The pathway to resolve dimeric forms distinguishes plasmids from megaplasmids in Enterobacteriaceae.

Area of Science:

• Microbiology
• Genetics
• Molecular Biology

Background:

• Bacterial genomes feature diverse secondary replicons.
• Circular DNA requires dimer resolution systems, often involving site-specific recombinases.
• The XerCD recombinase system resolves dimers in chromosomes and plasmids.

Purpose of the Study:

• To investigate XerCD recombinase function in bacterial secondary replicons.
• To determine the prevalence and regulation of XerCD sites across different replicon types.

Main Methods:

• Analysis of XerCD recombination sites in enterobacterial secondary replicons.
• Comparative study of XerCD usage in plasmids, megaplasmids, and secondary chromosomes.
• Investigation of FtsK protein involvement in XerCD regulation.

Main Results:

• XerCD is utilized by small plasmids, large secondary replicons (>250 kb), megaplasmids, and secondary chromosomes.
• Replicons >250 kb consistently host active XerCD recombination sites.
• Large replicons use chromosome-like XerCD regulation, linked to cell division via FtsK.

Conclusions:

• Chromosome-like XerCD dimer resolution is essential for the inheritance of large plasmids and chromids.
• Acquisition of this XerCD system is a prerequisite for plasmid evolution into secondary chromosomes.