Propagating DNA in Bacteria

Bacteria are equipped with all the necessary capacities to replicate DNA. Common bacterial species have bee adapted for use in the lab to carry DNA and propagate it for uses in biotechnology. In addition to chromosomal DNA of the bacterial genome, bacteria also have extrachromosomal DNA called plasmids. These plasmids replicate independently of the bacterial chromosome and can occur in high copy. These circular pieces of DNA are modified in labs to carry specific pieces of DNA so they can be studied or used for expression into proteins. Plasmids can naturally carry important traits, including antibiotic resistance. Plasmids are relatively small, ranging in size from 1000 bases to 1,000,000 bases long (1kb-1000kb).

Plasmid (english)
Bacterial DNA usually exists as a large circular chromosome (red). Plasmids are extrachromosomal and autonomously replicating pieces of DNA (blue).

Through a process called conjugation, bacteria can “sexually” transfer genetic material to another by passing plasmids through a structure called a conjugation pilus.

Conjugation
Conjugation process between a plasmid bearing donor and a plasmid-less recipient. The donor creates a conjugation pilus to create a cytosolic bridge with the donor where the plasmid is replicated into the recipient through the rolling circle method of replication. The recipient then becomes competent to act as a donor.

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