Temperature, pH and carbon source affect drastically indole acetic acid production of plant growth promoting yeasts

Abstract

Rhizosphere and phylloplane yeasts are able to produce phytohormones, acting as potential plant growth promoters. The aim of this study was to analyze the production of indole acetic acid (IAA) by yeasts using variations in the culture conditions. The yeasts evaluated were Rhodotorula mucilaginosa and Trichosporon asahii, which were cultivated in a potato broth medium with 20 g/L of glucose or sucrose as the carbon source. The cultivation was carried out at 22°C, 25°C or 30°C, and the initial pH was adjusted to 3.0, 4.5 or 6.0. The cultures were analyzed using a colorimetric technique with Salkowski reagent. The cell count was determined in all of the conditions. The results for T. asahii showed that IAA production with sucrose was superior at pH 6.0, and that with glucose was superior at pH 4.5. These results indicate an association between the carbon source and medium pH. Rh. mucilaginosa (2F32) presented a high IAA production when compared with T. asahii (3S44 and 4C06) or even with other microorganisms referenced in the literature. The highest production (0.655 g/L) was obtained at pH 6.0 with glucose as the carbon source. Variations in the culture conditions did not affect the cell growth of the yeasts.

Keywords
Rhodotorula mucilaginosa; Trichosporon asahii; culture conditions; kinetic evaluations