title: AmpN-AmpG operon is essential for expression of L1 and L2 beta-lactamases in Stenotrophomonas maltophilia.
abstract: AmpG is an inner membrane permease which transports products of murein sacculus degradation from the periplasm into the cytosol in Gram-negative bacteria. This process is linked to induction of the chromosomal ampC beta-lactamase gene in some members of the Enterobacteriaceae and in Pseudomonas aeruginosa. In this study, the ampG homologue of Stenotrophomonas maltophilia KJ was analyzed. The ampG homologue and its upstream ampN gene form an operon and are cotranscribed under the control of the promoter P(ampN). Expression from P(ampN) was found to be independent of beta-lactam exposure and ampN and ampG products. A DeltaampN allele exerted a polar effect on the expression of ampG and resulted in a phenotype of null beta-lactamase inducibility. Complementation assays elucidated that an intact ampN-ampG operon is essential for beta-lactamase induction. Consistent with ampG of Escherichia coli, the ampN-ampG operon of S. maltophilia did not exhibit a gene dosage effect on beta-lactamase expression. The AmpG permease of E. coli could complement the beta-lactamase inducibility of ampN or ampG mutants of S. maltophilia, indicating that both species have the same precursor of activator ligand(s) for beta-lactamase induction.
authors.affiliation: Graduate Institute of Microbiology and Public Health, National Chung-Hsing University, Taichung 402, Taiwan.
authors.forename: Yi-Wei
authors.initials: YW
authors.lastname: Huang
authors.forename: Cheng-Wen
authors.initials: CW
authors.lastname: Lin
authors.forename: Rouh-Mei
authors.initials: RM
authors.lastname: Hu
authors.forename: Yu-Tzu
authors.initials: YT
authors.lastname: Lin
authors.forename: Tung-Ching
authors.initials: TC
authors.lastname: Chung
authors.forename: Tsuey-Ching
authors.initials: TC
authors.lastname: Yang
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D018628:Gene Dosage; D015870:Gene Expression; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D026901:Membrane Transport Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation; D009876:Operon; D011401:Promoter Regions, Genetic; D020615:Stenotrophomonas maltophilia / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics*; D018440:beta-Lactam Resistance / Q000235:genetics; D001618:beta-Lactamases / Q000096:biosynthesis / Q000235:genetics*
chemical_list: C084284:AmpG protein, Bacteria; D001426:Bacterial Proteins; D017931:DNA Primers; D026901:Membrane Transport Proteins; C088032:beta-lactamase L1; C425104:beta-lactamase L2; D001618:beta-Lactamases
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