Conversion of Nitrite to Nitrate by Nitrite-resistant Yeasts

Candida species YK 11 and YK 92 and Geotrichum candidum YK 57, which were isolated as nitrite-resistants, converted nitrite in the culture medium to nitrate stoichiometrically during growth. The nitrite-oxidizing reaction was confirmed under aerobic conditions in the intact cell system with 15 mm nitrite, 150 mm glucose, and 100mm Tris-HCl buffer (pH 7.0). Glucose or other carbohydrate which supported the microbial growth was indispensable for the reaction. The rate of oxidation (0.9 ~ 1.3 × 10⁵ μg-N/g of YK 92 cells·day) and the maximum amounts of nitrate formed in the culture medium (200 mm, 2800 μg-N/ml) were much larger than those of other heterotrophic nitrifiers and almost the same as those of Nitrobacter.

The nitrite-oxidizing activity was demonstrated in many types of yeast species.