Propionic acid fermentation,

Bacteria from the genera Lactobacillus and Streptococcus are involved in the first steps of dairy production (3). The raw materials produced by their effects usually only acquire their final properties after additional fermentation processes. For example, the characteristic taste of Swiss cheese develops during a subsequent propionic acid fermentation. In this process, bacteria from the genus Propionibacterium convert pyruvate to propionate in a complex series of reactions (2). 

In propionic acid fermentations the starting materials are a sugar and the lactic and pyruvic acids that are derived from it. According to Barker and Lipmann pyruvate may be reduced to propionate without passing through lactate. Propionic acid itself can be reduced to n-propanol. ... 

Figure 17-10 Propionic acid fermentation of Propionobacte-ria and Veillonella. Oxidation steps are designated by the symbol "O" and reduction steps by "R." The two coupled reactions marked by asterisks are catalyzed by carboxyl-transferase.

Propionic acid might be also produced by fermentation of Propionibac-terium acidipropionici, thus providing an attractive alternative that can also meet consumer s demand for natural preservatives used in the food industry. However, conventional batch propionic acid fermentation suffers from low... 

Himmi, E.H., Bories, A., Boussaid, A., and Hassani, L. 2000. Propionic acid fermentation of glycerol and glucose by Propionibacterium acidipropionici and Propionibacterium freudenreichii ssp. sher-manii. Appl Microbiol Biotechnol 53, 435-440. 

Barbirato, F., Chedaille, D. and Bories, A. 1997. Propionic Acid Fermentation from Glycerol Comparison with Conventional Substrates. Appl. Microbiol. Biotechnol., 47, 441 —446. 

Lewis, V.P and Yang, S.T. 1992. Continuous Propionic Acid Fermentation by Immobilized Propionibacterium Acidipropionici in a Novel Packed-Bed Bioreactor. Biotechnol. Bioeng., 40, 465-474. 

Propionic acid CH3-CH2-COOH, a simple fatty acid, m.p. -22°C, b.p. 140.9°C.P.a. occurs as its salts (propionates) and esters in many plants. It is especially important in the metabolism of propionic bacteria, which perform a propionic acid fermentation. Propio-nibacterium shermanii synthezises P. a. from pyruvate (Fig.). Propionylcoenzyme A (see) is an important metabolic derivative. 

Hsu S.Yang ST. Propionic acid fermentation of lactose by Propionibacterium acidipropionici effects of pH. 

Barbirato F, ChedaiUe D, Bories A. Propionic acid fermentation from glycerol comparison with conventional substrates. Appl Microbiol Biotechnol 1997 47 441-6. 

Suwannakham S, Huang Y,Yang ST. Construction and characterization of ack knock-out mutants of Propionibacterium addipropionici for enhanced propionic acid fermentation. Biotechnol Bioeng 2006 94 383-95. 

Suwannakham S.Yang ST. Enhanced propionic acid fermentation by Propionibacterium acidipropionici mutant obtained by adaptation in a fibrous-bed bioreactor. Biotechnol Bioeng 2005 91 325-37. 

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... 

The most important property of the genus Propionibacterium is the production of propionic acid as a result of the propionic acid fermentation dependent on coenzyme B12. If the dependence on coenzyme Bn is disregarded, some clostridial strains that do not form spores may be erroneously attributed as propionibacteria. For example, Cl botulinum, Cl propionicum and some other species can produce propionic acid, but propionibacteria have the GC-type DNA (65-67 mol% G+C in classical and 53-62 mol% in cutaneous bacteria), while clostridial DNA is of the AT-type (25-30 mol% G+C). 

All propionic acid bacteria are catalase-positive P. arabinosum displays a very weak catalase activity). As a rule, members of the genus Propionibacterium produce significant amoxmts of vitamin Bn. We (Vorobjeva, 1976) suggested to differentiate propionibacteria by the nature of the coenzyme form of vitamin Bn. The presence of the isomerization reaction of succinyl-CoA methylmalonyl-CoA, which is the key reaction of propionic acid fermentation, represents another valuable taxonomic property of the genus. 

Typical of group 3 mutants is strain 16. In morphologic properties it is similar to the parental strain, but grows very slowly even in rich medium. In synthetic media it does not grow. Requirements for growth factors were tested according to Holliday s scheme (1956), and strain 16 was found to require uracil (Table 2.8), to form only 0.24 ig/ml of corrinoids and to accumulate metabolic products typical of propionic acid fermentation (propionic and acetic acids). 

The culture liquid obtained in propionic acid fermentation displayed antimutagenic activity with respect to NQO-induced mutagenesis in S. typhimurium TAIOO (Table 2.12). 

Propionic acid fermentation is of major significance for the energetics of propionic acid bacteria. The main fermentation products are propionic and acetic acids and CO2 (Mashur et al., 1971 Foschino et al., 1988). Formic and succinic acids (Mashur et al, 1971) as well as acetoin and diacetyl (Tomka, 1949 Antila, 1956/57 Lee et al., 1969, 1970) are also produced, but in smaller amounts. Other volatile aromatic substances are dimethylsulfide, acetaldehyde, propionic aldehyde, ethanol and propanol (Keenan and Bills, 1968 Dykstra et al., 1971). Propionic acid fermentation differs from the other types of fermentation by the high ATP yield and by some unique enzymes and reactions. 

Propionic acid fermentation is not limited to propionibacteria it functions in vertebrates, in many species of arthropods, in some invertebrates imder anaerobic conditions (Halanker and Blomquist, 1989). In eukaryotes the propionic acid fermentation operates in reverse, providing a pathway for the catabolism of propionate formed via p-oxidation of odd-numbered fatty acids, by degradation of branched-chain amino acids (valine, isoleucine) and also produced from the carbon backbones of methionine, threonine, thymine and cholesterol (Rosenberg, 1983). The key reaction of propionic acid fermentation is the transformation of L-methylmalonyl-CoA(b) to succinyl-CoA, which requires coenzyme B12 (AdoCbl). In humans vitamin B deficit provokes a disease called pernicious anemia. 

In vertebrates, in addition to the main pathway of propionate catabolism (conversion into succinate), alternative pathways may function under conditions when the main pathway is blocked. In the termite Zootermopsis angusticollis a high Bn content apparently is due to the presence of microorganisms in the stomach (Wakayama et al., 1984). There is evidence that vitamin Bn is used by termites for the conversion of succinate to methylmalonate and incorporation of the latter instead of malonyl-CoA into methyl-branched hydrocarbons. Therefore, in termites the direction of carbon flow is the same as in bacteria (from succinate to propionate), but opposite to that found in vertebrates. From the aforesaid it is clear that studying propionic acid fermentation is important not only for understanding the biochemistry of propionic acid bacteria, but of many other organisms, including humans. 

The discovery by the American scientists was confirmed in our investigations (Vorobjeva, 1958b, 1976) by estimating the carbon balance in the end products of propionic acid fermentation. Reactions leading to the production of propionic acid in propionibacteria can be represented by the following sequence (Delwiche, 1948 Johns, 1951) ... 

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