Phenotypic and genomic characterization of Bacillus sensu lato for their biofertilization effect and plant growth promotion features in soybean plants

Bacillus sensu lato were screened for their capacity to mineralize organic phosphorus (P) and promote plant growth, improving nitrogen (N) and phosphorus nutrition of soybean plants. Isolates were first identified based on their genomic sequences through TYGS and ANII. ILBB95, ILBB510 and ILBB592 were identified as Priestia megaterium, ILBB139 as Bacillus wiedmannii, ILBB44 as a member of a sister clade of B. pumilus (together with a human pathogenic strain), ILBB15 as Peribacillus butanolivorans and ILBB64 as Lysinibacillus sp. These strains were evaluated for their capacity to mineralize organic P as sodium phytate and solubilize inorganic P forms in liquid medium. These in vitro assays allowed the strains to be ranked according to their P mobilization potential, with ILBB15 and ILBB64 showing the highest orthophosphate production from phytate, ILBB592 the lowest and ILBB510 nil. In addition, features related to their rhizocompetence and plant growth promotion were evaluated in vitro and in silico. Finally, plant bioassays were deployed to assess the effect of the co-inoculation of Bacillus s.l. strains and rhizobial inoculant on nodulation, plant growth and nutrition. In planta bioassays showed that B. pumilus ILBB44 and P. megaterium ILBB95 increased P absorbed in plants grown on a poor substrate of sand and vermiculite and also on the richer mix of sand, vermiculite and peat. Priestia megaterium ILBB592 increased rhizobial nodulation and N content in plants grown on sand, vermiculite and peat mixture only. ILBB15 reduced plant growth and nutrition on both substrates. Genomes of ILBB95 and ILBB592 were characterized by genes related with plant growth and biofertilization whereas ILBB15 was differentiated by genes related to bioremediation. Priestia megaterium ILBB592 can be described as nodule-enhancing rhizobacteria (NER) and together with ILBB95, can be envisaged as prospective PGPR with the capacity to exert a positive effect on N and P nutrition of soybean plants.