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Mycoplasmas are tiny, virus-like non-motile prokaryotic organisms. They are the simplest and smallest known organisms capable of growing on cell free laboratory culture media containing sterols. Mycoplasmas lack definite cell wall and are characteristically delimited by a distinct, soft, flexible trilaminar unit membrane of lipoprotein.
Because of the soft and plastic membrane they can assume a variety of shapes and sizes (Pleomorphic). The electron micrographs have revealed that mycoplasmas are small spherical bodies or branched worm-like structures which are smaller than bacteria but are within the size range of large viruses.
They can pass easily through bacterial filter and can be squeezed through filter pores smaller than their actual diameter. They are highly resistant to many antibiotics.
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The unit membrane of mycoplasma surrounds the cytoplasm which is packed with ribosomes, fibrilar DNA, one or more electron dense areas, and some empty vacuoles (Fig. 1.10).
They are capable of performing all life activities. The genetic material of mycoplasma consists of a naked circular chromosome of fibrilar DNA which is about 3 nm in thickness and 1000 x 106 daltons in weight (1 dalton = 1/16 the atomic weight of oxygen = 1.650 x l0-24 g). This replicates in the same way as does the bacterial chromosome. The ribosomes are generally 72 S and are about 14 nm in diameter.
Reproduction in mycoplasma has not yet been conclusively proved. They can reproduce by binary fission, by formation of spores (elementary bodies), by filamentous growth and by budding.
