More than 200 genes required for methane formation from H₂ and CO₂ and energy conservation are present in Methanothermobacter marburgensis and Methanothermobacter thermautotrophicus

Abstract

The hydrogenotrophic methanogens Methanothermobacter marburgensis and Methanothermobacter thermautotrophicus can easily be mass cultured. They have therefore been used almost exclusively to study the biochemistry of methanogenesis from H₂ and CO₂, and the genomes of these two model organisms have been sequenced. The close relationship of the two organisms is reflected in their genomic architecture and coding potential. Within the 1,607 protein coding sequences (CDS) in common, we identified approximately 200 CDS required for the synthesis of the enzymes, coenzymes, and prosthetic groups involved in CO₂ reduction to methane and in coupling this process with the phosphorylation of ADP. Approximately 20 additional genes, such as those for the biosynthesis of F(430) and methanofuran and for the posttranslational modifications of the two methyl-coenzyme M reductases, remain to be identified.

Figure 1

Synteny between the genomes of Methanothermobacter marburgensis and Methanothermobacter thermautotrophicus. x-axis: position of CDS on the genome of M. marburgensis; y-axis: position of homologous CDS on the genome of M. thermautotrophicus. The chromosome of M. thermautotrophicus (extracted from NC_000916) was rearranged so that it starts at the corresponding CDS encoding the Cdc6 protein. Colinear similarities are depicted by red dots and anti-parallel similarities by blue dots. The synteny plot was produced by the programs of the MUMmer suite [51]. The CDS not in common are dispersed around the two genomes; many are concentrated at the four genome areas indicated by the four arrows.

Figure 2

Enzymes, coenzymes, and prosthetic groups involved in the energy metabolism of Methanothermobacter marburgensis and Methanothermobacter thermautotrophicus during growth on H₂ and CO₂. For the synthesis of these components, more than 200 coding sequences are required. A stoichiometry of 4 Na⁺/ATP of the A₁A₀-ATP synthase AhaA-IK was assumed to yield 0.5 ATP for every methane generated. This is also predicted from the thermodynamics at physiological H₂ concentrations. MFR, methanofuran; H₄MPT, tetrahydromethanopterin; CHO-MFR, formyl-MFR; CHO-H₄MPT, formy-H₄MPT; CH ≡ H₄MPT⁺, methenyl-H₄MPT⁺; CH₂ = H₄MPT, methylene-H₄MPT; CH₃-H₄MPT, methyl-H₄MPT; Fd, ferredoxin.