Indole acetic acid (IAA) can upregulate genes encoding enzymes responsible for the synthesis of carboxylates involved in phosphorus (P) solubilisation. Here, we investigated whether IAA and its precursor affect the P-solubilising activity of rhizobacteria. A total of 841 rhizobacteria were obtained using taxonomically selective and enrichment isolation methods. Phylogenetic analysis revealed 15 genera of phosphate solubilising bacteria (PSB) capable of producing a wide range of IAA concentrations between 4.1 and 67.2 µg mL-1 in vitro. Addition of L-tryptophan to growth media improved the P-solubilising activity of PSB that were able to produce IAA greater than 20 µg mL-1. This effect was connected to the drop of pH and release of a high concentration of carboxylates, comprising α-ketoglutarate, cis-aconitate, citrate, malate and succinate. An increase in production of organic acids rather than IAA production per se appears to result in the improved P solubilisation in PSB.
Keywords: Acidification; IAA; L-tryptophan; Rhizobacteria; Rock phosphate.
© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.