ABSTRACT
Trichoderma reesei has a long history in industrial enzyme production, and there has been considerable interest in developing T. reesei as a more versatile host for production of its own proteins for various industrial applications (see Chapters 1316). Many of the features that make Trichoderma an excellent industrial enzyme producer are also beneficial in foreign protein production. The advantages of prokaryotic and eukaryotic production hosts can be considered to a large extent to be combined in filamentous fungi, Trichoderma and Aspergillus species being the ones mainly used so far. Enzymes produced by T. reesei have also been approved for food and feed applications, and no toxin production has been observed in T. reesei (see Volume 1, Chapter 8)
Being a microbe, T. reesei is easy and inexpensive to cultivate. It is currently grown in fermenters up to 230 m3, which shows that its fermenter technical properties are good and it is not susceptible to contamination. Unlike mammalian or insect cell lines, there is no requirement for expensive nutrient additions or special propagation; Trichoderma can grow on simple and inexpensive media and on materials such as whey and various plant wastes. Being a eukaryote, it has the advantage of possessing a secretory machinery with protein modifications typical of eukaryotes. Compared with the yeast Saccharomyces cerevisiae, filamentous fungi generally secrete higher levels of protein and with shorter high mannose type Nglycosylation (Maras et al., 1997; Salovuori et al., 1987; see Volume 1, Chapter 6). There is, for instance, a clear difference in glycosylation of T. reesei cellulases (Penttila et al., 1987, 1988) and a mannanase (StAlbrand et al., 1995) when expressed in S. cerevisiae compared with the native host; production in yeast gives the enzymes a higher molecular weight in SDS-PAGE and a greater heterogeneity. The disadvantages of Trichoderma, and other filamentous fungi, are the slower growth rate and more time-consuming and tedious genetic engineering techniques. Thus it may not always be competitive with, for instance, E. coli in production of high-value products. The production economy of E. coli expression systems is often feasible even when the proteins are produced in small scale and even if they might end up in
intracellular inclusion bodies from which they need to be denatured and renatured to obtain the active, correctly folded product. However, Trichoderma should have a special advantage in production of foreign proteins that are needed in large amounts.
