Methane monooxygenase gene expression mediated by methanobactin in the presence of mineral copper sources
Methane monooxygenase gene expression mediated by methanobactin in the presence of mineral copper sources
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DOI：
10.1073/pnas.0702879104
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发表时间：
2007-07-17
影响因子：
11.1
通讯作者：
Graham, David W.
中科院分区：
文献类型：
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作者：
Knapp, Charles W.;Fowle, David A.;Graham, David W.
甲烷是一种与全球变暖有关的主要温室气体；然而，甲烷氧化细菌（甲烷氧化菌）的原位甲烷氧化模式（自然界抑制甲烷的主要生物机制）往往与实验室预测不一致。例如，人们预计甲烷氧化菌生态与铜水平之间存在密切关系，因为甲烷氧化菌需要铜来维持颗粒甲烷单加氧酶（pMMO），这是甲烷氧化最有效的酶。然而，在自然界中尚未观察到相关性，这令人惊讶，因为甲烷单加氧酶 (MMO) 基因表达与铜的可用性明确相关。在这里，我们对这种缺乏相关性提供了基本解释。我们认为，自然界中的 MMO 表达很大程度上受固相 Cu 地球化学和甲烷氧化菌（例如甲烷菌素 (mb)）中 Cu 获取系统从矿物来源获取 Cu 的相对能力控制。为了检验这一假设，我们针对毛孢甲基窦菌 OB3b（产生 mb）开发了 RT-PCR 表达测定法，以量化 pMMO、可溶性 MMO（当铜“不可用”时表达的替代 MMO）以及在逐渐严格的铜供应条件下的 16SrRNA 基因表达。当 Cu 以 CUC12 形式提供时，pMMO 转录水平显着增加，与实验室工作一致。然而，当 Cu 以 Cu 封闭氧化铁的形式提供时，只有当 mb 也存在时，pMMO 转录物水平才会增加。最后，当 Cu 以 Cu 封闭的硼硅酸盐玻璃形式提供时，pMMO 转录模式根据环境 mb:Cu 供应比而变化。 Cu 地球化学明显影响陆地系统中 MMO 的表达，因此，当地的 Cu 矿物学可能为自然环境中的甲烷氧化模式提供解释。
Methane is a major greenhouse gas linked to global warming; however, patterns of in situ methane oxidation by methane-oxidizing bacteria (methanotrophs), nature's main biological mechanism for methane suppression, are often inconsistent with laboratory predictions. For example, one would expect a strong relationship between methanotroph ecology and Cu level because methanotrophs require Cu to sustain particulate methane monooxygenase (pMMO), the most efficient enzyme for methane oxidation. However, no correlation has been observed in nature, which is surprising because methane moncloxygenase (MMO) gene expression has been unequivocally linked to Cu availability. Here we provide a fundamental explanation for this lack of correlation. We propose that MMO expression in nature is largely controlled by solid-phase Cu geochemistry and the relative ability of Cu acquisition systems in methanotrophs, such as methanobactins (mb), to obtain Cu from mineral sources. To test this hypothesis, RT-PCR expression assays were developed for Methylosinus trichosporium OB3b (which produces mb) to quantify pMMO, soluble MMO (the alternate MMO expressed when Cu is "unavailable"), and 16SrRNA gene expression under progressively more stringent Cu supply conditions. When Cu was provided as CUC12, pMMO transcript levels increased significantly consistent with laboratory work. However, when Cu was provided as Cu-cloped iron oxide, pMMO transcript levels increased only when mb was also present. Finally, when Cu was provided as Cu-cloped borosilicate glass, pMMO transcription patterns varied depending on the ambient mb:Cu supply ratio. Cu geochemistry clearly influences MMO expression in terrestrial systems, and, as such, local Cu mineralogy might provide an explanation for methane oxidation patterns in the natural environment.