The tiny cell that broke a big rule of biology | Grist
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We hand-package the week’s best Grist stories . Delivered free every Saturday morning.
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We hand-package the week’s best Grist stories . Delivered free every Saturday morning.
Jesse Nichols
Video Producer
Published<br>Jul 09, 2026
Topic
Climate + Science
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Bluesky
For decades, Jon Zehr was haunted by an organism he knew was here — but couldn’t see.
It all started in the ‘90s on a research boat in the middle of the ocean. Zehr was an oceanographer studying nitrogen-fixing bacteria — simple, microbial life forms that could pull the element straight from the air, making it bioavailable to plants and animals. Scientists at the time had only seriously studied one species of nitrogen-fixing bacteria in the entire ocean, but Zehr wanted to change that. His plan was to gather and test samples of seawater with the hope that he might find something that other scientists had missed.
Left: Jon Zehr (bottom center) sits aboard a research vessel. Right: Zehr studies nitrogen-fixing bacteria in the lab. Courtesy of Jon Zehr.
Zehr’s plans involved something pretty cutting-edge for the time: DNA. He gathered seawater samples and ran tests for the presence of the gene for nitrogenase, the enzyme that gives bacteria the ability to pull nitrogen out of the air. If he got a hit, it would hopefully mean the seawater contained some new kind of nitrogen-fixing bacteria.
And it worked. Almost immediately, he found traces of a species of nitrogen-fixing bacteria previously unknown to science. Looking at the genes themselves, he could get a pretty good idea of what this new bacteria should look like. It was likely a unicellular cyanobacteria, around 3 micrometers in size, that should fluoresce orange under the microscope. Full of anticipation, he popped the seawater samples under the microscope, expecting to see that bacteria everywhere.
Instead, he found nothing. There weren’t any organisms in the sample that matched the right description.
Surprised, Zehr repeated the process over and over. He tested samples of seawater from the tropical waters of Hawaii and the southern Caribbean, all the way to the cold waters in the Arctic. Again and again, the genetic signature surfaced but not the visible bacteria. It was as if he had discovered a footprint without an animal.
But he didn’t want to stop looking. He knew that any new discovery could represent a vital link in the Earth’s fragile nitrogen cycle. “This one I kept chasing, because it’s globally important,” Zehr said.
To understand Jon’s obsession, it helps to start with a peculiar biological constraint — a cruel joke, as one scientist put it — at the heart of all life on Earth. It goes like this: All living organisms need the element nitrogen to survive. It’s a key part of proteins, DNA, and RNA. But while our atmosphere is absolutely packed with nitrogen, the one enzyme that can pull nitrogen from the air so that living organisms can actually use it basically falls apart in the presence of oxygen. So even though plants, animals, and fungi are constantly surrounded by nitrogen in the air, they can’t get a hold of it on their own.
The only organisms that can actually pull this off are ones that can survive without oxygen: super simple bacteria and archaea. That means the entire natural world relies on a relatively small number of microscopic species to make nitrogen usable by more complex forms of life.
Animals, plants, and fungi rely on simple microbes like bacteria and archaea for nitrogen.<br>Jesse Nichols / Grist
This biological bottleneck has had major impacts on human civilization. Nitrogen is a major component of fertilizer, since plants need it to grow. Enriching soil with nitrogen drastically increases crop yields — important for feeding a growing population. Centuries ago, fertilizer was in such short supply that countries fought wars over islands covered in nitrogen-rich bird guano. In the early 20th century, German scientists created an industrial method to create synthetic, or lab-made, fertilizer. While this invention saved billions of lives from starvation, it also wreaked havoc on the environment. Producing synthetic fertilizer uses a massive amount of energy, and the overuse of fertilizer has polluted the water enough to lead to massive “dead zones” in the ocean.
These dueling problems — the consequences of too much and too little nitrogen — have led scientists to muse about innovations like self-fertilizing plants. But despite these dreams, researchers hadn’t been able to develop a form of complex life capable of fixing its own nitrogen. It seemed to be an ironclad...