bacteria. ⢠Provides additional genes for resistance to drugs ... plasmids( close circular molecules of DNA separate from chromosomes, or small ... Conjugation.
• And event in which one bacterium donates DNA to another bacterium is a type of genetic transfer termed recombination. • This property is due to extrachromosomal DNA(plasmid)
• The end result of recombination is a new strain different from donor and original recipient strain. • Unlike spontaneous mutation are beneficial to bacteria. • Provides additional genes for resistance to drugs and metabolic poisons, new nutritional and metabolic capabilities and increase virulance and adaptation to the environment.
Genetic recombination in bacteria • DNA transmitted between bacteria are plasmids( close circular molecules of DNA separate from chromosomes, or small chromosomal fragments that have escaped from a lysed cell. • Plasmids are not necessary to basic bacterial survival.
• Depending upon the mode of transmission these genetic recombinations are called: Conjugation Transformation Transduction
Conjugation(Bacterial sex) • Plasmids or other genetic material is transferred by a donor by a recipient cell via a specialized appendage(especially in gram negative bacteria) • The donor possess a plasmid( fertility or F,factor) • Allows to synthesize the sex pilus or conjugative pilus.
• The recipient cell is a relative species that has a recognition site on its surface. F+ for the cell which has the F plasmid F- for the cell which has none. Contact is made when a sex pilus grows out from the F+ cell ,attaches to the surface of F- cell and draws the two cell together.
• The replicated DNA passes across or through the bridge formed by the pilus.
•
According to findings with E.coli conjugative trasfer exhibits three patterns: 1. First F+ make a copy of its F factor and transmits this to F- cell and made F- cell capable of producing a sex pilus and conjugating with other cells. No additional genes are transferred at this time
2.In high frequency recombination(Hfr) donors, the fertility factor has been integrated into the F+ donor chromosome. 3. In specialized form of conjugation called sexduction an f factor originally integrated into the chromosome of a donor bacterium becomes free and carries away a segment of donor chromosomal DNA.
Conjugation
Hfr
R plasmid
tranforamtion
transduction
Transposons • A segment of DNA (e.g. and R-factor gene) which has a repeat of insertion sequence element at each end that can migrate from one plasmid to another at the same bacterium, to a bacterial chromosome or to a bacteriophage or from a chromosome to a plasmid(called jumping genes)
• Some transposons replicate before transposition or transmission and some change the sites without replication
Effects of transposons • Benefits: -genetic variations that result the change in antibody formation and receptor molecules in cells. -change in morphology of colonies,pigment production,pilli and antigenic alterations -change of damaged DNA -transmission of resistance between microbes
• Side effects; - Rearrangement of DNA results in point mutations and breaking the chromosome that result sever sequences and even death
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