[living organisms] see Clade Biota Wagner 2004 [Wiemann, de Queiroz, Rowe, Planavsky, Anderson, Gogarten, Turner & Gauthier 2020]
   Superkingdom Prokaryota
     Kingdom Bacteria Cavalier-Smith 2002 - bacteria see Domain Bacteria Woese et al. 1990
       Subkingdom Negibacteria Cavalier-Smith 2002 - negibacteria see Domain Bacteria Woese et al. 1990
         Phylum Proteobacteria Garrity et al. 2005 see Superphylum Proteobacteria Craig et al. 2010
           1 Class Alphaproteobacteria Garrity et al. 2006
           2 Class Betaproteobacteria Garrity et al. 2006
           3 Class Deltaproteobacteria Kuever et al. 2006
           4 Class Epsilonproteobacteria Garrity et al. 2006
           5 Class Gammaproteobacteria Garrity et al. 2005
           6 Class Zetaproteobacteria Emerson et al. 2007 [monotypic]