Na-phytate Decomposition by Aerobic Soil Microorganisms: Phosphate Release and Spectrometric Indexing of Phytase Efficiency

Phytates represent the most abundant organic phosphorus compounds, occurring primarily as constituents of plant residues in soil. The availability of phytate-related phosphorus to plant nutrition is constrained by the scarce pathways of phytate hydrolysis and can be improved by bio-technological approaches involving microbial bioactivation of soil-bound phosphates. With this purpose, we developed a three-stages experimental methodological framework comprising: 1) selection of beneficial microorganisms, 2) monitoring of phytate decomposition, and 3) indexing of phytase efficiency. Within this framework, we 1) revealed the capability of soil bacteria Bacillus megaterium IMV B-7287, B. megaterium DSM 32, and Kocuria rosea B-42 to metabolize sodium phytate as a sole source of carbon and phosphorus under nutrient limitation highlighting their value for the development of sustainable phosphorus management strategies; 2) combined application of vanado-molybdate photocolorimetry, UV-absorption spectroscopy and fluorescence spectrometry to facilitate the tracing of microbial phytate transformation in solution with a model Na-phytate substrate and the quantitation of phytase efficiency in soil upon rhizobox cultivation; 3) suggested a fluorometric phytate-decomposition ratio as an index expressing the efficiency of phytase activity for quantitation of phytate-originating phosphate released into soil. The applicability of this approach was tested on the rhizosphere of maize. The acquired phytate-decomposition maps show phytase efficiency to be higher in maize-root system developing from bacterized seed. Non-bacterized maize delivers relatively weaker phytate decomposition sites confined within a close root vicinity.