Regnum Prokaryotae

Unicellular microorganisms of 0.1 to 15 µm, presenting rod or coccus shape, sometimes occurring filamentous or mycelial forms. Widely distributed in nature (soil, water, foods, plants, animals, rarely in hot springs or radioactive environment). Cells have a single circular DNA chromosome, contained within a region called the nucleoid. The nucleoplasm is not separated from the cytoplasm by a nuclear membrane. Reproduction is most often asexual, through binary fission, occasionally by budding. Cells may remain attached after division resulting specific arrangements: strepto-, staphylo- etc. The organisms are surrounded by a rigid peptidoglicans based wall with the exception of the Mollicutes. The plasma membrane forms vesicular, lamellar or tubular intrusions into the cytoplasm. Respiratory and photosyntetic functions are associated with the plasma membrane system (where available). Ribosomes of the 70S type are dispersed in the cytoplasm.