I'm holding a bowl of dirt up to my nose, in hopes of getting high on the fumes of my backyard compost pile. The microbe that I'm after today is M. vaccae, a living creature that acts like a mind-altering drug once it enters the human body. It has been shown to boost the levels of serotonin and norepinephrine circulating in the systems of both humans and mice. In other words, it works in much the same manner as antidepressant pills. And yes, it is possible to dose yourself by simply breathing in the smell of good dirt.
The drug-like effects of this soil bacteria were discovered, quite by accident, about a decade ago. A doctor named Mary O'Brien created a serum out of the bacteria and gave it to lung-cancer patients, in hopes that it might boost their immune systems. Instead, she noticed another effect: The hospital patients perked up. They reported feeling happier and suffered from less pain than the patients who did not receive doses of bacteria. Further studies in mice confirmed the mood-boosting effect of the soil bugs.
So now I'm poking at the dirt in this dish, trying to release as much of the M. vaccae as I can. The compost looks like chocolate cake -- it's a rich brown-black color, and it holds together with that same kind of moistness that we love in baked goods. I'm eager for something to make me feel jaunty on this winter day. Outside, the sky glimmers a dim, silver-gray -- it's filled with clouds that Virginia Woolf would have described as "implacable." I have always been sensitive to such days. The dishwater light trickles through the window and infects me with malaise.
As I huff the soil, I have no way of knowing exactly how much M. vaccae is floating into my lungs -- or whether it's enough to change my mind. But I can sure smell this compost. The odor hits like a punch and triggers a memory: I recall a day in Western Massachusetts on a friend's farm, turning earth with a pitchfork. Dried mud extended up my arms, like a pair of long-sleeved gloves, as if I were dressed for a gala event with forest-fairies. I felt dazzled that day, boozed up on sunshine, and in love with the potatoes I'd just dug out of the soil.
That same smell hovers over this dish now -- a sexy, outdoorsy tang. It's an odor produced by microbes in the soil as they break down plants. Scientists call it "geosmin," this dirt smell that lends the earthy taste to beets and carrots. It's the flavor of life.
Cooks have another own word for it. "Terroir" is what makes a loaf of sourdough from San Francisco taste so different from its cousin in Bordeaux. The regional microbes, in the soil and air, impart their particular notes to the bread. You can taste terroir in your wine, your cheese, and even your chocolate -- all of which are produced with the help of specialized bacterias that can vary from town to town.
This soil in the bowl is redolent with my own particular terroir. It is made from the apples that plummeted to the ground in our backyard. It contains, too, a sweetening of ashes from our wood stove. It is the smell of an unfolding revolution in microbiology. New tools -- like desktop gene sequencers -- allow scientists to read a sample of soil and find every species of microbe inside it. This is science that you can smell and taste. And sometimes, you can get high on it too.