title: Identification of the dominant sulfate-reducing bacterial partner of anaerobic methanotrophs of the ANME-2 clade.
abstract: The anaerobic oxidation of methane (AOM) with sulfate as terminal electron acceptor is mediated by consortia of methanotrophic archaea (ANME) and sulfate-reducing bacteria (SRB). Whereas three clades of ANME have been repeatedly studied with respect to phylogeny, key genes and genomic capabilities, little is known about their sulfate-reducing partner. In order to identify the partner of anaerobic methanotrophs of the ANME-2 clade, bacterial 16S rRNA gene libraries were constructed from cultures highly enriched for ANME-2a and ANME-2c in consortia with Deltaproteobacteria of the Desulfosarcina/Desulfococcus group (DSS). Phylogenetic analysis of those and publicly available sequences from AOM sites supported the hypothesis by Knittel and colleagues that the DSS partner belongs to the diverse SEEP-SRB1 cluster. Six subclusters of SEEP-SRB1, SEEP-SRB1a to SEEP-SRB1f, were proposed and specific oligonucleotide probes were designed. Using fluorescence in situ hybridization on samples from six different AOM sites, SEEP-SRB1a was identified as sulfate-reducing partner in up to 95% of total ANME-2 consortia. SEEP-SRB1a cells exhibited a rod-shaped, vibrioid, or coccoid morphology and were found to be associated with subgroups ANME-2a and ANME-2c. Moreover, SEEP-SRB1a was also detected in 8% to 23% of ANME-3 consortia in Haakon Mosby Mud Volcano sediments, previously described to be predominantly associated with SRB of the Desulfobulbus group. SEEP-SRB1a contributed to only 0.3% to 0.7% of all single cells in almost all samples indicating that these bacteria are highly adapted to a symbiotic relationship with ANME-2.
authors.affiliation: Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, 28359 Bremen, Germany.
authors.forename: Lars
authors.initials: L
authors.lastname: Schreiber
authors.forename: Thomas
authors.initials: T
authors.lastname: Holler
authors.forename: Katrin
authors.initials: K
authors.lastname: Knittel
authors.forename: Anke
authors.initials: A
authors.lastname: Meyerdierks
authors.forename: Rudolf
authors.initials: R
authors.lastname: Amann
mesh_terms: D000693:Anaerobiosis; D004269:DNA, Bacterial / Q000235:genetics; D020564:Deltaproteobacteria / Q000145:classification / Q000235:genetics / Q000378:metabolism; D015723:Gene Library; D019015:Geologic Sediments / Q000382:microbiology; D017404:In Situ Hybridization, Fluorescence; D008697:Methane / Q000378:metabolism*; D059013:Microbial Consortia; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D016999:Sulfur-Reducing Bacteria / Q000145:classification* / Q000235:genetics / Q000378:metabolism; D013559:Symbiosis
chemical_list: D004269:DNA, Bacterial; D012336:RNA, Ribosomal, 16S; D008697:Methane