Precursor feed

We may describe the production of diverse penicillins using this strategy as directed biosynthesis using precursor feeding. We have listed some examples of penicillins in Table 6.2. 

Although a range of penicillins could be produced by directed biosynthesis using precursor feeding, this approach is limited by the toxicity of the precursors, the ability of the penicillin producing cells to take up the precursor and by the capability of the acyltransferase to transfer the acyl groups onto the 6-aminopenicillanic add moiety. 

In this chapter, by using the examples of -lactams we have briefly examined how microbial cultures may be used to produce sufficient antibiotics to meet market demands. We have also explained how enzymes (or cells) may be used to biotransform, and thereby diversify, antibiotics. By outlining the history of penicillin production, we explained how analysis and manipulation of culture regimes may be used to enhance the yields of antibiotics (and other secondary products). These studies led to die concept of directed biosynthesis by precursor feeding. 

Assume that the cost price of L-phenylalanine produced by direct fermentation is 285 kg 1 (100 tonnes per annum capacity). What percentage reduction in substrate costs are required for 1) precursor feeding and 2) biotransformation to be competitive on a cost price basis with direct fermentation ... 

It follows that for precursor feeding to be competitive, substrate costs would have to be reduced by 35.05 - 2830 = 635 kg 1. So, the percentage reduction in substrate... 

Manufacturing processes for cephalosporin C and benzylpenicilhn are broadly similar. In common with mai other antibiotic fermentations, no specific precursor feed is necessary for cephalosporin C. There is sufficient acetyl group substrate for the terminal acetyltransferase reaction available fiom the organism s metabolic pool. 

Figure 6.25. Deposition temperature versus (a) elemental composition, (b) crystalline orientation, and (c) deposition rate for CuInS2 films with precursor feed rate of 1.6 g/h. In plot (a), the accuracy limit of 5% per element resulted in an anomalous overall percent composition for the In-rich, S-poor deposited material.

HPLC systems were helpful in monitoring cephalosporin production [174] and p-cresol degradation [392]. Other HPLC systems have been reported to serve for the control of penicillin production, namely via the precursor feed [62, 288],3-chlorobenzoate conversion [375] or naphthalenesulfonic acid reduction [279], as well as amino acids [444,445]. HPLC is also found to be useful when linked to biochemical assays [316]. Mailinger et al. [262] have discussed many important aspects of on-line HPLC systems. 

Funk, C. and Brodelius, P.E. (1 990b) Phenylpropanoid metabolism in suspension cultures of Vanilla planifolia Andr. II. Effects of precursor feeding and metabolic inhibitors. Plant Physiology 94, 95-101. 

MORGAN, J.A., SHANKS, J.V., Determination of metabolic rate limitations by precursor feeding in Catharanthus roseus hairy root cultures., J Biotechnol., 2000,79,137-145. 

Fig. 6.9 Biosynthetic subunits of saxitoxin as determined by various precursor-feeding studies [104].

Van Uden, W., Pras, N. and Malingre, T.M. (1990) On the improvement of the podophyllotoxin production by phenylpropanoid precursor feeding to cell cultures of Podophyllum hexandrum Royle. Plant Cell Tiss. Org. Cult., 23, 217-24. 

Cost price of L-phenylalanine by precursor feeding is 35.05 kg" and substrate costs are 18.05 kg . 

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