(448d) Regulating Pyruvate Carboxylase in the Living Culture of Aspergillus Terreus NRRL1960 By L-Aspartate for Enhanced Itaconic Acid Production

Itaconic acid, also know as methylene succinic -acid (C₅H₆O₄), is an unsaturated 5-carbon dicarboxylic acid. It can be derived into many high value added chemicals or materials. To date, it is a potential building block that can be produced by fermentation using Aspergillus terreus. However, the low production yield from fermentation process rather limit the supply to the market. The lower production yield was claimed as the result of completing TCA cycle towards biomass synthesis with the sufficient phosphate and nitrogen sources. While under limiting phosphate and nitrogen, the glycolytic flux was somewhat shunted; thus lowering the flux in TCA cycle and consequently that towards itaconic acid production route. In this study, pyruvate carboxylase, one of the key responsible enzymes involved in itaconic acid production, was allosterically inhibited by L-aspartate. The presence of 10 mM L-aspartate in the production medium directly suppressed pyruvate carboxylase expression in the living A. terreus. By the repression, oxaloacetate in the cytosol was lowered. Subsequently, malic acid concentration was decrease in the cytosol resulting in the improved transport of malate and cis-aconitate, citrate isomer, towards the the malate/citrate antiporters  as the response of the living culture of A. terreus to complete TCA cycle. The transport of cis-aconitate via the antiporters induced citrate synthase and 6-phosphofructo-1-kinase activities in response to balance the fluxes of TCA intermediates. This eventually resulted in the improved itaconic acid production yield of 8.33% and final concentration of 60.32% compared to those obtained from the control fermentation with the shortened lag time to produce itaconic acid during the production phase.