Microcalorimetric measurements of the influence of glucose concentration on microbial activity in soils

Microcalorimetric techniques were used to investigate the kinetics of glucose uptake during exponential growth of soil microorganisms. Experiments were carried out using a humic cambisol soil amended with a nutrient solution containing different amounts of glucose (1.25–50.00 mg glucose g−1 soil). It was found that glucose uptake velocities increased up to a concentration corresponding to 15 mg of glucose in 0.2 ml of distilled water g−1 soil. Further increases of glucose gave similar μmax values (20 mg) or the velocity decreased (30–50 mg). Chemical analyses showed that, in all the cases the glucose was practically exhausted (>99%) at the peak time. Relevant kinetic parameters such as the Michaelis–Menten constant, Km=4.070±0.910 mM, maximum apparent growth rate μmax=0.069±0.003 h−1 and the inhibitory nutrient concentration were determined from the power–time curves recorded.