Fermentative production substrate selection

During the method development in paper II we desired to perform quantification of both the fermentation product and the substrate. Both the external and the internal standard method were evaluated, respectively. The internal standard method was chosen since it resulted in a higher precision. Initially, structurally related compounds were tested as I S. in the quantitative part described in paper II, according to the above I.S.-protocol for bioana-lytical approaches. However for biotechnological analysis no recommendations exist for the selection of internal standard. Thus in paper II an investigation was performed to see if the I.S.-protocol for bioanalytical methods could be applied also for biotechnological analysis. 

To see whether the unusual lack of substrate selectivity of the AT domain of module 4 could be mimicked in other modules of the epo PKS, AT4 was used to replace the native AT domain in module 3 in an M xanthus host that contained the epothilone biosynthesis gene cluster. The exchange of the DNA encoding AT3 for the DNA segment encoding AT4 was accomplished employing a two-step recombination process (Fig. 3). The resulting strain was fermented and the epothilone products were isolated and analyzed. As found in the parent strain... 

Industrially, fermentation is carried out using carefully selected microorgauisms appropriate to the substrate under precisely specified conditions. There are various fermentation products including alcohol, glycerol, butyl alcohol, acetone, as well as lactic, acetic, citric, gluconic, and glutamic acids, many of which are also important in food flavorings [35]. 

Abstract Biorefineries focus on fermentative production of butanol, isobutanol and isobutene. This paper encompasses the entire development process, such as strain and substrate selection and optimisation, fermentation modes and purification techniques. Special attention is dedicated to various natural or synthetic metabolic pathways for obtaining these compounds. 

The production of ethanol by yeasts is characterized by high selectivity and low formation of byproducts. The main variables describing the fermentation process are substrate (sugar) concentration, tolerance to ethanol, temperature, pH and oxygen. These effects are briefly reviewed. 

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