Formation of chromosomal tandem arrays of the SXT element and R391, two conjugative chromosomally integrating elements that share an attachment site

Area of Science:

• Microbiology
• Genetics
• Molecular Biology

Background:

• The SXT element from Vibrio cholerae and the IncJ R391 element from Providencia rettgeri are conjugative, self-transmissible, integrating elements (constins).
• These elements share genetic and functional similarities, including site-specific chromosomal integration into Escherichia coli at the prfC locus.

Purpose of the Study:

• To investigate the genetic and functional relationship between the SXT and R391 constins.
• To elucidate the mechanisms of their chromosomal integration, dissemination, and potential interactions within a host cell.

Main Methods:

• Comparative analysis of SXT and R391 genetic elements, including integrases and tra genes.
• Assays to determine the ability of recipient cells to acquire both elements.
• Experiments measuring the frequency of element loss to detect interference between R391 and SXT.

Main Results:

• SXT and R391 integrate at the identical prfC attachment site in E. coli, mediated by nearly identical integrases.
• Both elements encode similar tra genes, facilitating their dissemination.
• Cells could acquire both elements, indicating a lack of surface exclusion.
• Tandem integration of SXT and R391 was observed, with minimal role for homologous recombination.
• R391 exhibited stronger interference with SXT stability than SXT did with R391.

Conclusions:

• SXT and R391 possess highly similar mechanisms for chromosomal integration and dissemination.
• Integrase activity and expression levels likely mediate the observed interference between these related constins.