research Article; Streptococcus infections; Streptococcus mutans; Streptococcus mutans - genetics; Streptococcus mutans - growth & development; Streptococcus mutans - metabolism; Streptococcus sanguinis; Streptococcus sanguis - genetics; Streptococcus sanguis - metabolism; Transcription
• ISSN: 0021-9193; 1098-5530; 1098-5530
• DOI: 10.1128/jb.00227-24

As a biological byproduct from both humans and microbes, glycerol's contribution to microbial homeostasis in the oral cavity remains understudied. In this study, we examined glycerol metabolism by a commensal associated with oral health. Genetic mutants of glucose-PTS enzyme II ( ), glycerol metabolism ( and pathways), and transcriptional regulators were characterized with regard to glycerol catabolism, growth, production of hydrogen peroxide (H O ), transcription, and competition with . Biochemical assays identified the pathway as a novel source for H O production by that is independent of pyruvate oxidase (SpxB). Genetic analysis indicated that the pathway requires glycerol and a transcriptional regulator, GlpR, for expression and is negatively regulated by PTS, but not the catabolite control protein, CcpA. Conversely, deletion of either or increased the expression of and a second, H O -non-producing glycerol metabolic pathway ( ), indicative of a mode of regulation consistent with conventional carbon catabolite repression (CCR). In a plate-based antagonism assay and competition assays performed with planktonic and biofilm-grown cells, glycerol greatly benefited the competitive fitness of against . The pathway appears to be conserved in several commensal streptococci and actively expressed in caries-free plaque samples. Our study suggests that glycerol metabolism plays a more significant role in the ecology of the oral cavity than previously understood. Commensal streptococci, though not able to use glycerol as a sole carbohydrate source for growth, benefit from the catabolism of glycerol through production of both ATP and H O . Glycerol is an abundant carbohydrate in the oral cavity. However, little is understood regarding the metabolism of glycerol by commensal streptococci, some of the most abundant oral bacteria. This was in part because most streptococci cannot grow on glycerol as the sole carbon source. In this study, we show that , a commensal associated with dental health, can degrade glycerol for persistence and competition through two pathways, one of which generates hydrogen peroxide at levels capable of inhibiting . Preliminary studies suggest that several additional commensal streptococci are also able to catabolize glycerol, and glycerol-related genes are actively expressed in human dental plaque samples. Our findings reveal the potential of glycerol to significantly impact microbial homeostasis, which warrants further exploration.