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Mycoplasmas
INTRODUCTION
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.
CLASSIFICATION
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.
STRUCTURE
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.
DISEASES
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,
Pneumonia