Metabolic requirements, microbial

The terminal amino acids are under strict metabolic control. Some act as feedback inhibitors or repressors. Their synthesis is in equilibrium with metabolic requirement. This equilibrium position prevents their accumulation and hence the yield of these compounds is low. By changing the growth requirement (environmental stimulus) or by genetic manipulation, mutants could be found with limited or removed feedback inhibitors and repressors, e.g. auxotrophic and regulatory mutants 49). This needed a better understanding of biosynthesis and regulation of amino acid production. By selection of these mutants it became possible to alter microbial metabolism which led to the accumulation of the desired amino acids. 

The ultimate source of cobalamin for mammalian metabolism is microbial synthesis. The cobalamins from the microbial flora in the gastrointestinal system of herbivorous animals are absorbed by the host and stored by their tissues. From there cobalamin is passed on to other animals in the food chain. A normal daily adult human diet contains about 5 p,g of cobalamin, which is about three times the minimum daily requirement to maintain cobalamin homeostasis. The total amount of cobalamin in the human body is 3 mg. 

Application of modem analytical procedures and physical methods for structure determination. In studies of microbial metabolism, the advantages resulting from the requirement for only extremely small quantities of material needed for gas- and liquid-chromatographic quantification, coupled to mass spectrometric identification, can hardly be overestimated. 

All soil metabolic proce.sses are driven by enzymes. The main sources of enzymes in soil are roots, animals, and microorganisms the last are considered to be the most important (49). Once enzymes are produced and excreted from microbial cells or from root cells, they face harsh conditions most may be rapidly decomposed by organisms (50), part may be adsorbed onto soil organomineral colloids and possibly protected against microbial degradation (51), and a minor portion may stand active in soil solution (52). The fraction of extracellular enzyme activity of soil, which is not denaturated and/or inactivated through interactions with soil fabric (51), is called naturally stabilized or immobilized. Moreover, it has been hypothesized that immobilized enzymes have a peculiar behavior, for they might not require cofactors for their catalysis. 

Bioremediation systems in operation today rely on microorganisms indigenous to contaminated sites. The two main approaches, based on the actions of native microbial communities, are biostimulation and intrinsic bioremediation. In biostimulation, the activity of native microbes is encouraged, creating (in situ or ex situ) the optimum environmental conditions and supplying nutrients and other chemicals essential for their metabolism. The vast majority of bioremediation projects are based on this biostimulation approach. Intrinsic bioremediation is a remedial option that can be applied when there is strong evidence that biodegradation will occur naturally over time without any external stimulation i.e., a capable microbial community exists at the site, the required nutrients are available, and the environmental conditions are favorable. An additional prerequisite is that the naturally... 

Regardless of whether the microbes are native or artificially introduced into the soil, it is important to understand the mechanisms by which they degrade or detoxify hazardous pollutants through their metabolic activity. Understanding these mechanisms is essential for the proper design of bioremediation systems that provide the optimum conditions and the required nutritional supplements for the specific microbial process. 

Bioremediation also has its limitations. Some chemicals are not amenable to biodegradation, for instance, heavy metals, radionuclides, and some chlorinated compounds. In some cases, the microbial metabolism of the contaminants may produce toxic metabolites. Bioremediation is a scientifically intensive procedure that must be tailored to site-specific conditions, and usually requires treatability studies to be conducted on a small scale before the actual cleanup of a site.13 The treatability procedure is important, as it establishes the extent of degradation and evaluates the potential use of a selected microorganism for bioremediation. A precise estimate on vessel size or area involved, speed of reaction, and economics can therefore be determined at the laboratory stage. 

The primary metabolism of an organic compound uses a substrate as a source of carbon and energy. For the microorganism, this substrate serves as an electron donor, which results in the growth of the microbial cell. The application of co-metabolism for bioremediation of a xenobiotic is necessary because the compound cannot serve as a source of carbon and energy due to the nature of the molecular structure, which does not induce the required catabolic enzymes. Co-metabolism has been defined as the metabolism of a compound that does not serve as a source of carbon and energy or as an essential nutrient, and can be achieved only in the presence of a primary (enzyme-inducing) substrate. 

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