In 1753 Carolus Linneus , a Swedish botanist, proposed two kingdoms, plants and animals. He also proposed binomial nomenclature for addressing life forms, using genus and species. In 1969 Robert Whittaker proposed the five-kingdom system , which is part of the system used today. In 1978 Carl Woese proposed overlaying the five-kingdom system with three groups called domains . The three domains each contain organisms with unique ribosomal genetics.
Bacteria form a domain of prokaryotic cells that contain peptidoglycan in their cell walls.
Eukarya form a domain of eukaryotic cells, or those with true nuclei, or bound organelles. Proteobacteria The second Edition of Bergey's Manual groups most of our pathogenic gram negative bacteria into a phylum called proteobacteria, based on ribosomal RNA similarities. Alpha - this group includes the bacteria involved in nitrogen fixation in plant roots. The pathogens found in this group include obligate intracellular gram negative rods such as Brucella, Ehrlichia and Rickettsia. Beta - includes Neisseria, Bordatella, and Burkholderia.