Soil bacteria rank among the most diverse groups of organisms on Earth and actively impact global processes of carbon cycling, especially in the emission of greenhouse gases like methane, CO₂ and higher gaseous hydrocarbons. An abundant group of soil bacteria are the mycobacteria, which colonize various terrestrial, marine and anthropogenic environments due to their impermeable cell envelope that contains remarkable lipids. These bacteria have been found to be highly abundant at petroleum and gas seep areas, where they might utilize the released hydrocarbons. However, the function and the lipid biomarker inventory of these soil mycobacteria are poorly studied. Here, soils from the Fuoco di Censo seep, an everlasting fire (gas seep) in Sicily, Italy, were investigated for the presence of mycobacteria via 16S rRNA gene sequencing and fatty acid profiling. The soils contained high relative abundances (up to 34 % of reads assigned) of mycobacteria, phylogenetically close to the Mycobacterium simiae complex and more distant from the well-studied M. tuberculosis and hydrocarbon-utilizing M. paraffinicum. The soils showed decreasing abundances of mycocerosic acids (MAs), fatty acids unique for mycobacteria, with increasing distance from the seep. The major MAs at this seep were tentatively identified as 2,4,6,8-tetramethyl tetracosanoic acid and 2,4,6,8,10-pentamethyl hexacosanoic acid. Unusual MAs with mid-chain methyl branches at positions C-12 and C-16 (i.e., 2,12-dimethyl eicosanoic acid and 2,4,6,8,16-pentamethyl tetracosanoic acid) were also present. The molecular structures of the Fuoco di Censo MAs are different from those of the well-studied mycobacteria like M. tuberculosis or M. bovis and have relatively δ¹³C-depleted values (−38 ‰ to −48 ‰), suggesting a direct or indirect utilization of the released seep gases like methane or ethane. The structurally unique MAs in combination with their depleted δ¹³C values identified at the Fuoco di Censo seep offer a new tool to study the role of soil mycobacteria as hydrocarbon gas consumers in the carbon cycle.

中文翻译：

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新型利用烃的土壤分枝杆菌在西西里永恒的火焰中合成独特的分枝菌酸

土壤细菌是地球上最多样化的生物之一，并积极影响碳循环的全球过程，尤其是在甲烷，CO ₂等温室气体的排放中和高级气态碳氢化合物。分枝杆菌是土壤细菌的一大类，由于其不可渗透的细胞膜层含有大量脂质，它们在各种陆地，海洋和人为环境中定殖。已经发现这些细菌在石油和天然气渗漏区非常丰富，在那里它们可能利用释放的碳氢化合物。但是，对这些土壤分枝杆菌的功能和脂质生物标志物清单的研究很少。在这里，通过16S rRNA基因测序和脂肪酸谱分析研究了意大利西西里岛一场持续不断的大火（天然气渗出）Fuoco di Censo渗漏的土壤中是否存在分枝杆菌。土壤含有较高的分枝杆菌相对丰度（最高为指定读数的34％），在系统发育上与分枝杆菌相似复杂且与经过深入研究的结核分枝杆菌和利用烃的石蜡分枝杆菌较远。土壤显示出分枝杆菌酸（MAs）（分枝杆菌特有的脂肪酸）的丰度降低，并且与渗漏的距离增加。初步确定该渗水的主要MA为2,4,6,8-四甲基四二十二烷酸和2,4,6,8,10-五甲基六二十二烷酸。也存在在位置C-12和C-16处具有中链甲基支链的不寻常的MA（即2,12-二甲基二十烷酸和2,4,6,8,16-五甲基四二十烷酸）。Fuoco di Censo MA的分子结构与结核分枝杆菌或牛分枝杆菌等经过深入研究的分枝杆菌的分子结构不同，并且具有相对δ¹³ C损耗值（ -38  ‰至-48  ‰），表明直接或间接利用了所释放的诸如甲烷或乙烷之类的渗透气体。在组合的结构独特的MA与他们耗尽 δ ^13个C ^，在Fuoco的迪Censo漓标识值提供了一个新的工具来研究土壤分枝杆菌在碳循环中的作用为烃类气体的消费者。