Reduction of nitrate to ammonia by Lactobacillus pentosus

The reduction of both nitrate and nitrite by lactobacilli is a rare propertly, but is desirable in certain food fermentations. The utilization of these activities requires that the terminal products of the metabolism be known. L. pentosus reduces nitrite to ammonia (determined enzymatically) by a heme-depended nitrite reductase. Gaseous products like N₂ or N₂O (detected by gas-chromatography) are not produced. In addition, nitrate is quantitatively reduced to nitrite. 92% of the nitrogen was recovered as ammonia. We suggest that the reduction of nitrite belongs to the fermentative type since it takes place in the absence of oxygen, ammonia is the only terminal product and no energy is derived from the reaction.