Plasmids also have the ability of transferring themselves from one bacterium to another. This transfer is facilitated by the formation of a hair like growth known as sex pilus, formed of the outer membrane of the donor bacterium (as in bacterial conjugation; see Sexuality and Recombination in Bacteria and Viruses). The F sex pilus is upto 20 μm (1 μm = 10-3 mm) in length and 8 nm (1 nm = 10-6 mm) wide. The sex pili produced by different plasmids are distinguished by the reaction they show for attachment of certain phages. The sex pili produced by Col I and known as I-like sex pili differ from F-like sex pili on the basis of reaction shown with certain phages. When sex pilus is removed by injury or is absent due to genetic reasons, no transfer of plasmid DNA is possible, suggesting that sex pilus is essential for transfer.
© 2018 Biocyclopedia | All rights reserved.