Cell growth and metabolic products of Escherichia coli in nitrate respiration

When a culture of E. coli strain K‐10, grown in a complex medium was transferred to a defined medium containing glucose and ammonia, two‐phasic growth was observed under aerobic conditions; complex nutrients from the preculture were consumed for growth in the first phase and growth in the second phase depended on the defined nutrients. The cells in the second phase grew immediately in a defined medium when transferred after washing, but the cells from the preculture did not. Under anaerobic conditions, nitrate stimulated growth, but growth stopped at low levels depending on the amounts of complex nutrients, even though glucose remained. In nitrate respiration, cells could not adapt to growth on defined nutrients after the exhaustion of the complex nutrients, while cells obtained from an aerobic culture in defined medium could anaerobically grow in defined medium with nitrate. Metabolic products of glucose as well as cell growth were investigated under the conditions of nitrate respiration, fermentation, and respiration in defined and in complex media. When the pH was maintained at 7.4, ethanol, acetate, and formate were formed as main products in a ratio of 1:1:2 under anaerobic conditions in both media. Small amounts of succinate, lactate, and pyruvate were also formed, especially in the complex medium. In the presence of nitrate, ethanol disappeared and acetate increased with the formation of nitrite, while formate decreased a little at the end of the growth period. In the aerobic culture, transient formation of acetate was observed, especially in the complex medium; little ethanol, succinate, and lactate was formed in this case. The molar growth yields on glucose in the anaerobic cultures were twice as high in the presence of nitrate than in its absence in both media and 1.5 times higher in the complex than in the defined medium in the absence and presence of nitrate, but the yields under aerobic conditions were higher in the defined than in the complex medium.