When the Apostle Paul exhorted us to be hospitable (see 1 Peter 4:9 for example), I doubt he had microbes in mind. But God might have. We’re host to trillions of the little creatures—on our skin, in our gut, flowing through our veins, and in all of those moist and warm cavities our bodies possess. In fact, they’re in every part of us. And that’s a good thing.
The National Institute of Health’s 2014 Human Microbiome Project concluded that “10,000 microbial species occupy the human ecosystem.” That’s species, not individuals. Other estimates put that number much higher, with 40,000 species of bacteria in our gut alone.
For the most part, these tiny creatures do not make us sick. Yes, some are pathogens—disease causing—but normally, those of us with healthy immune systems simply fight them off. In fact, we need the practice. People living in too-clean environments lose resistance to disease.
Far from harming us, these microbes are an essential part of us. They benefit from living on and in our bodies, and we can’t live without them. For example, you may have noticed a sudden surge of interest about the bacteria that inhabit our digestive system. We’ve learned that our bodies are incapable of digesting everything we need in our diets. In order to benefit from the food we eat, we depend on an assortment of bacteria to break down the chemical compounds and make them available to our cells.
When we take antibiotics, the natural balance of those bacteria is disturbed. Different drugs affect the populations of different species, but often the end result is an upset digestive system. Various “healthy” practices, such as colonic cleansing, have the same effect. Once the antibiotics are discontinued, balance is eventually restored, although the actual species might be different from those originally present.
Or, consider our skin. You know we have pores in our epidermis. But did you know that those pores are inhabited? Studies show that pretty much everyone has two species of skin mite, Demodex folliculorum and Demodex brevis, living in their facial hair follicles. Yes mites—relatives of spiders and ticks. They live out their lives on our skin, eating and mating—but not pooping. (Lacking an anus, they hold a lifetime’s worth of poop inside, which is released when they die). We aren’t sure exactly what these mites eat—bacteria? Oils and other secretions? Dead skin or yeast cells? We aren’t quite sure if they’re helpful or harmful, either. In any case, there’s little anyone can do. You can kill them all, but a few weeks later they’ll be back, as plentiful as ever.
We even have microorganisms living inside our cells. You may remember learning about the “mighty mitochondria,” the organelles in which cellular respiration takes place, providing us with energy. Scientists believe that mitochondria started out as invasive bacteria, perhaps parasites. They have now become an essential component of all eukaryotic cells.
There is plenty of evidence. Mitochondria are similar to bacteria in a number of ways. They are surrounded by a double membrane, evidence that they once lived on their own. Furthermore, they have their own DNA, separate from that in the cell’s nucleus. They use their DNA to manufacture enzymes and other proteins, just as the nuclear DNA does.
Mitochondria reproduce on their own schedule, apart from the cell that contains them. When the cell divides, some mitochondria end up in one half and some in the other half.
Of course, not all our hitchhikers are so benign. Some are harmful, even fatal. Still, isn’t it nice to know that when you think you’re lonely and all alone—you’re not?
Mite photo: Alan R Walker, wikicommons
Mitochondrian images: https://cnx.org/contents/FPtK1zmh@8.25:fEI3C8Ot@10/Preface, wikicommons