Plant growth-stimulating rhizobacteria capable of producingL-amino acids

Pseudomonas putidaBIRD-1 is a microorganism that inhabits the rhizosphere and solubilizes phosphate and iron and produces indolacetic acid [Roca, A., Pizarro-Tobias, P., Udaondo, Z., Fernandez, M., Matilla, M.A., Molina-Henares, M.A.,et al.(2013) Analysis of plant growth-promoting properties encoded by the genome of the rhizobacterium Pseudomonas putida BIRD-1.Environ Microbiol15: 780-794]. In this study, we generated mutant strains that are capable of producing the plant growth stimulating compoundsL-tryptophan andL-phenylalanine. We prepared clones that overproduceL-tryptophan by first mutagenizingP. putidaBIRD-1, then by selecting for clones in the presence of inhibitory concentrations of 5-fluoro-D,L-tryptophan. The production of this aromatic amino acid was confirmed by chemical analysis and cross-feeding experiments with auxotrophs. One of the mutants, namedP. putidaBIRD-1-12, was mutagenized again to isolate clones that are also able to grow in the presence of inhibitory concentrations ofp-fluoro-D,L-phenylalanine. One of these resulting clones was then isolated and named BIRD-1-12F. Our analysis revealed that the strains that either overproduceL-tryptophan, orL-tryptophan andL-phenylalanine, excel at promoting the growth of a number of plant crops of agricultural interest.