Microcalorimetric investigation on the metabolic activity of Bacillus thuringiensis as influenced by kaolinite, montmorillonite and goethite

The metabolic activity of microorganisms in soil is influenced by various colloidal soil particles especially clay minerals or iron oxide. The knowledge of the impacts of soil minerals on microorganisms is essential in understanding microbially mediated processes in soil. However, to date, the available information on this regard is scarce. Based on microcalorimetric techniques, a powerful tool for monitoring the activity of microorganisms, the metabolic activity of Bacillus thuringiensis in the presence of goethite, kaolinite and montmorillonite was investigated. The clay minerals and iron oxide stimulated the exponential growth of B. thuringiensis, whereas the sporulation of B. thuringiensis was somewhat inhibited by kaolinite and montmorillonite. Goethite significantly depressed the sporulation and the total metabolic activity of the bacterium. The surface interaction between microbial cell and soil mineral probably account for the effect of these minerals on the metabolic activity of B. thuringiensis.