Fig. 2

The tree illustrates consistent phylogenetic relationships between various types of [FeFe]-hydrogenases. The ML tree was obtained using the program PhyML [48] from a manually curated alignment of hydrogenase sequences retrieved by DeltaBLAST searches extended to uncultured organisms (cf. Additional file 1: Figure S2B). The known structure of algal [10] and bacterial [41] [FeFe]-hydrogenases has been used to implement the alignment refinement, using Magnetospirillum HybA protein sharing ferredoxin motifs with type A hydrogenases (accession: WP_043744126) as outgroup. The δ proteobacterium Desulfotalea is in light blue while α proteobacterial taxa are in bold blue as in Fig. 1b. All nodes have statistical support larger than 0.5. Note that two metagenomic organisms, Acetobacter CAG:977 and Azospirillum CAG:239, have representative proteins of both type A and type M3 [FeFe]-hydrogenases (cf. Table 1)