General features and structure of cyanobacteria

SHORT NOTES ON CYANOBACTERIA

1. General Characters and Structure of
Cyanobacteria
Dr. V. RAMESH
Assistant Professor & Head In-Charge,
Department of Botany,
Vivekananda College,
Tiruvedakam West –625 234
Madurai

2. Cyanobacteria
Definition:Cyanobacteriarepresentsthemajorgroup
ofphotosyntheticbacteriathatcarryoutoxygenic
photosynthesis.Itreleasesoxygenanduseswateras
anelectron-donatingsubstrate,i.e.splitswater
moleculetoreleaseoxygen.Otherthanthis,theyare
alsocapableofnitrogen-fixing.
Classification of Cyanobacteria
Kingdom: Monera
Division: Eubacteria
Class: Cyanobacteria
Examples:Nostoc sp., Oscillotoria sp., Spirulina sp.,
Lyngbya sp., Azolla sp., Anaebina sp., Gleotrichia sp.
etc.

3. Characteristics of Cyanobacteria
Cyanobacteriaareprokaryotic,aerobicandphotoautotrophic
organisms.Itssizerangesfrom1-10µm.Itcontainsaprimitive
nucleus.Membrane-boundorganellesareabsentin
cyanobacteria.Chlorophylla,phycocyaninandphycoerythrin
arethephotosyntheticpigments
Chlorophyll a: Imparts green colour
Phycocyanin: Imparts blue colour
Phycoerythrin: Imparts red colour
As cyanobacteria also calledblue-green algae,is due to the
presence of chlorophyll a and phycocyanin. Chlorophyll
involves in photosystem I whereas phycocyanin involves in
photosystem II. Its photosynthesis is “oxygenic”.
Cyanobacteria have the ability to fix atmospheric N
2. The
reserve food material is “Cyanophycean starch”.

4. Habitat
Thesearethemostgeneticallydiverseorganismsthat
showabroadrangeofhabitat.Theycanlivein
freshwater,marinewater,dampplaces,moistsoil,hot
springsetc.
Types: Cyanobacteria can be of three kinds: Unicellular,
colonial and filamentous.
Unicellular: These are single-celled, having mucilage sheath
covering. Examples:Chroococcus sp.
Colonial: These are multicellular. It forms when single cells
colonise themselves. Examples:Gleocapsasp.
Filamentous: These founds in the form of a chain, covered by
a sheath. It consists of: Hetero-cysts: Helps in N
2fixation ,
Akinete: Collects the food material. Examples:Nostoc sp.,
Oscillotoriasp. etc.

5. Structure of Cyanobacteria

6. The structural components of cyanobacteria are:
Sheath: envelope of cyanobacteria, mucilaginous, hygroscopic in nature. It contains
“pectic substances”.Its appearance is fibrillar under the microscope.
Function: sheath protects the cell from unfavourable conditions. It keeps the cell
moist.
Cell Wall
It is present between the sheath and plasma membrane. The pores that are present on
the cell wall helps in secretion of mucilage. It consists of four layers represented by L-I,
L-II, L-III and L-IV and interconnects with each other by “Plasmodesmata“.
Plasma Membrane
It is a bilayer membrane, also called “Plasmalemma“. It is 70Å thick, selectively
permeable, maintains the structural integrity of the cell. There is a structure called
“Lamellosomes” forms when plasma membrane invaginates and fuses with lamellae. It
encloses cytoplasm and other cell inclusions.
Cytoplasm
It consists of two regions:
Chromoplasm: It comprises of a vesicular structure called thylakoids, having a capacity
of “Photophosphorylation”.
Centroplasm: It is colourless and regarded as the primitive nucleus (devoid of nuclear
membrane and nucleolus). Some granular structures present inside this.

7. Cytoplasmic inclusions: It includes:
Cyanophycean granules: It is the nitrogenous reserve material. It
constitutes about 8% of the total cell weight.
Gas vacuoles: These are hollow, tough and elongated in shape. Its
diameter is 75nm and length is 200-1000nm.
Carboxysomes: These are polyhedral bodies, contains 1,5-ribulose
biphosphate carboxylase.
Phosphate bodies: These are the volutin granules.
Phycobilisomes: Phycobiliproteins when aggregates into a ball like
structure form phycobilisomes. It is attached to the outer surface of
the thylakoid.
DNA matrix: Naked DNA fibrils dispersed in the cytoplasm, lacks
Nucleoplasm. The base composition of DNA differs. Cyanobacteria
contain covalently closed, non-functional, circular plasmid DNA.

8. Thank You All