Kleerebezem Robbert, Lücker Sebastian
Department of Biotechnology, Delft University of Technology, Delft, Netherlands.
Department of Microbiology, IWWR, Radboud University, Nijmegen, Netherlands.
Front Microbiol. 2021 Mar 24;12:622504. doi: 10.3389/fmicb.2021.622504. eCollection 2021.
The cyclic nature of specific conversions in the nitrogen cycle imposes strict limitations to the conversions observed in nature and explains for example why anaerobic ammonium oxidation (anammox) bacteria can only use nitrite - and not nitrate - as electron acceptor in catabolism, and why nitrite is required as additional electron donor for inorganic carbon fixation in anabolism. Furthermore, the biochemistry involved in nitrite-dependent anaerobic methane oxidation excludes the feasibility of using nitrate as electron acceptor. Based on the cyclic nature of these nitrogen conversions, we propose two scenarios that may explain the ecological role of recently discovered complete ammonia-oxidizing (comammox) spp., some of which were initially found in a strongly oxygen limited environment: (i) comammox spp. may actually catalyze an anammox-like metabolism using a biochemistry similar to intra-oxic nitrite-dependent methane oxidation, or (ii) scavenge all available oxygen for ammonia activation and use nitrate as terminal electron acceptor. Both scenarios require the presence of the biochemical machinery for ammonia oxidation to nitrate, potentially explaining a specific ecological niche for the occurrence of comammox bacteria in nature.
氮循环中特定转化的循环性质对自然界中观察到的转化施加了严格限制，例如解释了为什么厌氧氨氧化（anammox）细菌在分解代谢中只能使用亚硝酸盐而非硝酸盐作为电子受体，以及为什么在合成代谢中需要亚硝酸盐作为无机碳固定的额外电子供体。此外，依赖亚硝酸盐的厌氧甲烷氧化所涉及的生物化学排除了使用硝酸盐作为电子受体的可行性。基于这些氮转化的循环性质，我们提出了两种可能解释最近发现的完全氨氧化（comammox）菌生态作用的情景，其中一些最初是在氧气严重受限的环境中发现的：（i）comammox菌可能实际上利用类似于有氧亚硝酸盐依赖的甲烷氧化的生物化学催化类似厌氧氨氧化的代谢，或者（ii）清除所有可用氧气以激活氨并使用硝酸盐作为末端电子受体。这两种情景都需要存在将氨氧化为硝酸盐的生物化学机制，这可能解释了自然界中comammox细菌出现的特定生态位。
