Products of microbial metabolism

As might be expected, bacteria have been isolated from the plants that prodnce flnoroacetate, and these include an unidentified Pseudomonas sp. (Goldman 1965), a strain of Burkholderia Pseudomonas) cepacia from Dichapetalum cymosum (Meyer et al. 1990), and a strain of Morax-ella sp. (Kawasaki et al. 1981). In addition, fluoroacetate is an unusual product of microbial metabolism ... 

Photolytic. When propachlor in an aqueous ethanolic solution was irradiated with UV light (>, = 290 nm) for 5 h, 80% decomposed to the following cyclic photoproducts W-isopropyloxindole, W-isopropyl-3 hydroxyoxindole, and a spiro compound. Irradiation of propachlor in an aqueous solution containing riboflavin as a sensitizer resulted in completed degradation of the parent compound. 3-Hydroxypropachlor was the only compound identified in trace amounts which formed via ring hydroxylation (Rejtb et al, 1984). Hydrolyzes under alkaline conditions forming W-isopropylaniline (Sittig, 1985) which is also a product of microbial metabolism (Novick et al., 1986). 

Products of microbial metabolism, rust, salts of calcium, sodium, magnesium,... 

Microorganisms living at the oil-water interface in fuel storage systems can accumulate to form a distinct raglike layer of growth. This rag can break free and appear as an emulsion in fuel. The products of microbial metabolism are highly polar and can help to stabilize fuel emulsions. 

Non-enzymatic attack In non-enzymatic attack of minerals by microbes, reactive products of microbial metabolism come into play. The microbial enzymes responsible for metabolic product formation are located below the cell envelope, in the cytoplasm of prokaryotes (Bacteria and Archaea) and in cell organelles and/or the cytoplasm of eukaryotes (e.g. fungi, algae, lichens). In these instances of microbial attack, physical contact of the microbial cells with the surface of a mineral being attacked is not essential. The reactive metabolic products are formed intracellularly and are then excreted into the bulk phase where they are able to interact chemically, i.e. non-enzymatically, with a susceptible mineral. Depending on the type of metabolic product and mineral, the interaction with the mineral may result in mineral dissolution or mineral diagenesis by oxidation or reduction or acid or base attack. Mineral dissolution or diagenesis may also be the result of complexation by a microbial metabolic product with that capacity. In some instances mineral attack may involve a combination of some of these reactions. 

Pernicious anaemia was a fatal disease first reported in 1880. It was not until 1926 that it was discovered that eating raw liver effected a remission. The active principle was later isolated and called vitamin B12 or cyanocobalamin. It was initially obtained from liver but during the 1960s it was noted that it could be obtained as a by-product of microbial metabolism (Table 25.2). Hydroxycobalamin is the form of choice for therapeutic use and can be derived either by chemical transformation of cyanocobalamin or directly as a fermentation product. 

Organic acids are typical products of microbial metabolism. All organic acids occur naturally in a variety of vegetable and animal substrates and can, therefore, be either naturally present as constituents of foods as a result of normal biochemical metabolic processes, direct addition as acid-ulants, hydrolysis, or bacterial growth, or can later be added directly or indirectly to the products (Gomis, 1992). 

Stromatolites and microbialites Stromatolites are "laminated lithified sedimentary growth structures that form by accretion, through the addition of new laminae away from the point or surface of accretion." They normally are made up of carbonate minerals and thought to have formed in a shallow water environment. Modern freshwater stromatolites are made up of algal and cyanobacte-rial filaments. In the marine environment they form microbial mats and columns. These comparisons led many scientists to believe that stromatolites found in the ancient record are biogenic in origin and that they are in fact microbialites. That is, they are sedimentary structures in which minerals are precipitated as either a by-product of microbial metabolisms or as a by-product of microbial decay. 

For the foreseeable future, important new drug discoveries will be derived from products of microbial metabolism. If the full potentialities of this discovery source are to be realized, discovery processes will have to be refined and broadened in scope. These are some of the challenges and opportunities that I see for the decade ahead ... 

Oxide Reduction. Fe and Mn oxides can be solubilized as Fe " and Mn " under reducing conditions by both biogenic and abiogenic reactions (Krauskopf, 1957). Because Fe, Mn oxides may act as terminal electron acceptors for some microbial metabolic pathways or as oxidants of reduced products of microbial metabolism, the reduction of each of these oxides in surficial sediments is often depicted as a generalized metabolic reaction (Bostrom, 1967 Stumm and Morgan, 1970 Froelich et ai., 1979 Berner, 1980) ... 

The concentration of the partly stabilized products of microbial metabolism in the fine fraction of the soil coupled with the decreasing atmospheric COt S C value since industrialization means that old, refractory, clay-associated carbon has a higher S C value than coarser particulate carbon (Kracht and Bird, in review). In tropical savannas, this trend of increasing S" C values with decreasing particle size is augmented by the preferential accumulation of C4-derived carbon in the fine-particle-size fractions (Bird and Pousai, 1997). 

Small amounts of DDE have been reported in some studies (Table II). The quantity rarely exceeded 5% of the recovered products. In the more common case the amount of DDE recovered did not exceed the amount in the uninoculated controls. The occurrence of DDE as a product shows no consistent relationship to organisms or conditions studied. DDE can be formed easily by the chemical dehydrochlorination of DDT. Therefore, it is reasonable to conclude that DDE is not a normal product of microbial metabolism. The pH of the media may be a factor affecting the formation of DDE. The information given in most of the studies is not suflBcient to determine if this could be the case. 

The formation of phosphine as a product of microbial metabolism is still enigmatic and cannot be associated so far with any defined microbial culture. Phosphine cannot be formed from phosphate by microbial activities to any significant amounts, but traces of phosphine may be formed through metabolic side reactions that have not been understood yet. One of the key sources of... 

Chemical/Physical. Emits toxic fiimes of nitrogen oxides and chlorine when heated to decomposition (Sax and Lewis, 1987). Hydrolyzes under alkaline conditions forming A-isopropylaniline (Sittig, 1985) which is also a product of microbial metabolism (Novick... 

The interest in the electrochemistry associated with microbial metabolism came about as a result of observations made by Yudkin (6) related to the potentials developed by these systems. He came to the conclusion that the observed potentials were strictly fortuitous and they were not directly related to the activity of the bacteria. Rather, they represented the potentials developed by the secretion products of microbial metabolism. 

An important product of microbial metabolism and biodegradation is biomass or new cell material. In heterotrophic microorganisms, new cell... 

The biofiltration process under recirculation conditions does not require additional equipment. The only need is to get a developed nontoxic porous surface in the filter bed and to saturate treated water with the oxygen of air to create required living conditions for aerobic microorganisms. But in any case, to maintain this fouling at acceptable levels, one need to effectively remove the products of microbial metabolism from the treated water. 

The second advantage is the use of positive feedbacks that are arisen in the system at the recirculation mode of action due to saturation of filtered water with oxygen of air and effective removal of products of microbial metabolism, as described in Sections 8.5 and 8.6. The scheme of combined filtration-flotation device that operates continuously, under recirculating conditions (rotating wheel), is shown in Figure 8.14. In this device, the processes of filtration, bioflltration, bubble aeration (exchange absorption), and bubble-film extraction are realized in a common reaction space, separated by the unit case 1. The centrifugal pump 2 is used to ensure the circulation of treated... 

But the distinguished feature of the use of granular filter in conjunction with fiotator (bubble-fihn extractor) under recirculation conditions is the fact that the water is enriched with oxygen of air and then is fed continuously through the porous space of the filter material. And at the same time, the surface-active products of microbial metabolism are removed from that water flow due to the bubble-fihn extraction. 

All these natural products are known as secondary metabolites ( idiolites ). They are low molecular weight products of microbial metabolism (such as antibiotics, pheromones, sex hormones, etc.) that differ from primary metabolites (amino acids, vitamins, purines, pyrimidines, etc.) in that they are not involved in growth processes but rather in mechanisms of survival in nature. 

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