Effect of nitrate reduction on metabolic products and growth of Propionibacterium acidi‐propionici

From a culture of P. acidi‐propionici (formerly P. arabinosum) in a medium containing lactate and nitrate, a strain with high activity of nitrate reduction was isolated and used in this study. The growth rates on lactate and glucose were not significantly affected by nitrate under anaerobic and aerobic conditions. Addition of nitrate resulted in a decrease of propionate and an increase of acetate and pyruvate produced from lactate and glucose with accumulation of nitrite. In the reaction of cell suspensions in the absence of added nitrogeneous nutrient, a similar result was obtained. Accumulation of large amounts of polysaccharide observed in the presence of glucose under these conditions was not affected by the addition of nitrate. The molar growth yield on lactate but not on glucose in a defined medium was increased in the presence of nitrate. In cell suspensions glycerol, glucose, lactate, and propionate were utilized as electron donors for nitrate reduction to nitrite. Nitrate reduction was also found in cells grown in the absence of nitrate. Cytochrome b, found in the organism, was reduced by lactate and oxidized by nitrate or by fumarate in cell suspensions and in cell‐free extracts.