The effect of pH on indole-3-acetic acid (IAA) biosynthesis of Azospirillum brasilense Sp7

Abstract

This study reports on qualitative and quantitative aspects of indole-3-acetic acid (IAA) production of Azospirillum brasilense Sp7. Hereto, micro-aerobic batch cultures of Azospirillum were conducted in minimal medium with malate as the sole carbon source at different pH values (in the range of common soil pH values) in a controlled bioreactor. Biomass, malate, IAA concentrations as well as tryptophan (Trp) and anthranilate (AA) concentrations were measured. Irrespective of the imposed pH conditions, the kinetics of malate consumption and biomass accumulation are similar and can be modeled with a system of mass balance equations in which Monod type kinetics are assumed. Significant amounts of IAA are secreted only after a lag of several hours when malate gets depleted. The experiments illustrate that, while pH has no effect on this lag time, it has a significant effect on the amount of IAA produced. Furthermore, at the onset of IAA production, tryptophan also starts to accumulate in the medium while anthranilate is at its minimum value.