Bacillus subtilis

by Rob Dunn

Science is partially about the scientific method (testing and rejecting hypotheses, so as to winnow if not the truth, the truest) and partially about voodoo. Maybe you knew, maybe you did not. The voodoo is what no one talks about. The voodoo is the lightning in the storm-ridden minds of scientists. It is an inexplicable mix of chance, observation and pure who knows what [1]. It is also private.

We tend to hear about science through the work of science journalists. Sometimes against their will, scientists talk to journalists about what they have discovered. They talk about published papers and what is known or almost known. But often when you hear scientists discussing what they have “found,” they sound, well, unenthusiastic. “Yes,” they say, “it was me that discovered the…(insert slightly hard to understand detail of the living world here) and I could not be more thrilled.” But often they don’t seem thrilled. They seem bored. Maybe they are. For many scientists the real joy, that raw and yelping elation, is not in the revealed discoveries, but instead the untested ideas.

When the scientific brain creates ideas, it is a cat stalking a mouse. The mouse is the idea. One hears it first, the little feet. Or maybe a smell. Once detected, it runs around among the leaves. Meanwhile, the cat watches, titillated. Haunches bunch and tense. Feet tap ever so slightly. Then there is the moment in which the cat pounces and, with the pounce, a resolution. The science we see comes after the resolution. It is the moment in which a journalist presents a scientist and her dead mouse to the world. We do not see all of the times the mouse ran away. Nor, more importantly, do we see scientists stalking the wild mice. We do not see those thrilling moments—all fur, life and mystery—when the mouse is still out there, not yet revealed for what it is, whether world-changing revelation, bullshit, or something in between.

I want to give you a bit of that pleasure when it comes to Bacillus bacteria, but in doing so I need to show you the wild, untamed idea, which is a naked process, but I will do it for you. Then we can all pounce together and see what we catch.

First I want to give you the rocklike observations that made me think about Bacillus in the first place. See if you can get them to spark too. Maybe I have missed something obvious. This is what happens most of the time. Most of the time I later realize I have overlooked or misunderstood some well-known aspect of biology. Or maybe what seems exciting to me today is actually mundane. Or maybe I am right that there is a mystery, but I am wrong about the resolution. The clay is raw. But if I am to let you in on the process, I have to show it to you. Showing you an untested idea is uncomfortable (I want to read more and call more people and figure out whether the idea is good) and yet I owe it to you. You deserve to see an idea so new it has barely been considered, an idea that you too might enjoy as it runs around, or at least that you might enjoy until someone pounces on it, killing it out in the tall, wild grass.

Here are the basics. Your body is covered with the species you can read about elsewhere in this book, species of Staphylococcus, Corynebacteria and many more. An inch of your skin might house hundreds of species of life. The total surface of your skin, or really anyone’s skin—from ears to anus and back out—might house thousands of species. A great number of these species eat the substances oozing out of our bodies. For example, several of the bacteria species that lives on our feet, including Bacillus subtilis, eat leucine, an amino acid common in the sweat on our feet. When these species eat leucine, they fart isoflavic acid which smells like stinky feet [2]. The farts of B. subtilis are more awful smelling than those of other skin species, but Bacillus species, Staphylococcus species and a handful of others, when eating leucine, all stink [3]. It is an unavoidable consequence and requires no special circumstances [4]. All of this is known and contains, in and of itself, a hint of the idea I am about to offer. You now have the flint stones.

Most sweat is produced by the eccrine glands concentrated on our heads (for cooling), hands and feet (for what?….). The composition of amino acids in sweat is independent of what we eat. Perhaps the amino acids are independent of what we eat because our bodies are trying to favor a consistent set/amount/whatever of microbes? Maybe. Maybe not.

And then there is the issue of mastodons. Amino acids are costly, or at least historically they were. Now we can eat hot dogs to get amino acids. Once, we killed mastodons for their meat, meat made mostly of proteins, proteins made of amino acids. So why is your body leaking them back out, leaking back out all that hard earned mastodon juice? I haven’t done it yet, but I keep meaning to figure out what proportion of the amino acids we eat are being excreted out our skin. It could be big. Maybe we are all feeding our Bacillus and other bacteria. Or, maybe I have missed a key paper. Maybe I have missed some obvious reality of sweat or cells or bacteria. Maybe. We are still in this idea’s storm before the calm. It looks beautiful, to me, but could be revealed to be otherwise at any moment. There are thousands, maybe millions of ideas like this one in the brains of scientists. Such ideas are the most whimsical of the joys of science, its secret wonderfulnesses. We are so ignorant. Anything is possible. And, at this stage of an idea, it can be as fun to take the idea even further before reeling it back in, which brings me to your feet. I understand why your head sweats, to cool your brain. But why do your hands and feet sweat so much? Each human produces about a cup of sweat a day. It is hard to believe anyone ever died of overheating hands or feet, which leads to the second idea.

What if our hands and feet sweat more so as to feed their bacteria even more. What if those bacteria in turn help to ward off fungal infections in the very places—hands and feet—where we are most likely to be exposed to fungal or bacterial pathogens. What if our body has intentionally fortified us with microscopic forces precisely where such forces are most needed? One can find hints (or at least an excited idea maker can…) suggesting this could be right. Bacillus subtilis, the stinkiest species on our feet is known to produce antibiotics capable of killing foot fungus [7].

Wait! Could this be?! Jump around and pause to revel in the idea between us, an idea both naked and strange. Hoorah to the ideas! Hoorah to what remains possible to discover in this world. Hoorah to all of the undocumented moments in scientists’ private, naked lives, moments when they run around their offices shouting, to themselves, hoorah. Hoorah to all those things, and then when you are done with the hoorahs, pause, smile, wonder, tense your haunches. A naked idea can only be left to run around for a little while. Time to pounce. Let’s do it together. Martial your responses, edits, concerns about the idea and, of course, your citations to the contrary. You can even martial some data, though only do so after you have run around your office or room a couple of times “wh00ting” to yourself with joy.

Meanwhile I can’t help wondering, if Bacillus subtilis, that common common bug, is not using its antibiotics to ward of fungi, who is it warding off? On each of us there are wars.

Notes & References

1 – Sometimes a good nap. Other times a beer. More occasionally, well, see Kary Mullis

2 – The normal, and less offensive, smell of sweat is, in contrast, acetic acid, which is also produced by bacteria, but different species eating different amino acids as well as other compounds. Essentially all “human” odors are produced by bacteria.

3 – Ara, K. et al. (2006) Foot odor due to microbial metabolism and its control. Can. J. Microbiol. 52, 357–364

4 – Which is good, since “pull my finger” only works if you have fingers.

5 – Peschel A, Jack RW, Otto M et al. Staphylococcus aureus resistance to human defensins and evasion of neutrophil killing via the novel virulence factor MprF is based on modification of membrane lipids with l-lysine. J Exp Med 2001; 193:1067–76

6 – Hadorn, B., Hanimann, F., Anders, P., Curtius, H. C., and Halverson, R. (1967). Free amino-acids in human sweat from different parts of the body. Nature (Lond.), 215, 416.

7 – Landy, M. W., G. H., Roseman, S. B., and L. G. Colio. 1948. Bacillomycin, an antibiotic from Bacillus subtilis active against pathogenic fungi. Proc. Soc. Exp. Biol. Med. 67:539-541.

About the Author

Rob Dunn is an evolutionary biologist and writer. His research focuses on understanding the ecology and evolution of the species humans interact with every day but pay relatively little attention to. Much of the science he does is public science in which citizens are involved in data collection, crafting hypothesis and even conducting analyses. His most recent book, The Wild Life of Our Bodies tells the stories of the consequences of our changing relationships with other species for our health and well-being. His next book considers the story of the human heart and its history, biology, evolution and problems. Dunn’s magazine articles appear often in National Geographic, Smithsonian Magazine, Scientific American Magazine, and many other magazines. See more about Rob’s writing at See more about his science at