Kingdoms of Organisms:

This presentation has taken as standard the "three domain - six kingdom" model of organism diversity, based on 16S ribosomal RNA sequence comparisons, of Carl Woese and co-workers. This divides cellular organisms into:

Reference:
GJ Olsen and CR Woese (1993). FASEB Journal 7: 113-123.


However, Robert H Whittaker and Lyn Margulis have suggested that organisms should be divided into five kingdoms: that is,

This model includes some "plants" as protists, and makes no distinction between Archaea and Bacteria.

Reference:
RH Whittaker and L Margulis (1978). BioSystems 10: 3-18


To complicate matters, James Lake and co-workers have lately proposed a radical re-structuring of the "universal" phylogenetic tree, to split Archaea into Halobacteria, Methanogens and Eocytes. This would mean there are three major groupings of prokaryotes (Eubacteria + Halobacteria, Methanogens and Eocytes), which could all constitute kingdoms on their own, given each is as unrelated to the others as any are to Eukarya.

Reference:
JA Lake (1991). Trends in Biochemical Sciences 16: 46-50.


There is also a 2-empire / 8-kingdom scheme, with Archaeobacteria and Eubacteria as kingdoms in Empire Bacteria, and 6 kingdoms in Empire Eukaryota:

Reference:
Cavalier-Smith T (1993). Microbiological Reviews 57: 953-994


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