Lecture 33 Microbial Genetics: DNA Transfer in Microbes

Properties of the Bacterial Genome

  • Typically a single circular chromosome.

  • No nuclear membrane; the chromosome is confined to the nucleoid region.

  • Plasmids: Small, circular, self-replicating DNA molecules exist in the cytosol, separate from the main chromosome.

Vertical vs. Horizontal Gene Transfer

  • Vertical Gene Transfer: From parent to offspring.

  • Horizontal Gene Transfer: Direct transfer from one organism to another. 'De novo' mutation drives gene transfer.

Horizontal Gene Transfer: Virulence and Drug Resistance

  • Bacteria can transfer genes affecting virulence and drug resistance horizontally.

Attributes Transferred Horizontally

  1. Virulence Factors: Attributes aiding bacterial survival in the host, sometimes at the host's expense. Example: Capsules of Streptococcus pneumoniae.

  2. Antibiotic Resistance: Attributes reducing antibiotic effectiveness. Example: Plasmids carrying Beta-Lactamase, which inactivates Penicillin.

Types of Horizontal Gene Transfer

  1. Transformation: Uptake of short fragments of naked DNA by naturally transformable bacteria.

  2. Transduction: Transfer of DNA from one bacterium to another via bacteriophages (viruses that infect bacteria).

  3. Conjugation: Transfer of DNA material via a sexual pilus, requiring cell-to-cell contact.

Phage Therapy

  • Using viruses that target bacteria for therapeutic purposes.