If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Generation of Precursor Metabolites and Energy → Fermentation → Pyruvate Fermentation|
Expected Taxonomic Range: Firmicutes
Please note: The enzymes depicted in this superpathway are not induced simultaneously, and the organisms can not produce all of the products shown here at the same time. This superpathway is for illustrative purposes only, as it shows the branching points between the different products. For more information about the pathways leading to fermentation of individual compounds, please look at the respective sub-pathways - pyruvate fermentation to ethanol III, pyruvate fermentation to acetate I, pyruvate fermentation to butanoate, pyruvate fermentation to butanol I and pyruvate fermentation to acetone.
Clostridium acetobutylicum is a Gram-positive anaerobe of commercial importance, capable of fermenting a variety of sugars to solvents and acids. During acidogenesis acetate and butanoate are produced, while solventogenesis yields ethanol, acetone, and n-butanol. The production of acetone and butanol by Clostridium acetobutylicum was a thriving industrial process, but lost its importance since the fermentation could no longer compete economically with the chemical synthesis of solvents from petroleum.
In continuous culture, Clostridium acetobutylicum can be maintained in three different stable metabolic states [Girbal95]: acidogenic - production of acetate and butanoate when grown at neutral pH on glucose (see superpathway of Clostridium acetobutylicum acidogenic fermentation), solventogenic - production of acetone, n-butanol and ethanol when grown at low pH on glucose ( superpathway of Clostridium acetobutylicum solventogenic fermentation), and alcohologenic - formation of n-butanol and ethanol but not acetone when grown at neutral pH under conditions of high NAD(P)H availability. Despite numerous physiological studies, it is still unclear how the metabolic switch from acid to solvent production is regulated at the molecular level [Green98]. Once this metabolic transition has been initiated, most of the excreted acids are taken up and converted into solvents
The three key intermediates are acetyl-CoA, acetoacetyl-CoA, and butanoyl-CoA. Acetyl-CoA is a branching point for the production of acetate and ethanol. Acetoacetyl-CoA is the branching point for acetone production, and butanoyl-CoA is the branching point for butanoate and n-butanol production.
Subpathways: pyruvate fermentation to acetone, pyruvate fermentation to ethanol III, pyruvate fermentation to butanol I, superpathway of Clostridium acetobutylicum solventogenic fermentation, superpathway of Clostridium acetobutylicum acidogenic fermentation, acetate formation from acetyl-CoA I, pyruvate fermentation to acetate I, pyruvate fermentation to butanoate
Variants: pyruvate fermentation to acetate and alanine, pyruvate fermentation to acetate and lactate I, pyruvate fermentation to acetate and lactate II, pyruvate fermentation to acetate II, pyruvate fermentation to acetate III, pyruvate fermentation to acetate IV, pyruvate fermentation to acetate V, pyruvate fermentation to acetate VI, pyruvate fermentation to acetate VII, pyruvate fermentation to acetate VIII, pyruvate fermentation to butanol II, pyruvate fermentation to ethanol I, pyruvate fermentation to ethanol II, pyruvate fermentation to hexanol, pyruvate fermentation to isobutanol (engineered), pyruvate fermentation to lactate, pyruvate fermentation to opines, pyruvate fermentation to propanoate I, pyruvate fermentation to propanoate II (acrylate pathway), superpathway of fermentation (Chlamydomonas reinhardtii)
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