Scientists find proof of lower size limit of life in ultra-small bacteria

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Scientists at UC Berkeley and the Lawrence Berkeley National Laboratory have photographed the first detailed microscopy of ultra-small bacteria, proving the existence of a lower size limit of life.

Before the researchers’ discovery, scientists had long debated the existence of ultra-small bacteria, with the smallest bacteria known to be about 0.25 microns in diameter. UC Berkeley researchers, who published their findings in February, have captured evidence of even smaller minimal cells of 0.1 microns in diameter, according to Hoi-Ying Holman, director of Berkeley Synchrotron Infrared Structural Biology at the Berkeley lab.

The discovered bacteria were removed from groundwater aquifers in Rifle, Colorado, but scientists believe that these bacteria could be found in numerous other locations around the world.

“We passed the bacteria through a very fine filter and measured its volume and described its structural features,” said Jillian Banfield, a UC Berkeley professor and senior faculty scientist in the Berkeley lab’s earth sciences division. “Based on the filtration experiment, we found that the cells are very tiny, have small DNA and have a few number of ribosomes.”

Banfield further explained that many of the bacteria have appendages — external organelles that extend into its outer environment and connect with other organisms as a means to survive.

The majority of the genes within these ultra-tiny bacteria, however, whose genome is particularly small, have an unknown purpose. Furthermore, the cell as a whole appears to lack many basic functions, said Banfield, who concluded that the bacteria likely depend on other organisms to sustain its life.

According to Birgit Luef, a former postdoctoral researcher in Banfield’s research group who works at the Norwegian University of Science and Technology, Trondheim, the cell could possibly connect to other proteins and enzymes for reproduction, cell division and survival.

Despite this discovery, the nature of the ultra-small bacterial gene is not yet fully understood. Banfield added that one of the main objectives of the research is to not only better understand the organism but also its potential role in the carbon cycle, explaining that the bacterial cell might play an important role in the breakdown of organic carbon.

But UC Berkeley assistant professor of chemistry and molecular biology Dave Savage said the cell’s discovery could nevertheless augment existing research in related fields. To Savage, the bacteria cell could be used as a “minimal system,” allowing researchers to control every aspect of the cell to create new functionalities, which Savage said could help improve cancer research.

“From a gene perspective, it is interesting to know what is the minimal set of genes that is sufficient for life,” Savage said. “(The research) is very important — it gives us the minimal threshold for what life can be.”

Contact Emily Pedersen at [email protected] and follow her on Twitter @epedersendc.