About this Research Topic
Microbial methane metabolism is an important process in the global carbon cycle, and research to understand this biological process has significant impacts in global energy. About 1 Gt of methane is produced per year by methanogens in anoxic environments. The biologically produced methane can be oxidized back to CO2 anaerobically or aerobically by methanotrophs before it is emitted into the atmosphere. It is estimated that about 0.1 Gt per year of methane is oxidized by anaerobic methanotrophs (ANME).
The ecological balance between methanogens and methanotrophs may be considered to be a climate “tipping point” due to the fact that methane is about 20 times more potent as a greenhouse gas than CO2. Understanding the diversity, ecology, physiology, and biochemistry of methanogens and methanotrophs is critical for harnessing methane metabolism to both provide methane fuel and mitigate greenhouse emissions.
New methanogens and ANME and their ecological importance are waiting to be discovered and characterized. Both methanogens and ANME belong to the domain Archaea and are phylogenetically closely related to each other. Methanogens were originally thought to be restricted to the Euryarchaetota phylum, however recent environmental metagenomics studies have suggested their presence in the yet uncultivated Bathyarchaeota and Verstraetearchaeta phyla. ANME in marine sediments often form consortia with sulfate-reducing bacteria.
Despite intense attempts, ANME have not yet been cultivated in pure culture, indicating there is critical knowledge yet to be learned in order to unlock secrets of efficient methane metabolism in subsurface environments.
Remarkably, methane metabolism in methanogens and ANME presumably occur through the same set of core enzymes operating in reversible directions.
For example, the key methane-metabolizing enzyme, methyl coenzyme M reductase (MCR), catalyzes the formation of methane in methanogens and the initial oxidation of methane in ANME. Due to its intrinsic complexity and instability, the activation and reaction mechanism of MCR are still under debate after four decades of biochemical investigations. Notably, recent studies using enrichment cultures suggest that MCR may also metabolize alkanes other than methane, such as ethane, propane, and butane. The reaction mechanism and metabolic diversity of methane-metabolism enzymes remain a key area for future research.
Methanogens also have much to contribute to future energy and biotechnology. Genetic tools are available for several methanogens, and studies are underway to engineer methanogens for increased yield, rate, stress tolerance, and production of useful chemicals, both in traditional culture systems and in fuel cells. Due to their unmatched efficiency to interconvert CO2, acetate, and methane, engineered methanogens and methanotrophs are emerging as powerful chemical and energy platforms for the future economy.
With this background, the proposed Research Topic aims to gather contributions under the following themes:
‒ Diversity, ecology, and evolution of methanogenic or ANME archaea of environmental importance
‒ Isolation or enrichment of anaerobic methane metabolism microorganisms
‒ Physiology and systems-level characterization of methanogenesis or anaerobic methane oxidation
‒ Reaction mechanism of anaerobic methane production or oxidation enzymes
‒ Metabolic engineering and synthetic biology for improved methane production or conversion
Keywords: methane, methanogen, anaerobic methane oxidation, ANME, archaea
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