Rock phosphate solubilization by four yeast strains

The solubilization of rock phosphate (RP) by four yeast strains, Rhodotorula sp., Candida rugosa, Saccharomyces cerevisiae and Saccharomyces rouxii, which were isolated from wheat rhizospheric soils, was investigated in this study. The yeast isolates demonstrated diverse levels of soluble phosphate releasing abilities in modified Pikovskaya liquid medium containing RP as sole phosphate source. C. rugosa was the most effective solubilizer under different conditions, followed by Rhodotorula sp., S. rouxii and S. cerevisiae. Acidification of the broth seemed to be the major mechanism for RP solubilization by the yeast isolates, and the increase in soluble phosphate released was correlated significantly with an increase in titratable acidity and a drop in pH. The optimal composition for the solubilization of RP by the yeast isolates in the broth was 20 g L-1 glucose, 1 g L-1 yeast extract, 0.5 g L-1 (NH4)(2)SO4, and 5 g L-1 RP, respectively. The yeast isolates were able to solubilize RP at wide range of temperature and initial pH, with the maximum percentage of soluble phosphate released being recorded at 30-35 A degrees C and pH 5-6, respectively.