Gene transfer in bacteria

It includes details of Conjugation, Transformation and Transduction .

1. GENE TRANSFER IN BACTERIA By:- K@RTIK R@W@T

2. INTRODUCTION Gene transfer is defined simply as a technique to efficiently and stably introduce foreign genes into the genome of target cells. The directed desirable gene transfer from one organism to another and the subsequent stable integration & expression of foreign gene into the genome is referred as genetic transformation. Stable transformation occur when DNA is integrated into host genome and is inherited in subsequent generations. The transferred gene is known as transgene and the organism that develop after a successful gene transfer is known as transgenic.

3. METHODS OF GENE TRANSFER # CONJUGATION # TRANSFORMATION # TRANSDUCTION

4. CONJUGATION Definition:- It is the process of gene transfer via sex pili between cells of opposite mating types that are in physical contact (cell-to-cell) with each other. History:- F or the first time JOSHUA LEDERBERG & EDWARD L.TATUM in 1946 presented the evidence for bacterial conjugation i.e. a process of transfer of genetic material by cell-to-cell contact .

5. METHODOLOGY Requires the presence of a special plasmid called the F plasmid. Bacteria that have a F plasmid are referred to as F + or male. Those that do not have an F plasmid are F- or female. The F plasmid consists of 25 genes that mostly code for production of sex pilli . A conjugation event occurs when the male cell extends his sex pilli and one attaches to the female . This attached pilus is a temporary cytoplasmic bridge through which a replicating F plasmid is transferred from the male to the female . When transfer is complete, the result is two male cells. When the F+ plasmid is integrated within the bacterial chromosome, the cell is called an Hfr cell (high frequency of recombination cell).

6. Definition:- Transformation refers to the transfer of relatively small segment of naked DNA from donor cell(male) to competent recipient(female ) cell . HISTORY:- Bacterial transformation was first discovered by GRIFFITH in 1928 between the two strains of Streptococcus ( Diplococcus ) pneumonia which causes pneumonia in humans and mice. TRANSFORMATION

7. GRIFFITH’S EXPERIMENT The RII strain (non-pathogenic, rough colony forming, mutant strain) did not cause death to mice, whereas the SIII strain (virulent) caused death to mice & The heat killed SIII strain also showed similar results like that of RII strains. However, when heat killed SIII strain was mixed with RII strain and injected into mice, the mice died. This induction in change of RII strain was called TRANSFORMATION. Avery, Macleod and Mc Carty(1994) conducted the experiment and demonstrated that heat killed SIII strain transformed RII stain into virulent form which caused death of mice The transforming ability was not altered by treatment with enzyme or by RNase , but was completely destroyed by DNase . These findings showed that DNA has the ability to carry hereditary information

8. TRANSDUCTION DEFINITION:- Transfer of DNA from one bacterium to another via Bacteriophage HISTORY:- The phenomenon of transduction was first discovered by ZINDER & LEDERBERG in 1952. He discovered this while searching for sexual conjugation in Salmonella species .

9. PHASES OF TRANSDUCTION Transduction happens through either the  lytic  cycle or the  lysogenic   cycle . If the lysogenic cycle is adopted, the phage chromosome is integrated (by covalent bonds) into the bacterial chromosome, where it can remain dormant for thousands of generations . If the lysogen is induced (by UV light for example), the phage genome is excised from the bacterial chromosome and initiates the lytic cycle, which culminates in  lysis  of the cell and the release of phage particles. The lytic cycle leads to the production of new phage particles which are released by lysis of the host.

10. LYTIC CYCLE

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