2. • Old 3.5 billion years
• Dominated as biogenic reefs
• During Proterozoic – Age of Bacteria (2.5
bya – 750 mya) they were wide spread
• Then multicellularity took over
• Cyanobacteria were first algae!
CYANOBACTERIA
Evolution
3. Cyanobacteria terminology
• Division Cyanophyta
• Cyanobacteria ‘formerly known as ‘BlueGreen
Algae’
• Cyano = blue
• Bacteria – acknowledges that they are more
closely related to prokaryotic bacteria than
eukaryotic algae
4. CYANOBACTERIA
• Historical background :
• Previously called as blue green algae, kept under class
Cyanophyceae or Myxophyceae.
• Have simple structure like bacteria, indicates primitive nature
• Include many colourless forms like bacteria, both reproduce
asexually by method of fission
• Cohn (1871-72) suggested that blue green algae & bacteria should
be kept in single phylum Schizophyta, Stainier & Niel supported
Cohn’s view.
• Christensen (1962,64) proposed classification of Algae into
Prokaryota (cyanophyceae) & Eukaryota (Algae other than
cyanophyceae) on the basis of cell structure.
• Bacteriologists in 1978 proposed the name Cyanobacteria for blue
green algae according to ICNB.
5. Main characters which support inclusion of
blue green algae in bacteria:
• Both group include unicellular members.
• Absence of true nucleus
• Ability to fix nitrogen
• Cells enclosed by sheath
• Nature & structure of cell wall is similar in both
• Presence of diaminopimelic acid in wall absent in other algae
• Position of chromatin is similar in both
• RF is glycogen in both
• Some BGA are able to live on dead organic matter in absence of
light
• Asexual reproduction by fission & resting spores is common
• Able to tolerate high temperature
6. Importance
1) First organisms to have 2 photosystems and to produce
organic material and give off O2 as a bye-product.
Very important to the evolution of the earths’ oxidizing
atmosphere.
2) Many – fix or convert atmospheric nitrogen into usable
forms through Nitrogen Fixation when other forms are
unavailable.
IMPORTANT because atmospheric N2 is unavailable to most
living organisms because breaking the triple bond (N ≡ N)
is difficult
7. General Characters
• Unicellular body, tendency to
organise spherical, squarish or
filamentous colony of cells
• Absence of well defined nucleus
• Absence of membrane bound cell
organelles
• Dominant pigment – phycocyanin- c
• Nuclear material no differentiated
into chromosomes
• Sex organs & reproductive bodies
absent
• Sexual reproduction absent
• Vegetative reproduction by fission,
fragmentation etc
• Some differentiation of cells lie
heterocyst, extreme expression in
Rivularia with base & apex
9. Distribution
• Found throughout the world
• Majority are fresh water, few are marine
• Nostoc, Anabaena, Rivularia & Oscillatoria are most common
in ponds & pools
• Some are in soil can fix nitrogen
• Many are thermal growing on snow, also occur in hot water
springs at 770 C
• Nostoc & Anabaena can live as endophytes in Anthoceros and
roots of Cycas
• Some remain associated with fungi as lichens
• Ability to fix nitrogen & being photosynthetic are the
characteristics responsible for symbiotic association
10. Cell structure
Characterised by very primitive structure.
Cell consists of cell envelope & Protoplast.
• Cell envelope – comprises of two layers,
inner cell wall & outer mucilaginous sheath
• Sheath is thick & slimy surrounding each cell
in unicellular form & entire trichome in
filamentous forms
• Anabaena has interrupted sheath
• Sheath contains pectic substances, in most it
is colorless but in some it is yellowish or
brown due to pigments
• Sheath increases water absorbing & water
retaining capacity.
• Colored sheath protects against strong light
• Cell wall is present below the sheath
• Principal wall component group of
mucopolymers (glucosamine, amino acids &
muramic acid) with some glucopyranose,
galactose & pentoses – most belong to group
hemicelluloses
• Many contain greater or lesser amount of
cellulose.
11. Protoplast
• Central colourless centroplasm or central body & an outer
blue green pigmented chromoplasm.
• Contains Pigments – chl a, phycobiliproteins, phycoerythrin,
phycocyanin * BlueGreen Color, allophycocyanin
• Storage – glycogen
• Oil drops, glycogen & few spherical bodies known as
cyanophycin granules (probably proteinaceous)
• Pigments occur in organised units of various shapes & size,
scattered through out chromoplasm
• In some genera ultimate photosynthetic units are tiny granules
(0.3 – 0.5 µm in diam.) in others they are flattened sacs or
discs due to fusion of small granules.
• Discs (Photosynthetic lamellae or thylakoids)are separated &
not organized into definite sacks.
12. • Central body or centroplasm contains most of the chromatin of
nuclear nature not bounded by membrane & without nucleolus.
• Chromosomes absent, nuclear material in the form of a loose
reticuum, as rod shaped structure or as crystalline structure of
various shapes.
• Ribosomes are scattered throughout protoplasm & more
numerous in centroplasm.
• No central vacuole but scattered small vesicles sometimes
present.
• Gas vacuoles or bubbles are present
• Golgi apparatus, mitochondria & ER are absent
• α and β – granules are also present.
Protoplast
13. Heterocyst
• Non fiamentous form show little or no differentiation of cells.
• Certain filamentous genera like Nostoc & Stigonema produce
specialised cells called heterocyst.
• Heterocyst are enlarged, thick walled & pale yellowish.
• They are basal (Rivularia) or intercalary (Nostoc) .
• A heterocyst arises by metamorphosis of the lower half of
recently divided vegetative cell.
• It differs mainly in wall structure & yellowish transparent
contents.
• The wall is double layered, outer pectin (gelatinous) & inner of
cellulose.
• In early stages cytoplasmic connections with adjoining cells are
evident through polar pores but later on at maturity they
become filled with button like thickenings called polar nodules.
14. • Protoplasmic content become more & more transparent due to
their transformation into homogeneous viscous substance.
• In heterocyst thylakoids are present but ribosomes are reduced
in number
• Phycocyanin is either absent or present in low concentration
• Hetrocysts contain gycolipid & acyllipid which are absent in
vegetative cells.
Functions are not definitely known & in many instances have
taken secondary functions.
1. Store house of reserve food. 2. secrete growth & cell
division stimulating enzymes 3. serve as specific device for
the multiplication of trichomes. 4. they are vestigial spores
because in exceptional cases they germinate to form a new
trichome.
Heterocyst
20. Asexual Reproduction
Akinete – thick walled resting spore
Function – resistant to unfavorable environmental
conditions.
Appear as larger cells in the chain and different than
heterocyst. Generally lose buoyancy
A - akinete
H
