Filamentous fungi are widely used for enzyme and metabolite production for a wide variety of uses – for example food, feed, textile, paper and pulp, fuels and chemicals, detergents - due to the development of extremely productive strains and production processes. With the advent of molecular genetic tools, in the last two decades very successful strain improvement programs for protein and secondary metabolites have been developed. However, for primary metabolites, such as organic acids, which are still by volume the largest fungal bioproducts, real breakthroughs have not been made in recent years. In our research we have addressed the production of one of the commercially interesting building-block organic acids, itaconic acid. To unambiguously identify the itaconic acid biosynthetic pathway several parallel approaches were taken using Aspergillus terreus as parental host strain. Using a combination of controlled fermentation design, reversed genetics and transcriptomics approaches the pathway specific cis-aconitate decarboxylase (CAD) encoding gene was identified. This gene encodes the enzyme required to make itaconic acid from general TCA cycle intermediates. In addition to this gene several other target genes for improvement of itaconic acid production were identified.
A highly relevant issue for the bioproduction of bulk-products like organic acids is also the cost of production. As production costs rely for 30-60% on the cost of feedstock, in frame with our itaconic acid project we also evaluated performance and feedstock versatility of several potential microbial production hosts on lignocellulosic substrates. From this analysis Aspergillus niger was selected as one of the preferred hosts.