Salient Features:-
> Most of the species are fresh water (e.g., Oscillatoria, Rivularia), a few are marine (e.g., Trichodesmium, Darmocarpa), and some species of Oscillatoria and Nostoc are grown on terrestrial habitat.
> The individual cells are prokaryotic in nature. The nucleus is incipient type and they lack membrane bound organelles.
> Both vegetative and reproductive cells are non-flagellate.
> Cell wall is made up of microfibrils and is differentiated into four (4) layers. The cell wall composed of mucopeptide, along with carbohydrates, amino acids and fatty acids.
> Locomotion is generally absent, but when occurs, it is of gliding or jerky type.
> The principal pigments are chlorophylls a (green), c-phycocyanin (blue) and c-phyco- erythrin (red). In addition, other pigments like β-carotene and different xanthophylls like myxoxanthin and myxoxanthophyll are also present.
> Membrane bound chromatophore are absent. Pigments are found embedded in thylakoids.
> The reserve foods are cyanophycean starch and cyanophycean granules (protein).
> Many filamentous members possess specialized cells of disputed function (supposed to be the centre of N2 fixation) known as heterocysts.
> Reproduction takes place by vegetative and asexual methods. Vegetative reproduction takes place by cell division, fragmentation etc. Asexual reproduction takes place by endospores, exospores, akinetes, nannospores etc.
> Sexual reproduction is completely absent. Genetic recombination is reported in 2 cases.
Biological Importance of Cyanobacteria:-
i. They are one of the early colonizers of bare and barren areas. They provide suitable conditions for the growth of other organisms even in the most hostile environment.
ii. Blue green algae function as food to several aquatic animals. Spirulina is regularly collected for human consumption in parts of Africa. Nostoc is similarly used in China. In Rajasthan Anabaena and Spirulina are collected from Sambar Lake and used as fodder and manure. Spirulina is very easily cultivated in tanks and can be used as a palatable protein rich food supplement for humans and animals.
iii. Several cyanobacteria have the ability of nitrogen fixation. The filamentous forms possess special large pale cells or heterocyst’s for this. Some of the fixed nitrogen comes out as excretion. After death of cyanobacteria the substratum becomes rich in nitrogen. Such nitrogen fixing cyanobacteria are now regularly inoculated in the rice fields. This saves consumption of nitrogen fertilizers.
iv. Nitrogen fixing cyanobacteria are often used for reclaiming usar soils, e.g., Nostoc, Anabaena. These cyanobacteria produce acidic chemicals for counteracting alkalinity of the soil and nitrogenous compounds which are generally deficient in these soils.
v. Antibiotic can be manufactured from extract of Lyngbia.
vi. Species of Anabaena and Aulosira do not allow mosquito larvae to grow nearby. Such cyanobacteria can be inoculated in village ponds and rice fields to prevent the growth of mosquitoes.
vii. Cyanobacteria can grow on the walls and roofs of buildings during the rainy seasons causing discolouration, corrosion and leakage.
viii. They produce water blooms, imparting bad odour and colour to water bodies.
ix. Some cyanobacteria produce toxins harmful to most aquatic animals. They may prove equally toxic to human beings drinking or bathing in such water. The important toxins producing cyanobacteria are Microcytic aeruginosa (= Anacystis cyanea), Anabaena flosaquae, Aphanizomenon flos-aquae.
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