Walsh & Hoyt: Properties

Several characteristics separate the mycoplasmas from other bacteria and viruses. Mycoplasmas are pleomorphic microorganisms varying in shape from coccoid to helical to filamentous. Most are facultative anaerobes but others are obligate anaerobes that are easily killed by minute amounts of oxygen. The genomes of the mycoplasmas are the smallest of all replicating organisms and depend highly on exogenous sources for biosynthesis. Mycoplasmas replicate by binary fission. The growth of single cells into colonies produces a characteristic ""fried egg"" appearance caused by expansion of the cytoplasm around the nucleus). Mycoplasmas are often found as contaminants of cell cultures. Although the mechanism is not completely understood, most mycoplasmas move by gliding over surfaces via a system of microfilaments.