• A novel microcosm for identifying phytate-degrading soil microbes is introduced

Fertilizer phosphorus (P) is a finite resource, necessitating the development of innovative solutions for P fertilizer efficiency in agricultural systems. Myo-inositol hexakisphosphate (phytate) constitutes the majority of identified organic P in many soil types and is poorly available to plants. Incorporating phytase-producing biofertilizers into soil presents a viable and environmentally acceptable way of utilizing P from phytate, while reducing the need for mineral P application. A deeper understanding of the microbial ecology in relation to degradation of phytate under natural soil conditions is however needed to obtain successful biofertilizer candidates able to compete in complex soil environments. Here we present the development of a microcosm for studying microbial communities able to colonize and utilize Ca-phytate hotspots in solum. Our results provide evidence that the recruited microbial population mineralizes Ca-phytate. Furthermore, quantification of bacterial genes associated with organic P cycling in alkaline soils indicated that the phosphatases PhoX and PhoD may play a larger role in phytate mineralization in soil than previously recognized. Amplicon sequencing and BioLog® catabolism studies show that hotspots containing Ca-phytate, recruited a different set of microorganisms when compared to those containing an addition of C source alone, with the genus Streptomyces specifically enriched. We propose that Streptomyces represents an hitherto unexplored resource as P biofertilizer with competitive advantage for utilizing CaPhy in an inherently competitive soil environment. We further conclude that the use of our newly designed microcosm presents an innovative approach for isolating soil microorganisms with the potential to degrade precipitated phytate in solum.