Metabolic engineering of Aspergillus niger for accelerated malic acid biosynthesis by improving NADPH availability

Abstract

Microbial production of L‐malic acid from renewable carbon sources has attracted extensive attention. The reduced cofactor NADPH plays a key role in biotransformation because it participates in both biosynthetic reactions and cellular stress responses. In this study, NADPH or its precursors nicotinamide and nicotinic acid were added to the fermentation medium of Aspergillus niger RG0095, which significantly increased the yield of malic acid by 11%. To further improve the titer and productivity of L‐malic acid, we increased the cytoplasmic NADPH levels of A. niger by upregulating the NAD kinases Utr1p and Yef1p. Biochemical analyses demonstrated that overexpression of Utr1p and Yef1p reduced oxidative stress, while also providing more NADPH to catalyze the conversion of glucose into malic acid. Notably, the strain overexpressing Utr1p reached a malate titer of 110.72 ± 1.91 g L−1 after 108 h, corresponding to a productivity of 1.03 ± 0.02 g L−1 h−1. Thus, the titer and productivity of malate were increased by 24.5% and 44.7%, respectively. The strategies developed in this study may also be useful for the metabolic engineering of fungi to produce other industrially relevant bulk chemicals.

Synthetic biology for Monascus: From strain breeding to industrial production

“…The targeted integration of a 21 kb DNA fragment in Aspergillus nidulans based on Cre/loxP-mediated cassette exchange was successfully carried out, [52] indicating its potential application for extensive DNA fragment integration in Monascus. In addition, Cre recombinase has also been used in Aspergillus oryzae, [33] Aspergillus niger, [53] F I G U R E 1 Partial gene editing tools and applications in filamentous fungi.…”