// July 15th, 2012 // No Comments » // Recent Research
Something happened when I was spliced, something wrong. Some random event in my chromosomes, I suppose it was. In any event, I wound up lacking. My sister took all the toxin genes, and I was left with nothing.
It’s a scary world out there for a fungus without a toxin. How would I strike fear into the hearts of all animals who dared to eat the plants I was eating? How, without my precious aflatoxin to attack the liver, causing acute sickness or eventual cancer?
Quite simply, I’m surprised I lasted as long as I did before they found me.
Indeed, I’m not sure how they did find me. I had a pretty good disguise, growing colonies of blue along the endless islands of white rice grains, just like my toxic cousins always had. Safe from munching animals by my don’t-eat-me mimicry, the promise of sickness is the discoloured rice.
For some reason, these sake brewers saw past it all. I thought I was a goner when they lifted me up from the wild and plonked me into a house of wood.
Then I saw the food.
A. oryzae in heaven. Image by Forrest O.
It’s hard for mould like me to see, lacking in the eye department, but I knew it was there. An endless carpet of steamed rice. With my filamentous fronds I could touch it. Drill down into it and grow cottony soft, sprout fruiting bodies on the surface and spread on and on.
Call me legion, for we are many. Better yet, call me qū meí jūn in Pinwin, kōji-kin in Japanese, nulook-gyun in Korean or the grandiose Aspergillus oryzae in scientific circles. Back then, some 2000 years ago, I didn’t know who I was, or that I would one day be the National Fungus of Japan.
That’s when the changes happened.
I didn’t notice at first, I don’t know that there was ever a master plan. It felt… natural. Human hands, bristling with microbes and pitted with pores, dropped me into heaven. And when I had eaten the heaven for a time, they picked me up and dropped me once more into fresh heaven.
Incomprehensible! These hands must have spent hours polishing the rice to remove all the husks, then steamed it to perfection, cooled it so I didn’t burn my filaments, then spread it out – just for me! It was like being a king! King Kōji-kin!
I'm a national icon, and pretty cute too. Image by Ryoku Kasinn
As they fed me and I ate, we gradually adapted to please one another. Heaven grew ever more heavenly, until the temperature and humidity was just so
For my part, I started growing much faster, hell, I had brilliant conditions for it and not a doubt in the world that I could grow as fast as I pleased. Fearlessly fast.
Over generations, they selected only the best for their purposes, which at that stage I knew nothing about. They selected the sons and daughters (hell, we’re all of one gender here) that could best turn rice starch to sugar. They also preferred fungi of least colour, but most smell and flavour. Each generation, the best of me would be plucked and propagated.
Turning starch to sugar is a tricky thing. I suppose the point of starch is to tie up the sugar molecules into a big, complex network so the plant can use them later. For me, kōji-kin I secrete the amylase enzymes, biological machine that chops starch into pieces of sweet. From a couple of recently-licked hands, I’ve learned humans make the same enzyme in their saliva. My amylases, however, not only make glucose, but a few other sugars that produce a wonderful flavour.
But why, pray tell? Have you worked it out yet?
Winemakers use yeast to turn the natural sugars in grapes into alcohol. Beer brewers must malt their barley, partially growing the seed to convert starch to sugar, to ferment it with yeast into alcohol.
And I, the humble fungus, plucked from the wild a millennia ago for a deficit in character. My non-toxic self excels, above all other moulds, in turning rice starch into sugars.
From the beds of heaven, me and my alchemical rice is transferred to the fermenting tank. Mixed with yeast, water and more rice, then left to stew in our own juices for a month.
This mash is pressed and filtered, and the sweet, alcoholic liquid that pours forth is bottled as sake.
Not to ring my own bell filaments, but I make soy sauce and miso too. That’s a whole meal – appetizer, main, and a drink.
Domesticated A oryzae (left) and wild A flavus (right). Image by John Gibbons, Vanderbilt University
These days I hardly recognise myself! So much of me has changed by growing with the sake brewers. Though I still share some 95% of my genome with my wild and toxic cousin A. flavus
(and you, human reader, share 99% of yours with a chimpanzee), I am given all I could ever want to eat and praised world-over for my skill in sake making. While A. flavus
, the wild thing, is targeted daily for a war against fungi
with resistant crops and competitive yeasts.
What must the wolf think of the dog? Or the auroch of the cow? Well, to their accusations I say this: We may change our genes and appearance for protection and care, but, in doing so, we also mould the humans who cooperate with us. Through their attentions and skills, they, too, are domesticated.
This story was inspired by this recent research by Vanderbilt University into the domestication of microbes. “Although people don’t often think about it, we haven’t only domesticated animals and plants, but we have also domesticated dozens of different microbes.” – Assistant Professor of Biological Sciences Antonis Rokas in the press release. You can find more information on brewing sake here, and a beautiful description of koji pampering by interns at a sake house in Japan who blogged their experiences.
Gibbons, J. et. al. (2012). The Evolutionary Imprint of Domestication on Genome Variation and Function of the Filamentous Fungus Aspergillus oryzae Current Biology