Organic polymers, microbial

Organic polymers. Many of the thickening and suspending agents used in pharmaceutical formulations are subject to microbial depolymerization by specific classes of extracellular enzymes, yielding nutritive fragments and monomers. Examples of... 

An NIR method has been developed for measuring the hardwood content of bleached hardwood and the lignin content of vmbleached hardwood pulp. Work has also been carried out using NIR reflectance spectra of hardwoods to discriminate between the different species. Using a Fourier transform NIR instrument carbonate measurements have been made on soil samples. NIR analysis of forest humus samples has provided satisfactory calibrations for microbial basal respiration, based on the organic polymer content of the humans. NIR analysis of the lake sediments for pH has been used to construct the lake water history. 

When bacteria attach themselves onto metallic surfaces, they start to form a thin film known as biofilm [30] that consists of cells immobilised at a substratum, frequently embedded in an organic polymer matrix of microbial origin [33]. Biofilms are believed to typically contain about 95% water [34]. Figure 4.4 shows the steps of biofilm formation. 

G. Biopolymere E biopolym res The term b. is used for all polymers occuring in living organisms, such as - proteins, - polysaccharides, nucleic acids or mostly biotechnologi-cally produced polymers (- microbial gums, - sucrose, biotransformation to biopolymers), that have structures and/or properties similar to natural polymers (- dextrans, - levans, - polyhydroxybutyric acid, - polylactic acid, - pullulan, -+xanthan). 

Since lignins are polymers of phenolics and are major plant constituents with resistance to microbial decomposition, they are the primary source of phenolic units for humic acid synthesis (178, 179). Once transformed, these humic acids become further resistant to microbial attack and can become bound to soils (180) form interactions with other high molecular weight phenolic compounds (ex. lignins, fulvic acids) and with clays (181) and influence the biodegradation of other organic substrates in soils (182, 183). 

Work on the fermentation of microbial polysaccharides started in the mid 1970 s, with the aim of producing improved polymers. Many thousands of samples were screened for microorganisms which produced viscous polymers. Out of over 2000 such slime producing organisms isolated, only one, identified as a Pseudomonas species, now NCIB 11592, seemed to produce a polymer with interesting new properties. 

As an example, bulk modification by the organic reaction of unsaturated PHA with sodium permanganate resulted in the incorporation of dihydroxyl or carboxyl functional groups [106]. Due to the steric hindrance of the isotactic pendant chains, complete conversion could not be obtained. However, the solubility of the modified polymers was altered in such a way that they were now completely soluble in acetone/water and water/bicarbonate mixtures, respectively [106]. Solubility can play an important role in certain applications, for instance in hydrogels. Considering the biosynthetic pathways, the dihydroxyl or carboxyl functional groups are very difficult to incorporate by microbial synthesis and therefore organic chemistry actually has an added value to biochemistry. 

Highly halogenated organic compounds such as polychlorinated biphenyls and perchloroethylene appear to be too highly oxidised and low in energy content to serve as sources of electrons and energy for microbial metabolism. Bacteria are more likely to use them as electron acceptors in cell-membrane-based respiration processes [154]. The environmental fate of halogenated polymers such as polyvinylchloride or Teflon may depend on the question of whether it will be appropriate to sustain de-halorespiration processes. 

Microbial resistance to established organic antibiotics is a potentially serious problem and provides an impetus for the development of novel antimicrobial metal compounds. The potency of Ag(I) ions is well known—but how does Ag(I) kill a bacterium Much current attention is focused on Bi(III) on account of its ability to kill Helicobacter pylori, an organism which prevents ulcers from healing. Bis-muth(III) chemistry has many unusual features a variable coordination number, strong bonds to alkoxide ligands, the stereochemical role of its 6s2 lone pair, facile formation of polymers, and dual hard and soft character. 

Polymerization, or conjugation, is the process in which toxic organic molecules undergo microbially mediated transformation by oxidative coupling reactions. In this case, a contaminant or its intermediate product(s) combines with itself or other organic molecules (e.g., xenobiotic residues, naturally occurring compounds) to form larger molecular polymers that can be incorporated in subsurface humic substances. 

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