Systematic Analysis of the Glucose-PTS in Streptococcus sanguinis Highlighted its Importance in Central Metabolism and Bacterial Fitness

Previous work reported that deletion of the Enzyme IIAB subunits (EIIAB ^Man , manL ) of the glucose phosphotransferase system (glucose-PTS, manLMNO) in Streptococcus sanguinis impacted carbon catabolite repression (CCR) and bacterial fitness. Here, a single nucleotide polymorphism in ManN, ManNA91E, produced the unusual phenotype of increased excretion of organic acids and H ₂ O ₂ , yet elevated PTS activities. To characterize the contributions of each component of the glucose-PTS to bacterial fitness, we performed genetic analyses by deleting from S. sanguinis SK36 the entire operon and each EII ^Man subunit individually; and genes encoding the catabolite control protein CcpA (Δ ccpA ) and the redox regulator Rex (Δ rex ) for comparison. Deletion of each subunit incurred a growth defect on glucose partly due to elevated excretion of H ₂ O ₂ ; when supplemented with catalase this defect was rescued, instead resulting in a significantly higher yield than the parent. All glucose-PTS deletion mutants presented an increased antagonism against the oral pathobiont Streptococcus mutans , a phenotype absent in Δ ccpA despite increased H ₂ O ₂ output. A shift in the pyruvate node towards mixed acid fermentation and increased arginine deiminase activity enhanced pH homeostasis in glucose-PTS mutants, but not Δ ccpA . Despite the purported ability of Rex to regulate central carbon metabolism, deletion of rex had no significant impact on most of the phenotypes discussed here. These findings place glucose-PTS in the pivotal position of controlling central carbon flux in streptococci, with critical outcomes impacting acidogenicity, aciduricity, pH homeostasis, and antagonism, highlighting its potential as a therapeutic target for treating diseases with a dysbiotic microbiome.