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

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, 100 rpm, 150 rpm, and 200 rpm) 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 (419.86 mg L ^-1 ) after 48 h. By using the response surface methodology, the maximum IAA production (217.73 µg mL ^-1 ) was obtained with the highest initial pH 7.0, the lowest nitrogen, and glucose concentrations (5 g L ^-1 and 10 g L ^-1 , respectively) and the lowest agitator speed (100 rpm). Further tests indicated that nitrogen affected significantly IAA production and the absence of nitrogen in the medium promoted higher IAA production (457 µg mL ^-1 ). The results obtained here may contribute to the scaling up for industrial and agricultural applications of a yeast-based product with T. globosa .
Competing Interests: Conflict of interestThe authors declare that they have no competing interests.
(© King Abdulaziz City for Science and Technology 2022, Springer Nature or its licensor holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.)