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.

SWATH label-free proteomics analyses revealed the roles of oxidative stress and antioxidant defensing system in sclerotia formation of Polyporus umbellatus

“…In glycolysis, pyruvate can be converted to ethanol and aldehyde under hypoxia, which then be catalyzed by alcohol dehydrogenase and aldehyde dehydrogenase to generate aldehyde or carboxylate respectively. NAD(P)H formed in this process, can result in increased NAD(P)H/NAD(P) + ratio 36 and GSH accumulation ( Fig. 8 ).…”

Carbon source utilization and hydrogen production by isolated anaerobic bacteria

“…Other striking features are the lack of the butyrate excretion (except AK 1-4), the absence of lactate in all isolates, and the negligible excretion of dicarboxylates. These features may result either from intrinsic properties of isolates, or, as suggested by data of Collet et al (2006), from the experimental setup we used in our experiments The production of hydrogen was also strongly variable between isolates and was also affected by the carbon source. The most versatile producer seems to be the AK 1-5 strain.…”

Dark fermentation biorefinery in the present and future (bio)chemical industry

“…Both enzymes are present in all anaerobic bacteria that form acetyl-CoA in their energy metabolism and that use the acetyl-CoA to synthesise ATP (Thauer et al 1977). The detection of acetate kinase activity in C. thermolacticum confirmed the presence of the acetate branch from acetyl-CoA and the supplementary ATP formation associated to this pathway (Collet et al 2006). Another pathway for the generation of acetic acid is homoacetogenesis, reaction (14), which consumes H 2 and CO 2 (Zhao et al 2010).…”

“…The former catalyzes the reaction of acetyl-CoA to acetaldehyde (Thauer et al 1977). The later catalyzes the dehydrogenation of acetaldehyde to ethanol (Collet et al 2006). The synthesis of caproic acid by dark fermentation, reaction (15), is still under investigation.…”