title: Magnesium transport in Salmonella typhimurium: characterization of magnesium influx and cloning of a transport gene.
abstract: The influx of Mg2+ in Salmonella typhimurium LT-2 was studied by both kinetic and genetic techniques. Wild-type cells grown in a high MgSO4 concentration (10 mM) exhibited a Km of 15 microM for Mg2+ influx, with a Vmax of 0.25 nmol of Mg2+ per min per 10(8) cells. The apparent Km decreased to 3 microM, and the Vmax increased 60% after growth in a low MgSO4 concentration (10 microM). Co2+ was a simple competitive inhibitor (Ki = 30 microM) of Mg2+ influx in cells grown in high Mg2+ concentrations but blocked only a portion of the Mg2+ influx in cells grown in low Mg2+ concentrations. Co2+ influx exhibited kinetics similar to those of Mg2+ influx (Km = 30 microM; Vmax = 0.5 nmol of Co2+ per min per 10(8) cells) but was not affected by growth conditions. Co2+ influx was competitively inhibited by both Mg2+ and Mn2+. Mutations affecting Mg2+ uptake were isolated by selection for spontaneous resistance to toxic levels of Co2+. One class of mutants designated corA mapped at 84 min near metE with the following gene order: corA, metE, zie-3161::Tn10, pepQ. A second class designated corB mapped at 98 min near pyrB. Mg2+ influx was decreased in a corA mutant strain (relative to that of the wild type) when grown in high Mg2+ concentrations but was restored when grown in low Mg2+ concentrations. Co2+ transport was completely abolished by the corA mutation under all growth conditions. Recombinant plasmids carrying the corA region from either Escherichia coli K-12 or S. typhimurium complemented the corA mutation in S. typhimurium, restoring uptake of both Co2+ and Mg2+ and conferring sensitivity to Co2+. The S. typhimurium corA gene was localized to a restriction fragment of approximately 1.5 kilobases.
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001693:Biological Transport, Active; D003001:Cloning, Molecular; D003035:Cobalt / Q000378:metabolism / Q000494:pharmacology; D004352:Drug Resistance, Microbial; D004926:Escherichia coli / Q000235:genetics; D005796:Genes; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D012486:Salmonella typhimurium / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D011994:Recombinant Proteins; D003035:Cobalt; D008274:Magnesium