Microbial Response of Phytate Loading in Agricultural Soil

Inositol-hexakisphosphate (IP6) is the most dominant organic phosphorus (P) in soil, with myo-IP6 as the most reported stereoisomer than the other three (scyllo-IP6, D-chiro-IP6, and neo-IP6). In this study, we undertook a comparative study on the microbial response of myo-IP6 spiking on a historically cow manure and poultry litter fertilized agricultural soil. We analyzed P speciation and microbial diversity along with the expression of the b-propeller phytase (BPP; 3.1.3.8) and myo-inositol phosphate synthase (INO1; 5.5.1.4), which are enzymes involved in the mobilization of IP6 in the environment. The 31P NMR data showed myo-IP6 as the most common stereoisomer, while the other two stereoisomers, scyllo-IP6 and D-chiro-IP6, were lower by 10 folds. Over the incubation time, the content of myo-IP6 remarkably increased in the spiked soil, and that of the other two stereoisomers generally remained constant. Principal coordinate analysis (PCoA) and redundancy analysis (RDA) on soil elemental composition and P forms showed a notable difference between myo-IP6 spiked and control soil, especially the former generated the most diverse microbial community at the beginning, which gradually became similar to control by the third week of incubation. The linear discriminant analysis effect size (LEfSe) pointed to the major difference in Actinobacteria and Firmicutes caused by the spiking of myo-IP6. The expression of the BPP gene was three to six-fold higher in myo-IP6 spiked soil than in the control soil. These results suggest the synergistic relationship of microbial response to myo-IP6 loading towards synthesis and hydrolysis. These outcomes have multiple implications on P cycling in soil and the potential loss of orthophosphate derived from IP6 hydrolysis that may deteriorate water quality in adjoining water bodies.