Distinction within prokaryotes, formingthe primary taxonomic division within them, which is supported by both molecular sequence data and morphological features, is of the monoderm prokaryotes (Monodermata, i.e., those bounded by a single cell membrane) and the diderm prokaryotes (Didermata, i.e., those bounded by inner and outer cell membranes defining a periplasmic compartment). In that sense, b