Identification of carbon and nitrogen assimilating microbial populations in anaerobically methane-oxidising mats by stable isotope probing
Zusammenfassung der Projektergebnisse
Anaerobic oxidation of methane (AOM) is a process of global importance as it effectively reduces the emission of the greenhouse gas methane from marine sediments. The process of methane oxidation coupled to sulfate reduction had been assigned to anaerobically methane-oxidizing archaea (ANME) and associated SRB previously. Metagenome and biochemical analyses suggest that the anaerobic oxidation of methane proceeds through reversal of the methanogenesis in ANME archaea. However, the details of the metabolic interaction between ANME archaea and sulfate-reducing bacteria had remained enigmatic, especially the mechanism, possible metabolic intermediates, and the identity of all mat microorganisms involved. A better understanding of metabolic interactions in anaerobic methane oxidation requires knowledge on assimilatory carbon and nitrogen fluxes within AOM mat communities. Our project elucidated novel assimilatory, physiological capabilities, and novel community members of anaerobically methane oxidizing consortia. Besides the canonical sulfate-reducing elta-Proteobacteria, other taxa such as yet uncultivated microorganisms related to candidate division WS3, Chloroflexi, Spirochaetes, Bacteroidetes, and Planctomycetes were found. For most of these groups, however, a physiological role remains unknown. One of the key findings of the project was that ANME have high methanogenic capabilities and that AOM takes place simultaneously to AOM (AOM/methanogenesis ratio 2:1). Methanogenesis was methylotrophic and CO2-reducing, while acetoclastic methanogenesis was not essential in the studied ANME-1 and ANME-2 mats. Moreover, rate measurements and Lipid- SIP clearly demonstrated that ANME-2 associations much more rely on methane supply than ANME-1 consortia, which itself, contrary to ANME-2 communities, were found to have also a high heterotrophic potential. Surprisingly, rRNA-based isotope probing showed a stronger labelling of ANME-1 than ANME-2 from methanol when methane was not present. Single cell-based analysis revealed a substantial potential of Bacteroidetes for assimilating methanol in Black mats. The 15N-labelling experiments revealed that under AOM conditions, dinitrogen played an insignificant role as nitrogen source, while assimilatory and dissimilatory nitrate reduction occurred. High denitrification rates were stimulated by methane and sulfate supply, suggesting that oxidation of reduced sulfur compounds like sulfides was necessary. Mainly ammonium was used for biomass synthesis. In accordance with the versatile metabolic activities, we identified novel biomarkers for ANME associated bacteria. An unsaturated nC31-triene was abundant in ANME-2 consortia and the similarly high abundance of Chloroflexi in respective mats and the occurrence of the biomarkers in Chloroflexi from other settings suggests these bacteria as sources. Furthermore, members of the phylum Caldithrix have to be considered as sources for terminally branched pentadecanoic fatty acids and dihydrosqualenes in ANME-1 settings. While the role of Chloroflexi and members of the phylum Caldithrix in AOM-communities has still to be clarified, assimilation patterns suggest a heterotrophic role for both. Moreover, C35-isoprenoidal hydrocarbons were solely detected in ANME-1 dominated mats and 13C-uptakes were particularly high if growing under methanogenic conditions. This evidences C35-isoprenoidal hydrocarbons as novel phylogenetic marker for ANME-1 and a, furthermore, specific assimilation suggest these compounds as hydrogen sink during methanogenesis.
Projektbezogene Publikationen (Auswahl)
- (2008). A novel, multi-layered methanotrophic microbial mat system growing on the sediment of the Black Sea. Environmental Microbiology 10: 1934-1947
Krüger M, Blumenberg M, Kasten S, Wieland S, Känel L, Klock J-H, Michaelis W, Seifert R
- (2011). Accelerated methanogenesis from aliphatic and aromatic hydrocarbons under iron and sulfate reducing conditions. FEMS Microbiol. Letters 315: 6-16
Siegert M, Cichoka D, Herrmann S, Gründger F, Feisthauer S, Richnow H-H, Springael D, Krüger M
- (2011). Anaerobic Oxidation of Methane Dominates Hydrocarbon Degradation at a Marine Methane Seep in the Sumatra Forearc Basin, Indian Ocean. Frontiers in Extreme Microbiology 2: 1-16
Siegert M, Krüger M, Teichert B, Schippers A
- (2011). Identification of dominant dissimilatory sulfate reducing enzymes in Black Sea microbial mats mediating anaerobic oxidation of methane. Environ. Microbiol. 13: 1370-1379
Basen M, Krüger M, Milucka J, Küver J, Widdel F, Thauer K, Kahnt J, Shima S
- (2012). Crystal structure of a methyl-coenzyme M reductase purified from Black Sea mats catalyzing the anaerobic oxidation of methane with sulfate. Nature 481: 98-101
Shima S.,. Krüger M, Weinert T, Demmer U, Thauer RK, and Ermler U
- (2012). Terrestrial mud volcanoes of the Salse di Nirano (Italy) as a window into deeply buried organic-rich shales of Plio-Pleistocene age: Sedimentary Geology: 263-264, 202-209
Heller C., Blumenberg M., Hoppert M., Taviani M., and Reitner J.
(Siehe online unter https://doi.org/10.1016/j.sedgeo.2011.05.004) - Methanogenic capabilities of ANME archaea deduced from 13C-labelling approaches. Environmental Microbiology
Bertram S, Blumenberg M, Michaelis W, Siegert M, Krüger M, and Seifert R
(Siehe online unter https://doi.org/10.1111/1462-2920.12112)
