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Applied and Environmental Microbiology, March 2009, p. 1487-1499, Vol. 75, No. 6
0099-2240/09/$08.00+0     doi:10.1128/AEM.01812-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Variations in Archaeal and Bacterial Diversity Associated with the Sulfate-Methane Transition Zone in Continental Margin Sediments (Santa Barbara Basin, California){triangledown} ,{dagger}

Benjamin K. Harrison,1 Husen Zhang,1 Will Berelson,2 and Victoria J. Orphan1*

Division of Geological and Planetary Sciences, California Institute of Technology, Mail Code 100-23, Pasadena, California 91125,1 Department of Earth Sciences, University of Southern California, Zumberge Hall of Science (ZHS), 3651 Trousdale Parkway, Los Angeles, California 90089-07402

Received 5 August 2008/ Accepted 5 January 2009

The sulfate-methane transition zone (SMTZ) is a widespread feature of continental margins, representing a diffusion-controlled interface where there is enhanced microbial activity. SMTZ microbial activity is commonly associated with the anaerobic oxidation of methane (AOM), which is carried out by syntrophic associations between sulfate-reducing bacteria and methane-oxidizing archaea. While our understanding of the microorganisms catalyzing AOM has advanced, the diversity and ecological role of the greater microbial assemblage associated with the SMTZ have not been well characterized. In this study, the microbial diversity above, within, and beneath the Santa Barbara Basin SMTZ was described. ANME-1-related archaeal phylotypes appear to be the primary methane oxidizers in the Santa Barbara Basin SMTZ, which was independently supported by exclusive recovery of related methyl coenzyme M reductase genes (mcrA). Sulfate-reducing Deltaproteobacteria phylotypes affiliated with the Desulfobacterales and Desulfosarcina-Desulfococcus clades were also enriched in the SMTZ, as confirmed by analysis of dissimilatory sulfite reductase (dsr) gene diversity. Statistical methods demonstrated that there was a close relationship between the microbial assemblages recovered from the two horizons associated with the geochemically defined SMTZ, which could be distinguished from microbial diversity recovered from the sulfate-replete overlying horizons and methane-rich sediment beneath the transition zone. Comparison of the Santa Barbara Basin SMTZ microbial assemblage to microbial assemblages of methane seeps and other organic matter-rich sedimentary environments suggests that bacterial groups not typically associated with AOM, such as Planctomycetes and candidate division JS1, are additionally enriched within the SMTZ and may represent a common bacterial signature of many SMTZ environments worldwide.

* Corresponding author. Mailing address: Division of Geological and Planetary Sciences, Mail Code 100-23, 1200 E. California Blvd., Pasadena, CA 91125. Phone: (626) 395-1786. Fax: (626) 683-0621. E-mail: vorphan{at}gps.caltech.edu

{triangledown} Published ahead of print on 9 January 2009.

{dagger} Supplemental material for this article may be found at http://aem.asm.org/.

Applied and Environmental Microbiology, March 2009, p. 1487-1499, Vol. 75, No. 6
0099-2240/09/$08.00+0     doi:10.1128/AEM.01812-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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