Anaerobic metabolism propionic acid

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. 

Soil t,/2 = 10 d in sandy soils and t,/2 30 d in sandy clay soils while under anaerobic conditions, results were similar except that the very rapid cleavage of the ester bond by hydrolysis within one hour to propionic acid derivatives was experienced and within 2 d, up to 86% of the parent compound was metabolized into various free acid metabolites and up to 3.7% of phenol metabolites (Herbicide Handbook 1989) ... 

Ethanol is formed by the anaerobic metabolism of yeasts like Saccharomyces and many other species. In the presence of sulfite salts or in alkaline solutions, the alcohol formation can be changed to glycerin formation. Clostridium and Bacillus species participate in the production of butanol-acetone-butyric acid. Besides n-butanol, acetone and butyric acid, other organic compounds like propionic and lactic acids, 2-propanol, ethanol, and acetyl methylcarbinol (3-oxo-2-butanol) as well as C02 and H2 are produced as by-products. Some bacteria generate 2-propanol from acetone and others form acetone from ethanol. 

The formation and studying of the collections of propionic acid bacteria proceeded simultaneously with investigations of their biochemistry, first of all, biochemistry of their unique mode of fermentation. Propionic acid fermentation was discovered by A. Fitz, later, it was studied by H.G. Wood and C.H. Werkman. It was in propionibacteria that the heterotrophic assimilation of CO2 was discovered by H.G. Wood. Owing to the studies by Wood, Werkman and their school, then by H.A. Barker and F. Lipmann as well as E.A. Delwiche in the USA, the chemistry of this unique fermentation was elucidated. Another development at the second stage of biochemical investigations concerns the discovery of aerobic metabolism in propionic acid bacteria, previously considered anaerobic. Important contributions to this field of study were made by the school of A H. Stouthamer in the Netherlands and in our laboratory at the Moscow State University. These investigations demonstrated a surprising lability of the metabolism of propionic acid bacteria, which were found to be well equipped for both the... 

It has been established (Delwiche and Carson, 1953) that propionic acid bacteria are able to oxidize the intermediate products of the TCA cycle. Under anaerobic conditions the TCA cycle is also functional, and its role may not be limited to anabolic processes. In these conditions nitrate and fumarate can act as terminal electron acceptors in propionic acid bacteria. It is well known that the TCA cycle provides microorganisms with precursors for biosynthetic reactions, and plays an essential role in both the catabolic and anabolic metabolism. 

To summarize, corrinoids in propionic acid bacteria are involved not onh in fermentation, but also in such important anabolic processes as protein and DNA synthesis and DNA methylation. In this respect, corrinoids differ from other related tetrapyrrole compounds by their polyfunctionalit. The involvement of corrinoid-dependent enzymes in different metabolic processes in propionibacteria explains the propensity of anaerobic strains of the classical propionic acid bacteria to synthesize large amounts of corrinoids under suitable conditions. 

Strictly anaerobic and unable to metabolize carbohydrates. Found in association with streptococci and derive energy from the fermentation of lactate to propionic acid, acetic acid, carbon dioxide and hydrogen. Represent 0-60% of plaque bacteria, also common on tongue. 

Various bacteria own the ability to produce propionic acid within their metabolic pathways. Present-day research is focused on strains of Propionibacteriaceae and Clostridiaceae. Propionibacteria are using the dicarboxylic acid pathway (methylmalonyl coenzyme A-pathway) to produce the desired product. These gram-positive, anaerobic bacteria are able to use glucose, sucrose, lactate, lactose and glycerol as carbon source. The metabolic end products are propionate, succinate, carbon dioxide and acetate. Professionals acknowledge Propionibacterium... 

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),... 

Clostridium species are anaerobic, spore-forming microbes. The formic, acetic, propionic, and butyric acids produced as a result of their metabolic activity can enhance the corrosion of steel. 

The large intestine extends from the ileocecal valve to the anus. It is wider than the small intestine except for the descending colon, which when empty may have the same diameter as the small intestine. Major functions of the colon are absorption of water, Na+, and other electrolytes, as well as temporary storage of excreta followed by their elimination. The colon harbors large numbers of mostly anaerobic bacteria that can cause disease if they invade tissues. These bacteria metabolize carbohydrates to lactate, short-chain fatty acids (acetate, propionate, and butyrate), and gases (CO2, CH4, and H2). Ammonia, a toxic waste product, is produced from urea and other nitrogenous compounds. Other toxic substances are also produced in the colon. Ammonia and amines (aromatic or aliphatic) are absorbed and transported to the liver via the portal blood, where the former is converted to urea (Chapter 17) and the latter is detoxified. The liver thus protects the rest of the body from toxic substances produced in the colon. Colonic bacteria can also be a source of certain vitamins (e.g., vitamin K, Chapter 36). 

Following an abrupt transition of P. pentosaceum from anaerobic to aerobic metabolism (10 pM O2), the growth rate increases at first, but the formation of acetate from lactate and glucose is slowed down, propionate formation is completely repressed and pyruvate is accumulated in the medium (van Gent-Ruijters et al, 1976 Schwartz et al, 1976). A decrease in the activities of the citric acid cycle enzymes malate dehydrogenase, fumarase and NADH oxidase, lactate oxidase, NADH-dependent fiimarate reductase, lactate-dependent nitrate reductase is observed upon the transition from anaerobic to aerobic (10 pM O2) metabolism (van Gent-Ruijters, 1975). 

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. 

Wheat bran cellulose is much less well digested than that of fruit and vegetables and this has been attributed to its lignin content. The chief products of the anaerobic fermentation of fibre are volatile fatty acids (acetate, propionate and butyrate), gas (CO2, Ha and methane) and energy. Gas production is a normal part of colonic metabolism but may be one of the reasons why people in the West have tended to maintain a relatively low fibre intake. 

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