The barrier-ring plate technique for studying extracellular enzyme diffusion and microbial growth in model soil environments

Abstract

A novel technique has been developed to study complex spatial interactions between micro-organisms, enzymes and their substrates in soil using barriers composed of soil and soil components inserted into agar plates. This has allowed the investigation of extracellular enzyme diffusion and microbial growth through soil-like but carefully controlled environments. Using 'barrier-ring plates' the effects of small quantities of soil and various soil components on endoglucanase and β-D-glucosidase diffusion was shown. Bentonite, with a relatively high unit surface area and a high cation exchange capacity, reduced the distance diffused by both enzymes. Kaolinite, a clay with a relatively low unit surface area and a low cation exchange capacity, had no effect while the colloidal-size (<2 μm) clay-humic fraction separated from a slit loam soil reduced the distance diffused by endoglucanase by an amount intermediate between that of kaolinite and bentonite. The same barrier-ring plate technique was used to demonstrate how soil components differentially affect the radial growth of a cellulolytic Streptomyces sp. and Trichoderma viride, T. koningii and Botryotrichum piluliferum.