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This Could Be the Tiniest Organism on Earth

Scientists capture an image of ultra-small bacteria

More than 150,000 of these tiny bacterial cells could fit onto the tip of a human hair. (Berkeley Lab)
smithsonian.com

For 20 years, scientists have debated the existence of super-small bacteria. The theoretically tiny organisms presented a big problem to researchers—they were delicate, hard to capture and simply too small to see. But that all changed this week, when researchers announced that they were able to capture the first-ever detailed microscopy images of the miniature life forms.

An international team of scientists led by researchers from the U.S. Department of Energy’s Lawrence Berkeley National Laboratory and the University of California, Berkeley, theorized that ultra-small bacteria are actually quite common. But in order to capture images of the organisms, they had to capture the microbes first—and that proved no easy feat.

Using a series of tiny filters, they filtered groundwater down to a size of 0.2 microns. Then they flash-froze their delicate samples to -272°C and used a “cryo plunger” to transport the samples from the field to the lab. The team used state-of-the-art electron microscopes to capture an image of the super-small bacteria within before sequencing the organism’s genome. (They found about one million base pairs of DNA.)

So what did they see? Cells so tiny, 150,000 of them could fit on the tip of a single human hair. The team described the cells in a release:

They’re also quite odd, which isn’t a surprise given the cells are close to and in some cases smaller than several estimates for the lower size limit of life. This is the smallest a cell can be and still accommodate enough material to sustain life. The bacterial cells have densely packed spirals that are probably DNA, a very small number of ribosomes, hair-like appendages, and a stripped-down metabolism that likely requires them to rely on other bacteria for many of life’s necessities.

Though researchers believe the microbes are relatively common, several questions remain unanswered. How do the microbes, which lack many basic functions, work with other organisms? What purpose do the genes serve? And the existence of these infinitesimal organisms begs an even bigger question—are there even smaller life forms out there?

Those questions may remain open for now, but one thing is clear: we’ve come a long way since the first electron micrograph of an intact cell, which was photographed in 1945.

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