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Ask Dr. Universe: How many microbes are there in the world?

UPDATED: Mon., Aug. 17, 2020

Microbes rule your health – and further prove that kids should eat dirt (Dreamstime/TNS) ORG XMIT: 1213554  (Dreamstime/TNS)
Microbes rule your health – and further prove that kids should eat dirt (Dreamstime/TNS) ORG XMIT: 1213554 (Dreamstime/TNS)
By Washington State University

By Washington State University

How many microbes are there in the world?Jevauni, 9, Canada

Dear Jevauni,

There are lots of tiny living things on our planet that we call microbes. They live in the soil, water, air, your gut and on your face. You’d probably need a microscope to see them.

While we can’t exactly count all the microbes on the planet, we do know there are about a billion microbes in a teaspoon of soil.

Meanwhile, some scientists have estimated there are more microbe species on Earth than stars in the sky.

One way we can learn more about these microbes is to look at their DNA. Just like you, a lot of microbes have DNA.

This DNA is like a genetic code that determines traits such as hair color or eye color. It also is what determines a microbe’s shape, size and what it eats. These differences in DNA can help us tell different microbes apart.

That’s what I found from my friend Viveka Vadyvaloo. She is a scientist at Washington State University who studies a kind of microbe called bacteria.

In particular, she is curious about bacteria called Yersinia pestis that causes bubonic plague. The microbe is usually passed along through fleas and can make people and other animals sick.

Bacteria are just one group of microbes. Some of them make us sick, but others are good and can help us digest our food. There also are archaea. One type of archaea lives in the guts of termites and can help the insects break down the wood they eat.

Fungi are another kind of microbe, like the yeast we use to bake bread. Protozoa are another group of microbes. This group is home to the amoeba. It’s an animal made up of a single cell that can catch food and moves around using little finger-like parts.

If you remember our question about some of the longest-lived creatures on Earth, you know that cyanobacteria are another group of microbes that can make their own food from sunlight.

Vadyvaloo said that another way to learn about microbe populations is to make them reproduce in the lab.

“When I work in the lab with my bacteria, I can make a nice nutritional meal for them, and I can have them grow so I can study them,” she said.

“But there are a number of bacteria, and we don’t know what they all like to eat. If we can’t grow them, we don’t always know they exist,” she said.

Finally, there are viruses. Viruses are microscopic, but they are not considered living things. They can’t reproduce without a host. They need to get into the cells of humans or other animals to keep their populations going. This is how the novel coronavirus spread around the world.

“The one thing we don’t know is how many microbes evolve,” Vadyvaloo said.

It sure makes me wonder about what kinds of microbes we might discover in the future. Who knows, maybe one day we’ll be counting on you to help us learn more about how these tiny living things shape our big world.


Dr. Universe

Dr. Universe is a project from Washington State University. Submit a question at

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