Diagnostic lipid biomarker and stable carbon isotope signatures of microbial communities mediating the anaerobic oxidation of methane with sulphate Helge Niemann a, * , Marcus Elvert b a Max Planck Institute for Marine Microbiology Bremen, Celsiusstrasse 1, 28359 Bremen, Germany b Department of Geosciences, Organic Geochemistry Group, University of Bremen, Leobener Strasse, 28359 Bremen, Germany article info Article history: Received 3 October 2007 Received in revised form 6 November 2007 Accepted 7 November 2007 Available online 17 November 2007 abstract The anaerobic oxidation of methane (AOM) with sulphate is the most important sink for methane in marine environments. This process is mediated by a consortium of methano- trophic archaea and sulphate reducing bacteria. So far, three groups of anaerobic methane oxidisers (ANME-1, -2 and -3) related to the methanogenic Methanosarcinales and Methanomicrobiales were discovered. The sulphate reducing partner of ANME-1 and -2 are two different eco-types of SRB related to the Desulfosarcina/Desulfococcus cluster (Seep-SRB1), whereas ANME-3 is associated with Desulfobulbus spp. (DBB). In this article, we reviewed literature data to assign statistically significant lipid biomarker signatures for a chemotaxonomic identification of the three known AOM communities. The lipid sig- natures of ANME-2/Seep-SRB1 and ANME-3/DBB are intriguingly similar, whereas ANME- 1/Seep-SRB1 shows substantial differences to these AOM communities. ANME-1 can be distinguished from ANME-2 and -3 by a low ratio of the isoprenoidal dialkyl glycerol diethers sn2-hydroxyarchaeol and archaeol combined with a comparably low stable car- bon isotope difference of archaeol relative to the source methane. Furthermore, only ANME-1 contains substantial amounts of isoprenoidal glycerol dialkyl glycerol tetraethers (GDGTs), however, with the probable exception of the ANME-2c sub-cluster. In contrast to the ANME-1 archaea, the tail to tail linked hydrocarbon tetramethylhexadecane (cro- cetane) is unique to ANME-2, whereas pentamethylicosenes (PMIs) with 4 and 5 double bonds without any higher saturated homologues were only found in ANME-3. The sul- phate reducing partner of ANME-1 can be discerned from those of ANME-2 and -3 by a low ratio of the fatty acids (FAs) C 16:1x5 relative to i-C 15:0 and, although to a lesser degree, by a high abundance of ai-C 15:0 relative to i-C 15:0 . Furthermore, substantial amounts of 13 C depleted non-isoprenoidal monoalkyl glycerol ethers (MAGEs) were only found in the sulphate reducing partners of ANME-2 and -3. A differentiation of these SRB is possible based on the characteristic presence of the FAs cy-C 17:0x5,6 and C 17:1x6 , respec- tively. Generally, the data analysed here show overlaps between the different AOM com- munities, which highlights the need to use multiple lipid signatures for a robust identification of the dominating microbes involved. Ó 2007 Elsevier Ltd. All rights reserved. 1. Introduction Methane is an important greenhouse gas which is >20 times more potent than CO 2 (Manne and Richels, 2001; Wuebbles and Hayhoe, 2002). High amounts of methane are temporarily stored in sediments of the continental 0146-6380/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.orggeochem.2007.11.003 * Corresponding author. Present address: Institute for Environmental Geoscience, University of Basel, Bernoullistrasse 30, 4056 Basel, Switzer- land. Tel.: +41 61 2673615; fax: +41 61 2670479. E-mail address: helge.niemann@unibas.ch (H. Niemann). Organic Geochemistry 39 (2008) 1668–1677 Contents lists available at ScienceDirect Organic Geochemistry journal homepage: www.elsevier.com/locate/orggeochem