Fluctuations of formamide hydrolase activity in a barley field soil after drying and rewetting

Formamide hydrolase activity in a barley field soil was described by a two- component, rather than a one-component model of Michaelis-Menten kinetics. The two-component model had both a high-affinity (K-m values of 0.5-1.0 mM) and a low-affinity (K-m values of 30-60 mM) activity. Rapid and transient increases in both the overall heterotrophic activity (CO2 production) and t he high-affinity component of formamide hydrolase activity were observed in rewetted soil samples, suggesting that the high-affinity component represe nted enzyme activity of active microorganisms. Short-term field variations in the high-affinity component during a barley growth season were consisten t with rapid, transient responses of microbial activity to precipitation an d soil wetting. An assay of the high-affinity component of formamide hydrol ase activity as approximated by rate determination at a single low (1 mM) f ormamide concentration can provide an easy and rapid indication of enzyme a ctivity related directly to active microoganisms in the soil. (C) 2001 Else vier Science B.V. All rights reserved.