STUDY of INDOLE-3-ACETIC ACID BIOSYNTHESIS PATHWAYS in Bradyrhizobium japonicum BJBV-05

The bacterium Bradyrhizobium japonicum induces nodulation in Glycine max (soy) plants and other legumes. It is considered of great importance, since it is in the nodules that the bacteria are established, contributing to the biological fixation of N₂. The process is controlled by nitrogenase, an enzyme produced by the nif genes present in the genome of the bacterium. By metabolizing the nitrogenase, the indole acetonitrile transforms it into indole acetic acid (IAA) and releases a nitrogenated molecule. There have been other IAA synthesis routes reported in plants, other genera and species of bacteria, fungi, and algae, named tryptophan-dependent (TRP-D) or tryptophan independent (TRP-I), where this amino acid is the precursor. For TRP-D, there are four pathways to the synthesis of IAA, and only two for TRP-I. The microorganisms may or not have all the routes in their genomes, and the expression of the genes varies with the isolation and the genotype of the host plant. This work reports the results obtained from an B. japonicum soy isolate, cultivated in an enriched LB medium, or alternatively, with tryptophan. With the data obtained, we estimate that B. japonicum uses both TRP-D and TRP-I routes, since in the former type indole acetamide was detected, and in the latter, indole and anthranilic acid were found. Likewise, the presence of TRP in the medium may alter IAA synthesis routes.