Learning Objective

Explain the process of bacterial transformation, identify organisms capable of natural competence, and describe how incoming DNA becomes stably incorporated through homologous recombination.

Transformation is the uptake of naked (free) DNA from the environment by a bacterial cell that is competent.

Competence

• A bacterium must be competent to take up DNA.
• Competence = ability to bind short DNA fragments and transport them across the cell envelope.
• Competence occurs under specific environmental conditions (no need to memorize the triggers).

Naturally Competent Organisms (VERY testable)

Some Hot New Bacteria

➡️ Streptococcus pneumoniae
➡️ Haemophilus influenzae
➡️ Neisseria species
➡️ Bacillus species

These organisms perform natural transformation.

Source of DNA

• DNA comes from dead or lysed cells.
• DNA is linear and homologous to the recipient genome (usually from the same or similar species).

Stabilization

• Because the entering DNA is linear, it must be stabilized through homologous recombination.
• If recombination does not occur → DNA is degraded.

Impact

• Allows the spread of genetic variation, such as:
  • Capsule genes (classic Strep pneumoniae example)
  • Antibiotic resistance genes (in naturally competent species)

Activity

Activity