Clostridium metabolic products

Botulinum toxins are a collection of protein molecules that are exquisitely poisonous to the nervous system. These toxins6 are metabolic products of a common soil bacterium, Clostridium botulinum, which is frequently found on raw agricultural products. Fortunately, the bacterium produces its deadly toxins only under certain rather restricted conditions, and if foods are properly processed so that these conditions are not created, the toxins can be avoided. Food processors have to be extremely careful with certain categories of food — canned foods having low acidity, for example - because the slightest contamination can be deadly. Most reported cases of botulism have involved vegetables improperly canned in the home. 

Haidour and Ramos (1996) analyzed the degradation products of 2,4,6-trinitrotoluene, 2,4-dinitrotoluene, and 2,6-dinitrotoluene by the bacterium Pseudomonas sp. clone A under aerobic conditions utilizing 2,4-dinitrotoluene as a source of nitrogen. Two metabolites tentatively identified were 2-amino-4-nitrotoluene and 4-amino-2-nitrotoluene. Also, three azoxytoluenes were identified 4,4 -dinitro-2,2 -azoxytoluene, 2,2 -dinitro-4,4 -azoxytoluene, and 2,4 -dinitro-2, 4-azoxytoluene. 2-Amino-4-nitrotoluene and 4-amino-2-nitrotoluene were also identified as products of 2,4-dinitrotoluene metabolism by Clostridium acetobutylicum via the hydroxyl-aminonitrotoluene intermediates, namely 4-hydroxylamino-2-nitrotoluene and 2-hydroxylamino-4-nitrotoluene (Hughes et al., 1999). 

The formation of 1,3-propanediol from glycerol by Klebsiella pneumoniae, Citrobacter and Clostridium butyricum, respectively as well as 2,3-butanediol by Enterobacter aerogenes and their recovery and purification were central issues as well. The production was partly performed in a 2000 litre reactor. Glycerol metabolism in these microorganisms was established. In addition the application of the diols was investigated. 

Organisms such as Thiobacillus thiooxidans and Clostridium species have been linked to accelerated corrosion of mild steel. Aerobic Thiobacillus oxidizes various sulfur-containing compounds such as sulfides to sulfates. This process promotes a symbiotic relationship between Thiobacillus and sulfate-reducing bacteria. Also, Thiobacillus produces sulfuric acid as a metabolic by-product of sulfide oxidation. 

Figure 10.16 Metabolism of glucose or lactic acid by Clostridium tyrobutyricum with the production of butyric acid, C02 and hydrogen gas.

During cheese production lactose is converted to lactic acid by starter lactic acid bacteria (LAB). Any unfermented lactose is converted to d- and L-lactate by nonstarter lactic acid bacteria (NSLAB) and racemization, respectively. Lactate can be oxidized by LAB in cheese to acetate, ethanol, formic acid, and carbon dioxide at a rate dependent on oxygen availability (McSweeney, 2004). Other pathways include conversion to propionate, acetate, water, and carbon dioxide by Propionibacterium spp. carbon dioxide and water by Penicillium spp. yeasts and butyric acid and hydrogen by Clostridium spp. The rate of lactose metabolism influences proteolysis and flavor formation (Creamer et al., 1985 Fox et al., 1990). 

The activities of intracellular enzymes give an indication of the activity of certain metabolic pathways. They are classically assayed by performing their specific reactions in vitro, using the conversion of natural or artificial substrates and often some additional detection reaction. The sample preparation procedure involves cell harvesting and preparation of cell extracts. A well-studied example is the metabolic shift in Clostridium acetobutylicum from acid to solvent production, the so-called solvent shift. Andersch et al. [48] studied the activities of 10 different enzymes involved in this shift, in batch cultivations where the shift is self-induced by the products formed, and under continuous culture conditions with an externally induced shift. 

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. 

Nakayama S, Kosaka T, Hirakawa H, Matsuura K, Yoshino S, Furukawa K (2008) Metabolic engineering for solvent productivity by downregulation of the hydrogenase gene cluster hupCBA in Clostridium saccharoperbutylacetonicum strain N1 -4. Appl Microbiol Biotechnol 78 483 493... 

Sodinm nitrite is commonly utilized in food preservation. In spite of its known potential for metabolism to carcinogenic nitrosamines, nitrite snpplementation is still in widespread nse in nntrition because the addition of nitrite (plus a reducing agent such as ascorbate) has two desirable effects it imparts a red color to meats (primarily a result of the production of nitrosylheme from myoglobin ) and, perhaps more importantly, the organism responsible for botulism Clostridium botulinum) is exquisitely sensitive to this treatment. There is indeed a massive literature on the role of NO and its reactions in foods in the nutrition fields and is worthy of scrutiny by researchers in the biological effects of endogenously produced -NO in mammahan systems. 

Although CO2 is inhibitory to microbes, compressed hydrocarbon solvents may be appropriate for extractive bioconversions and extractions in biphasic (aqueous-compressed solvent) systems. Our laboratory investigated the metabolic activity of the anaerobic, thermophilic bacteria Clostridium ther-mocellum as a model system (45). Thermophilic bacteria have a distinct advantage over conventional yeasts for ethanol production in their ability to use a variety of inexpensive biomass feedstocks. Extractive fermentation using compressed solvents is an approach to address the end-product toxicity of these bacteria to ethanol and improve the economic viability of biofuel production by thermophilic organisms. 

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