Sexual Reproduction in Bacteria

a) Transformation:

• In transformation, a bacterium takes up DNA from its environment and often DNA that’s been shed by another bacteria.
• The phenomenon was first discovered by Griffith in 1928 and the mechanism was worked out by Avery in 1944.
• In this process, the DNA of a capsulated bacteria is transferred into a non-capsulated bacterium. If the DNA is circular, it is called a plasmid.
• The plasmid can be copied in the receiving cell and passed on to its descendants.

b) Transduction:

• In this type of sexual reproduction of bacteria, foreign genes are transferred into a bacterial cell with the help of a virus. These viruses are called bacteriophage and they are not virulent.
• The virus acts as a carrier vehicle and passes over genes from one host to another. Transducing bacteriophages may carry the same genes in which the reproduction method would be known as restricted transduction.
• They can also carry different genes at different times in which the reproduction process would be known as generalized transduction.

c) Conjugation:

• This process was first discovered in Escherichia coli by Tatum and Lederberg in 1946. They found that two different types of nutritional mutants grown together on minimal medium produced an occasional wild type.
• Bacteria that show conjugation are dimorphic, meaning that they have two types of cells, one male (F+) or donor cell and a female (F-) or recipient cell.
• The male or donor cell possesses 1 to 4 sex pili on the surface and fertility factor (transfer factor, sex factor) in its plasmid. It contains genes for producing sex pili and other characters needed for gene transfer.
• Sex pili are 1 to 4 narrow protoplasmic outgrowths. The sex pili and fertility factor are absent from the female or recipient cells.

• If these two types of cells happen to come nearer, a pilus of a male cell establishes a protoplasmic bridge or conjugation tube with the female cell. It takes 6-8 minutes for the process to complete.