Several Bacteria (like Escherichia Coli) exhibit a form of sexual reproduction called Bacterial Conjugation. It is the transfer of genetic material between bacterial cells by direct cell-to-cell contact or by a bridge-like connection between two cells. It was discovered by Nobel Prize winners, Joshua Lederberg and Edward L. Tatum in 1946.
The Process of Bacterial Conjugation:
There are two distinct requirements that must be met in order for conjugation to occur. The first of these requirements is that the cells be able to engage in a specific contact cycle. The second is that some DNA in the donor cell be capable of undergoing mobilization. Plasmid encodes all the necessary gene products to carry out conjugation. It is a circular extrachromosomal DNA present in the bacterial cell.
During Bacterial Conjugation, a donor bacterium (equivalent to male) passes Plasmid to the recipient bacterium (equivalent to female). If plasmid also contains a specific gene called the Fertility Gene or F gene, it makes the bacterium into a donor. A donor with F gene can produce filamentous protrusions called Sex Pili (singular: Pilus).
Pili are actually extensions of cell membrane through the cell wall. The Pilus can attach and pull in a recipient bacterium close to the donor. The donor plasmid passes through the pilus to the recipient. along with the plasmid. Following the conjugation, the progenies of the recipient express some of the characteristics of the donor.
Why was it compared to Sexual Reproduction?
Bacterial conjugation though different from eukaryotic sexual reproduction (involving meiosis and syngamy) is a means of making new genetic combinations (called recombination) which are expressed in the progeny.
Bacterial conjugation is often regarded as the bacterial equivalent of sexual reproduction because it involves the exchange of genetic material and is a means of making new genetic combinations (called recombinants) which are expressed in the progeny. But it is not sexual reproduction since no exchange of gametes occurs in this process.
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However, this type of gene transfer is not a true sexual reproduction. In bacterial gene transfer, one organism receives genetic information from a donor; the recipient is changed by that information. In sexual reproduction, two organisms donate equally (or nearly so) to the formation of a new organism, but only in exceptional cases is either of the donors changed.
References:
Prescott, Lansing M, John P Harley, and Donald A Klein. Microbiology. Dubuque, IA: McGraw-Hill Higher Education, 2005. Print.