Competence-mediated DNA uptake diversifies Vibrio cholerae sedentary chromosomal integrons

Area of Science:

• Microbiology
• Genetics
• Bacteriology

Background:

• Bacteria utilize gene sharing for defense against viral infections and environmental stress.
• The cholera pathogen *Vibrio cholerae* possesses a sedentary chromosomal integron (SCI) with numerous gene cassettes, including antiviral systems.
• Despite the known potential for gene cassette reshuffling under stress, the SCI in pandemic *V. cholerae* has shown remarkable stability for over six decades.

Purpose of the Study:

• To investigate the mechanism of SCI diversification in *Vibrio cholerae*.
• To understand how gene cassettes within the SCI are maintained or altered.
• To explore the role of the aquatic lifestyle in bacterial genetic adaptation.

Main Methods:

• Analyzing the genetic structure of the sedentary chromosomal integron (SCI) in *Vibrio cholerae*.
• Investigating horizontal gene transfer mechanisms in aquatic bacterial environments.
• Studying the uptake of extracellular DNA and its integration into the bacterial genome.

Main Results:

• SCI diversification in *Vibrio cholerae* is primarily driven by horizontal gene transfer, not internal cassette reshuffling.
• Extracellular DNA released from lysed cells is taken up by naturally competent vibrios.
• Integrated DNA is preferentially inserted at the first position of the SCI array, leading to enhanced expression and conferring resistance to phages.

Conclusions:

• Horizontal gene transfer, facilitated by the aquatic lifestyle, is the main driver of SCI diversification in *Vibrio cholerae*.
• The integration of new gene cassettes at the primary expression site provides rapid adaptation to phage and other environmental threats.
• This mechanism explains the maintenance of defense gene arrays in *Vibrio cholerae* despite the apparent stability of its SCI over long periods.