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Rolf Reissbrodt - One of the best experts on this subject based on the ideXlab platform.
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IRON-REGULATED EXCRETION OF ALPHA -KETO AcidS BY SALMONELLA TYPHIMURIUM
Journal of bacteriology, 1997Co-Authors: Rolf Reissbrodt, Robert Kingsley, Wolfgang Rabsch, Wieland Beer, Mark Roberts, Peter H. WilliamsAbstract: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.
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alpha keto Acids are novel siderophores in the genera proteus providencia and morganella and are produced by amino Acid deaminases
Journal of Bacteriology, 1993Co-Authors: Hartmut Drechsel, Andrea Thieken, G Jung, Rolf Reissbrodt, Günther WinkelmannAbstract:Abstract Growth promotion and iron transport studies revealed that certain alpha-keto Acids generated by amino Acid deaminases, by enterobacteria of the Proteus-Providencia-Morganella group (of the tribe Proteeae), show significant siderophore activity. Their iron-binding properties were confirmed by the chrome azurol S assay and UV spectra. These compounds form ligand-to-metal charge transfer bands in the range of 400 to 500 nm. Additional absorption bands of the enolized ligands at 500 to 700 nm are responsible for color formation. Siderophore activity was most pronounced with alpha-keto Acids possessing an aromatic or heteroaromatic side chain, like phenylpyruvic Acid and indolylpyruvic Acid, resulting from deamination of phenylalanine and tryptophan, respectively. In addition, alpha-keto Acids possessing longer nonpolar side chains, like alpha-ketoisocaproic Acid or alpha-ketoisovaleric Acid and even alpha-ketoadipic Acid, also showed siderophore activity which was absent or negligible with smaller alpha-keto Acids or those possessing polar functional groups, like pyruvic Acid, alpha-ketobutyric Acid, or Alpha-Ketoglutaric Acid. The fact that deaminase-negative enterobacteria, like Escherichia coli and Salmonella spp., could not utilize alpha-keto Acids supports the view that specific iron-carboxylate transport systems have evolved in members of the tribe Proteeae and are designed to recognize ferric complexes of both alpha-hydroxy Acids and alpha-keto Acids, of which the latter can easily be generated by L-amino Acid deaminases in an amino Acid-rich medium. Exogenous siderophores, like ferric hydroxamates (ferrichromes) and ferric polycarboxylates (rhizoferrin and citrate), were also utilized by members of the tribe Proteeae.
Günther Winkelmann - One of the best experts on this subject based on the ideXlab platform.
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alpha keto Acids are novel siderophores in the genera proteus providencia and morganella and are produced by amino Acid deaminases
Journal of Bacteriology, 1993Co-Authors: Hartmut Drechsel, Andrea Thieken, G Jung, Rolf Reissbrodt, Günther WinkelmannAbstract:Abstract Growth promotion and iron transport studies revealed that certain alpha-keto Acids generated by amino Acid deaminases, by enterobacteria of the Proteus-Providencia-Morganella group (of the tribe Proteeae), show significant siderophore activity. Their iron-binding properties were confirmed by the chrome azurol S assay and UV spectra. These compounds form ligand-to-metal charge transfer bands in the range of 400 to 500 nm. Additional absorption bands of the enolized ligands at 500 to 700 nm are responsible for color formation. Siderophore activity was most pronounced with alpha-keto Acids possessing an aromatic or heteroaromatic side chain, like phenylpyruvic Acid and indolylpyruvic Acid, resulting from deamination of phenylalanine and tryptophan, respectively. In addition, alpha-keto Acids possessing longer nonpolar side chains, like alpha-ketoisocaproic Acid or alpha-ketoisovaleric Acid and even alpha-ketoadipic Acid, also showed siderophore activity which was absent or negligible with smaller alpha-keto Acids or those possessing polar functional groups, like pyruvic Acid, alpha-ketobutyric Acid, or Alpha-Ketoglutaric Acid. The fact that deaminase-negative enterobacteria, like Escherichia coli and Salmonella spp., could not utilize alpha-keto Acids supports the view that specific iron-carboxylate transport systems have evolved in members of the tribe Proteeae and are designed to recognize ferric complexes of both alpha-hydroxy Acids and alpha-keto Acids, of which the latter can easily be generated by L-amino Acid deaminases in an amino Acid-rich medium. Exogenous siderophores, like ferric hydroxamates (ferrichromes) and ferric polycarboxylates (rhizoferrin and citrate), were also utilized by members of the tribe Proteeae.
Peter H. Williams - One of the best experts on this subject based on the ideXlab platform.
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IRON-REGULATED EXCRETION OF ALPHA -KETO AcidS BY SALMONELLA TYPHIMURIUM
Journal of bacteriology, 1997Co-Authors: Rolf Reissbrodt, Robert Kingsley, Wolfgang Rabsch, Wieland Beer, Mark Roberts, Peter H. WilliamsAbstract: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.
Hartmut Drechsel - One of the best experts on this subject based on the ideXlab platform.
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alpha keto Acids are novel siderophores in the genera proteus providencia and morganella and are produced by amino Acid deaminases
Journal of Bacteriology, 1993Co-Authors: Hartmut Drechsel, Andrea Thieken, G Jung, Rolf Reissbrodt, Günther WinkelmannAbstract:Abstract Growth promotion and iron transport studies revealed that certain alpha-keto Acids generated by amino Acid deaminases, by enterobacteria of the Proteus-Providencia-Morganella group (of the tribe Proteeae), show significant siderophore activity. Their iron-binding properties were confirmed by the chrome azurol S assay and UV spectra. These compounds form ligand-to-metal charge transfer bands in the range of 400 to 500 nm. Additional absorption bands of the enolized ligands at 500 to 700 nm are responsible for color formation. Siderophore activity was most pronounced with alpha-keto Acids possessing an aromatic or heteroaromatic side chain, like phenylpyruvic Acid and indolylpyruvic Acid, resulting from deamination of phenylalanine and tryptophan, respectively. In addition, alpha-keto Acids possessing longer nonpolar side chains, like alpha-ketoisocaproic Acid or alpha-ketoisovaleric Acid and even alpha-ketoadipic Acid, also showed siderophore activity which was absent or negligible with smaller alpha-keto Acids or those possessing polar functional groups, like pyruvic Acid, alpha-ketobutyric Acid, or Alpha-Ketoglutaric Acid. The fact that deaminase-negative enterobacteria, like Escherichia coli and Salmonella spp., could not utilize alpha-keto Acids supports the view that specific iron-carboxylate transport systems have evolved in members of the tribe Proteeae and are designed to recognize ferric complexes of both alpha-hydroxy Acids and alpha-keto Acids, of which the latter can easily be generated by L-amino Acid deaminases in an amino Acid-rich medium. Exogenous siderophores, like ferric hydroxamates (ferrichromes) and ferric polycarboxylates (rhizoferrin and citrate), were also utilized by members of the tribe Proteeae.
Jian Chen - One of the best experts on this subject based on the ideXlab platform.
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Enhanced Alpha-Ketoglutaric Acid production in Yarrowia lipolytica WSH-Z06 by regulation of the pyruvate carboxylation pathway
Applied Microbiology and Biotechnology, 2012Co-Authors: Xiaoxia Yin, Catherine Madzak, Jingwen Zhou, Jian ChenAbstract:In previous research, a thiamine-auxotrophic yeast for Alpha-Ketoglutaric Acid (KGA) overproduction was screened in our laboratory and named Yarrowia lipolytica WSH-Z06 (CCTCC no. M207143). However, the high concentration of by-products (mainly pyruvate) limited its application on an industrial scale. To enhance KGA production and reduce pyruvate (PA) accumulation, the pyruvate carboxylation pathway was regulated. By overexpressing the pyruvate carboxylase genes ScPYC1 from Saccharomyces cerevisiae and RoPYC2 from Rhizopus oryzae in Y. lipolytica WSH-Z06, the yields of KGA in Y. lipolytica-ScPYC1 and Y. lipolytica-RoPYC2 increased by 24.5 and 35.3 %, and the yields of PA decreased by 51.9 and 69.8 % in shake flasks, respectively. These changes in the expression levels and activities of key intracellular enzymes showed that enhancing the pyruvate carboxylation pathway had successfully redistributed the carbon flux from PA to KGA. Finally, by controlling the pH in a 3-L fermenter, the maximum concentration of KGA in Y. lipolytica-RoPYC2 reached 62.5 g L-1 with an evident decrease in PA yield from 35.2 to 13.5 g L-1.