A Look Into: Bacterial Recombination

Bacteria are usually regarded as non-complex lifeforms, sometimes even as primitive. One must understand that bacteria have been existing on this planet longer than humans and have found multiple ways to adapt. Though they may seem simple, they posses a variety of methods to survive the change of time. Bacteria are prokaryotes, which means they are single celled organisms, and unlike the multicellular organisms they coexist with, bacteria contain only one chromosome. It is known that two homologous chromosomes are required in order for recombination to occur. So how do they recombine their DNA to produce offspring that are genetically different to the population? Bacteria have a stunning capability of acquiring the extra DNA they need through three actions: transformation, conjugation, and transduction.

Through transformation bacteria are able to take DNA from the environment and recombine it with their chromosome.

Transformation amongst bacteria was discovered by an experiment conducted by Frederick Griffith and thus was properly named as "Griffith's Experiment". In this experiment, Griffith heat-killed virulent bacteria and introduced these dead bacteria to non-virulent bacteria. The non-virulent bacteria were later tested for virulence by being injected into mice. To Griffith's surprise, the mice injected with the seemingly non-virulent bacteria had died. He then postulated that a "transforming principle" from the virulent dead bacteria had been taken up from the non-virulent bacteria and caused it to become pathogenic. The "transforming principle" was later known to be the DNA from the dead bacteria. DNA from fellow corpses does not always go to waste amongst bacteria as they will pick it up and analyze if they can utilize it. Foreign DNA does not necessarily have to be from bacteria in order for a bacteria to integrate it within its chromosome. The ingested DNA requirement is to be homologous to an extent in where it can be adjusted within the chromosome.

Conjugation is the normal breeding process by which bacteria exchange genetic material. This is able to take place when a bacteria contains an F (fertility) factor episome. An F factor is a circular piece of DNA that has genetic information that is sometimes useful for a bacteria's survival, like coding for antibiotic resistance. The bacteria in possession of the F factor is known as the F+ bacteria and is able to extend a pilus towards an F- bacteria (a bacteria without an F factor) thanks to the F factor. Both bacteria are connected through this pilus, which allows for the F factor to pass through to the F- bacteria and be replicated inside it. The F factor then returns to the F+ bacteria and the pilus disassociates. The F- bacteria then becomes an F+ bacteria due to the F factor gained and is able to pass on the F factor onto another F- bacteria.

The final action, transduction, involves the use of viruses to transport bacterial DNA fragments into bacteria. This works due to the nature of virus DNA being packaged in capsids inside the bacterial host. Sometimes, viruses will make the mistake of packaging a bacterial DNA segment rather the viral DNA. This leads to generalized transduction, where the bacteria that gets "infected" by this kind of virus only gets the extra DNA segment and does not die due to there being no insertion of virus DNA. There is also specialized transduction, that only occurs when viruses integrate themselves in a bacteria's chromosome and is excised poorly with bacterial DNA attached to it. The virus then infects another bacteria and passes on the DNA, which the bacteria may use if it survives the viral attack.

Bacteria are quite complex organisms and should be credited for having such ingenious survival capabilities. The recombination abilities mentioned allow bacteria to develop new genes that have helped them live through the many hardships they have faced for millions of years.

Article Source: Salvador Barajas

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