Page 121 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

3.19 m 3.49 m 3.68 m 1.31 m 1.61m 1.81 m 3.64 m 3.74 m
Taxonomy Archaea
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Taxonomy Bacteria
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1.4 m 1.86 m 1.97 m 2.22 m
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AB
Senator Westphal Max
Westland S Gundelach Vittorio
0 25 50 75 100 0 25 50 75 100 Relative abundance (%)
Figure 6. Phylogenetic classification of amplified archaeal (A) and bacterial (B) 16S rRNA gene sequences obtained from the Vittorio, Max Gundelach, Senator Westphal, and Westland sites. The Y- axis values indicate the depth below sea level (dbsl). The maximum taxonomy depth is on family level. Taxonomic groups with < 2% abundance are grouped in “Other”.
Amendment with hydrogen and CO2 (H2/CO2) and acetate, two common substrates for methanogenic archaea, did not induce CH4 production within the period of incubation (60 days). Even though no methanogenesis was observed, the concentration of H2/CO2 changed. This may be indicative of competition for substrates, likely by sulfate-reducing microorganisms facilitated by abundant sulfate supplies that penetrate up to meters deep into the sediment in marine environments (Jorgensen 1983) or, in this case, incubations with ample supplies of sulfate. Amendment with methoxyphenol (MPH) and trimethoxybenzoate (TMB), substrates used by methoxydotrophic methanogens, did not induce CH4 production, and a TMB concentration of 3 mM appeared to be inhibitory to the methanogenic community. Neither aerobic nor anaerobic methanotrophic activity was observed, indicating the absence of an in situ biological CH4 filter (Fig. S2 and S3).
16S rRNA gene quantification shows dominance of archaea over bacteria in all cores
Archaeal and bacterial abundances in each core section were assessed by quantitative PCR. In all cores, archaea were more abundant than bacteria (Table S3). Cores 6 and 7 had archaea-to- bacteria ratios of 7.0 and 9.0, whereas cores 17 and 26 had ratios of 55.1 and 43.9, respectively.
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