Phylogenetic tree based on NifH protein sequences. The tree was derived from 28 NifH protein sequences from six bacterial species and one archaeal species (boxed list), and was constructed using MEGA 4.1 neighbor-joining method with 500 bootstrap replicates. The organisms were chosen from IMG based on their possession of multiple nifH gene homologs in their genome except for Klebsiella pneumoniae 342. The number of nifH gene homologs from each species are; five from Methanosarcina acetivorans C2A (blue bullets), six from Anabaena variabilis ATCC 29413 (green bullets), a total of nine from Firmicutes (red bullets); four from D. hafniense DCB-2 and five from Clostridium kluyveri DSM 555, and a total of eight from Proteobacteria (black bullets), including four from Rhodobacter sphaeroides ATCC 17025, one from K. pneumoniae 342, and three from Geobacter sp. FRC-32. The tree shows that the NifH encoded by Dhaf_1049 belongs to a more conserved NifH cluster and is distant from other NifH homologs of D. hafniense DCB-2.