Soil Colloids and Minerals Modulate Metabolic Activity of Pseudomonas putida Measured Using Microcalorimetry

Substantial interactions of microbes with soil particles present fundamental influences on microbial activities relevant to a series of biogeochemical processes. However, how soil surface-active particles modulate microbial metabolism has received scant attention. The extent to which composition of soil colloids alter the metabolism is not well addressed. This work examined the impacts of soil colloids and minerals on the metabolic activity of Pseudomonas putida using microcalorimetry and carbon utilization. The results showed that montmorillonite remarkably improved metabolic activity of P. putida, whereas kaolinite, goethite and soil colloids significantly inhibited the activity. Humus may weaken the inhibition of soil colloids on bacterial metabolism via interfacial interaction rather than nutrient supplements. Soils bearing higher amount of kaolinite and iron oxide may have greater depression on bacterial activity. The thermodynamic method provides different and complementary information to that from other techniques in characterizing microbial activities. The quantity and affinity for the adhesion of bacteria onto soil components together with the detoxification of metabolites were assigned to the modifications of bacterial activities.