Phosphate solubilization and indole acetic acid production by rhizosphere yeast Torulaspora globosa: improvement of culture conditions for better performance in vitro.

Abstract

The rhizosphere yeast Torulaspora globosa is known to produce indole acetic acid (IAA) and to solubilize minerals. Due to the prospective use of this yeast as a biostimulant for agricultural applications, this work aimed to optimize the cultural conditions for both IAA production and phosphate solubilization. For phosphate solubilization, the temperature (20, 25 and 30°C), initial medium pH (3.0, 5.0, and 7.0), and shaker speed (without mixing, 100rpm, 150rpm, and 200rpm) were considered using the one-factor-at-a-time (OFAT) design. Temperature of 25°C, initial medium pH 7.0, and static cultures were the conditions of greatest phosphate solubilization, with 40% of the total phosphorus content solubilized from calcium phosphate (419.86mg L-1) after 48h. By using the response surface methodology, the maximum IAA production (217.73µgmL-1) was obtained with the highest initial pH 7.0, the lowest nitrogen, and glucose concentrations (5g L-1 and 10g L-1, respectively) and the lowest agitator speed (100rpm). Further tests indicated that nitrogen affected significantly IAA production and the absence of nitrogen in the medium promoted higher IAA production (457µgmL-1). The results obtained here may contribute to the scaling up for industrial and agricultural applications of a yeast-based product with T. globosa.