Study of Conjugation in E.Coli Essay

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STUDY OF CONJUGATION IN E.coli AIM : To study the process of bacterial conjugation through transfer of genes,coding for antibiotic resistance. PRINCIPLE : From one bacterial strain(donor) to another strain(recipient) is a known event that occurs in nature with objective of mixing the gene pool. In otherwise asexually reproducing organism, DNA transfer among bacteria is in different mediating ways: I. Transformation II. Transduction III. Conjugation Conjugation is the most widespread process of transferring genetic material from one bacterial cell to another. It is a process in which unidirectional transfer of DNA is mediated by conjugal plasmid or conjugal transposons requiring cell to cell contacts. It was discovered by Lederberg and Tatum. Conjugation is best understood by considering properties of F-factor, which is a small circular plasmid DNA, that can replicate autonomously in the cell or can integrate into host chromosome and thus transfer host chromosomal marker. The individual cells with integrated F-factor are isolated and allowed to form pure colonies. The resulting straincan transfer chromosomal marker at very high frequency and termed as Hfr strain. INTRODUCTION: The E.coli strain A & B referred to as parental strains. Strain A carries an antibiotic resistant gene in F-plasmid coding for tetracycline, while Strain B is devoid of any F-factor, but carries streptomycin resistant gene in its chromosome. Therefore both the strains grows on medium containing tetracycline or streptomycin to which they are resistant on conjugating the two parental strains, the resulting culture will be resistant to both the antibiotics, i.e. the conjugate sample when plating on a medium containing tetracycline or streptomycin will survive suggesting that gene transfer has taken place from Strain A to B. However the parental strain when plated on the same medium does

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