Aspergillus niger is a fungus found in soil and is typically responsible for black mold in a variety of fruits and vegetables. The fungus produces toxic metabolites that primarily affect plants, but can also spread to humans through inhaling spores or eating infected plants.
Aspergillus niger has been present in soil since ancient times. According to National Geographic, the famous "curse of King Tut" that caused the death of several archeologists working on the tomb may have been caused by the presence of mold spores within the tomb. Tests on similar mummies have found the presence of aspergillus niger within the wrappings. Epidemiologists John S. Marr and Curtis Malloy theorized in the mid-1990s that the 10th biblical plague on Egypt may have been the result of a toxin such as the kind created by aspergillus niger infecting grain stores.
According to the EPA, aspergillus niger fungus is so widely distributed that the fungus is "ubiquitous in nature." The fungus can spread easily and will colonize a wide range of substrates. Aspergillus niger fungus may also be found in compost and other decaying organic material.
Although the fungus may be harmful to people and plants, it also has beneficial uses. Aspergillus niger excretes an enzyme that aids in fermentation and creation of citric acid. The fungus is also used in laboratory settings to test the effectiveness of various antifungal agents and preservatives. Because it is also sensitive to micronutrient deficiencies, aspergillus niger is used to test soil for nutrient content.
Aspergillus niger infects plants that are grown in conditions that the fungus favors. Root crops such as onions show signs of black mold infection along areas of tissue damage, such as broken skin layers and bruising around the neck of the plant. Gourds such as winter squash frequently show no signs of damage until after being stored for long periods. Fruit trees may develop black mold through misting systems that carry water through tubing buried underground.
Plants that become infected with aspergillus niger will exhibit signs that include rotting tissue around bruised or broken areas of the plant, sunken tissue and a withered or mummified appearance. Humans who exhibit signs that aspergillus niger may be affecting their health may have trouble breathing or show symptoms of an upper repertory infection. Advanced infection with aspergillus niger is called pulmonary aspergillosis. Patients who suffer from pulmonary aspergillosis already have a weakened immune system. The most severe symptom of aspergillosis that a patient will exhibit is coughing up blood.