Figure 6. The phylogeny of the Melainabacteria nitrogenase.
A maximum likelihood phylogenetic tree constructed with 865 nitrogenase nifH genes from sequenced genomes (Zehr et al., 2003) is shown. nifH groups I and III are shown. The ACD20 nifH (in group III) is denoted in red, while photosynthetic cyanobacterial nifH sequences (in groups I and III) are denoted in green. Relative to group I, group III is characterized by deep bifurcations and long-branch lengths (Zehr et al., 2003), which are represented in the constructed tree by low-bootstrap values (<50) for internal branch positions in group III. ACD20 sequences are monophyletic (but with low bootstrap support) with nifH sequences from anaerobic Clostridium and Fusobacterium species.