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  • Title: Uptake and export of citric acid by Aspergillus niger is reciprocally regulated by manganese ions.
    Author: Netik A, Torres NV, Riol JM, Kubicek CP.
    Journal: Biochim Biophys Acta; 1997 Jun 12; 1326(2):287-94. PubMed ID: 9218559.
    Abstract:
    The uptake as well as the export of citric acid by Aspergillus niger occur by active, deltapH-driven, H(+)-symport dependent systems. They are inhibited by nonmetabolizable tricarboxylic acid analogues and phthalic acid, and by several other mono-, di- and tribasic organic acids. However, citrate export could only be demonstrated in a mycelium cultivated under manganese-deficient growth conditions, whereas the uptake of citrate from the medium was only detectable upon precultivation of A. niger in a medium supplemented with Mn2+ ions. In addition, the uptake of citrate was dependent on the presence of Mn2+ ions in the assay, and inhibited by EDTA. This requirement for Mn2+ could also be partially fulfilled by Mg2+, Fe2+ or Zn2+, whereas Cu2+ ions inhibited citrate transport. The observed divergent effects of manganese ions on citrate uptake and citrate export may be a major reason for the well documented requirement for manganese deficiency of citric acid accumulation.
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