Ethane-oxidising archaea couple CO₂ generation to F₄₂₀ reduction

Area of Science:

• Microbiology
• Biochemistry
• Environmental Science

Background:

• Anaerobic oxidation of alkanes is crucial for mitigating oceanic hydrocarbon seeps.
• Marine archaea rely on sulfate-reducing bacteria for electron transfer during alkane oxidation.
• Archaeal CO2-forming enzymes are typically assumed to couple to ferredoxin reduction.

Purpose of the Study:

• To investigate the molecular mechanisms of CO2 generation during anaerobic ethane oxidation.
• To characterize the CO dehydrogenase and formylmethanofuran dehydrogenase from Candidatus Ethanoperedens thermophilum.
• To elucidate the electron transfer pathways in ethanotrophic archaea.

Main Methods:

• Biochemical assays on purified native enzymes.
• X-ray crystallography to determine enzyme complex structures.
• Metagenome mining for genomic context.

Main Results:

• CO dehydrogenase and formylmethanofuran dehydrogenase deliver electrons to the F420 cofactor.
• Both enzymes possess electronic bridges linking oxidation centers to a flavin-dependent F420 reductase.
• Robust coupled F420-reductase activities were observed, distinct from related organisms.

Conclusions:

• A novel model proposes electron delivery to F420 during catabolic oxidation in this organism.
• This pathway facilitates indirect electron transfer to sulfate-reducing partners.
• This adaptation is key to the energy conservation driving ethanotrophy.