Without this microscopic fungus, there would be no sake, no miso, no soy sauce, and no mirin. On October 12, 2006, the Society for Fermentation and Bioengineering, Japan, made official what Japanese cuisine had known for two millennia: it declared Aspergillus oryzae kokkin — Japan's national fungus.
Domestication by accident
Koji — the common name for Aspergillus oryzae — was domesticated at least two thousand years ago from a toxic wild relative: Aspergillus flavus, a producer of carcinogenic aflatoxins. At some point in that millennia-long process of artisanal selection — fermenting generation after generation with the strains that yielded the best flavor and greatest safety — koji lost the ability to produce these toxins, without anyone then knowing what was happening at a molecular level.
What the genome revealed
The complete genome sequencing of Aspergillus oryzae, published in Nature in 2005, showed a genome of 37 million base pairs with 12,074 genes — between seven and nine million more bases than its close relatives Aspergillus nidulans and Aspergillus fumigatus. This genetic expansion is concentrated precisely in genes related to secondary metabolism and secretory hydrolytic enzymes — the molecular machinery that makes it possible to break down starch and protein from rice, soy, and wheat into sugars and amino acids during fermentation.
An industrial secret guarded until 2005
For decades, industrial koji strains were jealously protected by Japanese sake and soy sauce producers; the genome was not made public until a consortium of Japanese biotechnological companies released it in late 2005. The proposal to name it the national fungus, formulated in 2004 by emeritus professor Eiji Ichishima of Tôhoku University, was approved the following year at the scientific society's annual assembly — the same formal recognition received by a country's national flower and bird, this time awarded to a mold.
References
- Machida M, Asai K, Sano M, et al. Genome sequencing and analysis of Aspergillus oryzae. Nature. 2005;438(7071):1157-1161. PMID: 16372010. DOI: 10.1038/nature04300