On the first day back to school after spring break, I was late (of course) and had not had my coffee (of course). Between scrambling to get something that resembled a lesson plan jotted down and thinking of something to keep my homeroom busy, I ran into the workroom to get a cuppa. Notebook in hand, I absent-mindedly reached for the coffeepot. The coldness of the coffee caught me off-guard at first, followed quickly by the white layer of fuzz growing on the surface. We had neglected to dump the coffee in the faculty workroom before the long school holiday. The morning was not going according to plan. At all.
As I examined the coffee pots more closely, I noticed an unexpected difference. One coffeepot was covered in half an inch of whatever the white fuzzy organism was; the other had almost none. Even as my caffeine addiction remained unsatisfied, my scientific curiosity rose to the occasion. After all, we were to begin our study of protists and fungi in science that day – the kingdoms that include molds, mildews, and other such unfairly maligned life. Instant lesson plan!
These pots were identical in nearly all the same ways: each was the same brand of coffee, each was brewed with the same water, each had sat unattended for the same period of time. There was, as far as I could tell, a single variable at play: the presence of caffeine. The regular coffee had very little growth, the decaffeinated a lot. Fortunately for my informal data set, teachers consistently have better things to do before long weekends than dump coffee pots. As a consequence, these results have been repeated (several times).
Why the difference, then? Caffeine is a naturally occurring alkaloid. It lends coffee and tea owe their stimulant effect and bitter taste. In the 7th grade science class I teach we learn about chlorophyll – a complex pigment in plants that traps sunlight for food. Chlorophyll, then, serves a function. The structure of caffeine, with its interlocking rings of nitrogen and carbon, has its own kind of complexity.
Complexity like this serves a function. So what function does caffeine serve? The answer depends on the species you ask. Humans use caffeine to drive schedules distinctly out of sync with our natural Circadian rhythms. In plants, however, caffeine serves a distinctly different function. Turns out caffeine works as a natural pesticide, killing or immobilizing insects that ingest it.
Caffeine works by inhibiting a chemical messenger called adenosine, a chemical messenger involved in just about every part of your physiology. In your brain, it dampens the release of the natural stimulants glutamate and dopamine. The structure of adenosine and caffeine are remarkably similar – in fact, caffeine mimics adenosine. It binds to adenosine receptors and prevents adenosine from doing so. As long as caffeine is bound to the adenosine receptors on your neurons, they will just keep squirting out dopamine and glutamate. This action in turn increases brain activity and allows me to resemble a human being in front of my 7th graders at 8:30 in the morning. One question naturally leads to another. One must ask, how does caffeine increase the activity of Mr. Burke and decrease the activity of coffee mold? The short (and frustrating) answer is that I do not know. However….
Humans, insects and the mold growing on the 10-day old coffee may look very different, but they are all written with the same genetic code. You share 44% of your genetic makeup with a fruit fly; you share 26% with a yeast. This genetic code we share creates the chemical pathways that define our anatomy and physiology. Adenosine, and the chemical pathways it regulates, is as intimately involved in the physiology of other organisms as it is in humans. In insects for example, it regulates muscle function, among other things. Caffeine precipitates some chemical pathway in insects and coffee mold that causes death. Though they have very different outcomes, these pathways share the same basic architecture.
This common architecture is no coincidence. As far as we can tell, these organisms – indeed all organisms – evolved from a common ancestor. Just as the mammalian forelimb diverged to form legs, arms, wings, and fins, chemical pathways in different groups diverge towards different ends. At first glance, coffee, molds and adenosine seem to have very little to do with each other. So what is our takeaway? If coffee is so bad for mold, could it as bad for us? Is it the next evil botanical substance, the tobacco of the coming decade? Or the next disinfectant spray?
For the time being, it meant I was skipping the coffee and having a cup of tea.