Bacterial Transformation:Definition|Classification|Mechanism

Definition

  • Bacterial Transformation is a processes in which a bacterial cell intake a segment of DNA from the environment or other bacteria,and get integrated with it by homologous recombination.
  • Transformation in bacteria was first demonstrated in 1928 by the British bacteriologist Frederick Griffith.
  • IN 1944  Oswald Avery, Colin MacLeod, and Maclyn McCarty experimentally proved that DNA is the main principle involve in gene transformation.

Classification

Transformation is classified into two classes,this are-
  1. Natural Transformation
  2. Artificial Transformation.
Natural Transformation: Some bacteria can naturally transformable they can take DNA From environment without any special treatment
Artificial Transformation: Most of the bacteria are not natural transformable. These bacteria can be made competence by certain chemical treatment or by strong electrical shock.

Mechanism of Transformation

The transformation mechanism first observe in Streptococcus pneumoniae Bacterial transformation is completed by this following step ,
  • A competence cell get attached with a double stranded DNA by the DNA binding protein.
  • Then an site specific endonuclease cleave one DNA strand and form a nick.
  • Next an envelop associated exonuclease will degrade the cleaved DNA strand.
  • Undergrad DNA strand will get attached with a competency protein, which help in the penetration through the plasma membrane of DNA strand into the cell..
  • After penetration into the cell the DNA strand will integrated with the bacterial genome by the homologous recombination,which is called successful transformation.
  • Or either the DNA strand will hydrolysed into fragment by enzymes which are suspended into bacterial cytoplasm,which is called unsuccessful transformation.

Griffith Experiment


In 1928 Frederick Griffith experimentally proved that the bacterial cells are transfer their gen through a processes which is called Transformstion.
For his experiment he took two different strains of Diplococcus pneumoniae and inject them into a mice.The two different strains are-
  • S – III Strain (Smooth,capsulated,virulent)
  • R – II Strain (Rough,uncapsulated,Nonvirulent).

PROCESSES

  1. At first he applied the S-III strain or virulent strain on mice the mice is died.
  2. After that he applied the R-II strain on mice,the mice is not effected because of its not a virulent strain it don’t contain capsule.
  3. Then he heat killed the S-III strain to destroy their virulent properties, and injected them into a mice.a a result the mice is not effected by the heat killed S-III strain.

Avery, Macleod and McCarty Experiment

Griffith was unable to prove that the DNA is the main principle in Transformation.Avery, Macleod and McCarty first experimentally proved that DNA is the main principle which is transfer During the Bacterial Transformation in 1944.The Smooth Strain of pneumococcus contain an polysaccharide encoded capsule which  induce the antibody formation.

Procedure

  • In his experiment he used the heat killed S-III strain bacteria in 5 batch
  • In first batch, he destroy the polysaccharide coated capsule of bacteria by the Chloroform.
  • In second batch they destroy the protein by enzymes.
  • In third batch they destroy the RNA by the RNase enzyme.
  • In fourth batch they Lipid.
  • In fifth batch, they destroy the DNA By DNase enzyme.
  • This all batches are individually mixed with the live R Strain of bacteria and injected them into a mice.
  • From all 5 mice, all of them died except the last mouse. From all the dead mice, live S strain bacteria was retrieved
  • This experiment clearly proved that when the DNA of the S strain bacteria were destroyed, they lost the ability to transform the R strain bacteria into live S strain ones. When other components, such as the polysaccharide coat, lipid, RNA or protein were destroyed, transformation still took place. Although the polysaccharide coat was a virulent factor, it wasn’t responsible for the transfer of the genetic matter.

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