3.2.2 Conjugation
In the process of conjugation, plasmids are transferred between two contacting bacteria via a hollow tube or pilus (Figure 25).
Figure 25 The process of conjugation. (a) A hollow pilus connects two bacteria and plasmid DNA is transferred from the donor bacterium to the recipient. (b) Scanning-electron micrograph of two bacteria attached by pili.
Show description|Hide descriptionPart (a) comprises a schematic representation of conjugation. Bacterial cells in blue are represented by a blue oval surrounded by a brown cell wall. Chromosomal DNA is represented as a purple squiggle. Plasmid DNA is represented as a green ring. The first part of the diagram shows two separate bacterial cells labelled donor and recipient. Both cells contain chromosomal DNA but only the donor contains the plasmid. In the next image the donor and recipient cells are connected by a tube which is coloured blue and surrounded by a brown cell wall. The tube is labelled pilus. The next images shows the plasmid DNA passing through the pilus. The final image shows the two bacterial cells still linked via a pilus however now both the donor and recipient cells contain plasmid DNA. Part (b) shows a scanning electron micrograph of two orange bacterial cells on a dark background. The cells are joined by two orange pili.
Since antibiotic resistance genes are often located on plasmids, conjugation can result in the transfer of antibiotic resistance from one bacterium to another.
