Horizontal gene transfer barriers: In an environment containing extracellular DNases, which DNA transfer pathway is most directly inhibited?

Introduction / Context:
Bacteria exchange genes via transformation, transduction, and conjugation. Environmental conditions and enzymes can selectively block one mechanism while leaving others intact. DNases are a classic example used experimentally to dissect these pathways.

Given Data / Assumptions:

• Extracellular DNases degrade free DNA outside cells.
• Transformation requires intact extracellular DNA for uptake by competent cells.
• Conjugation uses protected DNA transfer through mating pores; transduction packages DNA inside phage capsids.

Concept / Approach:

Identify the mechanism that relies on naked DNA in the medium. DNase will destroy this DNA before uptake, preventing gene acquisition. Other mechanisms protect DNA during transfer, making them DNase-resistant.

Step-by-Step Solution:

Verification / Alternative check:

Historical experiments distinguished transformation (DNase-sensitive) from transduction and conjugation (DNase-insensitive) using enzyme treatments.

Why Other Options Are Wrong:

Conjugation: DNA passes through cell-to-cell channels; DNase outside cannot access it readily.

Transduction: DNA is inside phage heads; extracellular DNase cannot degrade it prior to injection.

“None of the above” is incorrect because transformation is clearly inhibited.

Common Pitfalls:

Assuming DNase enters cells or phage capsids; it acts extracellularly on exposed DNA only.

Final Answer:

Natural transformation