Phenotypes of gene disruptants in relation to a putative mitochondrial malate citrate shuttle protein in citric acid producing Aspergillus niger
The mitochondrial citrate transport protein (CTP) functions as a malate citrate shuttle catalyzing the exchange of citrate plus a proton for malate between mitochondria and cytosol across the inner mitochondrial membrane in higher eukaryotic organisms. In this study, for functional analysis, we cloned the gene encoding putative CTP (ctpA) of citric acid producing Aspergillus niger WU 2223L. The gene ctpA encodes a polypeptide consisting 296 amino acids conserved active residues required for citrate transport function. Only in early log phase, the ctpA disruptant DCTPA 1 showed growth delay, and the amount of citric acid produced by strain DCTPA 1 was smaller than that by parental strain WU 2223L. These results indicate that the CTPA affects growth and thereby citric acid metabolism of A. niger changes, especially in early log phase, but not citric acid producing period. This is the first report showing that disruption of ctpA causes changes of phenotypes in relation to citric acid production in A. niger. Graphical abstract Disruption of the gene encoding the citrate transport protein (CTPA, i.e. malate citrate shuttle protein) affects the phenotype of Aspergillus niger.
Bioscience, biotechnology, and biochemistry