Volcanic and geothermal environments are characterized by low pH, high temperatures, and gas emissions consisting of mainly CO₂ and varied CH₄, H₂S, and H₂ contents which allow the formation of chemolithoautotrophic microbial communities. To determine the link between the emitted gases and the microbial community composition, geochemical and metagenomic analysis were performed. Soil samples of the geothermic region Favara Grande (Pantelleria, Italy) were taken at various depths (1 to 50 cm). Analysis of the gas composition revealed that CH₄ and H₂ have the potential to serve as the driving forces for the microbial community. Our metagenomic analysis revealed a high relative abundance of Bacteria in the top layer (1 to 10 cm), but the relative abundance of Archaea increased with depth from 32% to 70%. In particular, a putative hydrogenotrophic methanogenic archaeon, related to Methanocella conradii, appeared to have a high relative abundance (63%) in deeper layers. A variety of [NiFe]-hydrogenase genes were detected, showing that H₂ was an important electron donor for microaerobic microorganisms in the upper layers. Furthermore, the bacterial population included verrucomicrobial and proteobacterial methanotrophs, the former showing an up to 7.8 times higher relative abundance. Analysis of the metabolic potential of this microbial community showed a clear capacity to oxidize CH₄ aerobically, as several genes for distinct particulate methane monooxygenases and lanthanide-dependent methanol dehydrogenases (XoxF-type) were retrieved. Analysis of the CO₂ fixation pathways showed the presence of the Calvin-Benson-Bassham cycle, the Wood-Ljungdahl pathway, and the (reverse) tricarboxylic acid (TCA) cycle, the latter being the most represented carbon fixation pathway. This study indicates that the methane emissions in the Favara Grande might be a combination of geothermal activity and biological processes and further provides insights into the diversity of the microbial population thriving on CH₄ and H₂.

中文翻译：

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地热气体塑造了意大利潘泰莱里亚火山土壤的微生物群落

火山和地热环境的特征是低pH值，高温和主要由CO ₂以及CH ₄，H ₂ S和H ₂含量变化组成的气体排放，这些气体允许形成化学自养型微生物群落。为了确定排放气体与微生物群落组成之间的联系，进行了地球化学和宏基因组分析。在不同深度（1至50厘米）处采集了地热区Favara Grande（意大利潘特里亚）的土壤样品。气体成分分析表明，CH ₄和H ₂有潜力成为微生物群落的驱动力。我们的宏基因组学分析显示，顶层细菌的相对丰度较高（1至10 cm），但古细菌的相对丰度随深度从32％增至70％而增加。特别是，与康氏甲烷球菌有关的推定的氢营养产甲烷古菌似乎在深层具有较高的相对丰度（63％）。检测到多种[NiFe]-加氢酶基因，表明H ₂是上层微需氧微生物的重要电子供体。此外，细菌种群包括疣疣和蛋白细菌的甲烷营养菌，前者的相对丰度高出7.8倍。该微生物群落代谢潜力的分析表明，有明显的氧化需氧能力的CH ₄，因为检索到了几种不同的颗粒甲烷单加氧酶和镧系元素依赖性甲醇脱氢酶（XoxF型）的基因。CO ₂分析固定途径表明存在Calvin-Benson-Bassham循环，Wood-Ljungdahl途径和（反向）三羧酸（TCA）循环，后者是最有代表性的碳固定途径。这项研究表明，Favara Grande中的甲烷排放可能是地热活动和生物过程的结合，并进一步提供了关于在CH ₄和H ₂上繁荣发展的微生物种群多样性的见解。