School of Engineering, Newcastle University, NE1 7RU, Newcastle upon Tyne, UK; School of Engineering, Department of Infrastructure and Environment, University of Glasgow, Rankine Building, Glasgow, 12 8LT, UK.
School of Engineering, Newcastle University, NE1 7RU, Newcastle upon Tyne, UK.
Water Res. 2019 May 1;154:238-245. doi: 10.1016/j.watres.2019.01.054. Epub 2019 Feb 10.
The currently accepted biochemistry and bioenergetics of ammonia-oxidizing bacteria (AOB) show an inefficient metabolism: only 53.8% of the energy released when a mole of ammonia is oxidised and less than two of the electrons liberated can be directed to the autotrophic anabolism. However, paradoxically, AOB seem to thrive in challenging conditions: growing readily in virtually most aerobic environment, yet limited AOB exist in pure culture. In this study, a comprehensive model of the biochemistry of the metabolism of AOB is presented. Using bioenergetics calculations and selecting the minimum estimation for the energy dissipated in each of the metabolic steps, the model predicts the highest possible true yield of 0.16 gBio/gN and a yield of 0.13 gBio/gN when cellular maintenance is considered. Observed yields should always be lower than these values but the range of experimental values in literature vary between 0.04 and 0.45 gBio/gN. In this work, we discuss if this variance of observed values for AOB growth yield could be understood if other non-considered alternative energy sources are present in the biochemistry of AOB. We analyse how the predicted maximum growth yield of AOB changes considering co-metabolism, the use of hydroxylamine as a substrate, the abiotic oxidation of NO, energy harvesting in the monooxygenase enzyme or the use of organic carbon sources.
氨氧化细菌（AOB）的现有生物化学和生物能量学表明其代谢效率低下：当 1 摩尔氨被氧化时，只有 53.8%的能量被释放，并且释放的电子中不到两个可以被引导至自养生物合成。然而，矛盾的是，AOB 似乎在具有挑战性的条件下茁壮成长：它们很容易在几乎所有的需氧环境中生长，但在纯培养中 AOB 的数量有限。在这项研究中，提出了一个氨氧化细菌代谢生物化学的综合模型。使用生物能量学计算，并对每个代谢步骤中耗散的能量进行最小估计，该模型预测了最高可能的真实产率为 0.16 gBio/gN，当考虑细胞维持时，产率为 0.13 gBio/gN。观察到的产率应该总是低于这些值，但文献中的实验值范围在 0.04 和 0.45 gBio/gN 之间。在这项工作中，我们讨论了如果 AOB 生物化学中存在其他未考虑的替代能源，是否可以理解观察到的 AOB 生长产率的这种差异。我们分析了考虑共代谢、使用羟胺作为底物、NO 的非生物氧化、单加氧酶中的能量收获或使用有机碳源时，AOB 的最大预测生长产率如何变化。
