11th Class Biology Biological Classification And System Of Classification / जैविक वर्गीकरण और वर्गीकरण की प्रणाली Importance of Mycoplasma

(1) Diseases in human beings : Mycoplamsa hominis causes pleuropneumonia, inflammation of genitals and endocarditis, etc. Mycoplasma pneumoniae causes primary a typical pneumonia (PAP), haemorrhagic laryngitis, etc. Mycoplasma fermentatus and M. hominis cause infertility in man, otitis media (inflamation of middle ear).

(2) Diseases in animals : Mycoplasma mycoides causes pneumonia in cattle. Mycoplasma bovigenitalum, causes inflamination of genitals in animals. Mycoplamsa agalactia causes agalactia of sheep and goat.

(3) Diseases in plants : Common mycoplasmal diseases of plants are: Bunchy top of papaya, witches' broom of legumes, yellow dwarf of tobacco, stripe disease of sugarcane, little leaf of brinjal, clover phylloidy, big bud of tomato etc.

The new name of cyanobacteria has been given to myxophyceae or cyanophyceae. Cyanobacteria form a group of ancient Gram negative, photosynthetic prokaryotes. Many botanists prefer to call them blue-green algae. They have survived successfully for about 3 billion years. They may cause water blooms.

Cyanobacteria are predominantly fresh water forms, a few are marine. They impart unpleasant taste and smell to the water. One species of cyanobacteria containing red pigment (Trichodesmium erythraeum) flourishes in red sea and is responsible for the red colour of its water.

A few species grow in hot water springs having a temperature range of 70°–75°C (e.g., Phormidium, Hastigocladus) and other grow at very low temperature in the polar regions (e.g., Nostoc, Schizothrix, Microcoleus etc.).Some grow in the soil and help in fixation of nitrogen and utilize it in metabolism. Nostoc colony is found into the thallus of Anthoceros. Colonies of Nostoc and Anabaena grow in paddy fields. Anabaena cycadeae is found in coralloid roots of cycads. 

Characteristics of Cyanobacteria

(1) They have prokaryotic type of cells.

(2) Cells do not have any organised nucleus. The nucleolus is absent and the nucleoid is not to be bounded by a nuclear membrane. The type of nucleus called incipient nucleus.

(3) The photosynthetic pigments present in the cell are – chlorophyll a, b carotene, myxoxanthophyll, myxoxanthin, C-phycocyanin and C-phycoerythrin. The C-phycocyanin is blue and C-phycoerythrin is red in colour. If C-phycocyanin is more as compared to C-phycoerythrin, it gives characteristic blue- green colour to the algae.

(4) The photosynthetic pigment are present in lamellae, called thylakoids.

(5) The presence of chlorophyll–a, cyanobacteria synthesis their own food from carbon dioxide and water in the presence of sunlight. Certain cyanobacteria fix atmospheric nitrogen in the presence of oxygen.

(6) In cyanobacteria food is stored as cyanophycean starch or a–granules. 

(7) Some members possesses simple unbranched filament with heterocyst like Nostoc, Anabaena, Aulosira, Cylindrospermum etc.

(8) Some members possesses simple unbranched filamentous forms without heterocysts and akinetes, e.g., Arthospira, Oscillatoria, Spirulina, Phormidium, Lyngbya, Symploca, Microcoleus, Schizothrix etc.

(9) Cyanobacteria reproduce asexually by fission and fragmentation. Unicellular forms multiply by binary fission. Sexual reproduction is totally absent.

(10) Flagella are completely absent but the movement occurs in some genera by special gliding motion. Such movements are connected with the secretion of mucilage. The genus Oscillatoria exhibits pendulum like oscillating movement of its anterior region.

(11) Cell wall is composed of a gelatinous sheath which is made up of three layers of microfibrils in which cellulose is not present.

(12) Cells contain organelles like cyanophycean granules, gas vacuoles, polyhedral bodies, ribosomes, polyglucoside bodies, polyphosphate bodies etc.

(13) Cyanobacteria are economically important because of having immense capability of fixing atmospheric nitrogen in the soil. An enzyme nitrogenase present in the heterocyst is responsible for the fixation of free nitrogen. Application of heterocysts blue–green algae as biofertilizer enhances the production in paddy field crops. e.g., Anabaena, Nostoc, Cylindrospermum, Scytonema etc.