Bacterial action and chemical

Bacterial Action and Chemical Signalling in the Red Fox (Vulpes vulpes) and Other Mammals... 

P5Trite and calcite are mineral crystals that represent a wide Habitus and Tracht variation. Pyrite is the most persistent mineral among sulfide minerals, occurring in a wide range of modes, including inorganic processes and bacterial action, and it can also be synthesized by hydrothermal or chemical vapor transport methods. 

The most common preservatives and the tests for which the preservatives are required are listed in Table 2-6. Preservatives have different roles but are usually added to reduce bacterial action or chemical decomposition or to solubilize constituents that might otlierwise precipitate out of solution. Another application is to decrease atmospheric oxidation of unstable compounds. Some specimens should not have any preseiwatives added because of the possibility of interference with analytical methods. 

The effect of such an additive on the UV degradation of polyethylene is shown in Fig. 3 which shows carbonyl formation in the polymer with time in the presence and absence of additive. It can be shown that carbonyl formation correlates directly with the physical properties of the polymer which rapidly loses strength and embrittles. Embrittlement and fragmentation are particularly rapid in the case of the more crystalline polymers which crumble even under the influence of wind and weather (see Fig. 4). The polymer particles so formed are chemically modified by oxidation to be now subject to attack by normal bacterial action and it is anticipated that these will quickly become part of the soil. 

Figure 21.1 Compost in a compost bin. The pH of compost changes as the plant material is broken down by bacterial action. The chemical reactions in compost involve weak acids and weak bases.

Fiber components are the principal energy source for colonic bacteria with a further contribution from digestive tract mucosal polysaccharides. Rate of fermentation varies with the chemical nature of the fiber components. Short-chain fatty acids generated by bacterial action are partiaUy absorbed through the colon waU and provide a supplementary energy source to the host. Therefore, dietary fiber is partiaUy caloric. The short-chain fatty acids also promote reabsorption of sodium and water from the colon and stimulate colonic blood flow and pancreatic secretions. Butyrate has added health benefits. Butyric acid is the preferred energy source for the colonocytes and has been shown to promote normal colonic epitheUal ceU differentiation. Butyric acid may inhibit colonic polyps and tumors. The relationships of intestinal microflora to health and disease have been reviewed (10). 

Sulfur is widely distributed as sulfide ores, which include galena, PbS cinnabar, HgS iron pyrite, FeS, and sphalerite, ZnS (Fig. 15.11). Because these ores are so common, sulfur is a by-product of the extraction of a number of metals, especially copper. Sulfur is also found as deposits of the native element (called brimstone), which are formed by bacterial action on H,S. The low melting point of sulfur (115°C) is utilized in the Frasch process, in which superheated water is used to melt solid sulfur underground and compressed air pushes the resulting slurry to the surface. Sulfur is also commonly found in petroleum, and extracting it chemically has been made inexpensive and safe by the use of heterogeneous catalysts, particularly zeolites (see Section 13.14). One method used to remove sulfur in the form of H2S from petroleum and natural gas is the Claus process, in which some of the H2S is first oxidized to sulfur dioxide ... 

The last reaction cited above as shown is very effectively catalyzed by bacterial action but is very slow chemically by recycling the spent ferrous liquors and regenerating ferric iron bacterially, the amount of iron which must be derived from pyrite oxidation is limited to that needed to make up losses from the system, principally in the uranium product stream. This is important if the slow step in the overall process is the oxidation of pyrite. The situation is different in the case of bacterial leaching of copper sulfides where all the sulfide must be attacked to obtain copper with a high efficiency. A fourth reaction which may occur is the hydrolysis of ferric sulfate in solution, thus regenerating more sulfuric acid the ferrous-ferric oxidation consumes acid. 

Low power ultrasound offers the possibility of enhancing the effects of chlorine. The results of a study of the combined effect of low power ultrasound and chlorination on the bacterial population of raw stream water are shown (Tab. 4.2). Neither chlorination alone nor sonication alone was able to completely destroy the bacteria present. When sonication is combined with chlorination however the biocidal action is significantly improved [10]. The effect can be ascribed partly to the break-up and dispersion of bacterial clumps and floes which render the individual bacteria more susceptible to chemical attack. In addition cavitation induced damage to bacterial cell walls will allow easier penetration of the biocide. 

Waterside problems that lead to decreases in efficiency and material deterioration can be caused by a variety of mechanisms, such as electrochemical corrosion and deposition of foulants. These problems can be exacerbated by low flow, poor operational practice, process contamination, or specific stresses. It is also important to try to determine cause and effect relationships in order to provide a logical and practical water treatment solution. Such a solution will usually involve some form of cleaning, plus a combined engineering and chemical action plan. Inspection may be made easier by the use of a Boroscope or similar optical/video recording device. The color, texture, and quantity of all deposits should be noted, measurements of pits taken, and microbiological contaminants analyzed. It may be useful to conduct biocide efficiency tests on bacterial slimes. The period when a heat exchanger is open for inspection may be an opportune time for the permanent installation of ports for corrosion-monitoring probes. 

Cephalosporins and cephamycins are similar to penicillins chemically, in mechanism of action, and in toxicity. Cephalosporins are more stable than penicillins to many bacterial G-lactamases and therefore usually have a broader spectrum of activity. Cephalosporins are not active against enterococci and Listeria monocytogenes. 

Indirect methods of lowering blood ammonia are, in the main, more effective than the chemical techniques. These include withdrawal of protein from the diet (M3, P7) and antibiotic therapy (F3, S6). A completely protein-free diet leaves little nitrogen in the gut for bacterial action. Antibiotic therapy, particularly by die oral route (S10, W5), so alters the gut flora as to diminish the number of ammonia-forming organisms. It must be kept in mind that urea is always present in the gut as a substrate for ammonia formation even on a nitrogen-free diet. 

Nitrogen undergoes a complicated series of cyclic pathways in the ecosystem (Fig. 8.2). The atmospheric form of free nitrogen must be fixed —incorporated into chemical compounds (e.g., NH3) which can be utilized by plants. This nitrogen fixation can be accomplished by bacterial action of both free-living soil bacteria such as azotobacter and chlostridium and symbiotic bacteria such as rhizobium. It can also be... 

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