First Images of What May Be Smallest Bacteria on Earth

Scientists have captured the first detailed microscopy images of what may be the smallest bacteria on Earth, according to a new study.

It has been debated for the last two decades whether or not ultra-small bacteria exist, and until now scientists have been unsuccessful in obtaining a comprehensive electron microscopy and DNA-based description of the microbes.

Described in the journal Nature Communications, the new bacteria have an average volume of 0.009 cubic microns. They are so small that about 150 of them could fit inside an Escherichia coli cell, and more than 150,000 cells could fit onto the tip of a human hair.

"There isn't a consensus over how small a free-living organism can be, and what the space optimization strategies may be for a cell at the lower size limit for life. Our research is a significant step in characterizing the size, shape, and internal structure of ultra-small cells," Birgit Luef, one of the researchers, said in a news release.

The diverse bacteria, which are thought to be quite common, were found in groundwater. This groundwater was then filtered and 2-D and 3-D cryogenic transmission electron microscopy was used to characterize the cells' size and internal structure.

They found that the DNA of the bacterial cells is about one million base pairs in length. They have a basic metabolism and hair-like appendages, called pili, which likely serve as "life support" connections to other microbes. Researchers indicate that since these bacteria lack many basic functions, they probably rely on other bacteria for many of life's necessities.

"They're enigmatic. These bacteria are detected in many environments and they probably play important roles in microbial communities and ecosystems. But we don't yet fully understand what these ultra-small bacteria do," said researcher Jill Banfield, from the US Department of Energy's Lawrence Berkeley National Laboratory and the University of California, Berkeley.

These bacteria are thought to be about as small as life can get, but believe it or not this isn't the first time researchers have found ultra-small organisms. Recently, scientists estimated the cell volume of a marine bacterium at 0.013 cubic microns, and prior electron microscopy imaged a lineage of Archaea with cell volumes as small as 0.009 cubic microns, similar to these latest bacteria.

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