Filamentous fungi as cell factories for protein production: genomics and molecular genetic screening approaches for development of improved fungal production host strains

Filamentous fungi have been used as sources of metabolites and enzymes for centuries. In the last few decades molecular genetic tools have enabled us to improve metabolite and protein production in these organisms. The use of gene-transfer systems and the development of efficient and versatile fungal expression and secretion vectors has allowed the generation of protein overproducing host strains. Recent development of improved gene modification approaches has allowed further dedicated strain improvement.

For protein production further improvements of the first generation strains have been obtained by rational strain design in two directions; (i) the development of protease deficient host strains obtained by classical or molecular approaches, (ii) the development of host strains with improved fermentation characteristics related to culture viscosity and oxygen transfer. In several cases these types of strain design in combination with fermentation process development has resulted in achieving commercially relevant quantities of protein.

To gain more insight in complex processes such as protein and metabolite production and fermentation performance, we have used a combination of genomics / transcriptomics and novel molecular genetic screening approaches for developing improved filamentous fungal production systems. Examples of these approaches will be presented with a focus on novel protease deficient mutant strains.