Differential interaction of Aspergillus niger and Peniophora lycii phytases with soil particles affects the hydrolysis of inositol phosphates

The effect of the soil environment on the mobility, stability and catalytic activity of phytase from two sources was compared, as these factors have important implications for the efficacy of enzyme function in soil. Phytase from an ascomycete fungus (Aspergillus niger) and a basidiomycete fungus (Peniophora lycii) was added to soil suspensions from three contrasting soils and activities in the solution and solid phase were monitored. The two enzymes were compared because the P. lycii phytase was known to have greater specific activity and a more acidic isoelectric point (pI) than A. niger and therefore predicted to have different adsorption characteristics. When added to soil suspensions buffered at pH 7.5, both phytases remained in solution in all of the soils. In contrast at near natural soil pH (pH 5.5), only the P. lycii phytase remained in solution, while the A. niger phytase was rapidly adsorbed to the soil solid phase. The extent of this adsorption was reduced, however, in a soil-dependent manner by prior addition of bovine serum albumin (BSA) to the soil suspensions. At the natural pH of the soil, the stability of the P. lycii phytase in soil solution was improved under sterile conditions, whereas degradation of the A. niger phytase was unaffected. Subsequently, P. lycii phytase was shown to be more effective at hydrolysing myo-inositol hexakisphosphate added to the soil. Moreover, the P. lycii phytase also hydrolysed more organic phosphate that was endogenous to a range of soils. This research indicates that the physicochemical properties of fungal phytases affect their mobility and temporal stability and their capacity to hydrolyse inositol phosphates in soil environments.