Spontaneous Mutants of Streptococcus sanguinis with Defects in the Glucose-Phosphotransferase System Show Enhanced Post-Exponential-Phase Fitness

• Published in: Journal of bacteriology 2021-10, Vol.203 (22), p.e0037521
• Main Authors: Zeng, Lin, Walker, Alejandro R, Lee, Kyulim, Taylor, Zachary A, Burne, Robert A
• Format: Article
• Language: English
• Subjects: Ammonia; Arginine deiminase; Bacterial Proteins - metabolism; Bacteriology; Carbohydrates; Clinical isolates; Deletion mutant; Dental caries; DNA, Bacterial; Gene Deletion; Gene Expression Regulation, Bacterial; Genomes; Glucose; Glucose - metabolism; Glucose phosphotransferase; Hydrogen peroxide; Hydrogen Peroxide - metabolism; Hydrogen production; Lactic acid; Lactic Acid - metabolism; Monosaccharides; Mutants; Mutation; Nucleotide sequence; Pathogens; pH effects; Phosphotransferase; Phosphotransferases - genetics; Phosphotransferases - metabolism; Physiology and Metabolism; Pyruvic Acid; Research Article; Stationary phase; Streptococcus infections; Streptococcus sanguinis; Streptococcus sanguis - genetics; Streptococcus sanguis - metabolism; Subpopulations; Transcription
• ISSN: 0021-9193; 1098-5530
• DOI: 10.1128/JB.00375-21

Genetic truncations in a gene encoding a putative glucose-phosphotransferase system (PTS) protein ( , EIIAB ) were identified in subpopulations of two separate laboratory stocks of Streptococcus sanguinis SK36; the mutants had reduced PTS activities on glucose and other monosaccharides. To understand the emergence of these mutants, we engineered deletion mutants of and showed that the ManL-deficient strain had improved bacterial viability in the stationary phase and was better able to inhibit the growth of the dental caries pathogen Streptococcus mutans. Transcriptional analysis and biochemical assays suggested that the mutant underwent reprograming of central carbon metabolism that directed pyruvate away from production of lactate, increasing production of hydrogen peroxide (H O ) and excretion of pyruvate. Addition of pyruvate to the medium enhanced the survival of SK36 in overnight cultures. Meanwhile, elevated pyruvate levels were detected in the cultures of a small but significant percentage (∼10%) of clinical isolates of oral commensal bacteria. Furthermore, the mutant showed higher expression of the arginine deiminase system than the wild type, which enhanced the ability of the mutant to raise environmental pH when arginine was present. To our surprise, significant discrepancies in genome sequence were identified between strain SK36 obtained from ATCC and the sequence deposited in GenBank. As the conditions that are likely associated with the emergence of spontaneous mutations, i.e., excess carbohydrates and low pH, are those associated with caries development, we propose that glucose-PTS strongly influences commensal-pathogen interactions by altering the production of ammonia, pyruvate, and H O . A health-associated dental microbiome provides a potent defense against pathogens and diseases. Streptococcus sanguinis is an abundant member of a health-associated oral flora that antagonizes pathogens by producing hydrogen peroxide. There is a need for a better understanding of the mechanisms that allow bacteria to survive carbohydrate-rich and acidic environments associated with the development of dental caries. We report the isolation and characterization of spontaneous mutants of S. sanguinis with impairment in glucose transport. The resultant reprograming of the central metabolism in these mutants reduced the production of lactic acid and increased pyruvate accumulation; the latter enables these bacteria to better cope with hydrogen peroxide and low