28. Genetic Exchange in Bacteria. Transformation.

Transformation - the transfer of genetic material, comprising the recipient bacterium that captures (absorbed) from the environment of foreign DNA fragments. A transformation can be spontaneous or induced. Induced (artificially produced) transformation occurs when added to cultures of purified DNA obtained from cultures of the bacteria, genetic traits which tend to convey the studied culture. Spontaneous transformation occurs in vivo and is manifested in the appearance of recombinants by mixing genetically different cells.

It flows through the DNA released to the environment as a result of lysing the cells or from its active selection viable cell donor.

In the process of transformation are significant changes of surface cell layers, which promote DNA uptake. Cells autolytic enzymes in the cell wall was dissolved in areas where its synthesis occurs. In this mezosome through holes formed in contact with the external environment, absorb and draw the transforming DNA into the cell, where it comes into DNA recombination with the recipient. This produces merozigota. Cell divides, and her children inherit attributes derived from the donor and the recipient. However, in other cases DNA fragments trapped nucleases destroyed cells of the recipient and the transformation does not occur.

The effectiveness of induced transformation depends on the physiological state of the recipient cells, as well as the dimensions transforming DNA: high molecular weight DNA is absorbed harder than smaller fragments thereof. The ability to transform detected in several bacterial genera, but apparently its role in the exchange of genetic material of bacteria in vivo is less important than that of other mechanisms, because many bacteria

There are special systems of restriction and modification. These systems modify their DNA (usually by its methylation) and destroy foreign DNA in this way if it is not modified. Effectiveness of the method of genetic transformation of many times is increased if the mixture of DNA, and transformed cells using a special device subjected to a treatment by an electric pulse.

Electrical transformation method is universal, it is applicable to all types of bacteria.

29. Genetic Exchange in Bacteria. Conjugation.

By conjugation refers to the process of exchange of genetic material (the chromosome and plasmid), carried out by direct contact of the donor and recipient cells. This process is controlled only by the conjugative plasmids. Transfer apparatus are special donor hairs (pili, drinking), with which contact is made between conjugating cells. The number of donor cells in small pili and obviously corresponds conjugative plasmid copy number in the cell. Donor villi are detected by donor-specific phages, which are adsorbed on and penetrate into the cell and cause its lysis. Each group has its own conjugative plasmid donor-specific phages. Villi perform the following functions:

1) with a set of contact between the donor and recipient cells;

2) they facilitate the transfer of DNA strands (she probably dragged

through the villi);

3) mating tightening the cell, which increases the efficiency of conjugation.

The process of conjugation proceeds through the steps of the established contact between the donor and the recipient, dragging the DNA strand from

donor to recipient, completion transferred DNA strand complementary thereto thread in the recipient cell, and recombination between the transmitted

chromosome (fragment thereof) and the chromosome of recipient cells, the multiplication and the formation merozigote cells bearing characteristics of donor and recipient.

SUMMARY surface exception is that the bacteria are synthesized outer membrane proteins, impeding (excluding possibility) penetrate the cells carrying the plasmid,

different, but closely related to it or suppress plasmid conjugation actively replicating its DNA. Conjugative chromosomal replication is carried by the thread or plasmid DNA is also under the control of the lemma plasmid genes. A classic example of the conjugative plasmid

is the sex factor, or F-plasmid (F - from the English. fertility - fruit and toast). The main function of the plasmid - control of conjugation in bacteria of the intestinal group. This plasmid may be either a standalone

condition, and to integrate into the chromosome of the cell. Being in an autonomous state, it controls only its own transport, in which a cell devoid of F-plasmid is transformed into P + cells (cell

F-containing plasmid). F-plasmid can be integrated at certain sites of the bacterial chromosome, in this case, it will be control the conjugative transfer of chromosome cells. This is one of

filaments in chromosomal DNA integration F-plasmid is cut and its end through the bridge begins to stretch out the donor cell in the recipient. DNA replication occurs in this case on the principle of "spinning" of the ring. Thus, conjugation begins with the establishment of contact between the donor and the recipient with the donor hairs.

LATEST merges with the cell membrane receptor of the recipient cell. Often the contact is established not only between the two cells, and between many cells forming aggregates of mating.

Because the donor bridge is unstable, the process of conjugation

can be interrupted at any time. Therefore, the conjugation may be carried or part of a chromosome, or less, total chromosome.