IAA producing PGPR isolation, qualitative analysis and partial purification

Abstract

Plants constantly interact with a number of microbes in the rhizosphere micro-habitat, including bacteria, fungus, and viruses (Wang, H., Liu, R., You, M. P., Barbetti, M. J., & Chen, Y.2021). Interactions between beneficial microorganisms and pathogens have attracted a lot of attention because they are important for plant health and growth (Gupta, G., Parihar, S. S., Ahirwar, N. K., Snehi, S. K., & Singh, V. 2015). However, most study has concentrated only on the interaction of a single pair of interacting species. (i.e., one pathogen and one antagonist),skipping the enormous microbial diversity within these functional communities coexisting around or in plant roots. As a result, such investigations are really not important to natural soil conditions and oppose the idea that various species coexist in microbial communities (Van der Putten, W. H., Vet, L. E., Harvey, J. A., & Wäckers, F. L. 2001). Plant Growth Promoting Rhizobacteria are those microorganisms which colonizes plant roots and helps them in growth and improves fertility of the soil. (Priyanka, 2020) There are two kinds of mechanisms involved in beneficial activity of PGPR which is direct mechanism and indirect mechanism. The direct mechanism includes phytohormones production, mineral solubilization and nitrogen fixation. While in indirect mechanism involves antagonistic activity against pathogens, secondary metabolites production, fungicides involvement and siderophore production. (Meena et al., 2020) Hence Plant Growth Promoting Rhizobacteria are more effective on crop enhancement and for sustainable environment.(Meena et al., 2020) One of the mechanism for growth enhancement in crops is the production of phytohormones such as Indole acetic acid (IAA), Gibberellic acid and Cytokines. (Bhattacharyya & Jha, 2012). Indole acetic acid is the most active and commonly present in all the plants which helps and regulate in growth of the plant. (Kannojia et al., n.d.) Indole acetic acid (IAA) is the phytohormone involves in root initiation, root elongation and cell division. The effect of indole acetic acid is mainly depended on the sensitivity of the plant towards IAA and the concentration of IAA produced by plant associated bacteria. (Khan et al., 2014). Tryptophan-Independent Pathway Plants can synthesise IAA without the tryptophan precursor, according to mutants in the tryptophan biosynthetic pathway, and the branch point for this tryptophanindependent pathway occurs at indole-3-glycerol phosphate or indole-3- glycerol phosphate. However, no genes or proteins involved in this pathway have been identified in plants as of yet (Woodward and Bartel 2005). A tryptophan-independent route was suggested to occur inbacteria (A. brasilense) by feeding studies with tagged tryptophan (Prinsen et al. 1993). However, in this situation, no clear genetic or molecular evidence has been offered to support this pathway. Our major goal is to isolate bacteria that produce the most IAA from the substrate via a Tryptophan-dependent pathway and see if the IAA can be partially purified.