Approaches to increase the economy of the PHB production

The ability to synthesize PHB is widespread in prokaryotes. It is independent of the carbon source and the type of nutrition. PHB has several interesting properties. Although it is commercially attractive, PHB does not have a real market. The main reason for this is the price of the product, which is considerably caused by the costs of the raw materials, i.e. substrates, and the efficiency of the whole process. The experimentally obtained yield coefficients are low in comparison with the theoretical ones. Therefore, scientists and engineers are challenged to search for approaches to increase the efficiency and finally the productivity of the whole process. Mixing substrates according to the auxiliary substrate concept were shown to be suited. By using a mixture of acetate and glucose, a carbon conversion efficiency of about 82% was reached, and by adding formate to methanol, the efficiency increased from 22.3 to 36.7%. Continuous synthesis of PHB in a one-stage process is another approach, especially to increase the productivity. It becomes possible through growth-coupling. An example for growth-associated production was presented, and the preconditions were discussed. (C) 1998 Elsevier Science Limited. All rights reserved.