Large scale fermentations

Sterile aqueous D-sorbitol solutions are fermented with y cetobacter subo >gichns in the presence of large amounts of air to complete the microbiological oxidation. The L-sorbose is isolated by crystallisation, filtration, and drying. Various methods for the fermentation of D-sorbitol have been reviewed (60). A.cetobacter suboyydans is the organism of choice as it gives L-sorbose in >90% yield (61). Large-scale fermentations can be carried out in either batch or continuous modes. In either case, stefihty is important to prevent contamination, with subsequent loss of product. 

After a strain improvement and development programme similar to, but more complicated than that of penicillin, the D-a-aminoadipyl side chain containing cephalosporin C was obtained by large scale fermentation. However, cephalosporin C could not be isolated as easily as penicillin G or V. Due to its amphoteric nature it is soluble at any pH in the fermentation broth. Several costly isolation procedures involving ion-exchange chromatography have been developed, as a result of which cephalosporin C is much more expensive than penicillin G. 

The initial approach to recombinant insulin production taken entailed inserting the nucleotide sequence coding for the insulin A- and B-chains into two different E. coli cells (both strain K12). These cells were then cultured separately in large-scale fermentation vessels, with subsequent chromatographic purification of the insulin chains produced. The A- and B-chains are then incubated together under appropriate oxidizing conditions in order to promote interchain disulfide bond formation, forming human insulin crb ... 

One of the most important developments in the history of large scale fermentations is the fed-batch process. Again, this derives from the work of Marvin Johnson at the University of Wisconsin during development of the penicillin fermentation over 50 years ago. Soltero and Johnson wrote Glucose, intermittently fed to fermentations, has given penicillin yields on synthetic medium equal to, or even better than, those obtained with lactose. Penicillin yields of twice those of lactose controls have been obtained when glucose or sucrose is continuously added to the fermentations . 

Well developed and large scale fermentation processes to produce several amino acids snch as lysine, had already been developed. This know-how was then used as a basis to develop very cost-effective L-phenylalanine fermentation processes. 

The supply of the recombinant enzymes is warranted and some enzymes can be obtained in large amounts (in the case of transketolase A more than a million units were gained from a large-scale fermentation) so that even minor, but nonetheless interesting, substrates can be converted. 

The development of hybridoma technology by Milstein and Kohler in 1975 revolutionized the antibody field and radically increased the purity and specificity of antibodies used in the clinic and for diagnostic tests in the laboratory. Hybridomas consist of antibody-forming cells fused to immortal plasmacytoma cells. Hybrid cells that are stable and produce the required antibody can be subcloned for mass culture for antibody production. Large-scale fermentation facilities are now used for this purpose in the pharmaceutical industry. 

Furthermore, since most large-scale fermentations are carried out in batch mode, the kinetic parameters determined by the chemostat study should be able to predict the growth in a batch fermenter. However, due to the significantly different environments of batch and continuous fermenters, the kinetic model developed from the CSTF runs may fail to predict the growth behavior of a batch fermenter. Nevertheless, the verification of a kinetic model and the evaluation of kinetic parameters by running chemostat is the most reliable method because of its constant medium environment. 

The fraction of cells carrying plasmid in the total population was shown to be a function of the number of generations of growth (Imanaka and Aiba, 1981). Therefore, as the size of the fermenter increases, the number of generations of growth increases, and the fraction of cell carrying plasmid and the product yield decrease. The problem of the plasmid instability is more serious if the large-scale fermenter is operated continuously. 

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