Engineering D-galacturonic acid catabolism in Aspergillus niger

Citrus processing waste is a leftover from the citrus processing industry and is available in large amounts. Typically the citrus processing waste is dried to produce animal feed, but sometimes it is just dumped. Its main component is the peel, which is mostly consisted of pectin with D-galacturonic acid as main monomer. Another important source for pectin is sugar beet pulp. Sugar beet pulp is used as cattle feed however the required drying of the pulp is energy requiring so that alternative uses of this raw material are in demand.

 Aspergillus niger is a mould that efficiently produces pectinases for the hydrolysis of pectin and uses the resulting D-galacturonic acid and most of the other components of citrus peel or sugar beet pulp for growth. We engineered A. niger strains to convert D-galacturonic acid to useful compounds. Examples are meso-galactaric acid (mucic acid) L-galactonic acid and L-ascorbic acid.