Changes in Biochemical and Phenotypic Properties of Streptococcus mutans during Growth with Aeration

Abstract

Oxygen has a potent influence on the expression of genes and the activity of physiological and biochemical pathways in bacteria. We have found that oxygen significantly altered virulence-related phenotypic properties of Streptococcus mutans, the primary etiological agent of human dental caries. Transport of glucose, fructose, or mannose by the sugar:phosphotransferase system was significantly enhanced by growth under aerobic conditions, whereas aeration caused an extended lag phase and slower growth of S. mutans in medium containing glucose, fructose, or mannose as the carbohydrate source. Aeration resulted in a decrease in the glycolytic rate and enhanced the production of intracellular storage polysaccharides. Although aeration decreased the acid tolerance of S. mutans, aerobically grown cells had higher F-ATPase activity. Aeration altered biofilm architecture but did not change the ability of S. mutans to interact with salivary agglutinin. Growth in air resulted in enhanced cell-associated glucosyltransferase (Gtf) activity at the expense of cell-free Gtf activity. These results demonstrate that S. mutans can dramatically alter its pathogenic potential in response to exposure to oxygen, suggesting that the phenotype of the organism may be highly variable in the human oral cavity depending on the maturity of the dental plaque biofilm.Streptococcus mutans is an important component of the biofilms on human teeth that are associated with dental caries. The ability of this organism to cause dental caries is dependent on adherence to the tooth surface, formation of biofilms, conversion of a wide variety of carbohydrates to organic acids through glycolysis, and tolerance of low pH (8,9,15). Oral biofilms are subjected to considerable fluxes in environmental conditions, including pH, nutrient availability, carbohydrate source, and oxygen tension, all of which appear to influence the composition and biological activities of the microbial populations (8, 15). The ability of oral bacteria to survive and persist in oral biofilms depends on their capacity to respond to environmental changes at genetic, physiological, and biochemical levels. Consistent with this idea, S. mutans has evolved a remarkable capacity to coordinate the expression of a variety of genes in response to environmental factors (8,9,15,20).It is well known that oxygen is one of the most important environmental factors regulating microbial gene expression and metabolism. The oral cavity is an overtly aerobic environment, and oxygen is utilized by many oral bacteria for respiration and energy generation. Oxygen flows into the mouth from the environment and circulatory system and rapidly diffuses into the biofilms on teeth, which are generally 100 m deep or less (20). The oxygen concentration in oral biofilms can vary substantially, and thus, the mouth can support the growth of a wide variety of aerobic, facultative, and obligately anaerobic bacteria (13). In particular, cells that initially colonize an oral surface are exposed to higher levels of oxygen t...

Streptococcus mutans NADH Oxidase Lies at the Intersection of Overlapping Regulons Controlled by Oxygen and NAD + Levels

“…It is unclear whether differences observed between the ⌬nox strain and UA159 are directly due to the elevated oxygen concentration experienced by the ⌬nox strain or due to the loss of Nox functions other than oxygen reduction (such as regeneration of NAD ϩ ). Previously, changes in global transcription of S. mutans in response to acidic and oxygen stresses had been analyzed in cultures grown to exponential growth phase (58)(59)(60). Here, the tightly controlled environment of the chemostat was used to generate samples in which the external variables, such as nutrients, pH, and oxygen levels, could be rigorously regulated and adjusted.…”

Photodynamic Effects of Curcumin Against Cariogenic Pathogens

“…42 According to Ahn and Burne, 43 exposure of S. mutans to oxygen inhibits a biofilm formation on polystyrene surfaces and induces changes in the cell surface protein profiles. Exhibiting distinctive phenotypic properties, the organisms tend to react differently to antimicrobial agents or to photosensitizer drugs.…”

Inhibition of Streptococcus mutans biofilm formation, extracellular polysaccharide production, and virulence by an oxazole derivative

“…For the planktonic growth assays, overnight cultures of S. mutans UA159 were inoculated into BHI broth containing various concentrations of compound 5H6 (0.05, 0.5, 5, and 50 μg/mL) and incubated at 37°C for 16 h anaerobically without agitation, as previously described (Ahn et al 2009). Media containing 250 μg/mL ampicillin (Sigma) was used as positive control, and wells without bacteria received media only served as blanks.…”