A novel, multi-layered methanotrophic microbial mat system growing on the sediment of the Black Sea.

A novel microbially diverse type of 1- to 5-cm-thick mat performing anaerobic oxidation of methane (AOM) and covering several square metres of the seafloor was discovered in the Black Sea at 180 m water depth. Contrary to other AOM-mat systems of the Black Sea these floating mats are not associated to free gas and are not stabilized by authigenic carbonates. However, supply of methane is ensured by the horizontal orientation of the mats acting as a cover of methane enriched fluids ascending from the underlying sediments. Thorough investigation of their community composition by molecular microbiology and lipid biomarkers, metabolic activities and elemental composition showed that the mats provide a clearly structured system with extracellular polymeric substances (EPS) building the framework of the mats. The top black zone, showing high rates of AOM (15 mumol g(dw) (-1) day(-1)), was dominated by ANME-2, while the following equally active pink layer was dominated by ANME-1 Archaea. The lowest AOM activity (2 mumol g(dw) (-1) day(-1)) and cell numbers were found in the greyish middle part delimited towards the sediment by a second pink, ANME-1-dominated and sometimes a black outer layer (ANME-2). Our work clearly shows that the different microbial populations are established along defined chemical gradients such as methane, sulfate or sulfide.

Cooccurrence of aerobic and anaerobic methane oxidation in the water column of Lake Plusssee.

Dissolved methane was investigated in the water column of eutrophic Lake Plusssee and compared to temperature, oxygen, and sulfide profiles. Methane concentrations and delta-13C signatures indicated a zone of aerobic methane oxidation and additionally a zone of anaerobic methane oxidation in the anoxic water body. The latter coincided with a peak in hydrogen sulfide concentration. High cell numbers of aerobic and anaerobic methane-oxidizing microorganisms were detected by fluorescence in situ hybridization (FISH) or the more sensitive catalyst-amplified reporter deposition-FISH, respectively, in these layers.