Tuesday, January 6, 2009

Various Processes of Genetic Recombination in Bacteria

Following are the three processes by which genetic recombination can occur in bacteria.

There is no contact between the donor cell and the recipient cell. It is the random picking of DNA fragments released by some other cells. The recipient cell actively takes the DNA fragment and inserts it into the genome of the recipient bacteria.

This is the DNA transfer between two bacteria through a long protoplasmic connection established between the cells. Conjugation occurs between two different types of bacteria known as positive and negative strains, equivalent to male and female cells. They are called F+ and F-. The donor or the F+ strains of bacteria harbor a circular molecule of DNA known as F factor (F for fertility) or the sex factor. This factor is absent in the F-strains. The presence of F factor is responsible for the presence of a special type of pilus, known as F pilus or sex pilus. The sex pilus is responsible for the formation of the cell-to-cell contact and the formation of the protoplasmic connection, known as the conjugation tube, between the cells. After the establishment of the conjugation tube, one of the strands of the F-factor DNA passes through the sex pilus or the conjugation tube from the donor (F+) to the recipient (F-). In some cases, the F factor plasmid gets integrated with the genomic DNA and mobilizes the transfer of the genomic DNA to the recipient. Since such strains show high-frequency recombination, they are called Hfr strains.

This is another important type of genetic recombination in bacteria which takes place through bacteriophages. A fragment of DNA is transferred to a recipient through a bacteriophage. A bacteriophage is a virus, which infects bacteria. When a bacteriophage infects a bacterium, it injects its DNA into the bacterial cell and it gets integrated with the bacterial DNA. This phage DNA undergoes multiplication along with bacterial DNA. After some multiplications, the phage DNA comes out of the bacterial genome and will be encapsidated in protein coats to daughter phages. In this process a small bit of bacterial DNA will also be taken along with phage DNA. When this phage infects another bacteria, the DNA bit of the old bacterial host will be transferred to the new bacterial genome & causes a genetic recombination. The old bacterial host is the genome and the new bacterial host of the phage is the recipient.

Key words: Bio Genetics, Bio Technology, Genetic Recombination

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