Calorimetric Studies of Soil Microbes: Quantitative Relation between Heat Evolution during Microbial Degradation of Glucose and Changes in Microbial Activity in Soil

Abstract

Summary: Heat evolution during the microbial degradation of glucose in a brown arid andosol soil was studied in a conduction-type calorimeter at 30°C. Reproducibilities of the degradation thermograms in terms of the peak time of thermograms, their peak heights, and the total heat evolution, were within ±0.17%, ±1.1% and ±0·51%, respectively (percentage errors). Changes in the number of viable microbial cells and in the amount of glucose degraded revealed linear relationships both between heat evolution and the amount of glucose degraded, and between heat evolution and the viable cell counts, with correlation factors of 0·987 and 0·968, respectively. The heat evolution per unit glucose was α = 1287 ± 52 kJ (mol glucose)−1. The average heat effect per unit cell was q = 6.7 pW per cell, consistent with values determined for bacterial cells in pure culture. On the basis of these results, we propose a method to evaluate the rate of microbial degradation of organic substances in soil. The apparent rate constant (k d) for microbial degradation of glucose in the soil studied was 0·302 ± 0·002 h−1 at 30°C.