Page 70 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

Chapter 3. Metal corrosion protection potential of methanogenic communities
The methanogenic community is enriched 18-fold in deposit layers compared to the surrounding sediment
More than 18% of the reads were aligned to methanogen MAGs with more than 50% genome completeness. The methanogenic community consisted of hydrogenotrophic Methanobacteriales (4.9%), Methanomicrobiales (2.9%), and versatile Methanosarcinales (1.8%). Methanogens were enriched 18-fold in DL compared to AS in which only Methanomicrobiales were detected in AS sample 2 (1.1%). Metagenome binning resulted in MAGs from the orders Methanobacteriales (three MAGS obtained from DL with 8.7%, 3.2%, and 2.7% of total mapped reads), Methanomicrobiales (one MAG with 2.9% of total mapped deposit reads), and Methanosarcinales (one MAG with 0.9% of mapped DL reads) (Table 1; see also Table S4 in the supplemental material). The diversity of the methanogenic community supports a central role of H2 and acetate transfer. Acetate is essential for the growth of acetoclastic methanogens, but it is also important in supporting the growth of hydrogenotrophic Methanomicrobiaceae (Jetten, Stams and Zehnder 1990). 16S rRNA gene reads from the metagenomic data sets were extracted per phylogenetic group and assembled de novo for deeper phylogenetic analysis. This resulted in two Methanobacterium 16S rRNA gene contigs. Contig 1 (685 bp, 49x coverage) was most identical (99%) to the hydrogenotrophic methanogen Methanobacterium palustre strain F (NR041713.1) isolated from a mesophilic corn-fed on- farm biogas plant (Stantscheff et al. 2014). Contig 2 (839 bp, 29x coverage) was most identical (98%) to Methanobacterium kanagiense strain 169 (NR_112749.1) isolated from an anaerobic propionate-oxidizing enrichment culture from a rice paddy field soil (Kitamura et al. 2011).
To further investigate methanogen diversity of the deposit layers, the diversity of the methyl- coenzyme M reductase alpha subunit, mcrA, was investigated. mcrA reads were extracted from the raw read datasets and their analysis generally supported the high diversity of the methanogenic community. Of the translated mcrA reads, 22.7% were most identical to that of Methanobacterium sp. strain Maddingley MBC34 (EKQ53862) isolated from a coal seam gas formation water sample (Rosewarne et al. 2013) (Table S5). Of the translated reads, 6.2% gave best hits to sequences from uncultured archaeon sequences from Lake Pavin 90-m-depth samples which were dominated by sequences linked to hydrogenotrophic methanogenic
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