Orphan, V. J. and Jahnke, L. L. and Embaye, T. and Turk, K. A. and Pernthaler, A. and Summons, R. E. and Des Marais, D. J. (2008) Characterization and spatial distribution of methanogens and methanogenic biosignatures in hypersaline microbial mats of Baja California. Geobiology, 6 (4). pp. 376-393. ISSN 1472-4677 http://resolver.caltech.edu/CaltechAUTHORS:20090427-131232717
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Well-developed hypersaline cyanobacterial mats from Guerrero Negro, Baja California Sur, sustain active methanogenesis in the presence of high rates of sulfate reduction. Very little is known about the diversity and distribution of the microorganisms responsible for methane production in these unique ecosystems. Applying a combination of 16S rRNA and metabolic gene surveys, fluorescence in situ hybridization, and lipid biomarker analysis, we characterized the diversity and spatial relationships of methanogens and other archaea in the mat incubation experiments stimulated with methanogenic substrates. The phylogenetic and chemotaxonomic diversity established within mat microcosms was compared with the archaeal diversity and lipid biomarker profiles associated with different depth horizons in the in situ mat. Both archaeal 16S rRNA and methyl coenzyme M reductase gene (mcrA) analysis revealed an enrichment of diverse methanogens belonging to the Methanosarcinales in response to trimethylamine addition. Corresponding with DNA-based detection methods, an increase in lipid biomarkers commonly synthesized by methanogenic archaea was observed, including archaeol and sn-2-hydroxyarchaeol polar lipids, and the free, irregular acyclic isoprenoids, 2,6,10,15,19-pentamethylicosene (PMI) and 2,6,11,15-tetramethylhexadecane (crocetane). Hydrogen enrichment of a novel putative archaeal polar C_(30) isoprenoid, a dehydrosqualane, was also documented. Both DNA and lipid biomarker evidence indicate a shift in the dominant methanogenic genera corresponding with depth in the mat. Specifically, incubations of surface layers near the photic zone predominantly supported Methanolobus spp. and PMI, while Methanococcoides and hydroxyarchaeol were preferentially recovered from microcosms of unconsolidated sediments underlying the mat. Together, this work supports the existence of small but robust methylotrophic methanogen assemblages that are vertically stratified within the benthic hypersaline mat and can be distinguished by both their DNA signatures and unique isoprenoid biomarkers.
|Additional Information:||© 2008 The Authors. Journal compilation © 2008 Blackwell Publishing Ltd. Received 28 December 2007; accepted 6 May 2008. The authors are indebted to Brad Bebout for use of his laboratory facilities and support during this project. We also thank Bob Vjrenhoek and Ed DeLong for generous use of the MBARI sequencing facilities and Steve Carpenter, Mike Kubo, Mary Hogan, Beth Orcutt and Tori Hoehler for assistance with various aspects of this work. We acknowledge two anonymous reviewers for comments that greatly improved this manuscript. This research was made possible by grants from the NASA Exobiology program (DJD) and NRA-01- 01-EXB-035 (LLJ), grant no. NNG05GN62G (RES), a Moore Foundation Young Investigator award (VJO), and a National Research Council fellowship awarded to VJO and the logistical support of ESSA Exportadora del Sal, S.A., de C.V., Guerrero Negro, Baja California Sur, Mexico.|
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|Deposited By:||Tony Diaz|
|Deposited On:||07 Aug 2009 18:47|
|Last Modified:||26 Dec 2012 10:58|
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