Gene Transfer

Gene transfer in bacteria There are three types of gene transfer 1.Transformation 2.Conjugation 3.Transduction

All types of gene transfer Involve unidirectional transfer of information (donor-->recipient) Require the integration of newly acquired DNA “ homologous recombination ” Increases genetic diversity

What happens to DNA that is not integrated within a replicon?

DNA integrated can be inherited

Griffith ’ s experiments with Streptococcus pneumoniae

Transformation Requires competent cells to uptake DNA Need living cells and source of DNA

Conjugation Transfer of genes between 2 bacterial cells Gram negative cells use a sex pilus F(+) cells have F plasmid, F(-) lack F plasmid

Conjugation between (F+) and F(-) cells

F plasmid can integrate into the chromosome creating Hfr cell

Hfr cell can also become a F’ cell

Conjugation between Hfr cell and F(-) Does transfer of DNA occur? How is it different from F(+) X F(-)? **Note:figure #4 is wrong, should have an Hfr cell and a F(-) recombinant cell

Transduction Transfer of genes between a phage and a bacterial cell Generalized transduction: occurs with lytic or lysogenic phage (section 8.7) Specialized transduction: occurs with lysogenic phage (section 13.3)

Generalized Transduction

Specialized Transduction What type of phage is involved? Will it result in generation of new phage?

Comparison of mechanisms of DNA transfer

The Mobile gene pool In E. coli, 75% of genes are found in all strains Rest of the genome is made up of the mobile gene pool or mobilome Mobile gene pool made from plasmids, transposons, or phage DNA

Plasmids Found in many types of organisms as dsDNA Provide the cell new characteristics

Resistance Plasmids (R plasmids)

Transposons…way to move genes between organisms

How did this S. aureus become Vancomycin resistant S. aureus (VRSA)?