Understanding Bacterial Lateral Gene Transfer

Oct 12, 2024

Lateral Gene Transfer in Bacteria

Overview

  • Lateral gene transfer between species other than bacteria is uncommon but has been happening for billions of years.
  • Bacteria excel at lateral gene transfer, which is a routine process.
  • There are three major types of lateral gene transfer in bacteria:
    • Transformation
    • Conjugation
    • Transduction (to be discussed later)

Transformation

  • Definition: Uptake of naked DNA by competent bacteria.
  • Competence: Ability of a bacterium to take up foreign DNA, either naturally or through chemical treatment.
    • Natural Competence: Some bacteria are naturally competent (e.g., Neisseria, Streptococcus, Staphylococcus).
    • Induced Competence: Achieved using calcium chloride or electroporation.
  • Historical Example: Avery, McLeod, and McCarty's experiment with Streptococcus pneumoniae, demonstrating transformation.
    • Heat-killed S strain transferred DNA to live R strain, enabling it to form a capsule and become virulent.
  • Process:
    • When a bacterial cell dies, it releases DNA which can be taken up by related species and incorporated into their genome.
    • Stable transformation occurs when incorporated DNA is copied along with the bacterial genome.
  • Genetic Engineering Example:
    • Recombinant plasmids are used in genetic engineering to make bacteria like E. coli produce proteins such as human insulin.
    • E. coli are treated with calcium chloride to enhance DNA uptake.
  • Recent Findings:
    • Some bacteria actively seek out and uptake foreign DNA using appendages.

Conjugation

  • Definition: Transfer of plasmid DNA between bacteria via a sex pilus.
  • Process:
    • F+ cells contain the plasmid, while F- cells do not.
    • F+ cells form a sex pilus to connect to F- cells and transfer the plasmid.
    • The plasmid is copied through rolling circle replication, resulting in two F+ cells.
  • Significance:
    • Plasmids often carry genes, such as those for antibiotic resistance, which can be spread rapidly between bacteria.
  • Visual Aids:
    • Transmission electron microscopy images depict the sex pilus and plasmid exchange.

Next Steps

  • The lecture will continue with a discussion on transduction, a more complex form of lateral gene transfer.

These notes summarize the key concepts of lateral gene transfer in bacteria as discussed in the lecture, providing a basis for understanding this crucial biological process.

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