Purification and Optimization of Auxin (Indole-3-Acetic Acid) Hormone in Rhizobium Bacterium

The indole-3-acetic acid (IAA) is the most abundant and significant natural auxin that in addition to plants, different microorganisms are able to produce this hormone. In this study, the IAA production by different strains of Rhizobium was surveyed. All bacteria (consisted of 12 different strains of Rhizobium) were isolated from root nodules of Alfalfa (Medicago sativa), lentil (Lens culinaris), bean (Phaseolus luntus) and pea (Pisum sativum). The optimization of IAA production was done by "Design Taguchi Experiments" using Qualitek-4 (W32b) software. Extraction and purification of IAA was performed by thin layer chromatography (TLC) method. The results showed that nine strains were producers of IAA hormone and the best strain of these Rhizobia (strain 1) which was isolated from pea (Pisum sativum), had the highest production of IAA (439 ppm). Concentration of IAA production in these local strains was almost 4 times more than other analyzed strains in the literatures. It was revealed that mannitol, as a carbon source and potassium nitrate as a nitrogen source in the presence of 3 mg/ml L-tryptophan after 72h of incubation, were the optimum condition for production of IAA in vitro. Finally, pure IAA was obtained by TLC.