FIG 4.

Phylogenetic tree of Fpo, Nuo, and related 11-subunit complexes and [NiFe] hydrogenases of bacteria and archaea. The Fpo-like complexes of Methanomassiliicoccales do not cluster with the 11-subunit complexes of their closest relatives, Thermoplasmatales and “Ca. Aciduliprofundum boonei,” but share high sequence similarity with the Fpo and Fpo-like complexes of Methanosarcinales (strains indicated in bold). The tree is based on a translated amino acid alignment of the homologs encoding the large subunit of the respective complex and was reconstructed using a maximum-likelihood algorithm (PhyML). Nodes that were not supported by neighbor-joining and maximum-parsimony (MP) analyses are shown as multifurcations; highly supported nodes (1,000 bootstraps, MP) are marked (solid circles, >95%; open circles, >70%). Scale bar indicates 0.1 substitution per site.