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)
                           Azotobacter nigricans subsp. nigricansᵀ (Krasil'nikov 1949) Thompson and Skerman 1981