Growth of the Thermophilic Bacterium Geobacillus uralicus as a Function of Temperature and pH: An SCM-Based Kinetic Analysis

Abstract

The synthetic chemostat model (SCM), originally developed to describe nonstationary growth under widely varying concentrations of the limiting substrate, was modified to account for the effects of nontrophic factors such as temperature and pH. The bacterium Geobacillus uralicus, isolated from an ultradeep well (4680 m), was grown at temperatures ranging from 40 to 75°C and at pH varying from 5 to 9. The biomass kinetics was reasonably well described by the SCM, including the phase of growth deceleration observed in the first hours after a change in the cultivation temperature. At an early stage of batch growth in a neutral or alkalescent medium, bacterial cells showed reversible attachment to the glass surface of the fermentation vessel. The temperature dependence of the maximum specific growth rate (μ_m) was fitted using the equation μ_m = A exp (λT )/{1 + expB[1 – C/(T + 273)]}, where A, λ, B, and C are constants. The maximum specific growth rate of 2.7 h^–1 (generation time, 15.4 min) was attained on a complex nutrient medium (peptone and yeast extract) at 66.5°C and pH 7.5. On a synthetic mineral medium with glucose, the specific growth rate declined to 1.2 h^–1, and the optimal temperature for growth decreased to 62.3°C.