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Enhancing L-malate production of Aspergillus oryzae FMME218-37 by improving inorganic nitrogen utilization

Ding, Qiang, Luo, Qiuling, Zhou, Jie, Chen, Xiulai, Liu, Liming
Applied microbiology and biotechnology 2018 v.102 no.20 pp. 8739-8751
Aspergillus oryzae, absorption, ammonium sulfate, carbon, feedstocks, fermentation, industrial applications, mutants, organic nitrogen, petroleum, screening, synthesis
Microbial L-malate production from renewable feedstock is a promising alternative to petroleum-based chemical synthesis. However, high L-malate production of Aspergillus oryzae was achieved to date using organic nitrogen, with inorganic nitrogen still unable to meet industrial applications. In the current study, we constructed a screening system and nitrogen supply strategy to improve L-malate production with ammonium sulphate [(NH₄)₂SO₄] as the sole nitrogen source. First, we generated and identified a high-producing mutant FMME218-37, which stably boosted L-malate production from 30.73 to 78.12 g/L, using a combined screening system with morphological characteristics. Then, by analyzing the fermentation parameters and physiological characteristics, we further speculated the key factor was the unbalance of carbon and nitrogen absorption. Finally, the titer and productivity of L-malate was increased to 95.2 g/L and 0.57 g/(L h) by regulating the nitrogen supply module to balance carbon and nitrogen absorption, which represented the highest level in A. oryzae with (NH₄)₂SO₄ as nitrogen source achieved to date. Moreover, our findings using a low-cost substrate may lead to building an economical cell factory of A. oryzae for L-malate production.