2. Taxonomic classification of cyanobacteria
General features
I. Chroococcales: a Chroococcus, Cyanothece, Microcystis e
ruginosa.
II. Pleurocapsales: Pleurocapsa minor.
III. Oscillatoriales: g Planktothrix , Arthrospira jenneri,
Phormidium sp., Oscillatoria sp., Tolypothrix sp.,
IV. Nostocales: Dolichospermum (Anabaena), Nostoc sp.
V . Stigonematales: Stigonema sp.
4. 1. Non-filamentous forms
a. Unicellular forms
One, two or three cells with multilayered gelatinous
sheath. E.g.Chroococcus
containing exospores e.g. Chamaesiphon ,one club-
shaped cell
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5. b. Colonies
E.g. 1. Merismopedia, a tubular colony contains a
certain number of cells (16-32) arranged in a
homogenous mucilage.
2. Microcystis, irregular colony with cells containing
gas vacuoles.
.
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6. 2. Filamentous Forms
a. Non-heterocystous forms
- Trichome (a row of cells without sheath)
e.g. Oscillatoria.
- Filament ( a row of cells with sheath) (trichome +
sheath) e.g. Lyngbya.
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8. 8 9/21/2023
2. Branched Filaments
a. Pseudo-branching (false branching)
It does not arises from a vegetative cells, but
arises singly and mostly subtending a heterocyst.
E.g. Tolypothrix.
.
9. b. True Branching
It arises from vegetative cell in a filament, that
changed its division direction by a matter of 90
degrees from the main axis. E.g. Stigonema
Stigonema constitutes the algal component in lichens
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11. 1.Vegetative Reproduction
It occurs by several means:-
A. Binary fission
This type of reproduction takes place in unicellular
forms of cyanobacteria e.g.Chroococcus,.The cell with
all its
contents divides into two parts.
B. Fragmentation
This type of reproduction occurs in colonies and
filaments; where the alga divides into many
fragments; each fragment undergoes repeated cell
divisions to give rise to a new alga.
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12. C. Hormogonia
Hormogonia are small segments of trichome
containing one or more uniform cells; they are
formed either by the formation of separation disc
or by the death of one or more intracellular cells.
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13. - Hormogonia are formed in filamentous
cyanobacteria; they are irregular as in , Oscillatoria,
Lyngbya, Nostoc; or they are formed on the apical
part of branches as in Scytonma, or in the
meristematic region as in Rivularia.
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14. II. Asexual Reproduction
- The sexual reproduction occurs in cyanobacteria
when the conditions are not suitable for growth;it
occurs by the formation of asexual bodies:.
1. Endospores
- Endospores are formed in certain species of
cyanobacteria e.g. Dermocarpa, by dividing the
protoplast into many naked spores that can form
cell wall after getting out from the sporangium.
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15. 2. Exospores
Exospores are formed by the transverse division of
the parent cell, and they separate at the open end of
the sporangium, e.g. Chamaesiphon.
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16. 3. Akinetes
- Akinetes are vegetative cells accumulated large
amount of food and surrounded their selves by a thick
wall and turned yellow or dark brown in color.
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17. 4. Heterocysts
- Heterocystes are vegetative cells surrounded their
selves by a multilayered envelope and broke down
photosynthetic thylakoids.
- Function of heterocystes are nitrogen fixation and
asexual reproduction.
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18. - Heterocysts are classified on the basis of
their position in the filament into two types:-
1. A. Intercalary heterocysts
2. -they are found more or less at regular intervals;
each heterocyst has two polar nodules, one on
each side for attachment with the vegetative cells
as in Anabaena, Nostoc.
.
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19. 2. Terminal heterocysts
- They are found in terminal position of the
filament and each has only one polar nodule.
They may found at the apex of branches and
are called apical heterocysts e.g. in
Nostocopsis; or are found at the base of the
filament and are called basal heterocysts e.g. in
Rivularia
