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Journal of Bacteriology, April 2007, p. 2712-2719, Vol. 189, No. 7
0021-9193/07/$08.00+0     doi:10.1128/JB.01679-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Functional Interactions between Coexisting Toxin-Antitoxin Systems of the ccd Family in Escherichia coli O157:H7{triangledown}

Myriam Wilbaux,1 Natacha Mine,1 Anne-Marie Guérout,2 Didier Mazel,2 and Laurence Van Melderen1*

Laboratoire de Génétique des Procaryotes, Institut de Biologie et Médecine Moléculaires, Université Libre de Bruxelles, 12 Rue des Professeurs Jeener et Brachet, 6041 Gosselies, Belgium,1 Unité Plasticité du Génome Bactérien, Département Génomes et Génétique, Institut Pasteur, 25 Rue du Dr. Roux, 75724 Paris, France2

Received 30 October 2006/ Accepted 16 January 2007

Toxin-antitoxin (TA) systems are widely represented on mobile genetic elements as well as in bacterial chromosomes. TA systems encode a toxin and an antitoxin neutralizing it. We have characterized a homolog of the ccd TA system of the F plasmid (ccdF) located in the chromosomal backbone of the pathogenic O157:H7 Escherichia coli strain (ccdO157). The ccdF and the ccdO157 systems coexist in O157:H7 isolates, as these pathogenic strains contain an F-related virulence plasmid carrying the ccdF system. We have shown that the chromosomal ccdO157 system encodes functional toxin and antitoxin proteins that share properties with their plasmidic homologs: the CcdBO157 toxin targets the DNA gyrase, and the CcdAO157 antitoxin is degraded by the Lon protease. The ccdO157 chromosomal system is expressed in its natural context, although promoter activity analyses revealed that its expression is weaker than that of ccdF. ccdO157 is unable to mediate postsegregational killing when cloned in an unstable plasmid, supporting the idea that chromosomal TA systems play a role(s) other than stabilization in bacterial physiology. Our cross-interaction experiments revealed that the chromosomal toxin is neutralized by the plasmidic antitoxin while the plasmidic toxin is not neutralized by the chromosomal antitoxin, whether expressed ectopically or from its natural context. Moreover, the ccdF system is able to mediate postsegregational killing in an E. coli strain harboring the ccdO157 system in its chromosome. This shows that the plasmidic ccdF system is functional in the presence of its chromosomal counterpart.

* Corresponding author. Mailing address: Laboratoire de Génétique des Procaryotes, Institut de Biologie et Médecine Moléculaires, Université Libre de Bruxelles, 12 Rue des Professeurs Jeener et Brachet, 6041 Gosselies, Belgium. Phone: 32 2 650 97 78. Fax: 32 2 650 97 70. E-mail: lvmelder{at}ulb.ac.be.

{triangledown} Published ahead of print on 26 January 2007.

Journal of Bacteriology, April 2007, p. 2712-2719, Vol. 189, No. 7
0021-9193/07/$08.00+0     doi:10.1128/JB.01679-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Mine, N., Guglielmini, J., Wilbaux, M., Van Melderen, L. (2009). The Decay of the Chromosomally Encoded ccdO157 Toxin-Antitoxin System in the Escherichia coli Species. Genetics 181: 1557-1566 [Abstract] [Full Text]  
  • Saavedra De Bast, M., Mine, N., Van Melderen, L. (2008). Chromosomal Toxin-Antitoxin Systems May Act as Antiaddiction Modules. J. Bacteriol. 190: 4603-4609 [Abstract] [Full Text]  
  • Tsilibaris, V., Maenhaut-Michel, G., Mine, N., Van Melderen, L. (2007). What Is the Benefit to Escherichia coli of Having Multiple Toxin-Antitoxin Systems in Its Genome?. J. Bacteriol. 189: 6101-6108 [Abstract] [Full Text]  
  • Magnuson, R. D. (2007). Hypothetical Functions of Toxin-Antitoxin Systems. J. Bacteriol. 189: 6089-6092 [Full Text]  


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