title: Biosynthesis of 2-methylbacteriohopanepolyols by an anoxygenic phototroph.
abstract: 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.
authors.affiliation: Divisions of Geological and Planetary Sciences and Biology, California Institute of Technology and Howard Hughes Medical Institute, Pasadena, CA 91125, USA.
authors.forename: Sky E
authors.initials: SE
authors.lastname: Rashby
authors.forename: Alex L
authors.initials: AL
authors.lastname: Sessions
authors.forename: Roger E
authors.initials: RE
authors.lastname: Summons
authors.forename: Dianne K
authors.initials: DK
authors.lastname: Newman
mesh_terms: D000332:Aerobiosis; D002853:Chromatography, Liquid; D008401:Gas Chromatography-Mass Spectrometry; D008745:Methylation; D010788:Photosynthesis; D052817:Phototrophic Processes; D012241:Rhodopseudomonas / Q000145:classification / Q000378:metabolism*; D014315:Triterpenes / Q000737:chemistry / Q000378:metabolism*
chemical_list: C498821:2-methylhopane; D014315:Triterpenes