Anaerobic metabolism succinic acid

Many invertebrate animals are true facultative anaerobes, able to survive for long periods, sometimes indefinitely, without oxygen.145-147 Among these are Ascaris (Fig. 1-14), oysters, and other molluscs. Succinate and alanine are among the main end products of anaerobic metabolism. The former may arise by a mixed acid fermentation that also produces pyruvate. 

Succinic acid is a dicarboxylic acid produced as an intermediate of the tricarboxylic acid cycle and also as one of the fermentation products of anaerobic metabolism. It has been considered an important chemical because it can be used for the precursor of 1,4-butanediol, tetrahydrofu-ran, and y-butyrolactone as well as for application in polymers, foods, pharmaceuticals, and cosmetics (1,2). Currently, succinic acid is produced commercially through chemical synthesis. However, the production of... 

Heerde, E., Radler, F. (1978) Metabolism of the anaerobic formation of succinic acid by Saccharomyces cerevisiae. Arch. Microbiol., 117, 269-276. 

Dittrich CR, Bennett GN, San KY. Metabolic engineering of the anaerobic central metabolic pathway in Escherichia coli for the simultaneous anaerobic production of isoamyl acetate and succinic acid. Biotechnol Prog 2009 25 1304-9. 

Under anaerobic conditions P. pentosaceum can grow on erythritol (Wood and Liever, 1953), which only few microorganisms can utilize. Propionic, acetic, formic and succinic acids are produced from erythtritol. Metabolic pathways of erythritol (and other carbon sources) are shown above, in Chapter 3. 

Traces of succinic, fumaric, and shikimic acid, but not lactic acid, are generally considered to be formed by this anaerobic metabolism, while the ascorbic acid content decreases. Ascorbic acid concentrations decrease. There are also significant changes in the nitrogen compounds, including an increase in the amino acid content, probably dissolved from the solids in the must, as well as a decrease in protein nitrogen. 

Another overexpression strategy was tried with the NAD -dependent malic enzyme of E. coli Thermodynamically, the reduction of pyruvate to malate is favored, but in nature this reaction does not occur. A double mutant of E. coli, NZNlll, which is blocked in both pyruvate formate lyase pjT) and lactate dehydrogenase (Idh), was used as the host. It is unable to grow anaerobically because its pyruvate metabolism is blocked by the fermentation end products acetate, formate, ethanol, and lactic acid. The mutant NZNl 11 with multiple copies of malic enzyme accumulated succinic acid as a major end product only when the cells were switched to anaerobic metabolism gradually by metabolic depletion of oxygen in a sealed tube (Clark et al. 1988). Mutant strains blocked in either pfl or Idh did not alter their distribution of fermentation products when overexpressing malic enzyme. 

Succinic acid is an intermediate of the TCA cycle and one of the fermentation end products of anaerobic metabolism. Thus, it can be synthesized in almost all microbe, plants, and animal cells. Those organisms suitable for the efficient production of succinic acid can be categorized into fungi and bacteria. Note that the fact that CO2 is assimilated during succinic acid fermentation can be considered as an advantage of environmental benefits. Fermentative production of succinic acid is regarded as one of the most attractive options to replace the fossil oil-based production of bulk chemicals by bio-based production. 

Both the synthesis of propionate and its metabolism may take place under anaerobic conditions. In Desulfobulbuspropionicum, degradation could plausibly take place by reversal of the steps used for its synthesis from acetate (Stams et al. 1984)—carboxylation of propionate to methylmalonate followed by coenzyme Bi2-mediated rearrangement to succinate, which then enters the tricarboxylic acid cycle. The converse decarboxylation of succinate to propionate has been observed in Propionigenium modestum (Schink and Pfennig 1982),... 

The metabolism of anaerobic chytrids has not been studied in great detail, but it is known that most anaerobic chytrids studied so far produce formate, acetate, succinate, lactate and ethanol besides hydrogen and carbon dioxide when growing on cellulose, glucose or fructose as a carbon source (Julliand et al. 1998). Such a mixed acid fermentation is very similar to bacterial mixed acid fermentations that are, for example, well known for facultative anaerobic enteric bacteria, such as Escherichia coli. 

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