Functionally redundant formate dehydrogenases enable formate-dependent growth in Methanococcus maripaludis

Area of Science:

• Microbiology
• Biochemistry
• Environmental Science

Background:

• Methanogens are crucial for organic matter remineralization in anoxic environments.
• Hydrogenotrophic methanogenesis uses H₂ to reduce CO₂ to CH₄; formate can substitute H₂.
• Formate dehydrogenase (Fdh) is vital for formate oxidation, linking it to coenzyme F₄₂₀ reduction or heterodisulfide reductase (Hdr)-catalyzed reactions.

Purpose of the Study:

• To biochemically characterize the two Fdh isoforms involved in methanogenesis in *Methanococcus maripaludis*.
• To elucidate the roles and interactions of Fdh isoforms in the methanogenic pathway.

Main Methods:

• Biochemical characterization of Fdh isoforms.
• Analysis of enzyme interactions with Hdr.
• Assessment of F₄₂₀ reduction and flavin-based electron bifurcation.
• Genetic analysis of mutant strains (Δfdh1) and suppressor mutations (moeA).
• Metal content analysis of Fdh isoforms.

Main Results:

• Both Fdh1 and Fdh2 interact with Hdr for flavin-based electron bifurcation and reduce F₄₂₀ at similar rates.
• F₄₂₀ reduction precedes flavin-based electron bifurcation for both enzymes.
• A suppressor mutation (loss of moeA) was necessary for Fdh2 activity in a Δfdh1 mutant, enabling growth.
• Isoform activity appears dependent on molybdenum or tungsten availability.

Conclusions:

• The two Fdh isoforms are functionally redundant in *M. maripaludis*.
• In vivo activity of Fdh isoforms may be regulated by gene expression or metal cofactor availability.
• This study enhances understanding of formate oxidation and Fdh function in methanogenesis.