A novel microcosm for recruiting inherently competitive biofertilizer-candidate microorganisms from soil environments

Abstract

Fertilizer phosphorus (P) is both a necessary crop nutrient and finite resource, necessitating the development of innovative solutions for P fertilizer efficiency and recycling in agricultural systems. Myo-inositol hexakisphosphate (phytate) and its lower order derivatives constitute the majority of identified organic P in many soil types and has been shown to accumulate with increasing application of P fertilizer. Phytate is only poorly available to plants, and in alkaline soils it often precipitated as even more unavailable 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 Ca-phytate to recruit microorganisms with degradation activity towards phytate in solum. Our results show both direct and indirect evidence for Ca-phytate mineralization in vitro and in solum. Furthermore, the abundance of bacteria recruited was measured via 16S rRNA gene copy number, as was three genes relating to organic P degradation; phoX and phoD phosphatases and the BPP ({beta}-propeller phytase) gene. Amplicon sequencing as well as BioLog catabolism studies show that microcosm treatments containing the bait Ca-phytate, recruited a different set of microorganisms when compared to controls. These Ca-phytate microcosms recruited mainly Actinobacteria, Firmicutes, and Proteobacteria, and the genus Streptomyces was specifically enriched. We conclude that our microcosm presents an innovative approach for isolating soil microorganisms with the potential to degrade precipitated phytate in solum and represents a new isolation method with the potential to isolate inherently robust biofertilizer candidates directly from target soils.