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

Abstract

Previous work reported that deletion of the Enzyme IIAB subunits (EIIABMan, 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 H2O2, 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 EIIMan subunit individually; and genes encoding the catabolite control protein CcpA ({Delta}ccpA) and the redox regulator Rex ({Delta}rex) for comparison. Deletion of each subunit incurred a growth defect on glucose partly due to elevated excretion of H2O2; 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 {Delta}ccpA despite increased H2O2 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 {Delta}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. ImportanceManagement of carbohydrate metabolism and environmental stress is key to the survival of oral commensal species such as S. sanguinis. Antagonism of oral pathobionts and modulation of the environmental pH and oxidative potential by commensals are crucial to the maintenance of microbial homeostasis and prevention of oral diseases including dental caries. It is therefore vital to understand how these species regulate sugar fermentation, production of acids and ammonia, and stress management in an environment known for a feast-and-famine cycle of carbohydrates and similar fluctuations in pH and oxygen tension. Here, we detail that genetic alterations of the glucose-PTS transporter in S. sanguinis can significantly affect the regulation of factors required for bacterial fitness and homeostatic ability independent of known catabolic regulators, it is then discussed how these changes may impact the survival of streptococcal species and affect caries onset.