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Ø The mycoplasmas are the simplest self-replicating prokaryotes.

Ø Mycoplasma is considered as the smallest known cell of about 0.1 micron (µm) in diameter.

Ø First discovered by Pasteur in 1843, as a causal agent of pleuropneu­monia of cattle and called PPLO.

Ø Later, in 1898 Nocard and Roux, successful obtained pure culture of these microorganisms in media.

Ø Mycoplasmas are commonly found in soil, hot spring, sewage water and also in humans, plants and animals.


On the basis of their nutritional require­ment.

1. Mycoplasma: They need cholesterol for their growth.

2. Acholeplasma: They do not need choles­terol for their growth but will incorporate it into the membrane if it gets in the medium.

3. Thermoplasma: They do not require cholesterol for their growth.


Ø The mycoplasma cell contains a plasma membrane, ribosomes, RNA, proteins and ds circular DNA molecule.

Ø The cell is devoid of cell wall, highly pleomorphic and thus are called joker of microbiology.

Ø Taxonomically, the lack of a cell wall is used to separate mycoplasmas from other bacteria.

Ø They may be ring-like, granular, coccoid, pear-shaped, fila­mentous, etc.

Ø The colonies of mycoplasma have a characteristic round form with a thickened centre and a delicate periphery like a fried egg.

Ø They reproduce by vegetative means i.e., by binary fission and budding.


Mycoplasmas are widespread in nature as parasites of humans, mammals, reptiles, fish, arthropods, and plants.

Plant Diseases:

§ Little leaf disease of brinjal,

§ Bunchy top of papaya,

§ Big bud of tomato,

§ Witches broom of legumes,

§ Yellow dwarf of tobacco,

§ Strip disease of sugarcane,

§ Clover dwarf,

§ Cotton virescence.

Human diseases:

§ Pleuropneumonia is caused by Mycoplasma hominis

§ Primary a typical pneumonia is caused by Mycoplasma pneumonia

§ Mycoplasma hominis and Mycoplasma fermentants cause infertility in man.

§ Little leaf disease of brinjal,

§ Bunchy top of papaya,

Big bud of tomato,