An improved method to measure catalase 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.