Page 190 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

Chapter 8. Species-specific responses of enriched thermokarst lake sediments
temperature of M. spelaei is 33°C, but the organism can grow at temperatures down to 0°C (Ganzert et al. 2014). Its higher coverage on TMA at 10°C indicates the preference of this MAG to higher temperatures. MAG 5 contains acetate kinase (ack), phosphate acetyltransferase (pta) and acetyl-CoA synthetase (ACS) and CODH catalytic subunit (CooS, 2 copies) for carbon fixation through the Wood-Ljungdahl pathway.
Table 2. Functional gene analysis for the three Methanosarcinaceae MAGs. Green indicates presence of gene(s)/gene clusters (occurrence frequency ≥1), yellow indicates incomplete gene clusters, red indicates absence of gene(s)/gene clusters. Vho: membrane-bound F420-nonreducing hydrogenase, Hdr: heterodisulfide reductase subunits DE, Rnf: respiratory Rnf complex, cbp: cytochrome biogenesis proteins, cap: cytochrome assembly proteins, cyt c: cytochrome c proteins, TA II: Type II toxin-antitoxin system, ADH: alcohol dehydrogenase, Cat: catalase, Per: peroxidase, Che: chemotaxis gene cluster, T4P: type IV pilin, Fla: flagellin.
Vho Hdr DE
MAG 4 MAG 5 MAG 9
Rnf
cpb cap
cyt c
TA II
ADH Cat
energy metabolism
cytochromes
oxidative defense
Per Che
chemotaxis/ motility
T4P Fla
Methanosarcinaceae MAG 9 showed strongest enrichment on acetate at 4°C (2.2-fold increase) and on TMA at 10°C (17.2-fold increase). A complete mcrAGCDB gene cluster was found with 97.55-100% aa identity to Methanosarcina sp. Ant1. Closest cultured representatives are M. lacustris (93.4% AAI for McrA), M. horonobensis (92.7% AAI for McrG, 88.5% AAI for McrB), M. acetivorans (96.1% AAI for McrC), and M. barkeri (86.0% AAI for McrD). MAG 9 contained acetate kinase (ack), phosphate acetyltransferase (pta), and acetyl-CoA synthetase (ACS) and the CODH complex.
We performed a closer functional gene and gene cluster analysis to obtain insights into the metabolic potential of the three Methanosarcinaceae MAGs (Table 2, Supplementary Table S6-S8).
A membrane-bound F420-nonreducing hydrogenase (Vho) and a heterodisulfide reductase (HdrDE) were found in all Methanosarcinaceae MAGs. HdrDE was detected by BLASTP of Methanosarcina sp. sequences present in the Swiss-Prot database against the MAGs (E-values <1.69e-166) (Supplementary Table S5). MAG 9 only contained HdrE. The sodium ion
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