The atmospheric concentration of the potent greenhouse gases methane and nitrous oxide (N2O) has increased drastically during the last century. Methylomirabilis bacteria can play an important role in controlling the emission of these two gases from natural ecosystems, by oxidizing methane to CO2 and reducing nitrite to N2 without producing N2O. These bacteria have an anaerobic metabolism, but are proposed to possess an oxygen-dependent pathway for methane activation. Methylomirabilis bacteria reduce nitrite to NO, and are proposed to dismutate NO into O2 and N2 by a putative NO dismutase (NO-D). The O2 produced in the cell can then be used to activate methane by a particulate methane monooxygenase. So far, the metabolic model of Methylomirabilis bacteria was based mainly on (meta)genomics and physiological experiments. Here we applied a complexome profiling approach to determine which of the proposed enzymes are actually expressed in Methylomirabilis lanthanidiphila. To validate the proposed metabolic model, we focused on enzymes involved in respiration, as well as nitrogen and carbon transformation. All complexes suggested to be involved in nitrite-dependent methane oxidation, were identified in M. lanthanidiphila, including the putative NO-D. Furthermore, several complexes involved in nitrate reduction/nitrite oxidation and NO reduction were detected, which likely play a role in detoxification and redox homeostasis. In conclusion, complexome profiling validated the expression and composition of enzymes hypothesized to be involved in the energy, methane and nitrogen metabolism of M. lanthanidiphila, thereby further corroborating their unique metabolism involved in the environmentally relevant process of nitrite-dependent methane oxidation.

中文翻译：

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亚硝酸盐依赖的甲烷营养菌甲基拟南芥lanthanidiphila的配合物分析。

在上个世纪中，强大的温室气体甲烷和一氧化二氮（N2O）的大气浓度急剧增加。通过将甲烷氧化为CO2并将亚硝酸盐还原为N2而不会产生N2O，甲基omi菌可在控制自然生态系统中这两种气体的排放中发挥重要作用。这些细菌具有厌氧代谢，但被认为具有甲烷活化的氧依赖性途径。甲基rabi菌将亚硝酸盐还原为NO，并提议通过假定的NO歧化酶（NO-D）将NO歧化为O2和N2。然后，可通过颗粒甲烷单加氧酶将池中产生的O2活化为甲烷。到目前为止，甲基甲虫细菌的代谢模型主要基于（元）基因组学和生理学实验。在这里，我们应用了一个复杂的基因组分析方法来确定拟议中的哪些酶实际上在甲基拟南芥中表达。为了验证所提出的代谢模型，我们集中研究了与呼吸有关的酶以及氮和碳的转化。所有暗示与亚硝酸盐依赖的甲烷氧化有关的复合物，都在兰氏甲烷八叠球菌中鉴定出，包括推定的NO-D。此外，检测到了几种涉及硝酸盐还原/亚硝酸盐氧化和NO还原的复合物，它们可能在排毒和氧化还原稳态中起作用。综上所述，复杂的基因组图谱验证了被认为与兰氏甲烷八叠球菌的能量，甲烷和氮代谢有关的酶的表达和组成，