Bacterial lipids are well-preserved in ancient rocks and certain ones have been used as indicators of specific bacterial metabolisms or environmental conditions existing at the time of rock deposition. Here we show that an anaerobic bacterium produces 3-methylhopanoids, pentacyclic lipids previously detected only in aerobic bacteria and widely used as biomarkers for methane-oxidizing bacteria. Both Rhodopila globiformis, a phototrophic purple nonsulfur bacterium isolated from an acidic warm spring in Yellowstone, and a newly isolated Rhodopila species from a geochemically similar spring in Lassen Volcanic National Park (USA), synthesized 3-methylhopanoids and a suite of related hopanoids and contained the genes encoding the necessary biosynthetic enzymes. Our results show that 3-methylhopanoids can be produced under anoxic conditions and challenges the use of 3-methylhopanoids as biomarkers of oxic conditions in ancient rocks and as prima facie evidence that methanotrophic bacteria were active when the rocks were deposited.

细菌脂质在古代岩石中保存完好，某些脂质已被用作岩石沉积时存在的特定细菌代谢或环境条件的指标。在这里，我们表明厌氧细菌产生 3-甲基藿香，以前仅在需氧细菌中检测到并广泛用作甲烷氧化细菌的生物标志物的五环脂质。从黄石公园的酸性温泉中分离出的一种光养紫色无硫细菌球状红毛菌和新分离的红毛菌来自美国拉森火山国家公园的一个地球化学相似的春天的物种合成了 3-甲基藿香和一系列相关的藿香，并含有编码必要的生物合成酶的基因。我们的研究结果表明，3-甲基藿香可以在缺氧条件下产生，并挑战使用 3-甲基藿香作为古代岩石中含氧条件的生物标志物，并作为初步证据表明在岩石沉积时甲烷氧化细菌处于活跃状态。