Strohm TO, Griffin B, Zumft WG, Schink B

Growth yields in bacterial denitrification and nitrate ammonification

Appl. Environ. Microbiol. 73: 1420-1424 (2007).

Denitrification and nitrate ammonification are considered the most energy-yielding respiration systems in anoxic environments after oxygen has been consumed. The corresponding free energy changes are by 7 and 35 % lower than that of aerobic respiration, respectively. Growth yield determinations with pure cultures of Paracoccus denitrificans and Pseudomonas stutzeri revealed that far less energy is converted via ATP into cell mass than expected from the above calculations. Denitrification with formate or hydrogen as electron donor yielded about 2.4 - 3.0 g dry matter per mol formate or hydrogen, and 15 - 18 g dry matter per mol acetate. Similar yields with acetate were obtained with Pseudomonas stutzeri. Wolinella succinogenes and Sulfurospirillum deleyianum which reduce nitrate to ammonia both exhibited similar yield values with formate or H₂ plus nitrate. The results indicate that ATP synthesis in denitrification is far lower than expected from the free energy changes, and even lower than in nitrate ammonification. The results are discussed on the background of our present understanding of electron flow in denitrification, and with respect to the importance of denitrification and nitrate ammonification in the environment.