Transformation microbial

Microbial synthesis as a process is not catalytic. The excretion of the product into the fermentation broth is accompanied by, if not dependent on, the growth of the micro-organism, and, strictly, if the organism is changing during the process it cannot be a catalyst. In microbial syntheses many stages are 

Occasionally the synthesis of a microbial product, for example that of ethanol from glucose, is catalysed by non-viable cells (section 6.2.1.1). Then the process is properly catalytic because the Saccharomyces cerevisiae cells do not change, for a time at least. However there are some industrially important reactions in which micro-organisms are first grown to a high biomass and are then added to a substrate which is almost quantitatively converted to a product. These are effectively catalytic processes in which one or a few enzymes in the organism transform an added substrate into a useful product. These transformations are divorced from cell growth, in contrast to syntheses such as those in which carbohydrates are converted into citric acid or complex feedstocks into secondary metabolites. 

The division between the non-catalytic microbial syntheses and the catalytic microbial transformation is perhaps not very sharp. The oxidation of ethanol to acetic acid in the manufacture of vinegar by the traditional microbial route uses a permanent culture of bacteria growing on wooden slats. The bacteria oxidize the ethanol in the wine as it flows over the slats, and, at the same time they draw sufficient nutrients from the wine to maintain a population which is both constant and healthy. Individual organisms divide and die, but the overall bacterial culture is unchanged, and is catalytic in its action. Here, in a real sense, the distinction between a catalytic and a non-catalytic process depends on the scale on which the process is described. 

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Kieslich, K. 1976, Microbial Transformations of Non-Steroid Cyclic Compounds, Thieme Stuttgart Kim, B. M. Sharpless, K. B. 1990, Tetrahedron Lett. 1990, 3003... 

L. Y. Young and C. E. CemigUa, eds.. Microbial Transformation and Degradation of Toxic Organic Chemicals, WUey-Liss, New York, 1995. 

Plasteins ate formed from soy protein hydrolysates with a variety of microbial proteases (149). Preferred conditions for hydrolysis and synthesis ate obtained with an enzyme-to-substrate ratio of 1 100, and a temperature of 37°C for 24—72 h. A substrate concentration of 30 wt %, 80% hydrolyzed, gives an 80% net yield of plastein from the synthesis reaction. However, these results ate based on a 1% protein solution used in the hydrolysis step this would be too low for an economical process (see Microbial transformations). 

Fig. 2. Oxidation and reduction reactions using microbial transformation for steroid synthesis.

Pesticides are susceptible to a variety of transformations in the environment, including both chemical degradation and microbial metaboHsm. Microbial transformations are catalyzed exclusively by enzymes, whereas chemical transformations are mediated by a variety of organic and inorganic compounds. Many pesticide transformations can occur either chemically or biologically. Consequentiy, most pesticide dissipation studies include sterile treatments to... 

Processing Raw Materials. Along with the aforementioned chemical methods of processing steroid raw materials, microbial transformations have been and are used in a number of commercial degradation processes. The microbial degradation of the C17 side chain of the two most common sterols, cholesterol (2) and P-sitosterol (41), is a principal commercial method for the preparation of starting materials in Japan and the... 

Fig. 14. Commercialized processes for the microbial transformation of readily available sterols to useful synthetic intermediates.

A third advancement in microbial biotechnology of steroid production was the abiUty to introduce a 16a-hydroxyl group microbiologicaHy (163). Modifications of the liP-hydroxylation, 16a-hydroxylation 1,2-dehydrogenation microbial processes are used for the synthesis of hydrocortisone, prednisolone, triamcinolone, and other steroid pharmaceuticals. A few microbial transformations that have been used to manufacture steroids are Hsted in Table 1 (164). 

Table 1. Commercial Microbial Transformations Used To Produce Advanced Intermediates or Finished Products ...

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