bacterial conjugation dicovery U tube experiment HFR f plus f minus

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Natural Genetic Transfer in bacteria

• NEEKITA D. CHARAN
• M. SC MICROBIOLOGY
• SEM - 3
• DEPARTMENT OF LIFE SCIENCE HNGU,PATAN

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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 pilus.
• The 3 conjugative processes
• I. F-F conjugation
• F Hfr conjugation
• Hfr fconjugation

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Joshua Lederberg Edward l. Tatum experiment

• Conjugation gene transfer via direct cell to
  cell contact/ physical contact by Joshua
  Lederberg Edward l. Tatum.
• the evidence for conjugation is established by
  demonstration of experiment .
• They mixed two auxotrophic strain.
• Incubation
• Plated on minimal medium

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• To reduce reversion they used 2nd / 3rd
  auxotrophic mutant.
• Bio- ,phe -,cys-
  Bio ,phe,cys
• thi thr ,leu
  thi- thr ,leu-
• thr ,leu phe
• thi bio cys

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No colony obs.
No colony obs.

• colony
  observe

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• Strain 1 which is required biotin ,phenylalanine
  ,cysteine for growth
• Another stain required threonine leucine and
  thymine.
• The recombinant prototrophic colony are appeared
  on minimal medium after incubation indicate that
  chromosomes / gene of two strain are able to
  associate and can undergo recombination

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Bernard Davis U tube experiment

• Experiment of Lederberg and Tatum did not prove
  that the physical contact is necessary for gene
  transfer.
• physical contact is necessary for gene transfer
  is proved by Bernard davis in 1950
• U tube consisting two piece of curved glass tubes
  and fused at bottom base , in middle it is
  contain filter which is allow the passage of
  media but not bacterial cell.
• Each tube having different auxotrophic strain of
  E.coli into medium.
• During incubation medium transfer to one tube to
  another suction alternatively applied.
• After this kind incubation bacteria are placed in
  to minimal medium.

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• Microorganism ware not able to grow thus devis
  discovered that two strain are separated by
  filter ,so gene transfer couldn't take place
• Direct cell contact required for recombination.
• Lederberg and Tatum had observed that call having
  capacity to serving donor are differentiated by
  special surface appendage called Pilli.
• Synthesis of Pilli is controlled by genes codon
  on plasmid called F factors.
• Cell which is not having f factor called F ve
  cell recipient cell

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Conjugation
F bacteria
Mating Bridge
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Conjugation
F bacteria
Mating Bridge
Original F bacteria
F- bacteria
New F bacteria
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• William Hayes in 1952 demonstrated that gene
  transfer by conjugation is polar
• Non reciprocal recombination
• F factor replicates by rolling circle modal
• One copy moves to the recipient cell
• Transfer is initiated at specific side
• Nick strand transfer through conjugation bridge
• At the end both donor and recipient cell having
  one one copy of F- factors

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Hfr Recombination
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Hfr Recombination
Interruption of conjugation
Transfer of genetic material
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Hfr Recombination
Recombinant Bacteria
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HFR

• The F plasmid is episome and that can integrated
  into bacterial chromosome at random site / site
  specific recombination.
• In integrated form tra operon still functional
  and can direct the synthesis of pilli.
• Able to replication and able to gene transfer to
  F- cell .
• nicked formation occurs at Ori t site, transfer
  of F factor begin.
• F cell become F when the whole chromosome of
  HRF is transferred in to the F- cell

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