title: Metabolism of lactose by Clostridium thermolacticum growing in continuous culture.
abstract: The objective of the present study was to characterize the metabolism of Clostridium thermolacticum, a thermophilic anaerobic bacterium, growing continuously on lactose (10 g l(-1)) and to determine the enzymes involved in the pathways leading to the formation of the fermentation products. Biomass and metabolites concentration were measured at steady-state for different dilution rates, from 0.013 to 0.19 h(-1). Acetate, ethanol, hydrogen and carbon dioxide were produced at all dilution rates, whereas lactate was detected only for dilution rates below 0.06 h(-1). The presence of several key enzymes involved in lactose metabolism, including beta-galactosidase, glyceraldehyde-3-phosphate dehydrogenase, pyruvate:ferredoxin oxidoreductase, acetate kinase, ethanol dehydrogenase and lactate dehydrogenase, was demonstrated. Finally, the intracellular level of NADH, NAD+, ATP and ADP was also measured for different dilution rates. The production of ethanol and lactate appeared to be linked with the re-oxidation of NADH produced during glycolysis, whereas hydrogen produced should come from reduced ferredoxin generated during pyruvate decarboxylation. To produce more hydrogen or more acetate from lactose, it thus appears that an efficient H2 removal system should be used, based on a physical (membrane) or a biological approach, respectively, by cultivating C. thermolacticum with efficient H2 scavenging and acetate producing microorganisms.
authors.affiliation: Laboratory for Environmental Biotechnology (LBE), Swiss Federal Institute of Technology Lausanne (EPFL), Station 6, 1015, Lausanne, Switzerland.
authors.forename: Christophe
authors.initials: C
authors.lastname: Collet
authors.forename: Laurence
authors.initials: L
authors.lastname: Girbal
authors.forename: Paul
authors.initials: P
authors.lastname: Péringer
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Schwitzguébel
authors.forename: Philippe
authors.initials: P
authors.lastname: Soucaille
mesh_terms: D000084:Acetate Kinase / Q000378:metabolism; D019342:Acetic Acid / Q000378:metabolism; D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D018533:Biomass; D002245:Carbon Dioxide / Q000378:metabolism; D003013:Clostridium / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D000431:Ethanol / Q000378:metabolism; D024601:Glyceraldehyde 3-Phosphate Dehydrogenase (NADP+) / Q000378:metabolism; D006859:Hydrogen / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D007785:Lactose / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D050743:Pyruvate Synthase / Q000378:metabolism; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D009243:NAD; D002245:Carbon Dioxide; D000431:Ethanol; D000244:Adenosine Diphosphate; D006859:Hydrogen; D000255:Adenosine Triphosphate; D007770:L-Lactate Dehydrogenase; D024601:Glyceraldehyde 3-Phosphate Dehydrogenase (NADP+); D050743:Pyruvate Synthase; D000084:Acetate Kinase; D001616:beta-Galactosidase; D007785:Lactose; D019342:Acetic Acid