The composition of the core lipids and intact polar lipids (IPLs) of five Rubrobacter species was examined. Methylated (ω-4) fatty acids (FAs) characterized the core lipids of Rubrobacter radiotolerans, R. xylanophilus and R. bracarensis. In contrast, R. calidifluminis and R. naiadicus lacked ω-4 methyl FAs but instead contained abundant (i.e., 34–41 % of the core lipids) ω-cyclohexyl FAs not reported before in the order Rubrobacterales. Their genomes contained an almost complete operon encoding proteins enabling production of cyclohexane carboxylic acid CoA thioester, which acts as a building block for ω-cyclohexyl FAs in other bacteria. Hence, the most plausible explanation for the biosynthesis of these cyclic FAs in R. calidifluminis and R. naiadicus is a recent acquisition of this operon. All strains contained 1-O-alkyl glycerol ether lipids in abundance (up to 46 % of the core lipids), in line with the dominance (>90 %) of mixed ether/ester IPLs with a variety of polar headgroups. The IPL head group distribution of R. calidifluminis and R. naiadicus differed, e.g. they lacked a novel IPL tentatively assigned as phosphothreoninol. The genomes of all five Rubrobacter species contained a putative operon encoding the synthesis of the 1-O-alkyl glycerol phosphate, the presumed building block of mixed ether/ester IPLs, which shows some resemblance with an operon enabling ether lipid production in various other aerobic bacteria but requires more study. The uncommon dominance of mixed ether/ester IPLs in Rubrobacter species exemplifies our recent growing awareness that the lipid divide between archaea and bacteria/eukaryotes is not as clear cut as previously thought.

检测了五种Rubrobacter物种的核心脂质和完整极性脂质 (IPL) 的组成。甲基化 (ω-4) 脂肪酸 (FAs) 表征了Rubrobacter radiotolerans、R. xylanophilus和R. bracarensis的核心脂质。相比之下，R. calidifluminis和R. naiadicus缺乏 ω-4 甲基 FA，而是含有丰富的（即核心脂质的 34-41%）ω-环己基 FA，之前未在Rubrobacterales目中报道. 他们的基因组包含一个几乎完整的操纵子编码蛋白，能够产生环己烷羧酸 CoA 硫酯，它是其他细菌中 ω-环己基 FA 的构建模块。因此，对R. calidifluminis和R. naiadicus中这些环状 FA 的生物合成最合理的解释是最近获得了该操纵子。所有菌株都含有丰富的 1-O-烷基甘油醚脂质（高达 46% 的核心脂质），与具有各种极性头基的混合醚/酯 IPL 的优势 (>90%) 一致。R. calidifluminis和R. naiadicus的 IPL 头基分布不同，例如它们缺乏暂时指定为磷酸苏糖醇的新型 IPL。这五个人的基因组Rubrobacter物种包含一个推定的操纵子，该操纵子编码 1-O-烷基甘油磷酸盐的合成，这是混合醚/酯 IPL 的推定构建块，这与其他各种好氧细菌中能够产生醚脂的操纵子有一些相似之处，但需要更多研究. 混合醚/酯 IPL 在Rubrobacter物种中不常见的优势体现了我们最近越来越意识到古细菌和细菌/真核生物之间的脂质鸿沟并不像以前认为的那样明确。