CRISPR-Cas in mobile genetic elements: counter-defence and beyond

Area of Science:

• Microbiology
• Genetics
• Molecular Biology

Background:

• CRISPR-Cas systems primarily function as defense mechanisms against mobile genetic elements (MGEs) in prokaryotes.
• The interplay between CRISPR-Cas and MGEs is intricate, with MGEs influencing CRISPR-Cas evolution and vice versa.

Purpose of the Study:

• To investigate and expand the known range of CRISPR-Cas components carried by MGEs.
• To explore the functional implications of these MGE-encoded CRISPR-Cas variants.

Main Methods:

• Analysis of genomic data to identify CRISPR-Cas components within various MGEs.
• Comparative genomics to infer the evolutionary relationships and potential functions of these systems.

Main Results:

• Several Tn7-like transposable elements encode 'minimal' CRISPR-Cas derivatives (Type I and Type V) that may aid in transposon integration.
• Plasmids and prophages frequently carry Type IV CRISPR-Cas systems, potentially mediating competition.
• Prokaryotic viruses possess CRISPR mini-arrays involved in inter-virus conflicts or inhibiting host CRISPR-Cas.

Conclusions:

• MGEs have actively recruited and modified CRISPR-Cas systems for their own propagation and competitive advantages.
• CRISPR-Cas systems are not solely defense mechanisms but are also integrated into the life cycles and interactions of MGEs.