Evaluation of Bacillus subtilis as promoters of plant growth

Abstract Bacillus subtilis are plant growth promoting rhyzobacteria due to their production of metabolites such as auxins, siderophores, organic acids and antibiotics. There is no sufficient scientific evidence to know if all B. subtilis strains have the same growth promoting effect, regardless their capacity of producing different growth promoting metabolite concentrations. This research work aimed to assess the plant growth promoting capacity of the different B. subtilis test strains, as well as the production of siderophores, indolic acids, plant hormones and jasmonic acid. This research work focused on three B. subtilis strains (BSN, BS8 and BS14). We quantified the plant hormones in the fermentation broths using high-resolution liquid chromatography, and we detected the siderophores with chrome azurol. We used S. Bacillus subtilis to treat Solanum lycopersicum and Arabidopsis thaliana seeds, as well as Solanum lycopersicum seedlings inside a bioclimatic chamber. The results showed that every strain promotes different parameters. Some strains promote high germination rates, while other strains promote root growth or stem elongation. Therefore, we must select Bacillus subtilis strains according to the desired growth promoting effect. However, the plant hormones concentration must be the right one, because too much of too low concentration will inhibit plant growth.