cexA and its regulatory processes – a closer look into the citric acid production mechanisms of Aspergillus niger Authors: Aline Reinfurt, Valeria Ellena, Matthias G. Steiger Aspergillus niger is an important filamentous fungus used for the industrial production of citric acid. One of the main contributors to high citric acid accumulation by the fungus is the citrate transporter CexA. It belongs to the major faciliatory superfamily subclass DHA1 which act as drug-H+ antiporters1. Since cexA and its regulators are essential within the citric acid production process, it is important to study their regulatory mechanism, which is the focus of this work. LaeA for one is known to be a major regulator of the cexA gene. It regulates the expression via methylation levels of the histones H3K4 and H3K92. There are indications that other transcriptional regulators such as AmyR and XlnR are also involved in the regulation of cexA on a transcriptional level. Another factor that affects citric acid production is the amount of manganese that is present during the production process. Observations showed that the fungus develops a certain pellet-like morphology under manganese limitation conditions and that this limitation is decisive for high citric acid accumulation by A. niger3,4. However, the exact mode of action of manganese in the cell is not clear. The transcriptional influence of manganese on cexA and laeA is investigated in order to find out more about the connection between manganese limitation and citric acid production.