title: Novel tetracycline resistance determinant isolated from an environmental strain of Serratia marcescens.
abstract: Resistances to tetracycline and mercury were identified in an environmental strain of Serratia marcescens isolated from a stream highly contaminated with heavy metals. As a step toward addressing the mechanisms of coselection of heavy metal and antibiotic resistances, the tetracycline resistance determinant was cloned in Escherichia coli. Within the cloned 13-kb segment, the tetracycline resistance locus was localized by deletion analysis and transposon mutagenesis. DNA sequence analysis of an 8.0-kb region revealed a novel gene [tetA(41)] that was predicted to encode a tetracycline efflux pump. Phylogenetic analysis showed that the TetA(41) protein was most closely related to the Tet(39) efflux protein of Acinetobacter spp. yet had less than 80% amino acid identity with known tetracycline efflux pumps. Adjacent to the tetA(41) gene was a divergently transcribed gene [tetR(41)] predicted to encode a tetracycline-responsive repressor protein. The tetA(41)-tetR(41) intergenic region contained putative operators for TetR(41) binding. The tetA(41) and tetR(41) promoters were analyzed using lacZ fusions, which showed that the expression of both the tetA(41) and tetR(41) genes exhibited TetR(41)-dependent regulation by subinhibitory concentrations of tetracycline. The apparent lack of plasmids in this S. marcescens strain, as well as the presence of metabolic genes adjacent to the tetracycline resistance locus, suggested that the genes were located on the S. marcescens chromosome and may have been acquired by transduction. The cloned Tet 41 determinant did not confer mercury resistance to E. coli, confirming that Tet 41 is a tetracycline-specific efflux pump rather than a multidrug transporter.
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical College of Georgia, 1120 15th Street, Augusta, GA 30912-2100, USA. stthomps@mcg.edu
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Thompson
authors.forename: Elizabeth V
authors.initials: EV
authors.lastname: Maani
authors.forename: Angela H
authors.initials: AH
authors.lastname: Lindell
authors.forename: Catherine J
authors.initials: CJ
authors.lastname: King
authors.forename: J Vaun
authors.initials: JV
authors.lastname: McArthur
mesh_terms: D001482:Base Composition; D001483:Base Sequence; D002874:Chromosome Mapping; D004247:DNA / Q000378:metabolism; D004783:Environmental Microbiology; D008628:Mercury / Q000494:pharmacology; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D012706:Serratia marcescens / Q000187:drug effects* / Q000235:genetics; D013752:Tetracycline / Q000494:pharmacology; D013753:Tetracycline Resistance / Q000235:genetics*
chemical_list: D004247:DNA; D013752:Tetracycline; D008628:Mercury