CYANOBACTERIA

•Members of cyanobacteria are called Blue Green Algae or Myxophyceae

•They are fresh water, marine and terrestrial in habitat.

•Fresh water form-Dermocarpa

•Marine form-Trichodesmium

•Nostoc and Oscillatoria-Endophytes in roots of Cycas, Leaves in Azolla and Thalli of Anthoceros

•Sps of Chroococcus, Gloeocapsa, Nostoc, Scytonema and stigonema are the main algal component of lichens.

•Cyanobacteria growing in organically rich permanent waters form planktons.

•Thallus:

•Unicellular non motile forms-Chroococcus, Colonial-Gloecapsa, Gloeotricha

•Multicellular unbranched filamentous forms-Oscillatoria, Nostoc

•Filamentous forms with false branches-Scytonema

•Heterotrichous forms with true branches-Stigonema

•A trichome is the basic structural unit consisting of a row of cells, where as the trichome is surrounded by a sheath is called a filament.

•Cell structure:

•Cyanobacteria are prokaryotic in nature

•Cell is devoid of nucleus and well organized cell organells

•Cyanobacterial cells shows a mucilagenous layer called sheath, the cell wall, plasma membrane and cytoplasm

•The presence of mucilagenous sheath is the constant feature in of cyanobacteria.

•The mucilage is rich in glucose, xylulose, mannose and galactose.

•Because of mucilagenous sheath they are called myxophyceae

•A double layered cell wall is present.outer wall will be as same as gram negative bacteria and inner wall is rich with mucopeptide and muramic acid

•Plasmamembrane is present inner to the cell wall this membrane consists of two electron opaque layers separated by a translucent layer.Plasma membrane sometimes invaginates locally and fuses with the thylakoids to form a structure called lamellosomes.

•Cytoplasm is distinguished  into regions. The outer peripheriaal coloured region called the chromoplasm and the central colourless region called the centroplasm(Nucleoplams)

•Chromoplasm contains the flattened vesicular structures called photosynthetic lamellae or thylakoids. Phtosynthetic pigments C-Phycocyanin and C-Phyoerythrin and several phtosynthetic pigments such as Chl-a,c, xanthophyll and carotenoids are present inside the lamellae.

•Centroplasm: The central region of cyanobacterium cell appears some what transparent and contains the Genetic material. An organized nucleus and nuclear membrane is absent.The genetic material consist of DNA  fibrils, and they are not associated with histone proteins. RNA is present in addition to DNA.

•Cytoplasmic inclusions: Cyanophycean granules, polyhedral bodies and structural granules.

•Cyanophycean granules are considered as reserve food.

•Gas vacuoles are present  and these are visible in planktonic blue green algae and are useful in floating.

•Reproduction

•There is no sexual reproduction in BGA. They Reproduce only by means of vegetative and asexual modes only

•Vegetative reproduction occurs by fission, fragmentation, and by formation of harmogonia

•Asexual reproduction occurs by formation of akinetes, endospores, exospores and nannocytes.

•Fragmentation seen in Microcystis

•Harmogonia:

•Seen in Nostoc and Stigonema

•Eg: Nostoc, Oscillatoria, Scytonema, Stigonema, Rivularia.

•Akinetes:These are resting spores meant to tide over unfavourable conditions.Some vegetative cells accumulated food and enlarge in size become yellow to dark brown in colour.

•They become thick walled and change into spherical perennating structures called aKinites

•Scytonema, Stigonema, Rivularia.

•Exospores, Endospores and Nano cytes

•Endospores are produced in side the cell: Dermocarpa

•Some times vegetative cells undergoes repeated division at a very fast pace forming number of miniature spores called nanospores. Eg: Gloeocapsa, Microcystis

•Heterocyst

•Heterocyst are modified vegetative cells. They are thick walled , pale yellow and barrel shaped structure. It consists of Three layered enveloped .

•The outer layer is fibrous, middle homogenous and the inner layer  is lamellar in nature. The wall layer become thicker in the polar region and the pores are plugged with a refractile material called polar granules. They are helpful for nitrogen fixation

•They are produced singly  or in chains  and remain inter calalry ( Nostoc, scytonema), terminal (Gloetricha) or basal (Rivularia) in position.