Mercury resistance as a selective marker for recombinant mycobacteria

Laboratoire de Microbiologie Génétique et Moléculaire INSERM CJF9109, Institut Pasteur de Lille, 1 Rue du Prof. Calmette, F-59019 Lille Cedex, France Laboratoire de Microbiologie INSERM U411, Faculté de Médecine Necker-Enfants Malades, 156 rue de Vaugirard, 75730 Paris Cedex 15, France ABSTRACT The use of antibiotic-resistance markers for the selection of recombinant mycobacteria is widespread but questionable considering the development of live recombinant BCG vaccines. In contrast, vector-encoded resistance to heavy metals such as mercury may represent an interesting alternative for the development of live vaccines compatible with use in humans and in animals. The mercury resistance genes ( mer ) from Pseudomonas aeruginosa and from Serratia marcescens were cloned into the Escherichia coli -Mycobacterium shuttle vector pRR3. The resulting vectors, designated pMR001 and pVN2, were introduced by electroporation into Mycobacterium smegmatis, Mycobacterium bovis BCG and Mycobacterium tuberculosis . The recombinant mycobacteria were stable in vitro and in vivo , and had high-level mercury resistance, thus indicating that the mer genes can be useful as selective markers in mycobacteria. Author for correspondence: Camille Locht. Tel: +33 20 87 77 28. Fax: +33 20 87 79 06.