Microorganisms are classified in several ways, including by their cellular structure as unicellular or multicellular, and by the nature of their nuclear material as prokaryotes or eukaryotes. One influential classification system is the three domain system proposed in 1990 by Carl Woese, Otto Kandler, and Wheelis, which divides organisms into three domains - Bacteria, Archaea, and Eukaryota - based on differences in their ribosomal RNAs and cell membrane structures. The Bacteria domain includes unicellular or filamentous prokaryotes with diacyl glycerol diester membranes and bacterial-type rRNAs. Archaea organisms have isopyrenoid glycerol di