SUMMARY: Under anaerobic conditions, reduces nitrate to nitrite until nitrate is exhausted from the medium, when nitrite is converted into N or NO. In the presence of nitrate, fermentation patterns for lactate, glycerol and pyruvate were different from those obtained during anaerobic growth without an inorganic electron acceptor. In the presence of these substrates, a drastic decrease in propionate formation was observed, some pyruvate accumulated during growth with lactate, and acetate was produced from glycerol. Acetate production from lactate and pyruvate was not influenced by the presence of nitrate. Furthermore, CO was produced by citric acid cycle activity. The fermentation pattern during nitrite reduction resembled that of grown anaerobically without an inorganic electron acceptor. Nitrite has a toxic effect, since bacteria inoculated into a medium with 9 mM-nitrite failed to grow.

The cytochrome spectrum of anaerobically grown was similar with and without nitrate. In membrane fractions of bacteria grown anaerobically with nitrate, cytochrome functioned in the transfer of electrons from lactate, glycerol 1-phosphate and NADH to nitrate. Molar growth yields were increased in the presence of nitrate, indicating an increased production of ATP. This could be explained by citric acid cycle activity, and by oxidative phosphorylation coupled to nitrate reduction. Assuming that 1 mol ATP is formed in the electron transfer from lactate or glycerol 1-phosphate to nitrate, and that 2 mol ATP are formed in the electron transfer from NADH to nitrate, values (g dry wt bacteria/mol ATP) were obtained of between 5.0 and 12.6. The higher values were similar to those obtained during anaerobic growth without an inorganic electron acceptor. This supports the assumptions about the efficiency of oxidative phosphorylation for electron transport to nitrate. Low values were found when high concentrations of nitrite (15 to 50 mM) accumulated, and were probably due to the toxic effect of nitrite.


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