ABSTRACT
Traditionally, micro-organisms are differentiated based on their properties and divided into intracellular parasites (viruses), prokaryotes (Latin 'pro' means before and Greek 'karyon' means nucleus; without membraneenclosed nucleus) and eukaryotes containing a membrane-enclosed nucleus (fungi and protozoa). However, the development of molecular methods in recent years divided all living organisms into three domains (by Carl Woese in 1981 based on ribosomal RNA sequences).
