Lateral Gene Transfer in Bacteria

Overview

Lateral gene transfer between species (other than bacteria) is rare but has been happening for billions of years.
Evidence of lateral gene transfer is visible in many organisms' genomes.
Bacteria are proficient at lateral gene transfer, with three major methods: transformation, conjugation, and transduction.

Involves uptake of naked DNA molecules by competent bacteria.
- Competent bacteria: naturally able or chemically induced to uptake foreign DNA.
Early example: Avery, McCloid, and McCarty's work with Streptococcus pneumoniae demonstrated transformation.
Process: DNA from a dead bacterial cell is released, taken up by a related species, and incorporated into its genome.
Stable Transformation: New bacteria incorporate DNA into their genome which is then reproduced across generations.
Genetic Engineering: Use of plasmid DNA to introduce new genes into bacteria (e.g., pGLO lab using E. coli to produce medically relevant molecules).
Some bacteria actively seek out DNA to uptake, indicating evolutionary importance.

Competence involves the ability to uptake DNA through the cell wall and membrane.
Some bacteria are naturally competent, others are induced (e.g., calcium chloride treatment or electroporation).

Involves transfer of plasmid DNA between bacteria via a sex pilus.
F+ (donor) cells create a sex pilus to transfer plasmid to F- (recipient) cells, making them both F+.
Plasmids often carry genes for antibiotic resistance.
Rolling Circle Replication: Mechanism of plasmid replication during conjugation.
Plasmid DNA is much smaller than chromosomal DNA, allowing easy transfer.

Transduction is another form of lateral gene transfer to be discussed in a separate session.