Rumen propionic acid bacteria

Propionic (propanoic) acid-producing bacteria are numerous in the digestive tract of ruminants. Within the rumen some bacteria digest cellulose to form glucose, which is then converted to lactate and other products. The propionic acid bacteria can convert either glucose or lactate into propionic and acetic acids which are absorbed into the bloodstream of the host. Usually some succinic acid is also formed. 

Let us consider other natural habitats of propionic acid bacteria. In grasses used as fodder for livestock the content of cobalt is often below a certain limit (0.08 ppm), so that if cobaltous salts are not added to feeds, animals will suffer from cobalamin deficiency. Animals are supplied with corrinoids mainly through the biosynthetic activity of bacteria. If 1 mg of cobalt a day is added to the feed, then the content of cobalamins in the dry residue of lignin matter in rumen is 0.59 to 1.0 jag/g. When no cobalt is added, the content of cobalamins is lowered by an order of magnitude, to 0.081-0.108 ig/g (Smith and Marston, 1970) correspondingly, the content of vitamin in all animal tissues and fluids is low. Therefore, the concentration of vitamin in meat, milk and other products obtained from the animal will depend on the content of cobalt in the feed. 

Other natural habitats of propionic acid bacteria are represented by cheese and silage. If one recalls that there are at least 10 bacterial cells in 1 g of cheese, then it becomes clear that bacteria lead a cobalamin-deficient existence. The same is true of bacteria that live in silage, where the cobalamin content is about 0.1 to 2.0 xg per 100 g (Smith and Marston, 1970). In the rumen of ruminants, where cobalt is limited, the cobalamin content is in the range of 0.14-0.41 ng/ml (Dryden et al., 1962). It is clear that these bacteria live at a very low cobalamin level. Therefore, the conclusion is obvious—most propionic acid bacteria lead a vitamin B -deficient mode of life in nature, although they can readily attain high levels of corrinoids under favorable conditions. 

Propionic acid bacteria represent a distinct and ancient evolutionary branch ascending from an actinomycetous ancestor. It is a bridge that links the past and present. Three subgroups of propionic acid bacteria classical, cutaneous, and P. propionicum comprise the genus Propionibacterium, The classical propionibacteria inhabit mainly milk and cheese (hence their second name—dairy propionic acid bacteria), the cutaneous species inhabit human skin and the rumen of ruminants, and P. propionicum dwells in the soil. 

Silverman M and Werkman CH (1939) Adaptation of the propionic acid bacteria to vitamin Bi synthesis including method of assay. J Bacteriol 38 25-32 Siu PML and Wood HG (1962) Phosphoenolpyruvic carboxytransphosphorylase, a CO2 fixation enzyme from propionic acid bacteria. J Biol Chem 237 3044-3051 Sizova AV and Arkadjeva ZA (1968) Propionic acid bacteria of rumen and their capacity for vitamin B12 biosynthesis. Mikrobiol Sintez 10 8-13... 

In ruminants, lactic and propionic acids are the major precursors of glucose. This is particularly important during lactation, since all the carbohydrate in die food is fermented by die bacteria in the rumen, so diat no glucose enters the body but glucose is required for die formation of lactose for the milk (Chapter 6). 

Another reaction for the formation of succinyl-CoA is the carboxy-lation of propionyl-CoA (biotin enzyme) to methyl malonyl-CoA, and the conversion of methyl malonyl-CoA by a soluble vitamin B12 enzyme to succinyl-CoA. These enzymes provide reactions for the incorporation of propionic acid into the citric acid cycle the reactions are especially important in ruminants in which large amounts of propionic acid are formed by the bacteria in the rumen. The significance of this method of succinyl-CoA formation for the synthesis of ALA in fiver or red blood cell [Nakao and Takaku, 51b] is not known. This method is not used by higher plants, for they do not contain vitamin B12. 

The bacteria number 10 -10 ° per millilitre of rumen contents. Over 200 species have been identified, and for descriptions of them the reader is referred to the works listed at the end of this chapter. Most of these bacteria are non-spore-forming anaerobes. Table 8.3 lists a number of the more important species and indicates the substrate they utilise and the products of the fermentation. This information is based on studies of isolated species in vitro and is not completely applicable in vivo. For example, it appears from Table 8.3 that succinic acid is an important end product, but in practice this is converted into propionic acid by other bacteria such as Selenomonas ruminantium (see Fig. 8.6) such interactions between microorganisms are an important feature of rumen fermentation. A further point is that the activities of a given species of bacteria may vary from one strain of that species to another. The total... 

New (de novo) fatty acids are synthesized from two-carbon acetyl units produced during metabolism. Two enzyme complexes, acetyl-coenzyme A carboxylase and fatty acid synthetase, work in concert to build up fatty acid chains, two carbons at a time, until released by the complex. The primer in plants and animals is essentially a two-carbon acetyl group and the fatty acid chains have even numbers of carbons. If the primer is a three-carbon propionate group, odd-number carbon chains result. Odd-number fatty acids are common in microbial lipids and also are synthesized de novo from propionic VFA by rumen bacteria and deposited in adipose tissue. The length of the fatty acid synthesized depends on the tissue. Palmitic acid is produced in the liver and adipose tissue, and shorter-chain fatty acids are also produced in the mammary glands (49). 

Succinic acid is one of many organic acids (e.g. acetic, butyric, caproic, formic, propionic and succinic acid) produced from glucose by many rumen anaerobic bacteria. Only a very few accumulate succinate as the anaerobic end-... 

Limed straw and bagasse (the residue after the juice is pressed from sugarcane) can be fed to ruminant animals.214 These can replace corn, which requires large amounts of fertilizer, herbicides, and insecticides, that can lead to contamination of groundwater. Alternatively, it can be treated with rumen bacteria in an anaerobic fermentor to produce acetic, propionic, and butyric acids. Salts of these acids can be pyrolyzed to produce ketones. These can then be re-... 

The property of storing a polysaccharide within its cytoplasm is characteristic of the bacteria associated with the hydrolysis of starch in both the rumen and the caecum. Cl. butyricum is known to produce an amylase in vitrOy and a free amylase that occurs in the rumen of starch-fed sheep is presumably of bacterial origin, as no amylase is present in sheep s saliva. Similarly an amylase is produced in vitro by starch-splitting cocci, and although this enzyme hydrolyzes starch as far as the dextrin stage the end products of fermentation include acetic, propionic, and butyric acids. 

A high proportion of odd chain and of various polymethyl-branched fatty acids occurs in the adipose tissue triacylglycerols of sheep and goats when they are fed diets based on cereals such as barley. Cereal starch is fermented by bacteria in the rumen to form propionate, and when the animals capacity to metabolize propionate via methylmalonyl-CoA to succinate is overloaded, propionyl- and methylmalonyl-CoA accumulate. Garton and his colleagues showed that methylmalonyl-CoA can take the place of malonyl-CoA in fatty acid synthesis and that with acetyl- or propionyl-CoA as primers, a whole range of mono-, di- and tri-methyl branched fatty acids can be produced. 

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