Scientists have captured the first detailed microscopy images of what are believed to be some of the smallest organisms on Earth.
The existence of these super-small bacteria has been debated for decades, but there has been little concrete evidence available until now, DOE/Lawrence Berkeley National Laboratory reported. These cells have an average volume of 0.009 cubic microns, and about 150,000 cells could fit onto the tip of a human hair. This is the smallest a cell could be while still having the ability to hold enough material to sustain life.
"These newly described ultra-small bacteria are an example of a subset of the microbial life on earth that we know almost nothing about," said Jill Banfield, a Senior Faculty Scientist in Berkeley Lab's Earth Sciences Division and a UC Berkeley professor in the departments of Earth and Planetary Science and Environmental Science, Policy and Management.
The tiny bacteria were discovered in groundwater, and are believed to be relatively common. They contain densely packed spirals that are believed to be DNA, as well as a miniscule number of ribosomes and hair-like appendages. The bacteria have a "stripped-down" metabolism, which suggests they rely on other bacteria to live.
"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," said Birgit Luef, a former postdoctoral researcher in Banfield's group who is now at the Norwegian University of Science and Technology, Trondheim.
To sample these fascinating organisms, the team filtered groundwater to concentrate the cells in a sample. The cells were then frozen to negative 272 degrees Celsius in a state-of-the-art cryo plunger. The samples were transported to the Berkeley Lab, where researchers analyzed the cells' size and internal structure using 2-D and 3-D cryogenic transmission electron microscopy. The bacteria's genomes were also sequenced at the Joint Genome Institute. The findings revealed just how little scientists really know about these super-small bacteria.
"We don't know the function of half the genes we found in the organisms from these three phyla," Banfield said.
The findings were published in a recent edition of the journal Nature Communications.
