Mobile integrons encode phage defense systems.

Area of Science:

• Microbiology
• Genetics
• Bacterial Evolution

Background:

• Integrons are bacterial genetic elements that capture and modulate gene expression via cassettes.
• Mobile integrons (MIs) on plasmids facilitate the spread of antimicrobial resistance genes in pathogens.
• Gene cassettes of unknown function (gcus) within MIs have unexplored roles.

Purpose of the Study:

• To investigate the function of gene cassettes of unknown function (gcus) within mobile integrons.
• To determine if gcus encode adaptive traits beyond antimicrobial resistance.
• To characterize the nature and implications of phage resistance encoded by gcus.

Main Methods:

• Bioinformatic analysis of integron cassette sequences.
• Experimental validation of gcu functions.
• Assessment of fitness costs associated with different cassette arrays.

Main Results:

• Gene cassettes of unknown function (gcus) encode diverse and novel phage resistance systems, termed bacteriophage resistance integron cassettes (BRiCs).
• BRiCs can be combined with antimicrobial resistance cassettes, creating arrays conferring resistance to both drugs and multiple phages.
• The fitness cost of BRiCs is context-dependent and can be modulated by altering cassette order within the integron.

Conclusions:

• Mobile integrons function as adaptable defense islands, acquiring and deploying both antimicrobial and phage resistance genes.
• The discovery of BRiCs expands our understanding of bacterial defense mechanisms and integron evolution.
• Mobile integrons represent a significant factor in bacterial adaptation and pathogen evolution by providing low-cost, multi-faceted resistance strategies.