Reversible DNA condensation drives natural transformation

Area of Science:

• Microbiology
• Molecular Biology
• Biophysics

Background:

• Natural transformation is a key mechanism for horizontal gene transfer in bacteria, contributing to the spread of antibiotic resistance.
• The ComEA protein is a crucial DNA receptor involved in importing extracellular DNA into the bacterial periplasm, but its mechanism remains unclear.

Purpose of the Study:

• To elucidate the mechanism by which the ComEA DNA receptor facilitates DNA uptake during natural transformation.
• To investigate the role of ComEA oligomerization and DNA condensation in the DNA transport process.

Main Methods:

• Single-molecule optical tweezers were employed to measure forces exerted by ComEA on DNA.
• Electron microscopy was used to visualize ComEA-DNA complexes and their structures.
• Mutational analysis in Bacillus subtilis assessed the functional importance of ComEA conformations.

Main Results:

• Geobacillus stearothermophilus ComEA forms dynamic, concentration-dependent oligomers on DNA, switching between bridging and non-bridging conformations.
• Bridging oligomers, formed at low ComEA concentration, condense DNA and generate sub-piconewton pulling forces.
• Non-bridging oligomers, formed at high ComEA concentration, decondense DNA and do not generate force.
• Mutations favoring specific conformations led to transformation deficiency, highlighting the importance of both condensation and decondensation.

Conclusions:

• ComEA reversibly condenses DNA during natural transformation, utilizing force generation for periplasmic DNA translocation.
• The transition from force-generating condensation to decondensation by ComEA is essential for subsequent DNA transport into the bacterial cytoplasm.
• This study reveals a novel mechanism of DNA-protein interaction driving essential bacterial genetic processes.