Genomic and phenotypic analysis of rock phosphate-solubilizing rhizobacteria

Abstract

Livestock systems in Colombia depend on forages, which are established on soils with high phosphorus (P) retention that cause a limitation of the efficiency of phosphate fertilizers. The inoculation of plant growth-promoting bacteria (PGPB) can improve soil P availability through different mechanisms associated with P cycling. The goal of this study was to evaluate the effect of PGPB inoculation on the plant growth under P-deficient conditions as well as to determine the phenotypic and genomic characteristics associated with plant growth promotion. Among nine strains evaluated on P-deficient soil amended with rock phosphate, we selected Rhizobium sp. T88 and Herbaspirillum sp. AP21 for their ability to enhance the dry biomass in perennial ryegrass and red clover, with increases of 20.31 and 44.87%, respectively. Under in vitro conditions, these two selected strains showed the ability to solubilize tricalcium phosphate and rock phosphate by the production of diverse organic acids. It was also observed that both strains produced alkaline and acid phosphatases, while only Herbaspirillum sp. AP21 exhibited phytase synthesis for P mineralization. Finally, in silico genome analysis confirmed that the strains have different features to solubilize and mineralize P, of the 16 reported genes for these metabolic traits, Rhizobium sp. T88 and Herbaspirillum sp. AP21 genome encoded for 7 and 4 genes related to P solubilization, 3 and 6 genes related to P mineralization, respectively. In conclusion, the phenotypic and genomic characterization shows that Rhizobium sp. T88 present mainly mechanism related with P solubilization and Herbaspirillum sp. AP21 with P mineralization.