Aspergillus: The Ubiquitous Mold Behind Citric Acid, Cancer, and Hospital Infections

*Aspergillus* is a genus of filamentous fungi containing roughly 300 described species, found ubiquitously in soil, decaying plant matter, and indoor environments. Named by Pier Antonio Micheli in 1729 for the resemblance of its spore-bearing structure to an aspergillum (holy-water sprinkler), the genus spans the full spectrum from industrial workhorse to dangerous pathogen. ## A. niger: Industrial Powerhouse *A. niger* has been the primary production organism for citric acid since the 1920s, responsible for approximately 99% of the world's manufactured supply. It also produces glucoamylase for starch processing and other enzymes used in juice clarification, baking, detergents, and brewing. Selected strains carry FDA GRAS (Generally Recognized as Safe) status. ## A. fumigatus: Hospital Pathogen *A. fumigatus* produces tiny, thermotolerant spores (conidia) small enough to reach pulmonary alveoli. In healthy people, immune defenses clear them. In immunocompromised patients — transplant recipients, those on prolonged corticosteroids, or with blood cancers — it causes invasive aspergillosis, with mortality exceeding 50% despite antifungal treatment. Hospital HEPA filtration and air pressure differentials specifically target A. fumigatus spore reduction, as described in Hospital Airborne Fungal Monitoring and the Pollen API Landscape. ## A. flavus: Carcinogen Producer *A. flavus* produces aflatoxins — among the most potent naturally occurring carcinogens known. Aflatoxin B1 contaminates improperly stored cereals, peanuts, and maize, and is a significant cause of hepatocellular carcinoma in parts of sub-Saharan Africa and South Asia. The IARC classifies aflatoxins as Group 1 human carcinogens. **See also:** Fungal Chemical Deterrents and Pharmaceutical Discovery · Winter Aerobiology: How Spores and Dust Behave in Cold Weather