Bacterial Conjugation

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Chapter: Pharmaceutical Microbiology : Microbial Genetics and Variations

The copious volume of literature available in bacterial morphology provides several elaborated, authentic descriptions of ‘microscopic observations of cell pairs’ which were duly ascertained and identified as indicators of mating and sexuality in organisms.


Bacterial Conjugation

 

The copious volume of literature available in bacterial morphology provides several elabo-rated, authentic descriptions of ‘microscopic observations of cell pairs’ which were duly ascertained and identified as indicators of mating and sexuality in organisms. Lederberg and Tatum (1946) first and foremost comfirmed the phenomenon of conjugation* in E. coli by carefully mixing autotrophic mutants** and finally meticulously selected the rare recombinants***. In fact, they initially plated aseptically the E. coli mutants with triple and complementary nutritional requirements [i.e., abc DEF × ABC def] upon minimal agar, and duly accomplished the desired prototrophic bacteria* [ABCDEF]. Nevertheless, these recombinants were found to be fairly stable ; and, therefore, adequately propogated and raised at a frequency ranging between 10– 6 to 10– 7, as illustrated in Figure : 6.9.


 

An additional supportive evidence to demonstrate that the specific development of the ensuing ‘protrophic colonies’ essentially needed the absolute cooperation of the intact organism of either species (types), which was duly accomplished by the help of the U-Tube Experiment. In actual prac-tice, neither the culture filtrates nor the cell free culture extracts were found to be appreciable produc-tive in nature thereby suggesting that the actual cell contact was indeed an absolute must.

 

Lederberg and Tatum further critically screened a good number of the ‘prototrophic colonies’ to ascertain and confirm whether the said ‘conjugation phenomenon’ happened to be ‘reciprocal in nature’. However, their observations duly revealed that invariably most colonies did comprise of ex-clusively one particular class of recombinants thereby amply suggesting that the ensuing ‘recombi-nation in bacteria’ could be precisely of an ‘absolute unorthodox type’ in nature. Besides, an elaborative further investigation showed that the prototrophs initially found to be of heterozygous** in nature, but later on got duly converted to the corresponding ‘haploids’***. It is, however, pertinent to state here that these ‘investigative studies’ undoubtedly proved that bacteria predominantly possessed ‘sex’ that eventually rendered them to the following two vital and important characteristic profiles, namely :

 

(a) amenable to the ‘formal genetic analysis’, and

 

(b) revelation of the very existence of genetic material present in a ‘chromosomal organi-zation’.

 

The process of conjugation essentially suggests that :

 

(1) large fragments of DNA were adequately transferred from one bacterium to another in a non-reciprocal manner, and

 

(2) such transfer invariably took place from a given point.

 

One may also critically take cognizance of the fact that the exact size (dimension) of DNA transferred from one cell to another was found to be much larger in comparison to the corresponding transformation. Certainly, the process of conjugation proved to be much more an absolutely com-mendable and useful technique for the so called ‘gene mapping’ in organism.

 

Donor Bacteria i.e., such organisms that are responsible for transferring DNA, and Recipient Bacteria i.e., such organisms that are responsible for receiving DNA.

 

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