Citrate exporter enhances both extracellular and intracellular citric acid accumulation in the koji fungi Aspergillus luchuensis mut. kawachii and Aspergillus oryzae.

Eri Nakamura, Chihiro Kadooka, Kayu Okutsu, Yumiko Yoshizaki, Kazunori Takamine, Masatoshi Goto, Hisanori Tamaki, Taiki Futagami

Journal of bioscience and bioengineering 2021 Jan

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Citrate exporter CexA plays a key role in the production of citric acid in fungi; however, its role in intracellular metabolism has remained unclear. In this study, we comparably characterized homologous cexA genes in the white koji fungus Aspergillus luchuensis mut. kawachii and the yellow koji fungus Aspergillus oryzae, which exhibit high and low abilities, respectively, to produce citric acid. Disruption of cexA caused a significant decline of both extracellular and intracellular citric acid accumulation in Aspergillus kawachii, while overexpression of the A. kawachii cexA gene (AkcexA) into A. oryzae significantly enhanced both extracellular and intracellular citric acid accumulation in A. oryzae to a level comparable to that of A. kawachii. In addition, overexpression of two intrinsic cexA homologs (AocexA and AocexB) in A. oryzae also enhanced its extracellular and intracellular citric acid accumulation. Comprehensive analysis of intracellular metabolites from an AkcexA-overexpressing strain of A. oryzae compared with its control strain identified metabolic changes associated with intracellular citric acid accumulation via the glycolytic pathway, pentose phosphate pathway, and tricarboxylic acid cycle. Our results indicate that citric acid export enhances not only extracellular citric acid accumulation but also intracellular metabolic fluxes to generate citric acid. Copyright © 2020 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.

Citation

Eri Nakamura, Chihiro Kadooka, Kayu Okutsu, Yumiko Yoshizaki, Kazunori Takamine, Masatoshi Goto, Hisanori Tamaki, Taiki Futagami. Citrate exporter enhances both extracellular and intracellular citric acid accumulation in the koji fungi Aspergillus luchuensis mut. kawachii and Aspergillus oryzae. Journal of bioscience and bioengineering. 2021 Jan;131(1):68-76