What would happen if there were no microorganisms on the planet? Life would go on, but it might be permanently bubble-wrapped or smothered by feces—and it definitely wouldn’t last very long. This perspective was published in PLOS Biology this week.
To explore the value of microbial services, Jack Gilbert from Argonne National Laboratory and Josh Neufeld from the University of Waterloo wanted to see what would happen in a microbe-free world. They carried out their hypothetical scenario in three steps: First, they got rid of the human gut microbiome, then they cut out all bacteria and archaea (a kingdom of single-celled microorganisms), and finally they concluded by purging the world of all the little guys, including viruses, fungi, protists, and algae. Microbes may be life-sustaining thanks to their innumerable associations and key roles in all biogeochemical processes, but how accurate was Louis Pasteur when he said “life would not long remain possible in the absence of microbes”?
If we had no gut bacteria, we’d have weaker immune systems, reduced organ sizes, and problems with our bowels. However, most nutrition issues arising from a germ-free (or “gnotobiotic”) condition have already been solved: All required dietary components can be synthesized chemically. The most substantial barrier for embracing this lifestyle is having to be a bubble boy or girl... forever. Without helpful microbes to train our immune systems, sudden exposure to pathogens would shorten our lives.
You could, however, live a germ-free existence outside of a bubble if we knocked all things bacterial and archaeal. But global photosynthesis would cease in a year since bacteria are needed to fix nitrogen for plant growth, carbon dioxide in the atmosphere would increase, all the cows and sheep and goats would perish, and waste would build up and up and up. “Even though our dairy industries, cattle farmers, biotechnology companies, food producers, hospitals, and wastewater treatment systems would begin making headlines within a day or two, it would take us nearly a week to realize what had happened,” the authors write. “Annihilation of most humans and nonmicroscopic life on the planet would follow a prolonged period of starvation, disease, unrest, civil war, anarchy, and global biogeochemical asphyxiation.”
Without any microorganisms at all, the first thing we’d notice is the shocking (seemingly miraculous) absence of diseases ranging from the common cold and athlete’s foot to malaria and Ebola. But now we wouldn’t even have fungi to help out with decomposition, and we’d be smothered in our own waste. Small pockets of humans and insects would survive for a while, maybe even for as long as a few centuries. But long-term survival is doubtful.
“Their roles are not necessarily irreproducible,” the authors conclude. “When you next hear someone claim that we cannot live without microorganisms, it would be appropriate to ask them to qualify the statement. Would we still be able to eat and digest food? Yes. Would life be extinguished in the absence of bacteria and archaea or in a world without any microbes? Not immediately, not all life, and potentially not for a long time.”