BACTERIAL CONVERSION

Nadeau LJ, Z He, JC Spain (2003) Bacterial conversion of hydroxylamino aromatic compounds by both lyase and mutase enzymes involves intramolecular transfer of hydroxyl groups. Appl Environ Microbiol 69 2786-2793. 

In addition to bacterial conversion of L-methionine to cheese aroma compounds, certain cheese-ripening yeasts have been implicated. They include De-baromyces hansenii, Geotrichum candidum, and Yarrowia lipolytica, in addition to Kluyveromyces lactis and Saccharomyces cerevisiae (previously noted). Of these yeasts, Geotrichum candidum was most effective at producing sulfur compounds with the major product being S-methyl thioacetate, with smaller amounts of MT, DMS, DMDS, and DMTS. Kluyveromyces lactis had a similar profile, but produced a much smaller amount of S-methyl thioacetate than did G. candidum. S-Methyl thioacetate is formed by a reaction of MT and acetyl-CoA (Equation 7) ... 

Figure 5.2 Therapeutic interventions for decreasing colorectal mucosal bile acid exposure as a CRC chemoprevention strategy. 1) Lifestyle modifications including reduction in dietary animal fat and increased fibre intake may, at least partly, be explained by reduction in luminal primary (cholic acid [CA] and chenodeoxycholic acid [CDCA]) and secondary (deoxycholic acid [DCA] and lithocholic acid [LCA]) bile acids. 2) Reduction of secondary bile acids, which are believed to have pro-carcinogenic activity could be obtained by decreased bacterial conversion from primary bile acids. 3) Alternatively, bile acids could be sequestered by chemical binding agents, e.g. aluminium hydroxide (Al(OH)3) or probiotic bacteria. 4) Exogenous ursodeoxycholic acid (UDCA) can reduce the luminal proportion of secondary bile acids and also has direct anti-neoplastic activity on colonocytes in vitro.

The involvement of HA during bacterial conversion of nitrate to NH3 (known also as the nitrate ammonification phase of the nitrogen cycle) has been studied at the molecular level as part of an effort to delineate the mechanism of conversion of nitrite to NH3 by a group of multiheme cytochromes of bacterial origin. The overall reduction reaction is depicted in equation 3 for cytochrome c-nitrite reductase " ... 

Notably, nitrile-degrading enzymes (e.g. nitrilase that converts the CN group to carboxylic acid, and nitrile hydratase that produces an amide function) have been described, and they co-exist with aldoxime-degrading enzymes in bacteria (Reference 111 and references cited therein). Smdies in this area led to the proposal that the aldoxime-nitrile pathway, which is implemented in synthesis of drugs and fine chemicals, occurs as a natural enzymic pathway. It is of interest that the enzyme responsible for bacterial conversion of Af-hydroxy-L-phenylalanine to phenacetylaldoxime, an oxidative decarboxylation reaction, lacks heme or flavin groups which are found in plant or human enzymes that catalyze the same reaction. Its dependency on pyridoxal phosphate raised the possibility that similar systems may also be present in plants . 

The mercury cell thus gives very pure NaOH and, in terms of energy consumption, is also more economical than the diaphragm cell. However, the inevitable leakage of some mercury into local rivers or lakes can have (and has had) serious consequences because of the bacterial conversion of Hg to methylmercury ion, CHaHg4-, which then becomes concentrated in successive steps of the food chain ... 

An understanding of the environmental fate of these elements is necessary in the total assessment of associated health risks. Mercury is known to cycle between the geosphere and biosphere (35). Once in the hydrosphere, it can be converted by sediment flora into highly toxic methylmercury whereupon it is incorporated into aquatic life and ultimately accumulates in human food chains (31). Limited bacterial conversion of inorganic to organic mercury has been shown to occur in soil humus (36) and in animal tissue as well (37). There is no evidence that alkylated mercury is generated from coal combustion directly if it did it would probably be dissociated to the elemental form (14). 

The bacterial conversion of malic acid to lactic acid and carbon dioxide has been recognized since 1890 and is referred to as the malo-lactic fermentation. This conversion has been promoted under controlled conditions in the cooler viticultural regions of the world where grapes mature with excessive amounts of malic acid which causes taste imbalance... 

The literature concerning malo—lactic fermentation—bacterial conversion of L-malic acid to L-lactic acid and carbon dioxide in wine—is reviewed, and the current concept of its mechanism is presented. The previously accepted mechanism of this reaction was proposed from work performed a number of years ago subsequently, several workers have presented data which tend to discount it. Currently, it is believed that during malo-lactic fermentation, the major portion of malic acid is directly decarboxylated to lactic acid while a small amount of pyruvic acid (and reduced coenzyme) is formed as an end product, rather than as an intermediate. It is suspected that this small amount of pyruvic acid has extremely important consequences on the intermediary metabolism of the bacteria. 

Tyj"alo—lactic fermentation can be defined as the bacterial conversion of L-malic acid to L-lactic acid and carbon dioxide during storage of new wine. Malic acid is dicarboxylic, but lactic acid is monocarboxylic therefore, the net result of malo-lactic fermentation in wine, aside from the production of carbon dioxide, is a loss in total acidity. In commercial practice, this fermentation is not well understood, and better methods of controlling it are sought. 

A vexing factor in understanding CH3C1 sources is the observation that the bacterial conversion of CH3Br to CH3C1 with chloride has been reported in a biotrans-halogenation Sn2 reaction (293). Since bromide is a better nucleophile than chloride in aqueous media (294), the reverse biotranshalogenation reaction is plausible. 

Knowing that the inorganic mercury is biomagnified in the aquatic food chain through bacterial conversion to methyl mercury and then accumulated primarily in fish, this part is focused to the determination of methyl mercury in fish samples. The developed method described above using the combination of biphasic system and glucose oxidase biosensor was used. 

Given how the DOM-Fe-P complex influences ecosystem structure, it is also likely that the DOM-Fe-P complex influences humic lake ecosystem function in terms of C metabolism. First, the bacterial conversion of dissolved C into biomass it is quite low, with an average of 25 % across a trophic gradient (del Giorgio et al., 1997). And despite the evidence that bacteria may be better equipped to acquire the Fe and P bound to DOM, the added energetic expenditure in acquiring these elements may result in a significant... 

The fungal production of fumaric acid using rice bran and subsequent bacterial conversion of succinic acid using fungal culture broth were investigated. Since the rice bran contains abundant proteins, amino acids, vitamins, and minerals, it is suitable material that fungi use as a nitrogen source. The effective concentration of rice bran to produce fumaric acid was 5 g/L. 

Because yeast extract is very expensive, we studied the effect of CSL supplement in order to reduce the amount of yeast extract. CSL has been the focus of attention as an alternative nitrogen source (8,12). As shown in Fig. 7, the bacterial conversion was very poor when only CSL was used as a nitrogen source. Even if yeast extract had a significant effect on cell growth, when 5 g/L of yeast extract and 15 g/L of CSL were used as nitrogen sources, a bioconversion yield and productivity of 95% and 2.2 g/(L-h), respectively, could be obtained. 

Finally, we investigated the inhibition of concentrated fungal culture broth on succinic acid production and fumaric acid consumption. As shown in Fig. 8, we found that concentrated fungal culture broth slightly inhibited the bacterial conversion. Succinic acid could be efficiently produced from fungal culture broth until it was concentrated to three-fold (64 g/L of fumaric acid). However, the conversion time needed was severely prolonged when it was concentrated to more than four-fold (84 g/L of fumaric acid). Since E.faecalis RKY1 could efficiently convert fumaric acid... 

Vancauwenberge, J.E., Slininger, P.J. and Bothast, RJ. 1990. Bacterial Conversion of Glycerol to 3-Hydroxypropionaldehyde. Appl. Environ. Microbiol., 56, 329-332. 

Malo-Lactic Fermentation. The bacterial conversion of malic acid to lactic acid usually does not occur in North Coast white wines because of low pH, high S02, and cool storage temperatures, factors that inhibit lactic acid bacteria activity. Some work has been done in the North Coast with malo-lactic fermentation in Chardonnay, following the traditional practices in Burgundy. Factors used to encourage experimental malo-lactic fermentation in white wines have been bacterial inoculation, warmer (18°-21° C) fermentation temperatures, prolonged lees contact, and low free-S02 levels until fermentation is complete. 

Milk turns sour because of the bacterial conversion of carbohydrates to lactic acid. When the pH becomes strongly acidic, soluble proteins in milk are denatured... 

The anaerobic conversion of organic compounds is thought to occur in three steps. The first involves tne enzyme-mediated transformation (hydrolysis) of higher-weight molecular compounds into compounds suitable for use as a source of energy and cell carbon the second is associated with the bacterial conversion of the compounds resulting... 

SAFETY PROFILE Confirmed carcinogen of the lung, nasal sinus, brain, esophagus, stomach, liver, bladder, and kidney. They are often produced in food as by-products from processing and preparadon. They are found in whiskey, herbicides, and cosmetics, as well as in tanneries, rubber factories, and iron foundries. They can be formed within the body by reaction of amine-containing foods or drugs with the nitrites resulting from bacterial conversion of nitrates. See also N-NITROSO COMPOUNDS. 

Oral tryptophan causes marked pulmonary edema and emphysema. This appears to be due to the bacterial conversion of tryptophan to skatole (3-methylindole), which causes the same type of lung lesion.33... 

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