FIG 2.

Homologs of nitrogenase identified in the genomes of putative diazotrophs. (A) Histogram depicting the percentage of diazotrophs within each specified Nif lineage (see Fig. 1) that are aerobic, anaerobic, or facultatively anaerobic, as determined from surveys of the literature for cultivated organisms. (B) Venn diagram representing the numbers of genomes that encode one or more specified lineages of nitrogenase (see Fig. 1). Genomes that encode Nif-C and Nif-D do not encode other isoforms of nitrogenase and are thus depicted as separate.