Additional role for the ccd operon of F-plasmid as a transmissible persistence factor

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 109; no. 31; pp. 12497 - 12502
• Main Authors: Tripathi, Arti, Dewan, Pooja C, Barua, Bipasha, Varadarajan, Raghavan
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 31.07.2012; National Acad Sciences
• Subjects: active sites; Antibiotics; Antitoxins; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Biological Sciences; Cell death; Cell growth; Chromosomes; DNA; DNA Gyrase - genetics; DNA Gyrase - metabolism; DNA topoisomerase (ATP-hydrolysing); Escherichia coli; Escherichia coli - genetics; Escherichia coli - metabolism; Escherichia coli Proteins - genetics; Escherichia coli Proteins - metabolism; F Factor - genetics; F Factor - metabolism; Gene Expression Regulation, Bacterial - physiology; Genetic Loci - physiology; heat stress; loci; Mutagenesis, Site-Directed; mutants; operon; Operon - physiology; Operons; Plasmids; Protease La - genetics; Protease La - metabolism; proteinases; Toxins
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1121217109

Toxin-antitoxin (TA) systems are found on both bacterial plasmids and chromosomes, but in most cases their functional role is unclear. Gene knockouts often yield limited insights into functions of individual TA systems because of their redundancy. The well-characterized F-plasmid–based CcdAB TA system is important for F-plasmid maintenance. We have isolated several point mutants of the toxin CcdB that fail to bind to its cellular target, DNA gyrase, but retain binding to the antitoxin, CcdA. Expression of such mutants is shown to result in release of the WT toxin from a functional preexisting TA complex as well as derepression of the TA operon. One such inactive, active-site mutant of CcdB was used to demonstrate the contribution of CcdB to antibiotic persistence. Transient activation of WT CcdB either by coexpression of the mutant or by antibiotic/heat stress was shown to enhance the generation of drug-tolerant persisters in a process dependent on Lon protease and RecA. An F-plasmid containing a ccd locus can, therefore, function as a transmissible persistence factor.