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Applied and Environmental Microbiology, March 2008, p. 1316-1323, Vol. 74, No. 5
0099-2240/08/$08.00+0     doi:10.1128/AEM.02424-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Marker Removal in Staphylococci via Cre Recombinase and Different lox Sites{triangledown}

Martina Leibig,{dagger} Bernhard Krismer,{dagger},{ddagger} Martina Kolb, Alexandra Friede, Friedrich Götz, and Ralph Bertram*

Mikrobielle Genetik, Eberhard Karls Universität Tübingen, Waldhäuser Str. 70/8, 72076 Tübingen, Germany

Received 26 October 2007/ Accepted 14 December 2007

Allelic replacement in staphylococci is frequently aided by antibiotic resistance markers that replace the gene(s) of interest. In multiply modified strains, the number of mutated genes usually correlates with the number of selection markers in the strain's chromosome. Site-specific recombination systems are capable of eliminating such markers, if they are flanked by recombinase recognition sites. In this study, a Cre-lox setting was established that allowed the efficient removal of resistance genes from the genomes of Staphylococcus carnosus and S. aureus. Two cassettes conferring resistance to erythromycin or kanamycin were flanked with wild-type or mutant lox sites, respectively, and used to delete single genes and an entire operon. After transformation of the cells with a newly constructed cre expression plasmid (pRAB1), genomic eviction of the resistance genes was observed in approximately one out of ten candidates analyzed and subsequently verified by PCR. Due to its thermosensitive origin of replication, the plasmid was then easily eliminated at nonpermissive temperatures. We anticipate that the system presented here will prove useful for generating markerless deletion mutants in staphylococci.

* Corresponding author. Mailing address: Mikrobielle Genetik, Eberhard Karls Universität Tübingen, Waldhäuser Str. 70/8, 72076 Tübingen, Germany. Phone: 49 7071 29-78855. Fax: 49 7071-295937. E-mail: ralph.bertram{at}uni-tuebingen.de

{triangledown} Published ahead of print on 28 December 2007.

{dagger} M.L. and B.K. contributed equally to this study.

{ddagger} Present address: Dr. Petry Genmedics GmbH, Ferdinand-Lassalle-Strasse 57, 72770 Reutlingen, Germany.

Applied and Environmental Microbiology, March 2008, p. 1316-1323, Vol. 74, No. 5
0099-2240/08/$08.00+0     doi:10.1128/AEM.02424-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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