ABSTRACT
The microbial community inhabiting the shallow sulfate-methane-transition-zone in coastal sediments from Marine Lake Grevelingen (the Netherlands) was characterized, and the ability of the microorganisms to carry out anaerobic oxidation of methane coupled to sulfate reduction was assessed in activity tests. In vitro activity tests of the sediment with methane and sulfate demonstrated sulfide production coupled to the simultaneous consumption of sulfate and methane at approximately equimolar ratios over a period of 150 days. The maximum sulfate reduction rate was 5 umol sulfate per gram dry weight per day during the incubation period. Diverse archaeal and bacterial clades were retrieved from sequence analysis with the majority of them clustering to Euryarchaeota, Thaumarcheota, Bacteroidetes and Proteobacteria. The 16S rRNA sequence analysis showed that the sediment from Marine Lake Grevelingen contained anaerobic methanotrophic Archaea (ANME) and methanogens as archaeal clades with a role in the methane cycling. ANME at the studied site mainly belong to the ANME-3 clade. Sulfate reducing bacteria from Desulfobulbus clades were found among the sulfate reducers, however with very low relative abundance. Desulfobulbus is commonly associated with ANME, but ANME and Desulfobulbus were not visualized together, suggesting the possibility of independent AOM by ANME-3. This study provides one of the few reports for the presence of ANME-3 in a shallow coastal marine sediment.
