Biosynthesis of 2-methylbacteriohopanepolyols by an anoxygenic phototroph

Rashby, Sky E.; Sessions, Alex L.; Summons, Roger E.; Newman, Dianne K.

doi:10.1073/pnas.0704912104

Cited by 254 publications

(192 citation statements)

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“…By extrapolation, these molecules have been used as evidence for the antiquity of oxygenic photosynthesis and for the waxing and waning of cyanobacterial primary productivity and nitrogen fixation in the geological past (10,18,19). However, the robustness of this interpretation was weakened by the discovery that an anoxygenic phototroph, Rhodopseudomonas palustris TIE-1, produces 2-methylhopanoids when grown under strictly anaerobic conditions (20). Because a strain of the same clade had previously been reported not to make 2-methylhopanoids (21), an important question emerged: was this a chance and unrepresentative finding, or is biosynthesis of these molecules widespread?…”

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confidence: 99%

“…Because the majority of bacterial diversity has not been cultured (22) and because the production of 2-methylhopanopids varies under different growth conditions (15,20,23), it is likely that our assessment of the taxonomic distribution of these molecules is incomplete. As a result, there is inadequate data to unambiguously interpret sedimentary 2-methylhopanes as biomarkers for cyanobacteria or other taxa.…”

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confidence: 99%

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Identification of a methylase required for 2-methylhopanoid production and implications for the interpretation of sedimentary hopanes

Welander

Coleman

Sessions

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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The rise of atmospheric oxygen has driven environmental change and biological evolution throughout much of Earth's history and was enabled by the evolution of oxygenic photosynthesis in the cyanobacteria. Dating this metabolic innovation using inorganic proxies from sedimentary rocks has been difficult and one important approach has been to study the distributions of fossil lipids, such as steranes and 2-methylhopanes, as biomarkers for this process. 2-methylhopanes arise from degradation of 2-methylbacteriohopanepolyols (2-MeBHPs), lipids thought to be synthesized primarily by cyanobacteria. The discovery that 2-MeBHPs are produced by an anoxygenic phototroph, however, challenged both their taxonomic link with cyanobacteria and their functional link with oxygenic photosynthesis. Here, we identify a radical SAM methylase encoded by the hpnP gene that is required for methylation at the C-2 position in hopanoids. This gene is found in several, but not all, cyanobacteria and also in α -proteobacteria and acidobacteria. Thus, one cannot extrapolate from the presence of 2-methylhopanes alone, in modern environments or ancient sedimentary rocks, to a particular taxonomic group or metabolism. To understand the origin of this gene, we reconstructed the evolutionary history of HpnP. HpnP proteins from cyanobacteria, Methylobacterium species, and other α-proteobacteria form distinct phylogenetic clusters, but the branching order of these clades could not be confidently resolved. Hence,it is unclear whether HpnP, and 2-methylhopanoids, originated first in the cyanobacteria. In summary, existing evidence does not support the use of 2-methylhopanes as biomarkers for oxygenic photosynthesis.biomarkers | cyanobacteria | hopanoids | phylogeny | radical SAM

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confidence: 99%

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confidence: 99%

Identification of a methylase required for 2-methylhopanoid production and implications for the interpretation of sedimentary hopanes

Welander

Coleman

Sessions

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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205

179

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“…0.2-0.5 min earlier on the DB-XLB column) and the change in major MS fragment from m/z 191 to 205. Localization of the methyl at C-2 had been confirmed in R. palustris by Rashby et al (2007). A 20-methyl isomer of tetrahymanol was also tentatively assigned as largely coeluting with 2-methyltetrahymanol (Bravo et al, 2001).…”

Section: Hopanoid Identificationmentioning

confidence: 98%

“…Although the functionalized hopanoids of R. palustris have been previously described (Rashby et al, 2007;Talbot et al, 2008), there has not been a direct comparison of quantitative GC-MS and LC-MS measurements on the same extract. Absolute concentration of hopanoids was calculated using FID peak areas relative to the epianderosterone internal standard for GC, and using m/z 191 or 205 peak areas relative to a 4 point calibration curve generated with an authentic standard of pregnone diacetate for LC, assuming unit response factor for all analytes (Sáenz et al, 2011).…”

Section: Comparison With Lc-ms-mentioning

confidence: 99%

“…In modern sediments, functionalized BHPs are being explored as diagnostic for varying clades of bacteria (reviewed by ).In rocks and oils,the relative abundance of different hopane isomers can provide information about both environmental conditions during deposition, as well as maturity (Seifert and Moldowan, 1980;Brassell et al, 1983;Peters and Moldowan, 1991;Peters et al, 2005). For ancient rocks, hopanoids methylated at C-2 or C-3 have received particular attention because they have been proposed as diagnostic markers for cyanobacteria and aerobic methylotrophs, respectively (Zundel and Rohmer, 1985a,b;Summons and Jahnke, 1990;Summons et al, 1994Summons et al, , 1999Farrimond et al, 2004).A current research focus lies in understanding the cellular function of BHPs in bacteria, the genetic basis for their biosynthesis and modification, and their distribution and evolutionary relationships among extant organisms (Fischer et al, 2005;Blumenberg et al, 2006;Fischer and Pearson, 2007;Rashby et al, 2007;Doughty et al, 2009;Welander et al, 2009Welander et al, , 2010Welander et al, , 2012Bradley et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

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Identification and quantification of polyfunctionalized hopanoids by high temperature gas chromatography–mass spectrometry

Sessions

Zhang

Welander

et al. 2013

Organic Geochemistry

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Hopanoids are triterpenoids produced mainly by bacteria, are ubiquitous in the environment, and have many important applications as biological markers. A wide variety of related hopanoid structures exists, many of which are polyfunctionalized. These modifications render the hopanoids too involatile for conventional gas chromatography (GC) separation, so require either laborious oxidative cleavage of the functional groups or specialized high temperature (HT) columns. Here we describe the systematic evaluation and optimization of a HT-GC method for the analysis of polyfunctionalized hopanoids and their methylated homologs. Total lipid extracts are derivatized with acetic anhydride and no further treatment or workup is required. We show that acid or base hydrolysis to remove di-and triacylglycerides leads to degradation of several BHP structures. DB-XLB type columns can elute hopanoids up to bacteriohopane-tetrol at 350 °C, with baseline separation of all 2-methyl/desmethyl homologs. DB-5HT type columns can additionally elute bacteriohopaneaminotriol and bacteriohopaneaminotetrol, but do not fully separate 2-methyl/ desmethyl homologs. The method gave 2-to 7-fold higher recovery of hopanoids than oxidative cleavage and can provide accurate quantification of all analytes including 2-methyl hopanoids. By comparing data from mass spectra with those from a flame ionization detector, we show that the mass spectromet (MS) response factors for different hopanoids using either total ion counts or m/z 191 vary substantially. Similarly, 2-methyl ratios estimated from selected-ion data are lower than those from FID by 10-30% for most hopanoids, but higher by ca. 10% for bacteriohopanetetrol. Mass spectra for a broad suite of hopanoids, including 2-methyl homologs, from Rhodopseudomonas palustris are presented, together with the tentative assignment of several new hopanoid degradation products.

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Biomarkers: Informative Molecules for Studies in Geobiology

Summons

Lincoln

2012

Fundamentals of Geobiology

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Biosynthesis of 2-methylbacteriohopanepolyols by an anoxygenic phototroph

Cited by 254 publications

References 53 publications

Identification of a methylase required for 2-methylhopanoid production and implications for the interpretation of sedimentary hopanes

Identification of a methylase required for 2-methylhopanoid production and implications for the interpretation of sedimentary hopanes

Identification and quantification of polyfunctionalized hopanoids by high temperature gas chromatography–mass spectrometry

Biomarkers: Informative Molecules for Studies in Geobiology

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