Methanogens Diversity during Anaerobic Sewage Sludge Stabilization and the Effect of Temperature

Anaerobic sludge stabilization is a commonly used technology. Most fermenters are operated at a mesophilic temperature regime. Modern trends in waste management aim to minimize waste generation. One of the strategies can be achieved by anaerobically stabilizing the sludge by raising the temperature. Higher temperatures will allow faster decomposition of organic matter, shortening the retention time, and increasing biogas production. This work is focused on the description of changes in the community of methanogenic microorganisms at different temperatures during the sludge stabilization. At higher temperatures, biogas contained a higher percentage of methane, however, there was an undesirable accumulation of ammonia in the fermenter. Representatives of the hydrogenotrophic genus Methanoliea were described at all temperatures tested. At temperatures up to 50 °C, a significant proportion of methanogens were also formed by acetoclastic representatives of Methanosaeta sp. and acetoclastic representatives of the order Methanosarcinales. The composition of methanogens in the fermenter significantly changed at 60 °C when typically thermophilic species, like Methanothermobacter marburgensis, appeared. A decrease in the diversity of methanogens was observed, and typical hydrogenotrophic methanogenic archaea isolated from fermenters of biogas plants and anaerobic wastewater treatment plants represented by genus Methanoculleus were no longer present.

Complete Genomic Sequence of the Thermophilic and Hydrogenotrophic Methanogen Methanothermobacter sp. Strain KEPCO-1

Here, we describe the complete genome of Methanothermobacter sp. strain KEPCO-1, a thermophilic and hydrogenotrophic methanogen that was isolated from an anaerobic digester in Seoul, Republic of Korea. The genome of KEPCO-1 shares 96.98% of its sequence with Methanothermobacter marburgensis strain DSM 2133 and consists of 1,741,029 bp, with 1,822 protein-coding genes, 44 noncoding RNAs, and a GC content of 48.47%. The development of this genome will facilitate future genomic studies of KEPCO-1.

Effect of N2 on Biological Methanation in a Continuous Stirred-Tank Reactor with Methanothermobacter marburgensis

In this contribution, the effect of the presence of a presumed inert gas like N2 in the feed gas on the biological methanation of hydrogen and carbon dioxide with Methanothermobacter marburgensis was investigated. N2 can be found as a component besides CO2 in possible feed gases like mine gas, weak gas, or steel mill gas. To determine whether there is an effect on the biological methanation of CO2 and H2 from renewable sources or not, the process was investigated using feed gases containing CO2, H2, and N2 in different ratios, depending on the CO2 content. A possible effect can be a lowered conversion rate of CO2 and H2 to CH4. Feed gases containing up to 47N2 were investigated. The conversion of hydrogen and carbon dioxide was possible with a conversion rate of up to 91 but was limited by the amount of H2 when feeding a stoichiometric ratio of 4:1 and not by adding N2 to the feed gas.

Simulating putative Enceladus-like conditions: The possibility of biological methane production on Saturn’s icy moon

In this study (Taubner et al.2018), three different methanogenic archaea (Methanothermococcus okinawensis, Methanothermobacter marburgensis, and Methanococcus villosus) were tested for metabolic activities and growth under putative Enceladus-like conditions, including high pressure experiments and tests on the tolerance towards potential gaseous and liquid inhibitors detected in Enceladus’ plume. In particular, M. okinawensis, an isolate from a deep marine trench (Takai et al.2002), showed tolerance towards all of the added inhibitors and maintained methanogenesis even in the range of 10 to 50 bar. Further, we were able to show that H2 production based on serpentinization may be sufficient to fuel such methanogenic life on Enceladus. The experiments revealed that methanogenesis could, in principle, be feasible under Enceladus-like conditions.

Biochemical Characterisation of Phage Pseudomurein Endoisopeptidases PeiW and PeiP Using Synthetic Peptides

Pseudomurein endoisopeptidases cause lysis of the cell walls of methanogens by cleaving the isopeptide bond Ala-ε-Lys in the peptide chain of pseudomurein. PeiW and PeiP are two thermostable pseudomurein endoisopeptidases encoded by phage ΨM100 ofMethanothermobacter wolfeiand phages ΨM1 and ΨM2 ofMethanothermobacter marburgensis, respectively. A continuous assay using synthetic peptide substrates was developed and used in the biochemical characterisation of recombinant PeiW and PeiP. The advantages of these synthetic peptide substrates over natural substrates are sensitivity, high purity, and characterisation and the fact that they are more easily obtained than natural substrates. In the presence of a reducing agent, purified PeiW and PeiP each showed similar activity under aerobic and anaerobic conditions. Both enzymes required a divalent metal for activity and showed greater thermostability in the presence of Ca2+. PeiW and PeiP involve a cysteine residue in catalysis and have a monomeric native conformation. The kinetic parameters,KMandkcat, were determined, and theε-isopeptide bond between alanine and lysine was confirmed as the bond lysed by these enzymes in pseudomurein. The new assay may have wider applications for the general study of peptidases and the identification of specific methanogens susceptible to lysis by specific pseudomurein endoisopeptidases.

A novel cytosolic NADH:quinone oxidoreductase from Methanothermobacter marburgensis

A novel NADH:quinone oxidoreductase, MmNQO, from Methanothermobacter marburgensis was identified. MmNQO oxidizes NADH with several electron acceptors and is structurally similar to bacterial MdaB. It is localized in the cytosol and may provide a useful tool to prevent overflow metabolism.