2. Domain – Bacteria
Phylum – Cyanobacteria
Class - Cyanophyceae
Order – Nostocales
Family – Nostocaceae
Genus - Anabaena
3. Anabaena is a genus of filamentous
cyanobacteria, or blue-green algae.
It found as plankton. It is known for its nitrogen
fixing abilities.
They form symbiotic relationship with certain
plants, such as the mosquito ferns.
Some species of anabaena are endophytes.
They live in the roots of Cycas and Azolla.
4. Anabaena has filamentous structure.
The filaments of anabaena consists of string of
beaded cells.
Several intercalary heterocyst are present in the
trichome.
The filaments are either straight or circulate or
irregular.
Filaments occur within the sheath.
Sheath are always hyaline and watery.
5. A heterocyst is a differentiated cyanobacterial
cell that carries out nitrogen fixation.
The heterocyst function as the site for nitrogen
fixation under aerobic conditions.
They are formed in response to a lack of fixed
nitrogen (NH4 or NO3).
They contain only photosystem 1, which
enables them to carry out cyclic
photophoshorylation and ATP regeneration
6. These changes provide the appropriate
conditions for the functioning of oxygen-sensitive
nitrogenase.
Heterocyst are of same shape as of vegetative
cell and are mutually interdependent.
During times of low environmental nitrogen
about one cell out of every ten will differentiate
into a heterocyst. Heterocyst then supply
neighboring cells with fixed nitrogen in return for
the products of photosynthesis, that they can no
longer perform.
7. An akinete is a thick walled dormant cell derived
from enlargement of a vegetative cell.
It serves as a survival structure. It is a resting
cell of cyanobacteria.
Akinetes appear thick walled with granular
looking cytoplasm, under magnification.
The akinetes are filled with food reserves, and
have a normal cell wall surrounded with 3 layer
coat.
8. Development of akinetes from a vegetative
cell involves:
• Increase in size,
• Gradual disappearance of gas vacuoles,
• Increase in cytoplasmic density, number of
ribosomes and cyanophycin granules.
9. Anabaena is reproduced only by vegetative and
asexual methods.
The sexual reproduction is completely absent.
Anabaena reproduce vegetatively by the following
methods-
Fragmentation
• Old trichome becomes very large and irregular
due to which it gets to break up into short
fragments.
10. • These short fragments of trichome divide
vegetative cells and develop into new
trichome.
Hormogones
• Hormogones are the short fragments of
trichomes. Developed in the region of
heterocyst.
• Then they came out of th trichome due to
some movement.
11. • They divide vegetative cells and developed
heterocyst and again surrounded by sheath.
In this way new trichome is formed.
12. Akinetes
• The akinetes are produced in mature colonies.
They are formed in unfavorable conditions.
• They are also called arthrospore or resting
spore. They are penetrating bodies.
• In favorable conditions they directly or indirectly
giving rise to new filaments.
• The contents of akinete divide into bits prior to
germination.
13. Heterocyst
• Heterocyst cell divide transverly and form (2-4)
celled hormogones.
• These hormogones come out by bursting the
thick wall of heterocyst and germination occurs
to give rise to new trichome.
14. Anabaena and azolla have formed a symbiotic
relationship in which the cyanobacterium
receives carbon and nitrogen sources from the
plant in exchange for fixed nitrogen. This
relationship is useful to humans in production of
food; especially in the fertilization of rice
paddies.
15. Anabaena perform oxygenic photosynthesis
very similar to that of eukaryotic plant and algae,
by utilizing water as a reductant source ,
consequently producing molecular oxygen.
Anabaena provides a model for the study of
gene differentiation in the formation of
heterocyst. The recent sequencing of the
genome of anabaena species strain PCC 7120
is yet another step towards understanding this
process.
17. Domain – Bacteria
Phylum – Cyanobacteria
Class – Cyanophyceae
Order – Nostocales
Family – Scytonemataceae
Genus - Scytonema
18. Scytonema is filamentous forms with false
branching and relatively wide sheaths.
It grows in filaments that form dark mats.
Scytonema is a nitrogen fixer, and can provide
fixed nitrogen to leaves of plants on which it is
growing.
Some species of scytonema form a relationship
with fungi to produce a lichen.
It is predominantly a sub-aerial and aquatic mostly
freshwater genus.
They vary in color from blue green ,dirty bule
green, yellowish brown to brown.
19. Thallus structure
• It is filamentous. The filaments are interwoven
to form different types of thalli.
• Each filaments consist of a single trichome. The
branching in scytonema is peculiar.
• The trichome breaks at one point and one or
both, the broken ends protrude out of the
sheath and develop into branches. This
branching is called false branching.
• False branching are said to be single or
germinate.
20. In false branching ,there is an appearance of the
branch, but the cells in one branch are actually
continuous with those of the other.
False branching is characteristically at right –
angled bends, either forming a loop or two
parallel branches at right angles to original
filaments.
Double false branching often forms when a
filaments breaks apart at the side if a dead cell.
21. Both ends of the filaments then break
through the mucilage sheath and continue to
grow as branches.
Occasionally, false branching also forms at a
heterocyst where the filament breaks apart in
a similar manner.
These of the false branching can be readily
distinguished from true branching.
22. The trichomes are generally of uniform thickness
and form sheath.
Trichome is composed of a single row of cells lying
end to end to form a long and short thread like
structure.
In some species trichome sre constricted at septa.
The trichome have heterocyst distributed at regular
and irregular intervals throughout its length.
Generally heterocyst are intercalary. The cell
contents may be homogenous and granular.
23. The granules are of various sizes and their
arrangement also varies in cell.
The cell may be discoid, squarish, cylindrical, or
rectangular.
The trichome increase in size by the repeated
division of its cell. The cell division is mainly
restricted to the apical or sub-terminal cells.
24. Branching starts with breaking of the trichome
at a certain point. It is a kind of vegetative
multiplication.
The branching in scytonema is affected by
either of the following methods:
By the degeneration of one or more intercalary
cell.
By formation of separation discs.
By breaking of the trichome near the intercalary
heterocyst.
By the formation of the loop.
25. In scytonema, hormogone formation is the
principle method of reproduction.
Hormogone formation
• The hormogone are delimited by the death of
an intercalary cell, by the formation of
biconcave discs or by breaking at the
heterocyst.
• Usually the hormogonia are formed at the ends
of the trichomes.
• They are of short length. The hormogone creep
out by breaking open the sheath.
26. The liberated hormogone germinates to give
rise to a new filaments of scytonema.
In most of the terrestrial species the
hormogones during the dry period of the year
secrete thick, lamellate sheath.
The cell contents become densely granular and
pale yellow or yellowish brown.
During the rainy season the sheathed
hormogones become active and grow into new
filaments.
27. Scytonema crispum is important ecologically
because it has the ability to fix nitrogen from the
environment. Because of this, scytonema can
also form symbiotic relationship with other
organisms such as fungi.
The genus scytonema is especially important
because these bacterium have been found to
produce special chemicals such as toxins. In
2003, an anti-HIV protein, scytovirin was
isolated.
28. Scytonema crispum is the first species of
scytonema to produce saxitoxin, which are
fast acting neurotoxin that inhibits nerve
conduction by blocking sodium channels.
29. David G. Adams, Noel G. Carr.1981.The
Developmental Biology Of Heterocyst And
Akinete Formation In Cyanobacteria.Volume
10.Pages 45-100.
Hans W.Paerl,Penelope
E.Kellar.1978.Significance Of Bacteria
Association With Respect To N2
Fixation.Journal of Phycology.Volume
14.Issue 3.Pages 245-260.
30. Waseem Raja, Asha Chadha.1979.Certain
observation on scytonema.Journal of Biology
And Biochemistry.Volume 40.Issue 1.Pages
362-372.
