Two-phase fermentation for itaconic acid production by Aspergillus terreus NRRL1960 and its enzymatic and transcriptomic analyses

Abstract

Typical itaconic acid fermentation usually suffers from low product concentration and yield due to a failure to balance the metabolic flux towards itaconic acid production. In this study, two approaches were employed to better understand the root causes mentioned above and to enhance itaconic acid production. In the first approach, ATP regeneration was manipulated during itaconic acid production by using L-aspartate. The presence of 10 mM L-aspartate in the production medium repressed the pyruvate carboxylase activity. This resulted in the limited malate flux in the cytosol and the large pool of pyruvate in the mitochondria. A. terreus stimulated the conversion of the large pool of cis-aconitate into itaconic acid via the antiporters. Successively, itaconic acid production yield and final concentration were improved from the control by 8.33 % and 60.32 %, respectively. In the second approach, the 2-phase fermentation process was employed. Itaconic acid was first observed when ammonium and phosphate became limited. Contrary to those claimed in 1-phase fermentation, by this technique, low DO level enhanced itaconic acid production because it promoted the correct morphology in the form of mycelial clumps. Also, low DO level initiated the uncouple glycolysis and oxidative phosphorylation, which stimulated substrate level phosphorylation for ATP regeneration. The available pyruvate was then reacted with coenzyme A by pyruvate-formate lyase, resulting in formate and acetyl CoA which induced the metabolite flux to produce itaconic acid.