Cyanobacteria : general characteristics,classification and economic importance

1. PRESENTED BY – SADAAT ALTAF KANTH
Msc. Microbiology ( 1st Semester)
UNIVERSITY OF KASHMIR

2. INTRODUCTION
 Cyanobacteria ( cyano = blue) are prokaryotic organisms and placed in
Volume 1 of Bergey’s Manual of Systematic Bacteriology .
 They were originally studied by botanists and classified as blue green algae
incorrectly. These organisms due to their prokaryotic structure were
studied separately and called cyanobacteria due to their close relationship
with bacteria ( R. Y Stanier & Cohen-Bazire ).
 There are about 150 genera and 1500 species of cyanobacteria
 They are considered to be 1st oxygen evolving phototrophs that paved way
for evolution of other life forms on Earth and thus responsible for
conversion of atmosphere of earth from anoxic to oxic ( Great Oxygenation
Event).
 Cyanobacteria constitute a large, morphologically, ecologically and
physiologically diverse group of phototrophic bacteria.
 They are different from algae because of their prokaryotic structure and
differ from other photosynthetic bacteria because they perform oxygenic
photosynthesis.

3. EVOLUTION
Purple bacteria (Anoxygenic phototrophic bacteria)
Origin of Cyanobacteria (slow oxygenation )
Origin of Eukaryotes
Algal diversity
Shelly invertebrates
Vascular plants
Mammals
Humans

4. ECOLOGY ( OCCURANCE)
 Cyanobacteria are widely distributed in nature especially tropical countries.
They can be found in terrestrial as well as aquatic habitats including freshwater
and marine water.
 One of the most characteristic habitat is tropical paddy fields.
 Other conspicuous places where they can be found includes microaerobic/
reducing habitats like mangrove marshes & hypersaline lakes
 They are more tolerant to extreme environments than algae and are sole
oxygenic phototrophs in hot springs, saline lakes and other extreme
environments.
 They are also found on surface of rocks/soil and occasionally within rocks.
 They form extreme crusts over the surface of desert soil and remain dormant
there for years and grow during the brief winter and spring rains
 Cyanobacterial mats of considerable thickness form on shallow marine bay.
 Blooms are formed in freshwater lakes those rich in nutrients (formed due to
high growth rates , tolerance to dessication and production of allochemicals)
 They also form symbiotic association with liverworts, ferns and cycads.
 Symbiotic association of species of Anabaena with water fern Azolla is
responsible for nitrogen fixation

6. GENERAL CHARACTERISTICS
 They have a prokaryotic cell organization ( lack membrane bound
organelles, and a typical double membraned nucleus)
 Size varies considerably between taxa. Cell size ranges from 0.5- 1
micrometre for unicellular cyanobacteria to as large as 40 micrometres in
filamentous cyanobacteria, Oscillatoria princeps.
 Cyanobacterial cells can be spherical, ellipsoid, barrel shaped, cylindrical ,
conical or disc shaped.
 Cyanobacteria have 5 morphological forms
1. Unicellular forms , usually dividing by binary fission like Gleotheca ,
which is around 5-6 micrometres in diameter.

7. 2.Unicellular, Colonial form dividing by multiple fission (Dermocarpa)
3. Filamentous conatining heterocysts that function in Nitrogen
fixation.(Anabaena -5 micrometres in diameter)
4.Filamentous , non heterocystous forms (Oscillatoria- 15 micrometres)
5. Filamentous,branching forms like Fischerella

8.  The cell wall is similar to that of gram negative bacteria . Peptidoglycan ,
LPS and proteins are present in the cell wall.
 They produce mucilagenous envelopes and sheaths that binds group of
cells in colonial forms. Mucilage is secreted in directional manner and
helps in sticking to solid surface
 They do not posses flagella. Filamentous forms of cyanobacteria show
gliding motility when they are in contact with solid surface . They also show
directional movements like phototaxis and chemotaxis.
 Peripheral region of cell is transversed by large number of lamellae or
thylakoids. Thylakoids act as the site for photosynthesis and respiration.
 The adjacent thylakoids are seperated from each other by a space which is
occupied by phycobilisomes.
 Phycobilisomes consists of Phycobiliprotien pigment and allophycocyanin
surrounded by other pigments in stacklike structures.
 Photosynthetic pigments present in cyanobacteria are chlorphyll a, and
characteristic biliprotien pigments called phycobilins. Phycocyanin (blue) ,
phycoerythrin (red).

10.  The color of the water blooms formed by cyanobacteria depends on ratio
of these pigments to each other.
 Chromatic adaptation – The phenomena where pigmentation is
determined by quality of light or capacity to change color complementary
to light. Cyanobacteria use different strategies for doing so like sensory
rhodopsins, phytochromes and membrane associated receptors that sense
UV and blue light.
 There are various subcellular organelles observed in cynobacterial cells
1. RIBOSOMES (70 S) which are involved in protien synthesis.
2. POLYPHOSPHATE BODIES which are sites of phosphorus storage
3. CARBOXYSOMES also called polyhedral bodies which contain enzyme
Ribulose- 1,5 bisphosphate carboxylase that is responsible for C02
fixation
4. GAS VACOULES / AEROTPOES measuring about 15 micrometre in
diameter and 1 micrometre in length. This structure regulates cell
buoyancy such that cells can retain a position in water column

11. 5. CYANOPHYCIN is a Copolymer of arginine and aspartic acid and a nitrogen
storage product. Constitutes 10% of cell mass.
 It is also an energy reserve in cyanobacteria
Aginine + ADP+ Pi +H20 Ornithine+ 2NH3+ CO2+ATP
(Arg dihydrolase)
6. HETEROCYSTS are specialized, enlarged and rounded cells distributed
regularly along filament or located at one end of filamnent.
 They arise from differentiation of vegatative cells.
 Allow fixation of atmospheric Nitrogen ( diazotrophy)
 They have intercellular connections with adjacent vegetative cells.
 Surrounded by thickened cell wall containing large amounts of glycolopids.

12. NUTRITION
 They require nitrate or ammonia as nitrogen source
 They are mostly obligate phototrophs that are unable to grow in dark
 Few grow in dark on glucose using sugar as both cabon and energy source
 Media used for growing them is BG 11 medium ( liquid broth) optimized
for their growth and maintainence
REPRODUCTION
 Asexual reproudction is seen in cyanobacteria
1. Binary fission where parent cell divides into 2 daughter cells.
2. Baeocytes , small spherical cells arise from multiple fission and are
released after rupture of fibrous outer wall layer of parental cell.
3. Fragemtation – in filamentous cyanobacteria filaments fragment to small
pieces called hormogonia.
4. Spore formation – endospores as well as exospores can be formed
5. Akinites – thick walled specialized cells meant for perennation and
protect organism during unfavourable conditions.

13. CLASSIFICATION

16. ECONOMIC IMPORTANCE
 Cyanobacteria have a wide number of industrial,biotechnological,medical and
agricultural applications.
 They are one of the earliest colonizers of extreme environments and provide
conditions for growth of organisms even in most hostile environment.
 They fulfill vital ecological functions being global contributors of carbon and
nitrogen
 Function as food for aquatic animals.
 Spirulina also called single cell protein,high in proteins is used as supplement
for humans and animals.
 In Rajasthan Anabaena and Spirulina are collected from Sambar lake and used
as fodder and manure.
 They can be used as natural food coloring agents.
 Several cyanobacteria have ability of nitrogen fixation. Some of the fixed
nitrogen comes out as excretion and the substratum becomes rich in N. Such
cyanobacteria are inoculated in rice fields, thus saving consumption of nitrogen
fertilizers.
 Nitrogen fixing cyanobacteria are also used for reclaming usar soil like
Anabaena , Nostoc
 Efficiently used as biofertilizers and plant growth promoters

17.  Improve tolerance of plants to abiotic stresses and reduce biotic stresses.
 Recently used in heavy metal bioremediation.
 Antibiotics can be manufactured from extract of Lyngbia.
 Fischerella muscicola synthesizes some antibiotic that kills related algae
(fischerellin)
 Synechocystic sp was 1st prokaryotic genome whose whole genome
sequence was completely sequenced. It continues to be an model
organism for study.
 They can be used to generate renewable energy by directly converting
sunlight into electricity.
 Sulfate polysaccharides secreted by them exhibit antitumor,
antimutagenic,antifungal and even antiviral action against HIV , herpes
and hepatitis.
 Some secondary metabolites produced by them are algicidal as well.
 Cyanovin secretes this secondary metabolite having anti HIV activity
 Edible cyanobacteria are also known to reduce risk of cataracts and age
related macular degeneration.

18.  Some Cyanobacteria can also show negative effects
 They can grow on walls and roofs of buildings during rainy seasons and
cause discoloration and leakage.
 Water blooms growing on nutrient rich water bodies can be toxic to the
aquatic fauna and can also make the water unfit for drinking.
 Apart from this they cause aesthetic problems by altering the color and
odour of the water bodies.
 Water blooms and their accumulation in water bodies can cause poisoning
of aquatic fauna like shellfish
 Few cyanobacteria also produce geosmins which have a earthy musty
odour
 Cyanobacteria produce toxins which are called as cyanotoxins which can be
of 3 types
1. Hepatotoxins
2. Neurotoxins
3. Endotoxins (LPS)

19.  Acute illness can be caused by consumption of drinking water
contaminated by these cyanotoxins.
 BMAA ( beta-methylamino-L-alanine) is a type of neurotoxin and has a
potential role in various neurodegenerative disorders like Parkinson’s
disease, Dementia and Amyotrophic lateral sclerosis.
 Several species of Anabaena and Aulosira are used to prevent growth of
mosquito larva.
 The oldest known fossils are also of Cyanobacteria
 In addition to photosynthetic pigments , they produce pigments that
protect cells from intense irradiation (UV rays) eg the Scytonemin ,a black
pigment produced by Scytonema species.