Phenotypic and genomic characterization ofBacillus sensu latofor their biofertilization effect and plant growth promotion features in soybean plants

Abstract

SummaryBacillus sensu latowere 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 asPriestia megaterium, ILBB139 asBacillus wiedmannii, ILBB44 as a member of a sister clade ofB. pumilus(together with a human pathogenic strain), ILBB15 asPeribacillus butanolivoransand ILBB64 asLysinibacillussp. These strains were evaluated for their capacity to mineralize organic P as sodium phytate and solubilize inorganic P forms in liquid medium. Thesein vitroassays 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 evaluatedin vitroandin silico.Finally, plant bioassays were deployed to assess the effect of the co-inoculation ofBacillus s.l.strains and rhizobial inoculant on nodulation, plant growth and nutrition.In plantabioassays showed thatB. pumilusILBB44 andP. megateriumILBB95 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 megateriumILBB592 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 megateriumILBB592 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.