Electron flow in hydrogenotrophic methanogens under nickel limitation

Area of Science:

• Microbiology
• Biochemistry
• Environmental Science

Background:

• Methanogenic archaea produce methane, a potent greenhouse gas, using CO2 and H2.
• Key enzymes like heterodisulfide reductase (Hdr) and [NiFe]-hydrogenase (Mvh) facilitate electron transfer in standard laboratory conditions.
• F420-reducing [NiFe]-hydrogenase (Frh) also supplies electrons via F420.

Purpose of the Study:

• To investigate the metabolic response of Methanothermobacter marburgensis under nickel-limited conditions.
• To identify alternative electron transfer pathways when nickel is scarce.
• To understand the role of [Fe]-hydrogenase (Hmd) and electron-donating proteins (Elp) in methanogenesis.

Main Methods:

• Culturing Methanothermobacter marburgensis under strictly nickel-limited conditions.
• Biochemical and structural characterization of enzyme complexes (Elp-Hdr).
• Gene conservation analysis in CO2-reducing hydrogenotrophic methanogens.

Main Results:

• Nickel limitation strongly downregulates [NiFe]-hydrogenase production.
• Frh is substituted by a coupled reaction involving [Fe]-hydrogenase (Hmd).
• F420-dependent electron-donating proteins (Elp) replace the function of Mvh, with Hmd providing all electrons for reducing metabolism.

Conclusions:

• Methanothermobacter marburgensis employs an alternative electron transfer system under nickel-limited conditions, utilizing Hmd and Elp.
• This Hmd-based system represents a significant metabolic adaptation for methanogenesis in nickel-scarce environments.
• The findings suggest a conserved alternative pathway for electron flow in related methanogens.