Microbial phytase activity in soils and methods to improve the activity and application: a review

Abstract:

Phosphorus (P) is a finite and non-renewable resource. Soil P deficiency is a main limiting factor for crop growth and agricultural production. Once entering into soils, inorganic P (P_i) in fertilizers is readily being fixed by soil solid phase, binds to metal ions to form the insoluble complex, or transform into organic P (P_o) which fails to be directly uptake by plants. Soil P mainly exists as P_o, which accounts for 20%-80% of total P. Phytic acid or phytate is the predominant form of P_o, accounting for about 50% of P_o. Phytate can not be directly uptake by plants, while can release P via dephosphorylation by the specific enzyme phytase. Phytase is mainly secreted by microbes and its activity is affected by temperature, pH, soil adsorption, Ca content, Ca/P ratio and substrate concentration and availability, leading to reduced activity or inactivation. Therefore, it is of great importance for reducing the application of exogenous P fertilizer and ensuring agricultural production to understand how to maintain or improve phytase activity in soils and improve the utilization of soil endogenous phytate. Thus, this paper reviews the sources, classification, and function mechanisms of microbial phytase and influencing factors of soil phytase activity, focusing on methods to maintain or improve phytase activity and the application efficiencies. In terms of the low activity and poor stability, methods to improve phytase properties including adjusting optimal pH range, improving thermal stability, loading phytase on nano-materials, and genetic engineering, are proposed. As such, this review is expected to help better understand the influencing factors of phytase activity in soil and provide theoretical and technical supports to improve endogenous phytic acid utilization efficiency. This is of great importance to reduce the application rate of P fertilizer, P loss, and risk of soil non-point source/water pollution and ensuring agricultural sustainable development.

Key words:microbe;phytate;phytase;enzyme activity;influencing factor;application efficiency