Nitrogen Transformations in Vitro by some Soil Yeasts

Candida tropicalis, Geotrichum capitatum, Geotrichum candidum and Rhodotorula minuta were isolated from soils of Saudi Arabia. The ability of these soil yeasts to mediate nitrogen transformations in vitro was investigated. An incubation study was conducted to determine the ability of these soil yeasts to nitrify ammonium to nitrate via nitrite in Czapek Dox medium. The yeast of R. minuta formed the largest amount of nitrate (94 μg/ml) followed by G. capitatum (70 μg/ml). Moderate ammonium oxidation was exhibited by G. candidum (55 μg/ml). Ammonium nitrification was highly correlated with yeast biomass formed. The oxidation processes led to a marked reduction in the pH of the medium.