ABSTRACT
INTRODUCTION Fungi play a crucial role in nature by degrading organic material. They secrete a wide variety and large amount of enzymes that cleave complex substrates into small products that can be taken up by the cell. The filamentous mode of growth of mycelial fungi contributes to the efficacy of degradation. By growing at their tips, hyphae can penetrate the substrate. Moreover, the hypha exposes a large surface that contacts the substrate, which may thereby facilitate uptake of nutrients. Yeast-like fungi do not effectively penetrate organic material. Their mode of growth only allows superficial colonization. The capacity of fungi to secrete proteins is used by the industry to produce large amounts of homologous and heterologous proteins. Fungal enzymes are applied in the food and feed industry as well as in other industrial sectors, such as the paper and pulp industry. Fungi are also interesting hosts for producing therapeutic proteins of animal or human origin, especially since the first steps of glycosylation of proteins in fungi and animals are similar (Gerngross, 2004). Genetic engineering of the yeast Pichia pastoris is now one step away from completion to produce proteins with a glycosylation pattern identical to that found in humans (Hamilton et al., 2003; Bobrowicz et al., 2004).
