Cyanophyceae protoplasmic structure, Cyanoprokaryotes,phycobilisomes,Carboxysomes,cyanophycin,polyphosphate bodies etc

1. Cyanoprokaryotes
Presented by Debanjan pandit , Faculty of Raidighi college

2. Cyanoprokaryotes : Protoplasmic structure, genome and genetic properties.
What is Cyanoprokaryote ??
It is a primitive group of algae, consists of 150 genera and about 2,500 species. In India, the division is represented
by 98 genera and about 833 species. Members of the class Myxophyceae (Cyanophyceae) are commonly known as
blue green algae. The name blue green algae is given because of the presence of a dominant pigment c-phycocyanin,
the blue green pigment.
Why it is prokaryote ??
a. Nucleus is of prokaryotic nature i.e., devoid of nuclear membrane and nucleolus.
b. Absence of well-organised cell organelles.
c. Pigments are distributed throughout the chromoplasm (the outer part of protoplasm).
Depending on the above prokaryotic characteristics many microbiologists consider the members of Cyanophyceae
as bacteria. Based on prokaryotic cell structure like bacteria, Christensen (1962) placed both Cyanophyta and
bacteria under a common phylum Prokaryota.

3. Important Characteristics of Cyanophyceae :
1. The individual cells are prokaryotic in nature. The nucleus is incipient
type and they lack membrane bound organelles.
2. Both vegetative and reproductive cells are non-flagellate.
3. Cell wall is made up of microfibrils and is differentiated into four (4)
layers. The cell wall composed of mucopeptide, along with
carbohydrates, amino acids and fatty acids.
4. Locomotion is generally absent, but when occurs, it is of gliding or
jerky type.
5. The principal pigments are chlorophylls a (green), c-phycocyanin
(blue) and c-phyco-erythrin (red). In addition, other pigments like β-
carotene and different xanthophylls like myxoxanthin and
myxoxanthophyll are also present.

4. Important Characteristics of Cyanophyceae :
6. Membrane bound chromatophore are absent. Pigments are found
embedded in thylakoids.
7. The reserve foods are cyanophycean starch and cyanophycean granules
(protein).
8. Many filamentous members possess specialized cells of disputed
function (supposed to be the centre of N2 fixation) known as heterocysts.
9. Reproduction takes place by vegetative and asexual methods.
Vegetative reproduction takes place by cell division, fragmentation etc.
Asexual reproduction takes place by endospores, exospores, akinetes,
nannospores etc.
10. Sexual reproduction is completely absent. Genetic recombination is
reported in 2 cases.

5. Protoplasmic structure :
In the central protoplasm are the circular fibrils of DNA which are not associated with basic proteins (histones).
The amount of DNA in unicellular cyanobacteria varies from 1.6×109 to 8.6×109 daltons. This is similar to the
genome size in bacteria (1.0×109 to 3.6×109 daltons). Cytoplasm is covered by protoplasmic membrane. It is a
semi-transparent membrane made up of protein. Cytoplasm can be divided into two parts:
(a) Chromatoplasma:
It is the outermost part of the cell, which contains
thylakoids or lamellae. They are arranged in parallel
rings or scattered. They are flat, sac-like structures,
enclosed by unit membrane. Each membrane is 70-80
Å thick. At their surface phycobilisome and
biliproteins are present.
Apart from these structures, cytoplasm also contains
ribosomes, cyanophycin granules, polyglucan
granules, carboxysome, polyhedral bodies, Gas
vacuoles, polyphosphate granules etc,
(b) Centropiasm:
Central transparent part of the cell is called
centroplasm. Genetic material is found in this portion.
Genetic material is in the form of DNA. Nuclear
membrane, nucleoli and histones are absent. In this
part besides DNA, RNA is also present. Thus, in
Cyanobacteria organised nucleus is not present and
this nucleus is called incipient nucleus. The 70S
ribosomes are dispersed throughout the
cyanobacterial cell but are present in the highest
density in the central region around the nucleoplasm.

6. Cyanophycin :
Cyanophycin is a nitrogen-storage polymer composed of a
polyaspartate backbone with arginine side chains attached
with their α-amino group to the β-carboxy group of each
aspartate. It is synthesized by the
enzyme cyanophycin synthase and deposited as granules in
cyanobacteria as well as several photosynthetic and non-
photosynthetic bacteria (Berg et al., 2000; Oppermann-
Sanio and Steinbüchel, 2002). While arginine is the most
common side chain attached to the polyaspartate backbone,
other amino acids have also been found
in cyanophycin produced in heterologous hosts, such as
lysine, ornithine, or citrulline (Steinle et al., 2009).
Although cyanophycin is not suitable for material
applications, it is a useful source of polyaspartate.

7. Function of Cyanophycin :
Cyanophycin functions as a temporary
nitrogen reserve in nitrogen-fixing
cyanobacteria, accumulating during the
transition from the exponential to the
stationary phase and disappearing when
balanced growth resumes. Nitrogen is stored in
phycobilisomes in cyanobacteria that do not
fix nitrogen.

8. Phycobilisomes :
Phycobilisomes are aggregates of light-harvesting proteins attached to the stroma side
of the thylakoid membranes of the cyanobacteria (blue-green algae) and red algae. The
water-soluble phycobiliproteins, tetrapyrrole chromophores covalently bound to
apoprotein. Several additional protiens are found within the phycobilisome and serve to
link the phycobiliproteins to each other in an ordered fashion and also to attach the
phycobilisome to the thylakoid membrane.

10. Carboxysomes (polyhedral bodies) :
Carboxysomes are polyhedral inclusion bodies that
contain the enzyme ribulose 1,5-diphosphate
carboxylase. This is responsible for carbon dioxide
fixation in cyanobacteria.They contain the carbon
dioxide-fixing enzyme ribulose-1,5-bisphosphate
carboxylase/oxygenase(Rubisco). There are two
types of carboxysomes, α-carboxysomes and β-
carboxysomes, which differ in their protein
composition. Cyanobacteria with α-carboxysomes
occur in environments where dissolved carbon is
not limiting (e.g., oligotro phicoceanic waters),
Overview of the general CCM characteristics of α-
and β-cyanobacteria,

11. Overview of the general CCM characteristics of α-
and β-cyanobacteria,
whereas cyanobacteria with β-
carboxysomes occur in environments
where dissolved carbon is limiting (e.g.,
mats, films, estuaries, and alkaline lakes
with higher densities of photosynthetic
organisms) Carboxysomes also contain
the enzyme carbonic anhydrase that
converts HCO3 into carbon dioxide, the
only form of carbon that is fixed by
Rubisco, Bicarbonate (HCO3) is
transported into the cell and
carboxysome. Carbonic anhydrase in the
carboxysome converts HCO3 into CO2
which is fixed by Rubisco into
carbohydrates.

12. Function in brief:
The carboxysome encapsulates the RubisCO enzyme,
with a selectively permeable shell layer that provides a
diffusion barrier to CO2 efflux and O2 influx yet
permits transit of ribulose-1,5-bisphosphate (RuBP), 3-
PGA, Mg2+, and HCO3
− between the carboxysomal
and cytoplasmic pools. Within the lumen of the
carboxysome, a carboxysomal CA. enzyme
dehydrates HCO3
− to CO2, where it is fixed into 3-
carbon sugars by RubisCO

13. Polyphosphate bodies (Volutin granules):
Contain stored phosphate; polyglucan granules (a-granules)
are common in the space between the thylakoids in actively
photosynthesising cells. These granules contain a
carbohydrate, composed of 14 to 16 glucose molecules, that is
similar to amylopectin.
Volutin granules are intracellular storages of complexed
inorganic polyphosphate (poly P).
typical characteristics of volutin granules: (i) volutin staining,
(ii) green UV fluorescence when stained with 4',6-diamidino-
2-phenylindole, (iii) electron-dense and rich in phosphorus
when determined with transmission electron microscopy and
X-ray microanalysis, and (iv) 31P NMR poly P resonances of
isolated granules dissolved in EDTA. MgCl2 addition to the
growth medium stimulated granule formation but did not
effect expression of genes involved in poly P metabolism.

14. Typical characteristics of volutin
granules:
(i) volutin staining, (ii) green UV fluorescence
when stained with 4',6-diamidino-2-
phenylindole, (iii) electron-dense and rich in
phosphorus when determined with transmission
electron microscopy and X-ray microanalysis,
and (iv) 31P NMR poly P resonances of
isolated granules dissolved in EDTA. MgCl2
addition to the growth medium stimulated
granule formation but did not effect expression
of genes involved in poly P metabolism.

15. Polyglucan granules (α-granules):
They are also known as iodophilic or polysaccharide granule sare common in the space
between the thylakoids in actively photosynthesizing cells. These granules contain
carbohydrate, composed of 14 to 16 glucose molecules, that is similar to amylopectin α1-4
linkage and branch point α1-6 linkage (Hough et al., 1952; Frederick,1951).