Bacterial variation

1. Bacterial variation A- Phenotypic variation Transient –not heritable B- Genotypic variation Permanant –heritable (I) Gene mutation (II) Gene transfer • Transformation • Conjugation • Transduction

2. Transformation • Transformation is gene transfer resulting from the uptake of nakedDNA by a recipient cell from a donor cell. • Certain bacteria (e.g.Bacillus, Haemophilus, Neisseria, Pneumococcus)can take up DNA from the environment and the DNA that is taken up can be incorporated into therecipient's chromosome. • Can be facilitated by heat shock or Ca Cl2

4. Conjugation • Transfer of DNA from a donor bacterium to a recipient by direct physical contact between thecells through F plasmid.; DNA is transferred from a donor to a recipient. • Bacterial cells that contain an F plasmid are called “F+”. Bacteria that don’t have an F plasmid are called “F-”. • F+ cells grow special tubes called “sex pilli” from their bodies & form conjugation tube. When an F+ cell bumps into an F- cell, the sex pilli hold them together, and a copy of the F plasmid is transferred from the F+ to the F-. Now both cells are F+. • Why aren’t all E. coli F+, if it spreads like that? Because the F plasmid can be spontaneously lost.

6. Transduction • Def : The transfer of genetic information between cells through the mediation of a virus particle (bacteriophage). • It therefore does not require cell to cell contact and is DNase resistant.

7. Generalized Transduction • Anybacterial gene from the donor (chromosome or plasmid) can be transferred to the recipient. (Generalized) • After infection by such a phage, the cell contains an exogenote (linear DNA injected by the phage) and an endogenote (circular DNA that is the host’s chromosome).