Strohm Tobin O, Griffin Ben, Zumft Walter G, Schink Bernhard
Fachbereich Biologie, Universität Konstanz, D-78457 Konstanz, Germany.
Appl Environ Microbiol. 2007 Mar;73(5):1420-4. doi: 10.1128/AEM.02508-06. Epub 2007 Jan 5.
Denitrification and nitrate ammonification are considered the highest-energy-yielding respiration systems in anoxic environments after oxygen has been consumed. The corresponding free energy changes are 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 to 3.0 g dry matter per mol formate or hydrogen and 15 to 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 against 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.
在氧气被消耗后，反硝化作用和硝酸盐氨化作用被认为是缺氧环境中能量产生最高的呼吸作用系统。相应的自由能变化分别比有氧呼吸低7%和35%。对反硝化副球菌和施氏假单胞菌纯培养物的生长产量测定表明，通过ATP转化为细胞物质的能量远低于上述计算预期。以甲酸盐或氢气作为电子供体的反硝化作用，每摩尔甲酸盐或氢气产生约2.4至3.0克干物质，每摩尔乙酸盐产生15至18克干物质。施氏假单胞菌利用乙酸盐也获得了类似的产量。将硝酸盐还原为氨的琥珀酸沃林氏菌和德莱氏硫螺旋菌，在以甲酸盐或H2加硝酸盐为底物时，均表现出类似的产量值。结果表明，反硝化作用中ATP的合成远低于自由能变化预期，甚至低于硝酸盐氨化作用中的合成。本文将结合目前对反硝化作用中电子流的理解以及反硝化作用和硝酸盐氨化作用在环境中的重要性来讨论这些结果。
