Cyanobacteria (BGA) differ from archaebacteria and mycoplasma how is it

 CYANOBACTERIA 

                                                          BLUE GREEN ALGAE 

According to two kingdom system BGA were included in class Cyanophyceae, Myxophyceae or Cyanophyta. But now they are included in kingdom monera , because blue green algae are prokaryote. It is also known as cyanobacteria. First oxygen evolving bacteria on our earth mostly found in fresh water and also in marine water and terrestrial habitat.

Cyanobacteria are photosynthetic prokaryotes. It have following pigments:-

      Chlorophyll A  -  Green ( similar to green plant )

      Carotenoids – Yellow

      C - Phycocyanin – Blue

      C – Phycoerythrin – red

BGA are not always of blue – green colour for e.g. Trichodesmium is red coloured . The red colour of this algae due to this algae.

Different forms of BGA or cyanobacteria like the cyanobacteria are unicellular (spirulina) , colonial (Anabaena) or filamentous ( Oscillatoria, Nostoc)

STRUCTURE OF B.G.A.

The structure of BGA is similar to Gram (-ve) eubacteria . BGA are surrounded by a mucilaginous sheath. This sheath is made up of mucopolysaccharides ( Pectic Acid ) . The cell wall of BGA is also bilayered and outer wall is made up of lipopolysaccharides  and their inner wall is made up of peptidoglycan. The cell membrane of BGA is also made up of lipoproteins.

Cytoplasm of BGA contains following structure :-

Thylakoids or chromatophores : These are membrane bound structure which contain photosynthetic pigments. They are present in form of vesicles lamellae .

Inclusion bodies:  Cyanophyceae granules and gas vacuole and it is non membranous structures. BGA store its food in the form of cyanophycean starch. It is not actually starch, it is structurally similar to glycogen. 

Gas vacuole – It is found in blue green algae, purple and green photosynthetic eubacteria. And it is found in Nucleoid (Double stranded naked DNA) and 70s type Ribosomes.

NITROGEN FIXATIONS

Some of the BGA , fix atmospheric nitrogen in specialized cells called heterocyst. It is a thick walled, non green cell and it does not perform photosynthesis like other vegetative cells.   They convert  atmospheric nitrogen into amino and then nitrogenous compounds like amino acids  and nitrates. These nitrates increase fertility of soil by nitrogen fixation.  

BGA fix nitrogen in two forms :-

(A)  Symbiotic form – These BGA form symbiotic association with many plants and perform nitrogen fixation.  E.G. – Anabaena & Nostoc like :- 

Azolla – If azolla is grown with rice , than the production increases up to 50% because Anabaena are found in the leaves of azolla

 

(B)  Free living form – Some BGA are found free living in water and soil and perform nitrogen fixations E.G. – Anabaena & Nostoc  like :-

Aulosira   - This BGA is found in plenty in paddy fields. This BGA perform nitrogen fixation due to which the production of rice is increased and Oscillatoria also fix nitrogen in paddy fields.

 REPRODUCTION :-

In BGA reproduction is done by two main process

(a)   Vegetative reproduction by binary fission (Spirulina)  and fragmentations (Oscillatoria) .

(b)   Asexual reproduction – It is a method of protection to overcome unfavourable conditions. E.g. -  Akinete formation in nostoc

   Water bloom : - Excessive growth of BGA in polluted water body called water bloom. 

ARCHAE BACTERIA

It is a primitive type of bacteria. They were the first to be born our planet and they are present now a days with their primitive characters and they are the “Oldest living fossils”. They are found in harsh habitat like swampy/ marshy area , hot sulphur , spring , salina area etc.

Mostly archaebacteria are anaerobes. Cell wall of this bacteria made up of complex polypeptide and complex polysaccharides and cell membrane are made up of monolayer branched lipid chain.

It is also methane providing bacteria called as methanogens. These bacteria convert CO2 of swampy areas into methane (CH4).  And these bacteria convert the organic substance (cellulose) present in cow dung into methane by fermentation. Methanogens are present in the rumen or gut of several ruminants animals/cattles as a symbiotic organism and they are responsible for the production of methane gas (biogas).

These bacteria found in highly saline /salty area called as halophiles. And also which is found in high temperature (80 degree – 100 degree Celsius).

MYCOPLASMA

Mycoplasma are unicellular, smallest prokaryotic organisms. They are smallest living cells known. They completely lack cell wall , so the outer most covering is only cell membrane . cell membrane is made up of lipoprotein and both DNA (ds DNA , circular mainly) and RNA are present.

They are cell wall less hence, they exhibit pleomorphism and thus called as joker of microbiology. They show osmotrophic mode of nutrition (absorption of nutrients by osmosis)  is found in mycoplasma.

They are resistant to antibiotics like penicillin which act on cell wall. And sensitive to tetracycline and chloramphenicol that act on metabolic activities. It can survive without oxygen and species of mycoplasma are saprophyte or parasite. Many mycoplasma are pathogenic in animals and plants.