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

Microcalorimetric techniques were used to investigate the kinetics of gluco se uptake during exponential growth of soil microorganisms. Experiments wer e 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 concentratio n corresponding to 15 mg of glucose in 0.2 ml of distilled water g(-1) soil . Further increases of glucose gave similar mu(max) values (20 mg) or the v elocity decreased (30-50 mg). Chemical analyses showed that, in all the cas es the glucose was practically exhausted (>99%) at the peak time. Relevant kinetic parameters such as the Michaelis-Menten constant, K-m = 4.070 +/- 0 .910 mM, maximum apparent growth rate mu(max) = 0.069 +/- 0.003 h(-1) and t he inhibitory nutrient concentration were determined from the power-time cu rves recorded. (C) 1999 Elsevier Science Ltd. All rights reserved.