EUBACTERIA
They are called ‘true bacteria’ and are characterised by
the presence of a rigid cell wall and if motile, have
flagellum.
anol vacteria
Cyanobacteria, member of this group, have many
characters similar to bacteria. These are also known as
blue-green algae. The examples of cyanobacteria are
Nostoc, Oscillatoria, Spirulina, Rivularia, Anabaena,
etc. They can survive in a wide variety of habitats, such
as hot springs, seawater, polluted water, etc. They are
predominantly aquatic but many species are known to
be terrestrial also.
These can grow even in minimal moisture conditions
Cyanobacteria have following three forms
(i) Unicellular as in Chrococcus and Synechococcus.
(ii) Colonial as in Microcystis and Gloeocapsa.
(iii) Filamentous as in Nostoc, Oscillatoria and Anabaena.
Cell Structure
‘l Cells of eubacteria have a definite firm and rigid cell wall
surrounded by mucilaginous sheath. It is bilayered. The inner
layer is made up of peptidoglycan. The cell wall is followed by
plasma membrane made up of lipid and proteins. The
membrane bound structures like true mitochondria,
endoplasmic reticulum, Golgi bodies, etc., are absent.
The photosynthetic pigments presents in the cell are located in
broad sheet-like lamellae called thylakoids. The pigments are
chlorophyll-a, [Rarotene, myxoxanthophyll, myxoxanthin,
C-phycocyanin and C-phycoerythrin. The C-phycocyanin is
blue in colour while C-phycoerythrin is red. The former is
present in more amount than later, this gives the cyanobacteria
its characteristic blue-green colour. The nucleolus is absent and
the nucleoid is not bound by nuclear membrane.
Some cyanobacteria (Nostoc, Anabaena, Scytonema, etc.)
possess special type of cells called heterocysts to perform special
functions. These are large cells with walls so thick that they are
impermeable to oxygen. Heterocysts are the sites of nitrogen
fixation.

Nutrition
Cyanobacteria are mostly photoautotrophs. They contain
chlorophyll-a and other photosynthetic pigments.
Reproduction
Cyanobacteria multiply asexually and vegetatively. Sexual
reproduction does not occur.
The types of multiplication are
(i) Binary fission occurs in unicellular forms.
(ii) Fragmentation occurs in colonial and filamentous
forms. The small segments formed are called
hormogonia.
(iii) Asexual reproduction involves formation of
following structures
• Endospores These are the spores produced
endogenously within a vegetative cell.
• Exospores These are the exogenously produced
spores.
• Akinetes These are thick-walled spores that also
have material stored in them.
cyanophycean starch.
Uses of Cyanobacteria
Some uses of cyanobacteria are
(i) Some cyanobacteria have the ability to fix
atmospheric nitrogen. The green manuring by
farmers is done on this basis to enrich the soil with
nitrogenous fertilisers.
(ii) Cyanobacteria like Anabaena, Tolypothrix, etc., help in
prevention of soil erosion and its conservation.
(iii) Spirulina is a protein rich supplement for humans. It
is a fast growing cyanobacteria. It is also known as
Single Cell Protein (SCP).
(iv) Cyanobacteria like Anabaena and Aulosira prevent
mosquito larvae to grow in surroundings.
Harmful Effects of Cyanobacteria
Some harmful effects of cyanobacteria are
(i) Cyanobacteria discolour the walls and roofs of
buildings, movements and statues.
(ii) Oscillatoria causes asthma and gastrointestinal
problems by releasing its toxins.
(iii) Growth of Oscillatoria in water bodies shows
pollution by organic matter.
(iv) Excessive growth of cyanobacteria causes water
blooms, which decreases oxygen level in water
causing death of aquatic animals.