THERMOPHILES AND FERMENTATION TECHNOLOGY

Thermophilic microorganisms have been of great scientific interest for several decades, principally in regard to their biotechnological pote ntial and also of the thermostable enzymes they produce. Optimal culti vation techniques for these organisms are required, therefore, not onl y for basic study but also for evaluation of their thermostable microb ial products. Operating a fermentor at elevated temperatures may be ad vantageous in terms of increased solubility of substrates, improved ma ss transfer due to decreased viscosity, and increased diffusion rates. However, the cultivation of thermophiles also has many associated pro blems. A high cultivation temperature can give unexpected problems aff ecting the choice of reactor design and construction materials, and wi th the heating and cooling of the fermenter. Other problems may be cau sed by the low solubility of gases and the instability of substrates a nd other reagents used. Furthermore, high productivity requires high c ell densities to be achieved and in many cases thermophiles are charac terised by low growth rates, low growth yields and susceptibility to s ubstrate and product inhibition at low concentrations. Different ways to circumvent some of these problems, such as using gas-lift fermenter s, dialysis fermenters or cultivation with cell recycling are discusse d. (C) 1997 Elsevier Science Inc.