title: Nitrate-based niche differentiation by distinct sulfate-reducing bacteria involved in the anaerobic oxidation of methane.
abstract: Diverse associations between methanotrophic archaea (ANME) and sulfate-reducing bacterial groups (SRB) often co-occur in marine methane seeps; however, the ecophysiology of these different symbiotic associations has not been examined. Here, we applied a combination of molecular, geochemical and Fluorescence in situ hybridization (FISH) coupled to nanoscale secondary ion mass spectrometry (FISH-NanoSIMS) analyses of in situ seep sediments and methane-amended sediment incubations from diverse locations (Eel River Basin, Hydrate Ridge and Costa Rican Margin seeps) to investigate the distribution and physiology of a newly identified subgroup of the Desulfobulbaceae (seepDBB) found in consortia with ANME-2c archaea, and compared these with the more commonly observed associations between the same ANME partner and the Desulfobacteraceae (DSS). FISH analyses revealed aggregates of seepDBB cells in association with ANME-2 from both environmental samples and laboratory incubations that are distinct in their structure relative to co-occurring ANME/DSS consortia. ANME/seepDBB aggregates were most abundant in shallow sediment depths below sulfide-oxidizing microbial mats. Depth profiles of ANME/seepDBB aggregate abundance revealed a positive correlation with elevated porewater nitrate relative to ANME/DSS aggregates in all seep sites examined. This relationship with nitrate was supported by sediment microcosm experiments, in which the abundance of ANME/seepDBB was greater in nitrate-amended incubations relative to the unamended control. FISH-NanoSIMS additionally revealed significantly higher (15)N-nitrate incorporation levels in individual aggregates of ANME/seepDBB relative to ANME/DSS aggregates from the same incubation. These combined results suggest that nitrate is a geochemical effector of ANME/seepDBB aggregate distribution, and provides a unique niche for these consortia through their utilization of a greater range of nitrogen substrates than the ANME/DSS.
authors.affiliation: Division of Biology, California Institute of Technology, Pasadena, CA, USA.
authors.forename: A
authors.initials: A
authors.lastname: Green-Saxena
authors.affiliation: Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA.
authors.forename: A E
authors.initials: AE
authors.lastname: Dekas
authors.affiliation: Global Environmental Center, California Institute of Technology, Pasadena, CA, USA.
authors.forename: N F
authors.initials: NF
authors.lastname: Dalleska
authors.affiliation: Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA.
authors.forename: V J
authors.initials: VJ
authors.lastname: Orphan
mesh_terms: D001105:Archaea / Q000145:classification / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D020564:Deltaproteobacteria / Q000145:classification / Q000235:genetics* / Q000378:metabolism*; D017753:Ecosystem; D004783:Environmental Microbiology; D019015:Geologic Sediments / Q000382:microbiology*; D017404:In Situ Hybridization, Fluorescence; D008697:Methane / Q000378:metabolism*; D008969:Molecular Sequence Data; D009566:Nitrates / Q000378:metabolism*; D010084:Oxidation-Reduction; D010802:Phylogeny
chemical_list: D009566:Nitrates; D008697:Methane