conjugation and transduction

Conjugation
• A second mechanism by which genetic transfer takes place is conjugation.
• This mechanism requires the presence of a special plasmid called the F plasmid.
o The F plasmid, for example, facilities conjugation.
? This can give a bacterium new genes that may help it survive in a changing environment.
? An integrated plasmid is called an episome.
• Bacteria that have a F plasmid are referred to as F+ or male.
o Those that do not have an F plasmid are F- of female.
• The F plasmid consists of 25 genes that mostly code for production of sex pilli.
• A conjugation event occurs when the male cell extends his sex pili and one attaches to the female.
o This attached pilus is a temporary cytoplasmic bridge through which a replicating F plasmid is transferred from the male to the female.
o When transfer is complete, the result is two male cells.
• The F plasmid can behave as an episome.
o When the F+ plasmid is integrated within the bacterial chromosome, the cell is called an Hfr cell (high frequency of recombination cell).
• The Hfr cell still behaves as a F+ cell, transferring F genes to a F-cell, but now it can take some of the bacterial chromosome with it.
• Replication of the Hfr chromosome begins at a fixed point within the F episome and the chromosome is transferred to the female as it replicates.