The Route of Sucrose Utilization by Streptococcus mutans Affects Intracellular Polysaccharide Metabolism

Abstract

Streptococcus mutans converts extracellular sucrose (Suc) into exopolysaccharides (EPS) by glucosyl-transferase and fructosyl-transferase enzymes and internalizes Suc for fermentation through the phosphotransferase system (PTS). Here, we examined how altering the routes for sucrose utilization impacts intracellular polysaccharide [IPS; glycogen, (glg)] metabolism during carbohydrate starvation. Strain UA159 (WT), a mutant lacking all exo-enzymes for sucrose utilization (MMZ952), and a CcpA-deficient mutant (∆ccpA) were cultured with sucrose or a combination of glucose and fructose, followed by carbohydrate starvation. At baseline (0h), and after 4 and 24h of starvation, cells were evaluated for mRNA levels of the glg operon, IPS storage, glucose-1-phosphate (G1P) concentrations, viability, and PTS activities. A pH drop assay was performed in the absence of carbohydrates at the baseline to measure acid production. We observed glg operon activation in response to starvation (p<0.05) in all strains, however, such activation was significantly delayed and reduced in magnitude when EPS synthesis was involved (p<0.05). Enhanced acidification and greater G1P concentrations were observed in the sucrose-treated group, but mostly in strains capable of producing EPS (p<0.05). Importantly, only the WT exposed to sucrose was able to synthesize IPS during starvation. Contrary to CcpA-proficient strains, IPS was progressively degraded during starvation in ∆ccpA, which also showed increased glg operon expression and greater PTS activities at baseline. Therefore, sucrose metabolism by secreted enzymes affects the capacity of S. mutans in synthesizing IPS and converting it into organic acids, without necessarily inducing greater expression of the glg operon.

Virulence traits-based behavior of Streptococcus mutans bacteria from dental plaque and dental caries conditions

“…This finding was consistent with the results of Valdez et al (2017). S. mutans secretes glycosyltransferases Gtfs which is responsible for glucan production and biofilm formation (Ranganathan and Akhila 2019;Alhobeira et al 2021;Oliveira et al 2021). S. mutans isolates were examined by PCR for the presence of S. mutans gene gtfB.…”

Inhibitory effects of Stevioside on Streptococcus mutans and Candida albicans dual-species biofilm

“…In galactose metabolism, the upregulated genes were lacEF (encoding a lactose-specific enzyme), lacG (encoding 6-phospho-β-galactosidase), lacAB (encoding galactose-6-phosphate isomerase), lacC (encoding tagatose-6-phosphate kinase), and lacD (encoding tagatose-1,6-bisphosphate aldolase) in the tagatose pathway, while galK (encoding galactokinase), galT (encoding hexose1-phosphate uridyltransferase), and galE (encoding UDP-galactose 4-epimerase) in the Leloir pathway in the stevioside group (versus the sucrose group) ( Figure 7C ; Supplementary Table S1 ; Abranches et al, 2004 ). In addition, the glg operon, which includes glgA (encoding glycogen synthase), glgB (encoding branching enzyme), glgC&D (encoding two subunits of the ADP-glucose pyrophosphorylase, ADP-Glc-PP), and glgP (encoding glycogen phosphorylase), was also upregulated that encoded enzymes responsible for IPS synthesis and degradation ( Supplementary Table S2 ; Costa Oliveira et al, 2021 ).…”

Anti-Inflammatory and Anti-Bacterial Potential of Mulberry Leaf Extract on Oral Microorganisms

“…Periodontitis and caries are the major oral diseases, in relation to oral microbiota [38]. It is now well-established that S. mutans are associated with initiation of dental caries by acid production, sugar fermentation, and acid tolerance [4,39]. Periodontitis is an infectious and inflammatory disease characterized by progressive infiltration of bacteria and inflammatory cytokines into periodontal tissues, resulting in attachment loss, alveolar bone destruction, and the loss of teeth [40,41].…”