Materials microbial systems

Although dynamic responses of microbial systems are poorly understood, models with some basic features and some empirical features have been found to correlate with actual data fairly well. Real fermentations take days to run, but many variables can be tried in a few minutes using computer simulation. Optimization of fermentation with models and reaf-time dynamic control is in its early infancy however, bases for such work are advancing steadily. The foundations for all such studies are accurate material Balances. 

When a more detailed analysis of microbial systems is undertaken, the limitations of unstructured models become increasingly apparent. The most common area of failure is that where the growth is not exponential as, for example, during the so-called lag phase of a batch culture. Mathematically, the analysis is similar to that of the interaction of predator and prey, involving a material balance for each component being considered. 

Pyrolysis MS (PyMS) has been applied to the characterisation and identification of a variety of microbial systems over a number of years (for reviews see [25-27]) and, because of its high discriminatory ability [28-30], presents a powerful fingerprinting technique applicable to any organic material. Whilst the pyrolysis mass spectra of complex organic mixtures may be expressed in the simplest terms as sub-patterns of spectra describing the pure components of the mixtures and their relative concentrations [24], this may not always be true because during pyrolysis intermolecular reactions can take place in the pyrolysate [31-33]. This leads to a lack of superposition of the spectral components and to a possible dependence of the mass spectrum on sample size [31]. However, suitable numerical methods (or chemometrics) can still be employed to measure the concentrations of biochemical components from pyrolysis mass spectra of complex mixtures. 

Finally, the term carbohydrate polymers can be stretched to include natural polyalkanoates based on hydroxy acids of carbohydrate origin. The chemistry and properties of poly-6-hydroxybutyrate (PHB) make it a biomass transducer. A material which is intermediate between carbohydrates and fats, PHB is readily derived from microbial systems. Its potential as a natural thermoplastic, a biomedical implant and a source of chemicals from biomass is described. 

Weber, J., Kedro, M. (Eds.) (1996a), COST 511 -Interactions of microbial systems with industrial materials, Helsinki Workshop 1995. Luxembourg Office for official publications of the European Communities. 

Microbial systems present a unique potential for biological monitoring of toxic constituents in foods and other materials, as well as the environment. As indicators of toxicity, they are comprehensive, rapid and reliable. They may also provide insight into the nature of the toxicity in question, for example mutagenic and genetic activities. 

Therapeutics. Therapeutic materials represent a class of polypeptides that are a low volume, high value product. The production system need not be very efficient but the quaHty of the recombinant protein has to be extremely pure (33,34). Thus high cost mammalian production systems can be tolerated. However, some of the therapeutic proteins such as insulin, human growth hormone, interleukins, interferon, and streptokinase are produced microbially. 

Reverse osmosis membrane separations are governed by the properties of the membrane used in the process. These properties depend on the chemical nature of the membrane material, which is almost always a polymer, as well as its physical stmcture. Properties for the ideal RO membrane include low cost, resistance to chemical and microbial attack, mechanical and stmctural stabiHty over long operating periods and wide temperature ranges, and the desired separation characteristics for each particular system. However, few membranes satisfy all these criteria and so compromises must be made to select the best RO membrane available for each appHcation. Excellent discussions of RO membrane materials, preparation methods, and stmctures are available (8,13,16-21). 

Biopolymers are the naturally occurring macromolecular materials that are the components of all living systems. There are three principal categories of biopolymers, each of which is the topic of a separate article in the Eniyclopedia proteins (qv) nucleic acids (qv) and polysaccharides (see Carbohydrates Microbial polysaccharides). Biopolymers are formed through condensation of monomeric units ie, the corresponding monomers are amino acids (qv), nucleotides, and monosaccharides, for proteins, nucleic acids, and polysaccharides, respectively. The term biopolymers is also used to describe synthetic polymers prepared from the same or similar monomer units as are the natural molecules. 

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