Natura - nature
   actualia - actual entities
     Mundus Plinius - physical world
       naturalia - natural bodies
         [crown] Clade Biota Wagner 2004 [Wiemann, de Queiroz, Rowe, Planavsky, Anderson, Gogarten, Turner & Gauthier 2020]
           Domain Bacteria Woese et al. 1990 [paraphyletic?]
             Superphylum "Proteobacteria" Craig et al. 2010
               Phylum "Gammaproteobacteria" Garrity et al., 2005 [monotypic]
                 Class Gammaproteobacteriaᵀ Garrity et al. 2005
                   Order Pseudomonadales Orla-Jensen 1921 (Approved Lists 1980)
                     Family Pseudomonadaceaeᵀ Winslow et al. 1917 (Approved Lists 1980)
                       Genus Azotobacter Beijerinck 1901 (Approved Lists 1980)
                         Azotobacter nigricans Krasil'nikov 1949 (Approved Lists 1980)
                           1 Azotobacter nigricans subsp. achromogenes Thompson and Skerman 1981
                           2 Azotobacter nigricans subsp. nigricansᵀ (Krasil'nikov 1949) Thompson and Skerman 1981