Molecular Analysis and Improvement of Protein Production by Aspergillus oryzae Grown on Solid Substrates

Aspergillus oryzae grown in submerged and solid state fermentations revealed a number of differences in molecular and physiological aspects that are correlated with the different growth conditions. First, the aerial hyphae that occur only in solid state fermentation are mainly responsible for oxygen uptake. Second, solid state fermentation is characterised by gradients in temperature, water activity and nutrient concentration, and inside the hyphae different polyols are accumulating. Third, pellet growth in submerged and mycelial growth in solid state fermentations show different gene expression and protein secretion patterns. With this integrated approach we aim to expand our basic knowledge of mechanisms of growth of filamentous fungi on solid substrates and to exploit the biotechnological applications. Introduction Solid state fermentations (SSF) are applied in many traditional food fermentation processes and offer possibilities for improved production of novel as well as existing food products and ingredients (Pandey et al. 2000). In recent developments, SSF is used to produce high yield quantities of pure enzymes. In SSF these enzymes, are much more efficiently produced compared to submerged fermentations (smF) (Pandey et al. 1999, Machida 2002, Holker et al. 2004). Filamentous fungi play a key role in SSF for their hyphal development allows them to effectively colonise and penetrate the solid substrate (Pandey et al. 2000, Machida 2002). As a consequence of hyphal growth the fungus is confronted with gradients in concentration of substrates and enzymes, the presence of a substrate-air interface and gradients in water and temperature (Hata et al. 1998). Water is frequently a limiting factor for fungal growth in SSF and heat removal is one of the