Fermentation anaerobic metabolism

Winemaking by carbonic maceration (CM) is a process exploiting the adaptability of intact grape berries to an oxygen-deprived medium enriched with carbon dioxide (C02). This adaptation is reflected almost instantly inside each berry by the transition from a respiratory to fermentative anaerobic metabolism (AM). 

Fermentation Anaerobic metabolism of the pyruvic acid produced in glycolysis. 

Kluge C, A Tschech, G Fuchs (1990) Anaerobic metabolism of resorcylic acids (m-dihydroxybenzoates) and resorcinol (1,3-benzenediol) in a fermenting and in a denitrifying bacterium. Arch Microbiol 155 68-74. 

However, if an anaerobic metabolism such as ethanol fermentation occurs in a fermentor in the presence of high concentration of glucose, the RQ value becomes larger than 1.0, known as the Crabtree effect. This is because CO2 evolves without O2 consumption as follows. 

Deep-sea explorations have revealed many species of marine life at great ocean depths, where the oxygen concentration is near zero. For example, the primitive coelacanth, a large fish recovered from depths of 4,000 m or more off the coast of South Africa, has an essentially anaerobic metabolism in virtually all its tissues. It converts carbohydrates to lactate and other products, most of which must be excreted. Some marine vertebrates ferment glucose to ethanol and C02 in order to generate ATP. 

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. 

The anaerobic metabolism of acrylate and 3-mercaptopropionate (3-MPA) was studied in slurries of coastal marine sediments. The rate of these compounds is important because they are derived from the algal osmolyte dimethylsulfoniopropionate (DMSP), which is a major organic sulfur compound in marine environments. Micromolar levels of acrylate were fermented rapidly in the slurries to a mixture of acetate and propionate (1 2 molar ratio). Sulfate-reducing bacteria subsequently removed the acetate and propionate. 3-MPA has only recently been detected in natural environments. In our experiments 3-MPA was formed by chemical addition of sulfide to aciylate and was then consumed by biological processes. 3-MPA is a known inhibitor of fatty acid oxidation in mammalian systems. In accord with this fact, high concentrations of 3-MPA caused acetate to accumulate in sediment slurries. At lower concentrations, however, 3-MPA was metabolized by anaerobic bacteria. We conclude that the degradation of DMSP may ultimately lead to the production of substrates which are readily metabolized by microbes in the sediments. 

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... 

FIGURE 1.1 Scheme of carbonic maceration winemaking. AM, anaerobic metabolism of grape berries YAF, yeast alcoholic fermentation M, maceration qd = pair temperature (q°C) action duration (days). (Figure from CEnologie—fondements scientifi-ques et techniques. Flanzy et al. collection Sciences Techniques Agroalimentaires. Technique Documentation, 1998, p. 780. Reproduced with the permission of the Editor.)... 

Tesniere, C., Baumes, R., Bayonove, C., and Flanzy, C. (1989). Effect of simulate alcoholic fermentation on aroma components of grape berries under anaerobic metabolism. Am. ]. Enol. Viticult. 40,183-188. 

In animal fermentations, an organic molecule (e.g., pyruvate) serves as a terminal proton and electron acceptor, forming an organic end product (e.g., lactate). In contrast, 02 is required as a terminal acceptor for the complete oxidation of substrates such as glucose, glycogen, fatty acids, or amino acids. As discussed in chapter 3, 02 was not always available as one of the substrates for oxidative metabolism and organisms in primordial times had to rely on anaerobic metabolic processes. 

It is among the most capable of invertebrate anaerobes, the helminths and the marine bivalves, that we find the best examples of alternative fermentation pathways. Many of these have been reviewed several times elsewhere, so only a brief summary will be considered here. Current concepts view the organization of anaerobic metabolism as a series of linear, and loosely linked, pathways. The most important of these, aside from classical glucose — lactate fermentation (yielding 2 moles ATP per mole glucose) are summarized by Hochachka and Somero (1984) as follows (see chapter 2) ... 

From the above discussion, it is evident that anaerobic metabolism in many animals can be far more versatile than commonly observed in higher vertebrates and that this raises the possibility of utilizing energetically more efficient fermentations. Estimating how much more efficient than anaerobic glycolysis is complicated by the observation that different combinations of pathways can be utilized at different times in anoxia. 

These compounds are common in soils and sediments as the products of anaerobic fermentation reactions. Metabolism of these compounds can directly consume O2 (through monooxygenase enzymes) or indirectly, through formation of NADH which is shuttled into oxidative phosphorylation and the electron transport chain. Oxidative metabolism of Ci compounds is an important microbial process in soils and sediments, consuming the methane produced by methanogenesis. 

Recent progress in molecular biology on the anaerobic metabolism of Escherichia coli has elucidated the enzymes and genes responsible for fermentative hydrogen production (1,2). Ecoli produces hydrogen by mixed acid fermentation, mainly from glucose. In Ecoli,... 

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