Itaconic acid production from D-xylose by Aspergillus terreus
Itaconic acid (2-methylenesuccinic acid; IA) is a five-carbon dicarboxylic acid, frequently used as a building block chemical for the synthesis of plastics, coatings and resins. IA is commercially produced by large-scale submerged fermentations employing the filamentous Ascomycete fungus Aspergillus terreus and using molasses or hydrolized corn starch as primary carbon sources. The objective of this study was to test whether IA can be produced on D-xylose in concentrations and specific yields (Yp/s) similar to D-glucose by A. terreus.
Production of IA is the result of the metabolic overflow of primary metabolism. High (Yp/s>0.8) molar yields on D-glucose require high (>10%, w/v) concentrations of carbon, strong aeration and carefully set cultivation parameters, of which Mn(II) ion limitation is the most prominent. When D-glucose was replaced with D-xylose under identical fermentation conditions, the plot depicting specific IA yield vs. initial carbon concentration was notably different. Maximum IA yield was significantly reduced (Yp/s=0.55), but it was achieved at a relatively low (5%, w/v) initial D-xylose concentration. Any further increase above this level did not affect yield, which was, however, subject to severe Mn(II)-related regulation. Mn(II) ion concentrations as low as 5 ppb decreased IA yield on D-xylose by 15%. In contrast to the situation on D-glucose, IA yield did not drop below 0.3 on D-xylose even in the presence of 1000 ppb of Mn(II) ions. In conclusion, while it is possible to produce IA from D-xylose by A. terreus, the technology has to be improved considerably to be competitive with traditional glucose-based fermentations.
Research was supported by the EU and co-financed by the European Regional Development Fund under the project GINOP-2.3.2-15-2016-00008 and by the Hungarian Scientific Research Fund (NN116519) to LK.