Cyanobacteria : general characters, thallus organisation and species of cyanobacteria.

Cyanobacteria

General characters:

• Also called as Blue-green algae.
• Found in water and other wet places.
• These are oxygenic photosynthetic, prokaryotic and gram negative bacteria.
• The outer layer of cell wall is made of lipo-polysaccharides and inner layer is having peptidoglycon.
• Ribosomes, thylakoids and phycobilosomes are present in cytoplasm.
• Ribosomes are 70s type, thylakoids contains phycobilosomes which has photosynthetic pigments like phycocyanin, phycoerythrin and small amount of protein.
• Reserve food material is cyanophycin granules, starch, glycogen, phosphate granules.
• Gas filled vacoules helps the bacteria to float on the surface of water.
•  Vegetative reproduction is by fission, fragmentation and by locomotion harmagonia.
• Asexual reproduction is byformation of akinites, endospores, exospores and nanocytes.

Thallus organisation in cyanobacteria:

Thallus organisation in the sense no differntiation of organism into different parts. It is in  three forms.

1. Unicellular form.
      Ex. Chrochroocus.
2. Colonial form.
      Ex. Merismopodia.
3. Filamentous form.

•       It consist of trichomes.
•    Trichome may be branched or unbranched. Ex. Nostoc.
•    Truly branched trichome. Ex. Nostocopsis.
•    False branched trichome. Ex. Cytonema.
•    Heterotrichous. Ex. Pulvinaria.

Species of cyanobacteria.

1. Oscillitoria

•  It is afresh water blue-green algae and filamentous covered by mucilage.
•  The terminal cell of bacteria is dome shaped and covered by thick cap called as calyptra.
•  It shows goidular phenomenon of chromatic adaptation.
•  Reproduction is by fragmentation and harmagonia.

2. Nostoc

•    Nostoc forms mucilage colonies in aquatic and terrestrial habitat and occurs abundantly in Rice fields.
•  Some species grows as Epiphytes within the thallus, Anthoceroes(bryophytes), and corolloid roots of cycas.
•  It is jelly like mass or ball like structure and brownish.
•  The filament shows light yellowish thick walled cells called as Heterocyst.
•  Reproduction is by harmogonia or akinites.

3. Anabena

•    Anabena is a fresh water blue green algae. Few species of Anabena are Epiphytes living in roots of cycas ans leaves of Azolla.
•  Covered by mucilage layer and contains Intercalary heterocyst.
•  Reproduction is by fragmentation or Akinites.