Microbial Genetics SSCG 2753 PDF

Microbial genetics SSCG 2753 2  Natural mechanisms of genetic recombination in bacteria include: a) Transformation b) Transduction c) Conjugation Genetic recombination - transfer of DNA from one organism (donor) to another (recipient). The tr...

Microbial genetics SSCG 2753 2  Natural mechanisms of genetic recombination in bacteria include: a) Transformation b) Transduction c) Conjugation Genetic recombination - transfer of DNA from one organism (donor) to another (recipient). The transferred donor DNA may then be integrated into the recipient's nucleoid/host DNA. Overview 4  1. Transformation Recipient cell uptake free DNA released into the environment. DNA is released it to the environment when another bacterial cell (i.e. donor) dies and undergoes lysis Not all bacteria are able to go for transformation, only some bacteria are able to take free DNA and are able to go transformation. These type of bacterial are called competent bacteria. Pathogenic bacteria showing competence Haemophilus spp Streptococcus spp Neisseria spp The 4 steps in Transformation 6  2. Transduction Genetic exchange occur when a DNA fragment is transferred from one bacterium to another by a bacteriophage Structure of T4 bacteriophage Contraction of the tail sheath of T4  Transduction Transduction has been found to occur in a variety of bacterial populations including: 1.Escherichia coli 2.Pseudomonas spp 3.Salmonella spp 4.Staphylococcus spp 8 There are two types of transduction: – Generalized transduction: A DNA fragment is transferred from one bacterium to another by a lytic bacteriophage – The bacteriophage carrying donor bacterial DNA due to an error in maturation during the lytic life cycle. – An example of a lytic bacteriophage is T4, which infects E. coli found in the human intestinal tract. – Seven steps in Generalised Transduction 10 11 Specialized transduction: A DNA fragment is transferred from one bacterium to another by a temperate bacteriophage The phage carry donor bacterial DNA due to an error in spontaneous induction during the lysogenic life cycle. An example of a bacteriophage: phage lambda of E. Coli 12 Six steps in Specialised Transduction 13 14  3. Bacterial Conjugation Bacterial Conjugation is genetic recombination in which there is a transfer of DNA from a living donor bacterium to a recipient bacterium. Often involves a sex pilus. The 3 conjugative processes + I. F conjugation II. Hfr conjugation III. Resistance plasmid conjugation  I. F+ Conjugation Process F+ Conjugation- Genetic exchange in which there is a transfer of an F+ plasmid (coding only for a sex pilus) but not chromosomal DNA The exchange occur from a male donor bacterium to a female recipient bacterium. Involves a sex (conjugation) pilus. The 4 stepped F+ Conjugation 17  II. Hfr Conjugation Genetic exchange in which fragments of chromosomal DNA from a male donor bacterium are transferred to a female recipient bacterium Due to the integration of F+ into chromosomal DNA Involves a sex (conjugation)pilus. 5 stepped Hfr Conjugation 19 20  III. Resistant Plasmid Conjugation Genetic exchange in which there is a transfer of an R plasmid (a plasmid coding for multiple antibiotic resistance and often a sex pilus) from a male donor bacterium to a female recipient bacterium. Involves a sex (conjugation) pilus 4 steped Resistant Plasmid Conjugation http://www.cat.cc.md.us/courses/bio141/lecguide/unit4/genetics/recombination/conjugation/r.html 22 23