prokaryotes - bacteria see Domain Bacteria Woese et al. 1990 stat. inval.
   Domain "Bacteria" Woese et al. 1990 stat. inval. see Domain Bacteria Woese et al. 2024
     Phylum "Proteobacteria" Garrity et al. 2005 stat. inval. see Phylum Pseudomonadota Garrity et al. 2021
       1 Class "Zetaproteobacteria" Emerson et al. 2007 nom. pro-inval. [monotypic]
       2 Class Alphaproteobacteria Garrity et al. 2006
       3 Class Betaproteobacteria Garrity et al. 2006
       4 Class Deltaproteobacteria Kuever et al. 2006
       5 Class Epsilonproteobacteria Garrity et al. 2006
       6 Class Gammaproteobacteria Garrity et al. 2005
       7 Class Oligoflexia Nakai et al. 2014 [monotypic]