BACKGROUND Natural gas seeps contribute to global climate change by releasing substantial amounts of the potent greenhouse gas methane and other climate-active gases including ethane and propane to the atmosphere. However, methanotrophs, bacteria capable of utilising methane as the sole source of carbon and energy, play a significant role in reducing the emissions of methane from many environments. Methylocella-like facultative methanotrophs are a unique group of bacteria that grow on other components of natural gas (i.e. ethane and propane) in addition to methane but a little is known about the distribution and activity of Methylocella in the environment. The purposes of this study were to identify bacteria involved in cycling methane emitted from natural gas seeps and, most importantly, to investigate if Methylocella-like facultative methanotrophs were active utilisers of natural gas at seep sites. RESULTS The community structure of active methane-consuming bacteria in samples from natural gas seeps from Andreiasu Everlasting Fire (Romania) and Pipe Creek (NY, USA) was investigated by DNA stable isotope probing (DNA-SIP) using 13C-labelled methane. The 16S rRNA gene sequences retrieved from DNA-SIP experiments revealed that of various active methanotrophs, Methylocella was the only active methanotrophic genus common to both natural gas seep environments. We also isolated novel facultative methanotrophs, Methylocella sp. PC1 and PC4 from Pipe Creek, able to utilise methane, ethane, propane and various non-gaseous multicarbon compounds. Functional and comparative genomics of these new isolates revealed genomic and physiological divergence from already known methanotrophs, in particular, the absence of mxa genes encoding calcium-containing methanol dehydrogenase. Methylocella sp. PC1 and PC4 had only the soluble methane monooxygenase (sMMO) and lanthanide-dependent methanol dehydrogenase (XoxF). These are the first Alphaproteobacteria methanotrophs discovered with this reduced functional redundancy for C-1 metabolism (i.e. sMMO only and XoxF only). CONCLUSIONS Here, we provide evidence, using culture-dependent and culture-independent methods, that Methylocella are abundant and active at terrestrial natural gas seeps, suggesting that they play a significant role in the biogeochemical cycling of these gaseous alkanes. This might also be significant for the design of biotechnological strategies for controlling natural gas emissions, which are increasing globally due to unconventional exploitation of oil and gas.

中文翻译：

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新型兼性甲烷球菌菌株是陆地天然气渗漏时的活性甲烷消耗者。

背景技术天然气渗漏通过将大量的强力温室气体甲烷和其他包括乙烷和丙烷的气候活性气体释放到大气中，从而对全球气候变化做出了贡献。但是，能够将甲烷用作唯一的碳和能量来源的甲烷营养菌在减少许多环境中的甲烷排放中起着重要的作用。甲基球菌状兼性甲烷氧化菌是一类独特的细菌，除了甲烷以外，还会在天然气的其他组分（例如，乙烷和丙烷）上生长，但对甲基球菌在环境中的分布和活性知之甚少。这项研究的目的是确定与循环从天然气渗漏中释放出的甲烷有关的细菌，最重要的是，调查类似甲基球菌的兼性甲烷营养生物是否是渗漏点的天然气的积极利用者。结果使用13C标记甲烷，通过DNA稳定同位素探测（DNA-SIP）研究了来自Andreiasu Everlasting Fire（罗马尼亚）和Pipe Creek（纽约州，美国）的天然气渗漏样品中活性甲烷消耗细菌的群落结构。从DNA-SIP实验中检索到的16S rRNA基因序列表明，在各种活性甲烷营养生物中，甲基球菌是两种天然气渗流环境共有的唯一活性甲烷营养生物。我们还分离了新型兼性甲烷营养菌，甲基球菌属sp。Pipe Creek的PC1和PC4能够利用甲烷，乙烷，丙烷和各种非气态多碳化合物。这些新分离株的功能和比较基因组学揭示了与已知甲烷甲烷营养菌的基因组和生理差异，特别是缺乏编码含钙甲醇脱氢酶的mxa基因。甲基球菌 PC1和PC4仅具有可溶性甲烷单加氧酶（sMMO）和依赖镧系元素的甲醇脱氢酶（XoxF）。这些是发现的第一种甲烷变形杆菌，具有降低C-1代谢功能的冗余性（即仅sMMO和仅XoxF）。结论在这里，我们提供了使用依赖于培养物和不依赖于培养物的方法的证据，表明甲基球菌在陆地天然气渗漏中丰富且活跃，表明它们在这些气态烷烃的生物地球化学循环中起着重要作用。