Page 187 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

We could also reconstruct an Anaerolineales MAG with highest coverages in the unamended sediments (Table 1). The Class Anaerolineae consists of chemoorganotrophic bacteria within the phylum Chloroflexi (Yamada et al. 2006). Our previous 16S rRNA gene-based dataset highlighted the presence of Anaerolineales in the bacterial communities of the original sediment cores (4-8% relative abundance) (de Jong et al. 2018). The reconstructed MAG was highly fragmented and contained eight 16S rRNA gene sequences which did not support further species identification. Closer identification on rpo sequences indicated highest identity to environmental sequences of Anaerolineaceae (data not shown). The genome contained NADH dehydrogenase (nuoABDEFGHIJKLMN), succinate dehydrogenase (including the cytochrome b556 subunit), cytochrome d ubiquinol oxidase subunit I and II that are part of the aerobic respiratory chain. A cytochrome c nitrite reductase subunit c552 and a nitric oxide reductase link to its potential to use nitrate/nitrite as terminal electron acceptor (Chen and Strous 2013). However, we could not detect genes involved in fermentation, nitrogen and sulfur metabolism (Supplementary Table S7 and S8). In addition, little data is available on their occurrence in natural ecosystems, and data on their potential metabolic role is lacking (Huang et al. 2019). Further research into their environmental role is therefore highly needed.
Acetate amendment results in an increase of acetoclastic Methanosaetaceae/ 8 Methanotrichaceae
Acetate is a major methanogenic substrate at lower temperatures, mainly due to a reduction in syntrophic activity and an increase in homoacetogenesis (Kotsyurbenko 2005b; Schulz, Matsuyama and Conrad 2006; Blake et al. 2015). For the thermokarst lake sediments studied
here, this was supported by a dominance of strictly acetoclastic Methanosaetaceae/Methanotrichaceae in the unamended sediment incubations at both temperatures. Methanosaetaceae/Methanotrichaceae are common inhabitants of thermokarst lake sediments, including the thermokarst lake sediments studied here (Negandhi et al. 2013; de Jong et al. 2018; Matheus Carnevali et al. 2018). Upon acetate amendment, a further increase in Methanosaetaceae/Methanotrichaceae was observed (9.0% and 4.1% of the aligned reads at 4°C and 10°C, respectively). Versatile Methanosarcinaceae were also detected, but at lower relative abundances.
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