prokaryotes - bacteria see Domain Bacteria Woese et al. 1990
   Domain "Bacteria" Woese et al. 1990
     Phylum "Proteobacteria" Garrity et al. 2005 see Superphylum Proteobacteria Craig et al. 2010
       1 Class "Zetaproteobacteria" Emerson et al. 2007 [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]