Biocatalysts, sources

Biocatalyst Source Material and reactor configuration Application... 

When compared to traditional chemical synthesis, processes based on biocatalysts are generally less reliable. This is due, in part, to the fact that biological systems are inherently complex. In bioprocesses involving whole cells, it is essential to use the same strain from the same culture collection to minimise problems of reproducibility. If cell free enzymes are used the reliability can depend on the purity of the enzyme preparation, for example iso-enzyme composition or the presence of other proteins. It is, therefore, important to consider the commercial source of the enzyme and the precise specifications of the biocatalyst employed. 

Enzyme-mediated chiral sulfoxidation has been reviewed comprehensively in historical context [188-191]. The biotransformation can be mediated by cytochrome P-450 and flavin-dependent MOs, peroxidases, and haloperoxidases. Owing to limited stability and troublesome protein isolation, a majority of biotransformations were reported using whole-cells or crude preparations. In particular, fungi have been identified as valuable sources of such biocatalysts and the catalytic entities have not been fully identified in all cases. 

In some cases it is more attractive to use whole microbial cells, rather than isolated enzymes, as biocatalysts. This is the case in many oxidative biotransformations where cofactor regeneration is required and/or the enzyme has low stability outside the cell. By performing the reaction as a fermentation, i.e. with growing microbial cells, the cofactor is continuously regenerated from the energy source, e.g. glucose. 

Compared with isolated enzymes, application of whole cells as biocatalysts is usually more economical since there is no protein purification process involved. Whole cells can be used directly in chemical processes, thereby greatly minimizing formulation costs. Whole cells are cheap to produce and no prior knowledge of genetic details is required. Microorganisms have adapted to the natural environment and produce both simple and complex metabolic products from their nutrient sources through complex, integrated pathways. 

Biocatalyst, final C source, mg/L S source, (mg/L) b C/S ratio, Final DS Volumetric Volumetric Reference... 

For R. erythropolis KA2-5-1, DBT and 2-aminoethanesulfonicacid were compared as the sole sulfur source for growth with ethanol as carbon source. The 2-aminoethanesulfonicacid was found to be a better sulfur source (for growth) than DBT [189], A summary of the various studies investigating biocatalyst production are given in Table 10. It is clear that a balance between the growth rate and the sulfur utilization rate is necessary to obtain an optimum biocatalyst. Preventing accumulation of sulfate is the key to optimum activity of the final biocatalyst preparation. Thus, a... 

Growth of the biocatalyst/microorganism in a fermentative process using suitable carbon and sulfur sources and other nutrients ... 

It was specifically stated that the proposed metabolic pathway, which suggest C—N bond cleaving and so, a N-specific mechanism, was found when PTA-806 was employed as the biocatalyst. However, when the quinoline-adapted microorganisms, initially isolated from the chemostats (the native P. ayucida), were tested, they were found to fully degrade quinoline, utilizing it as both, a carbon as well as a nitrogen source. 

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