Gene deletion of cytosolic ATP: citrate lyase leads to altered organic acid production in <i>Aspergillus niger</i>

With the availability of the genome sequence of the filamentous fungus <i>Aspergillus niger</i>, the use of targeted genetic modifications has become feasible. This, together with the fact that <i>A. niger</i> is well established industrially, makes this fungus an attractive micro-organism for creating a cell factory platform for production of chemicals. Using molecular biology techniques, this study focused on metabolic engineering of <i>A. niger</i> to manipulate its organic acid production in the direction of succinic acid. The gene target for complete gene deletion was cytosolic ATP: citrate lyase (<i>acl</i>), which had previously been identified by using genome-scale stoichiometric metabolic model simulations. The <i>acl</i> gene was deleted using the bipartite gene-targeting method, and the mutant was characterized in batch cultivation. It was found that the succinic acid yield was increased threefold by deleting the <i>acl</i> gene. Additionally, the total amount of organic acids produced in the deletion strain was significantly increased. Genome-scale stoichiometric metabolic predictions can be used for identifying gene targets. Deletion of the <i>acl</i> led to increased succinic acid production by <i>A. niger