NITRIFICATION, S-OXIDATION AND P-SOLUBILIZATION BY THE SOIL YEAST WILLIOPSIS-CALIFORNICA AND BY SACCHAROMYCES-CEREVISIAE

Addition of fresh sugar beet to soils leads to a marked increase in numbers of the soil yeast, Williopsis californica. The ability of a W. californica isolate to mediate nutrient transformations in vitro was compared with that of a laboratory strain of Saccharomyces cerevisiae. Both yeasts isolates hydrolysed urea to ammonium and oxidized ammonium to nitrate forming trace amounts of nitrite. They also oxidized elemental sulphur to thiosulphate, tetrathionate and sulphate; tetrathionate was formed in particularly large amounts by W. californica. Both yeasts also solubilized insoluble phosphate in vitro. It is suggested that soil yeasts might be used as inoculants to stimulate beneficial processes like S-oxidation and P-solubilization in soils.