O1 - Temperature Impacts on Streptococcus Mutans Growth and Substrate Utilization Kinetics

Abstract

Streptococcus mutans has been studied as a model cariogenic bacterium for decades. In spite of myriad studies, growth and substrate utilization kinetics studies have been largely limited to human body temperature (37 C). This makes it difficult to quantitatively assess the impact of temperature on metabolic kinetics. The objective of this study is to evaluate the effect of temperature, substrate, and nutrient conditions on S. mutans biokinetic parameters to provide comparability between biokinetic studies. S. mutans UA159 from ATCC (700610) was maintained on brain heart infusion (BHI) agar plates. S. mutans was grown in a chemostat fed BHI with either sucrose or glucose to calculate yield, maximal substrate utilization rate, endogenous decay, and half saturation constant from cellmass and substrate data assuming Monod kinetics. Pseudo-first order growth rates were determined in batch culture grown on sucrose or glucose with rich (100% BHI) and diluted (10% BHI) media at different temperatures (20-37 C). An Arrhenius plot was used to assess the impact of temperature on growth. Statistical significance was determined at the 95% confidence interval. Cell yield was statistically significantly greater on sucrose compared to glucose (0.2 g biomass/g sucrose compared to 0.1 g biomass/g glucose) at 37 C. The maximal substrate utilization rate was greater on glucose-amended media compared to sucrose. At lower temperatures, cell growth rate was statistically significantly greater on glucose compared to sucrose, but at 37 C, the growth rate was statistically significantly greater for sucrose-amended diluted media. This indicates that growth on sucrose is more strongly impacted by changes in temperature under nutrient-limited conditions, as confirmed by Arrhenius slope for S. mutans at 65 +/- 15 kJ/mol while growing on glucose and 84 +/- 20 kJ/mol on sucrose. Growth on glucose under nutrient rich conditions had the greatest Arrhenius slope of 132 +/- 8 kJ/mol. These findings enhance the understanding of S. mutans biokinetics and provide useful data for comparing studies under different environmental conditions. S. mutans has a greater cell growth yield on sucrose compared to glucose. Further, growth at lower temperatures is more strongly dependent on having rich media regardless of substrate, as growth rate was approximately double in rich media compared to either sucrose or glucose in diluted media at 20 C. At greater temperatures, these nutritional requirements were less important, as kinetic rates were only 10-20% greater when grown in rich media at human body temperature.