CRISPR interference limits horizontal gene transfer in staphylococci by targeting DNA

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Horizontal gene transfer (HGT) in bacteria and archaea facilitates the spread of traits like antibiotic resistance.
• Conjugation is a significant HGT mechanism, particularly for antibiotic resistance dissemination.
• Clustered regularly interspaced short palindromic repeat (CRISPR) systems provide sequence-specific immunity against phages.

Purpose of the Study:

• To investigate the role of CRISPR systems in preventing bacterial conjugation and plasmid transformation.
• To determine if CRISPR interference targets DNA or RNA during gene transfer.

Main Methods:

• Utilizing a clinical isolate of Staphylococcus epidermidis with a CRISPR spacer targeting a common staphylococcal conjugative plasmid gene.
• Employing genetic manipulation, including insertion of a self-splicing intron into the target gene.
• Assessing the impact of CRISPR interference on conjugation and plasmid transformation efficiency.

Main Results:

• CRISPR interference was demonstrated to effectively prevent both conjugation and plasmid transformation in S. epidermidis.
• Insertion of an intron into the nickase gene blocked CRISPR interference, even when the target sequence was restored in spliced mRNA.
• This indicates that the CRISPR interference mechanism directly targets DNA, not the resulting mRNA.

Conclusions:

• CRISPR loci play a crucial role in counteracting multiple pathways of HGT in bacteria.
• CRISPR systems can limit the spread of antibiotic resistance among pathogenic bacteria.
• The direct targeting of DNA by CRISPR interference machinery has significant implications for understanding bacterial immunity and HGT dynamics.