Summary auto-generated
This study used calorimetry to quantify the relationship between heat evolution and microbial activity in soil degrading glucose. Researchers incubated brown arid andosol soil with glucose at 30°C while measuring heat output in a conduction-type calorimeter. They found excellent reproducibility of degradation thermograms and established strong linear correlations between heat evolution and both glucose degradation (r=0.987) and viable cell counts (r=0.968). The average heat per unit glucose was 1287±52 kJ/mol, and per-cell heat production was 6.7 pW, consistent with pure culture bacterial values. From kinetic analysis, the apparent degradation rate constant for glucose in this soil was 0.302±0.002 h⁻¹ at 30°C, with a doubling time of 2.3 hours. The authors propose this calorimetric method as a quantitative tool for evaluating microbial degradation rates of organic substances in soil systems, providing information about microbial activity in complex multi-species communities.
Key findings
- Heat evolution during glucose degradation showed linear relationships with both glucose consumed (r=0.987) and viable cell counts (r=0.968), indicating heat reflects microbial biomass activity
- Average heat per cell (6.7 pW) matched values from pure bacterial cultures, validating calorimetry for measuring soil microbial activity
- Apparent glucose degradation rate constant was 0.302 h⁻¹ with 2.3-hour doubling time in the brown arid andosol soil studied
- Thermogram reproducibility was excellent (±0.17% peak time, ±1.1% peak height, ±0.51% total heat), demonstrating the method's reliability
- Calorimetry can quantitatively characterize organic material degradation in soil and assess microbial susceptibility to different substrates
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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 (kd) for microbial degradation of glucose in the soil studied was 0·302 ± 0·002 h-1 at 30°C.