ABSTRACT
From a morphological point of view, the most fundamental dichotomy within prokaryotes (the term “prokaryotes” is used here in its primary etymological sense-that is, single-celled organisms without nuclei as opposed to eukaryotes, without any further phylogenetic considerations1) is between those bound by a single biological membrane (monoderm prokaryotes)—that is, the cytoplasmic membrane, and those bound by two concentric but topologically different membranes (diderm prokaryotes)—that is, the inner membrane (cytoplasmic membrane) and the asymmetric outer membrane.2 In accordance with holistic and teleonomic concepts, organisms are far more than mere collections of genes,3,4 and such difference in membrane organization, and thus cell compartmentation, is not trivial but has profound phylogenetic, structural, metabolic, and physiological implications. Based on the most recent advances in biological evolution and megaclassication of organisms,5-7 monoderm prokaryotes are regrouped under the term Monodermata (also called Unibacteria), which essentially includes Archaea together with Posibacteria (formerly called Grampositive bacteria).
