Ricci, J. N. and Michel, A. J. and Newman, D. K. (2015) Phylogenetic analysis of HpnP reveals the origin of 2-methylhopanoid production in Alphaproteobacteria. Geobiology, 13 (3). pp. 267-277. ISSN 1472-4677. http://resolver.caltech.edu/CaltechAUTHORS:20150202-095339879
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Hopanoids are bacterial steroid-like lipids that can be preserved in the rock record on billion-year timescales. 2-Methylhopanoids are of particular interest to geobiologists because methylation is one of the few chemical modifications that remain after diagenesis and catagenesis. 2-Methylhopanes, the molecular fossils of 2-methylhopanoids, are episodically enriched in the rock record, but we do not have a robust interpretation for their abundance patterns. Here, we exploit the evolutionary record found in molecular sequences from extant organisms to reconstruct the biosynthetic history of 2-methylhopanoids using the C-2 hopanoid methylase, HpnP. Based on HpnP phylogenetic analysis, we find that 2-methylhopanoids originated in a subset of the Alphaproteobacteria. This conclusion is statistically robust and reproducible in multiple trials varying the outgroup, trimming stringency, and ingroup dataset used to infer the evolution of this protein family. The capacity for 2-methylhopanoid production was likely horizontally transferred from the Alphaproteobacteria into the Cyanobacteria after the Cyanobacteria's major divergences. Together, these results suggest that the ancestral function of 2-methylhopanoids was not related to oxygenic photosynthesis but instead to a trait already present in the Alphaproteobacteria. Moreover, given that early 2-methylhopane deposits could have been made solely by Alphaproteobacteria before the acquisition of hpnP by Cyanobacteria, and that the Alphaproteobacteria are thought to be ancestrally aerobic, we infer that 2-methylhopanoids likely arose after the oxygenation of the atmosphere. This finding is consistent with the geologic record—the oldest syngenetic 2-methylhopanes occur after the rise of oxygen, in middle Proterozoic strata of the Barney Creek Formation.
|Additional Information:||© 2015 John Wiley & Sons Ltd. Received 2 December 2014; accepted 10 January 2015. Article first published online: 29 January 2015. We would like to thank Woodward Fischer, James Hemp, Jena Johnson, and members of the Newman Lab for their helpful suggestions. We are grateful to John Spear for providing samples from Yellowstone National Park through the Yellowstone Center for Resources (permit #5664). This work was supported by grants from NASA (NNX12AD93G), the National Science Foundation (1224158), and the Howard Hughes Medical Institute (HHMI) to DKN. JNR is supported by an NSF graduate fellowship. DKN is an Investigator of the Howard Hughes Medical Institute.|
|Official Citation:||Ricci, J. N., Michel, A. J. and Newman, D. K. (2015), Phylogenetic analysis of HpnP reveals the origin of 2-methylhopanoid production in Alphaproteobacteria. Geobiology, 13: 267–277. doi: 10.1111/gbi.12129|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||04 Feb 2015 23:09|
|Last Modified:||08 May 2015 16:39|
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