Microbial ecology surrounding persistent phytate in agricultural soils

Phosphorus (P), a core component of applied fertilizer, is a finite resource, thus necessitating the development of innovative solutions to maintain and improve the efficiency of P fertilizer application and recycling of P in agricultural systems. Myo-inositol hexakisphosphate (phytate) and its lower order derivatives constitutes the majority of identified organic P in many soil types and has been shown in some cases to accumulate in soils with increasing application of P fertilizer. Phytate, however, is only poorly available to plants, and in alkaline soils may be precipitated as calcium (Ca)-phytate. Incorporating phytase-producing biofertilizers (i.e., microbial-based products with capacity to mineralize phytate) into soil presents a viable and environmentally acceptable way of utilizing P from phytate, whilst reducing the need for mineral P application. Here we present an in-soil microcosm that utilizes precipitated calcium phytate to recruit microorganisms with distinct taxonomic identities and functional capacities related to phytate degradation under real soil conditions. Furthermore, the 'bait' phytate used in the microcosm significantly influenced taxonomic composition of the recruited microbes when compared to controls. Treatments containing Ca-phytate showed both direct and indirect evidence for Ca-phytate mineralization in vitro and in vivo, as well as an increased abundance of phoX and phoD genes that relate to organic P mineralization. The microcosms recruited increased relative amounts of Actinobacteria, Firmicutes, and Proteobacteria, and the genus Streptomyces was specifically enriched in the presence of Ca-phytate. We consider that the microcosm presents a viable method for enriching for functionally-oriented microorganisms from soil that facilitates the isolation of inherently competitive organisms. This new method has the potential to provide a novel influx of biofertilizer candidates.