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72% at 10°C) as the most abundant archaeal group. The archaeal communities in the incubations with H2/CO2 and H2/MeOH did not change much with respect to microbial community structure. In general, the bacterial community was still highly diverse in these incubations, with a similar community structure as the control (Supplemental Figure S4).
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TMA
Acetate
H2/CO2
H2/MeOH
Control
Methanosarcinaceae Methanosaetaceae Bathyarchaeota
Rice Cluster II Methanoregulaceae Terrestrial Misc Gp Methanobacteriaceae GOM Arc I Woesearchaeota Others
4oC 10oC 4oC 10oC 4oC 10oC 4oC 10oC 4oC 10oC
Figure 3. Phylogenetic classification of amplified archaeal 16S rRNA genes in the methanogenic incubations after 270 days, except for H2/CO2 after 64 days. The maximum taxonomy depth is on family level. Taxonomic groups with less than 2% abundance are grouped in others.
Activity and community composition of aerobic methanotrophs
To determine aerobic methanotrophic activity, batch incubations with original sediment were amended with CH4 and oxygen (O2) and CH4 consumption was followed for 62 days (Fig. 4A). Maximum methanotrophic oxidation rate increased by up to 57% with temperature rise, from 90 ±8 μmol CH4 gdw-1 d-1 at 4°C to 141 ± 0.2 μmol CH4 gdw-1 d-1 at 10°C. The Q10 coefficient had a maximum value of 2.6 after 46 days, indicating temperature sensitivity. The cumulative CH4 consumption over 62 days was 2.2 ± 0.08 mmol CH4 gdw-1 at 4°C and 2.5 ± 0.06 mmol CH4 gdw-1 at 10°C (Fig. 4B), which indicated on average a 10% increase in CH4 consumption rate at 10°C. Cell-specific rates were 83 and 112 fmol cell-1 h-1 for 4°C and 10°C, which is within the range previously reported for aerobic methanotrophs (Supplemental Table S6) (in ‘t Zandt et al. 2018). The 16S rRNA gene analysis (Fig. 5) showed that type I methanotrophs from the Methylococcales order dominated the enrichment cultures (20% to 22% of bacterial reads). There were no reads affiliated with type II methanotrophs. The non-methanotrophic
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Relative abundance (%)
