A priest named this mold after a holy water sprinkler
Peering through a microscope in 1729, the Italian priest Pier Antonio Micheli saw spore heads shaped like the aspergillum used to scatter holy water, and named the genus Aspergillus. Its hundreds of species now brew sake, supply citric acid, gave medicine lovastatin, and live in millions of pillows.
By March 2010 the genus held 837 species, spread across climates worldwide and split today into six subgenera and 27 sections. They thrive where sugar or salt levels are high, need plenty of oxygen, and often grow as a fuzzy surface layer. Many can also survive in nutrient-poor places, which is why A. niger forms mildew on damp walls and several species colonise bathrooms and window frames.
The genus cuts both ways. More than 60 species cause disease. A. fumigatus is the usual culprit in people with weak immune systems, A. lentulus causes invasive infections with high death rates, and A. flavus is the main producer of carcinogenic aflatoxins in crops. Yet A. oryzae and A. sojae make sake and soy sauce possible: brewer's yeast cannot digest rice starch, so koji mold first breaks it into simple sugars. A. niger accounts for over 90 percent of global citric acid output, more than 2.54 million metric tonnes a year, and A. terreus was the original source of lovastatin.
Sex turned out to be hiding in plain view. About 64 percent of the 250 species examined have no known sexual stage, but researchers found mating cycles in A. fumigatus and A. flavus in 2009 and in A. lentulus and A. terreus in 2013, when strains of opposite mating types were grown together. Most species that do reproduce sexually fertilise themselves, as A. nidulans does, a pattern that fits the idea that sex dates back to the common ancestor of all eukaryotes. Guido Pontecorvo used A. nidulans to show a looser gene-swapping process called parasexuality.
Three genome papers published together in Nature in December 2005 made Aspergillus the leading genus for comparing filamentous fungi. Measured against animal divergence, its genetic diversity rivals that of all vertebrates.
Source: Aspergillus
