Manganese(II) ions suppress the transcription of the citrate exporter encoding gene cexA in Aspergillus niger

Aline Reinfurt; Susanne Fritsche; Vivien Bíró; Alexandra Márton; Valeria Ellena; Erzsébet Fekete; Erzsébet Sándor; Levente Karaffa; Matthias G Steiger

doi:10.3389/fbioe.2023.1292337

Manganese(II) ions suppress the transcription of the citrate exporter encoding gene cexA in Aspergillus niger

Front Bioeng Biotechnol. 2023 Nov 22:11:1292337. doi: 10.3389/fbioe.2023.1292337. eCollection 2023.

Authors

Aline Reinfurt^{1

2}, Susanne Fritsche^{1

2}, Vivien Bíró^{3

4}, Alexandra Márton^{3

4}, Valeria Ellena^{1

2}, Erzsébet Fekete³, Erzsébet Sándor⁵, Levente Karaffa³, Matthias G Steiger^{1

2}

Affiliations

¹ Research Group Biochemistry, Institute of Chemical, Environmental and Bioscience Engineering, TU Wien, Vienna, Austria.
² Austrian Centre of Industrial Biotechnology (ACIB GmbH), Vienna, Austria.
³ Department of Biochemical Engineering, Faculty of Science & Technology, University of Debrecen, Debrecen, Hungary.
⁴ Juhász-Nagy Pál Doctoral School of Biology and Environmental Sciences, University of Debrecen, Debrecen, Hungary.
⁵ Institute of Food Science, Faculty of Agricultural and Food Science and Environmental Management, University of Debrecen, Debrecen, Hungary.

Abstract

Aspergillus niger is an important filamentous fungus used for the industrial production of citric acid. One of the most important factors that affect citric acid production is the concentration of manganese(II) ions present in the culture broth. Under manganese(II)-limiting conditions, the fungus develops a pellet-like morphology that is crucial for high citric acid accumulation. The impact of manganese(II) ions on the transcription of the major citrate exporter encoding gene cexA was studied under manganese(II)-deficient and -sufficient conditions. Furthermore, citric acid production was analyzed in overexpression mutant strains of cexA in the presence and absence of manganese(II) ions, and the influence of CexA on fungal morphology was investigated by microscopy. Transcriptional upregulation of cexA in the absence of manganese(II) ions was observed and, by decoupling cexA expression from the native promoter system, it was possible to secrete more citric acid even in the presence of manganese. This effect was shown for both an inducible and a constitutive overexpression of cexA. Furthermore, it was found that the presence of CexA influences fungal morphology and promotes a more branched phenotype. According to this study, manganese(II) ions suppress transcription of the citrate exporter cexA in Aspergillus niger, causing citric acid secretion to decrease.

Keywords: Aspergillus niger; cexA regulation; citric acid overflow; citric acid transporter; major facilitator superfamily; manganese effect; metal ions.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and publication of this article from the COMET center acib: Next-Generation Bioproduction is funded by BMK, BMDW, SFG, Standortagentur Tirol, Government of Lower Austria, and Vienna Business Agency in the framework of COMET - Competence Centers for Excellent Technologies. The COMET-Funding Program is managed by the Austrian Research Promotion Agency FFG. Hungarian National Research, Development and Innovation Fund (grants: NN 128867 to LK, and K 138489 to EF). EuroMicropH COST Action CA18113 funded the STSM grant of AR. VB, and AM were respectively supported by the ÚNKP-23-3-II-DE-359 and the ÚNKP-23-4-I-DE-362 New National Excellence Programs of the Hungarian Ministry for Culture and Innovation from the source of the National Research, Development and Innovation Fund. VB was also supported by the PhD Excellence Scholarship from the Count István Tisza Foundation for the University of Debrecen.