Microbial  Recombination and Plasmids:

Bacterial Conjugation: 
The initial evidence for bacterial conjugation,the transfer of genetic information by direct cell to cell contact, came from an elegant experiment performed by Joshua Lederberg and Edward L.
Tatum in 1946. They mixed two auxotrophic strains, incubated
the culture for several hours in nutrient medium, and then plated
it  on  minimal  medium. To  reduce  the  chance  that  their  results
were due to simple reversion, they used double and triple auxotrophs on the assumption that two or three reversions would not
often occur simultaneously.

Lederberg and Tatum did not directly prove that physical
contact of the cells was necessary for gene transfer. This evidence was provided by Bernard Davis (1950), who constructed
a U tube consisting of two pieces of curved glass tubing fused
at the base to form a U shape with a fritted glass filter between
the halves. The filter allows the passage of media but not bacteria. The U tube was filled with nutrient medium and each side inoculated with a different auxotrophic strain of E.coli.

During incubation, the medium was pumped back and
forth through the filter to ensure medium exchange between the
halves. After a 4 hour incubation, the bacteria were plated on
minimal  medium.  Davis  discovered  that  when  the  two  auxotrophic strains were separated from each other by the fine filter, gene transfer could not take place. Therefore direct contact was required for the recombination that Lederberg and Tatum had observed.


Please visit these links:
www.ncbi.nlm.nih.gov › NCBI › Literature › Bookshelf
www.microbeworld.org › History of Microbiology › 1930s-1940s
www.sciences360.com › Biology › Microbiology

Cited By Kamal Singh Khadka
Msc Microbiology, TU
Assistant Professor in Pokhara University, Regional College Of Science & Technology, PNC, LA, NA 
Pokhara, Nepal 


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