Novel Tetracycline Resistance Determinant Isolated from an Environmental
Strain of Serratia marcescens
Stuart A. Thompson,1 Elizabeth V. Maani,1 Angela
H. Lindell,2 Catherine J. King,2 and J. Vaun Mc
Arthur2
1Department of Biochemistry and Molecular Biology, Medical
College of Georgia, Augusta, GA 30912
2Savannah River Ecology Laboratory, University of Georgia,
Aiken, SC 29802
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 tatracycline resistance
determinant was cloned in Escherichia coli. Within the cloned 13-kb
segment, the tatracycline 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 the 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.
SREL Reprint #3029
Thompson,
S. A., E. V. Maani, A. H. Lindell, C. J. King, and J. V. Mc Arthur. 2007.
Novel Tetracycline Resistance Determinant
Isolated from an Environmental Strain of Serratia marcescens.
Applied and Environmental Microbiology 73(7):2199-2206.
