title: Heterotrophic metabolism of the chemolithotroph Thiobacillus ferrooxidans.
abstract: Glucose-6-phosphate dehydrogenase and the enzymes of the Entner-Doudoroff pathway, 6-phosphogluconate dehydrase and 2-keto-3-deoxy-6-phosphogluconate aldolase (assayed together), are induced during heterotrophic growth of Thiobacillus ferrooxidans on an iron-glucose-supplemented medium or on glucose alone. By contrast, autotrophic cells (iron-grown) contain low levels of these enzymes. Fructose 1, 6-diphosphate aldolase, an enzyme of the Embden-Meyerhof pathway, is present at low levels irrespective of the growth medium, suggesting that this enzyme is not involved in energy-yielding reactions but merely provides intermediates for biosynthesis. The Entner-Doudoroff and pentose-phosphate pathways are the principle means through which glucose is dissimilated and is presumed to be concerned with energy production. Isotopic studies showed that a high rate of CO(2) formation from specifically labeled glucose came from carbon atoms 1 and 4. An unexpectedly high rate of evolution of CO(2) also came from carbon 6, suggesting that the triose phosphate formed during glucose breakdown and specifically as a result of 2-keto-3-deoxy-6-phosphogluconate aldolase activity, was metabolized via some unorthodox metabolic route. Cells grown in the iron-supplemented and glucose-salts media have a complete tricarboxylic acid cycle, whereas autotrophically grown T. ferrooxidans lacked both alpha-ketoglutarate dehydrogenase and reduced nicotinamide adenine dinucleotide oxidase. Two isocitrate dehydrogenases [nicotinamide adenine dinucleotide (NAD) and NAD phosphate (NADP) specific] were present. NAD-linked enzyme was constitutive, whereas the NADP-linked enzyme was induced upon adaptation of autotrophic cells to heterotrophic growth.
mesh_terms: D000446:Aldehyde-Lyases / Q000378:metabolism; D002245:Carbon Dioxide / Q000096:biosynthesis; D002247:Carbon Isotopes; D002474:Cell-Free System; D002951:Citrates; D002952:Citric Acid Cycle; D003470:Culture Media; D005636:Fructosephosphates; D005650:Fumarates; D005942:Gluconates; D005947:Glucose / Q000378:metabolism*; D005954:Glucosephosphate Dehydrogenase / Q000378:metabolism; D006836:Hydro-Lyases / Q000378:metabolism; D007501:Iron / Q000378:metabolism; D007521:Isocitrate Dehydrogenase / Q000378:metabolism; D007656:Ketoglutaric Acids; D008956:Models, Chemical; D009249:NADP; D010088:Oxidoreductases / Q000378:metabolism; D010428:Pentosephosphates / Q000378:metabolism; D010710:Phosphates; D010734:Phosphogluconate Dehydrogenase / Q000378:metabolism; D013053:Spectrophotometry; D013385:Succinate Dehydrogenase / Q000378:metabolism; D013855:Thiobacillus / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*
chemical_list: D002247:Carbon Isotopes; D002951:Citrates; D003470:Culture Media; D005636:Fructosephosphates; D005650:Fumarates; D005942:Gluconates; D007656:Ketoglutaric Acids; D010428:Pentosephosphates; D010710:Phosphates; D002245:Carbon Dioxide; D009249:NADP; D007501:Iron; D010088:Oxidoreductases; D007521:Isocitrate Dehydrogenase; D010734:Phosphogluconate Dehydrogenase; D005954:Glucosephosphate Dehydrogenase; D013385:Succinate Dehydrogenase; D000446:Aldehyde-Lyases; D006836:Hydro-Lyases; D005947:Glucose