Cyanobacteria

Cyanobacteria:-

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.