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MARGINALIA

All Things Small and Great

It's time for a new, conservation-minded view of the microbial communities that live on and in us

Robert L. Dorit

Our Debt to the Unsung Masses

Fortunately for the planet, we are beginning to realize the folly of acting as though we can have dominion over it. Belatedly, we now acknowledge that we are part of the vast network of interactions that sustain life on this planet (even if we do not always act accordingly). In my lifetime, the notion of conservation as both an ethical and a pragmatic imperative has finally begun to take hold in the collective imagination.

And yet our ecological sensibilities seem to stop at the edge of the visible. For anything alive that we cannot see with the naked eye, we tend to act in keeping with the old 13th-century Crusaders' approach: "Kill them all, and let God sort them out." But the limits of human vision mark no important boundary in the living world, and our fear of the invisible makes no biological sense at all.

Our overuse of antibacterials and antibiotics and the common belief that all microorganisms are harmful reflect our obsession with destroying the unseen. In much of the developed world, and certainly in the United States, we appear determined to make the planet microbe-free. The advertising, pharmaceutical and home-products industries have tried to persuade the public that every microbe is the enemy. But the more we learn about the biological world, the less this perspective makes sense. I argue instead for a new take on the world of the unseen—one that acknowledges the vital and subtle relationships that all plants and animals have with microorganisms. Without the microbial worlds that accompany us, human life would not exist. We should honor these relationships. We should develop a conservation ethic towards the organisms that we cannot see with the naked eye.

We have known for some time how important microorganisms are to the functioning of the planet. Microbes provide vital ecological services: They break down complex molecules into simpler ones, they recycle essential raw materials, they detoxify dangerous chemicals, they sequester CO2. But those are merely the macro-level life-sustaining activities of the microbial world. What we are only now beginning to realize is how much our individual survival depends on the ability of the invisible world to live in and on us. In exchange for room, board and a steady thermostat, our microbial partners—with few exceptions—work tirelessly on our behalf, supplying us with key nutrients and keeping infections and invaders at bay.

Let's start with the numbers: As a first approximation, each of us harbors approximately 10 bacterial cells for every one of our eukaryotic cells—about 5 × 1014 bacterial cells keeping our 50 trillion human cells in business. Although we are, strictly speaking, eukaryotic organisms, we might more accurately be described as a series of linked and densely populated ecosystems, each a rich mixture of interacting eukaryotic, bacterial and archaeal cells. But the importance of single-celled organisms goes far beyond their numbers. Over the past decade, we have discovered how vital to us these bacterial communities really are.


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