Rashby Sky E, Sessions Alex L, Summons Roger E, Newman Dianne K
Divisions of Geological and Planetary Sciences and Biology, California Institute of Technology and Howard Hughes Medical Institute, Pasadena, CA 91125, USA.
Proc Natl Acad Sci U S A. 2007 Sep 18;104(38):15099-104. doi: 10.1073/pnas.0704912104. Epub 2007 Sep 11.
Sedimentary 2-methyhopanes have been used as biomarker proxies for cyanobacteria, the only known bacterial clade capable of oxygenic photosynthesis and the only group of organisms found thus far to produce abundant 2-methylbacteriohopanepolyols (2-MeBHPs). Here, we report the identification of significant quantities of 2-MeBHP in two strains of the anoxygenic phototroph Rhodopseudomonas palustris. Biosynthesis of 2-MeBHP can occur in the absence of O(2), deriving the C-2 methyl group from methionine. The relative abundance of 2-MeBHP varies considerably with culture conditions, ranging from 13.3% of total bacteriohopanepolyol (BHP) to trace levels of methylation. Analysis of intact BHPs reveals the presence of methylated bacteriohopane-32,33,34,35-tetrol but no detectable methylation of 35-aminobacteriohopane-32,33,34-triol. Our results demonstrate that an anoxygenic photoautotroph is capable of generating 2-MeBHPs and show that the potential origins of sedimentary 2-methylhopanoids are more diverse than previously thought.
沉积性2-甲基藿烷已被用作蓝细菌的生物标志物替代物，蓝细菌是唯一已知的能够进行产氧光合作用的细菌进化枝，也是迄今为止发现的唯一能产生大量2-甲基细菌藿烷多元醇（2-MeBHPs）的生物群体。在此，我们报告在两株厌氧光合细菌沼泽红假单胞菌中鉴定出大量的2-MeBHP。2-MeBHP的生物合成可以在无氧条件下发生，其C-2甲基基团来源于甲硫氨酸。2-MeBHP的相对丰度随培养条件变化很大，从占总细菌藿烷多元醇（BHP）的13.3%到痕量水平的甲基化。对完整的BHP进行分析发现存在甲基化的细菌藿烷-32,33,34,35-四醇，但未检测到35-氨基细菌藿烷-32,33,34-三醇的甲基化。我们的结果表明厌氧光合自养生物能够产生2-MeBHPs，并且表明沉积性2-甲基类藿烷的潜在来源比之前认为的更加多样。
