title: Iron-regulated excretion of alpha-keto acids by Salmonella typhimurium.
abstract: Excretion of alpha-keto acids by clinical isolates and laboratory strains of Salmonella typhimurium was determined by high-performance liquid chromatography analysis of culture supernatants. The levels of excretion increased markedly with increasing iron stress imposed by the presence of alpha,alpha'-dipyridyl or conalbumin in the medium. The major product was pyruvic acid, but significant concentrations of alpha-ketoglutaric acid, alpha-ketoisovaleric acid, and alpha-ketoisocaproic acid were also observed. Maximal excretion occurred at iron stress levels that initially inhibited bacterial growth; the concentration of alpha,alpha'-dipyridyl at which this was observed differed between strains depending on their ability to secrete and utilize siderophores, suggesting that the intracellular iron status was important in determining alpha-keto acid excretion. However, prolonged incubation of the siderophore-deficient S. typhimurium strain enb-7 under conditions of high iron stress resulted in significant delayed bacterial growth, promoted by tonB-dependent uptake of iron complexed with the high accumulated levels of pyruvic acid and other alpha-keto acids. Strain RB181, a fur derivative of enb-7, excreted massive amounts of alpha-keto acids into the culture medium even in the absence of any iron chelators (the concentration of pyruvic acid, for example, was >25 mM). Moreover, RB181 was able to grow and excrete alpha-keto acids in the presence of alpha,alpha'-dipyridyl at concentrations threefold greater than that which inhibited the growth of enb-7.
authors.affiliation: Robert Koch Institute, Wernigerode Branch, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Reissbrodt
authors.forename: R
authors.initials: R
authors.lastname: Kingsley
authors.forename: W
authors.initials: W
authors.lastname: Rabsch
authors.forename: W
authors.initials: W
authors.lastname: Beer
authors.forename: M
authors.initials: M
authors.lastname: Roberts
authors.forename: P H
authors.initials: PH
authors.lastname: Williams
mesh_terms: D015082:2,2'-Dipyridyl / Q000494:pharmacology; D001426:Bacterial Proteins / Q000378:metabolism; D001692:Biological Transport; D003207:Conalbumin / Q000494:pharmacology; D003470:Culture Media; D004758:Enterobactin / Q000378:metabolism; D045782:Hemiterpenes; D007501:Iron / Q000378:metabolism*; D007651:Keto Acids / Q000378:metabolism*; D007656:Ketoglutaric Acids / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D019289:Pyruvic Acid / Q000378:metabolism; D012486:Salmonella typhimurium / Q000254:growth & development / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D003470:Culture Media; D045782:Hemiterpenes; D007651:Keto Acids; D007656:Ketoglutaric Acids; D008565:Membrane Proteins; C057616:tonB protein, Bacteria; D003207:Conalbumin; D004758:Enterobactin; D015082:2,2'-Dipyridyl; C001505:alpha-ketoisovalerate; C013082:alpha-ketoisocaproic acid; D019289:Pyruvic Acid; D007501:Iron