β-Phosphoglucomutase contributes to aciduricity in Streptococcus mutans

Streptococcus mutans encounters an array of sugar moieties within the oral cavity due to a varied human diet. One such sugar is beta-D-glucose 1-phosphate (beta DG1P), which must be converted to glucose 6-phosphate (G6P) before further metabolism to lactic acid. The conversion of beta DG1P to G6P is mediated by beta-phosphoglucomutase, which has not been previously observed in any oral streptococci, but has been extensively characterized and the gene designated pgmB in Lactococcus lactis. An orthologue was identified in S. mutans, SMU.1747c, and deletion of the gene resulted in the inability of the deletion strain to convert beta DG1P to G6P, indicating that SMU.1747c is a beta-phosphoglucomutase and should be designated pgmB. In this study, we sought to characterize how deletion of pgmB affected known virulence factors of S. mutans, specifically acid tolerance. The Delta pgmB strain showed a decreased ability to survive acid challenge. Additionally, the strain lacking beta-phosphoglucomutase had a diminished glycolytic profile compared with the parental strain. Deletion of pgmB had a negative impact on the virulence of S. mutans in the Galleria mellonella (greater wax worm) animal model. Our results indicate that pgmB plays a role at the juncture of carbohydrate metabolism and virulence.