Biologists Discover Smallest of Propellers That Make Archae Faster Than Cheetahs

The molecular structure of the propellers. Source Exeter University

Biologists at the University of Exeter, England, have discovered new information on tiny locomotive structures or propellers used by archaea. The study also identified the structural elements that helped propellers to improve flexibility.

Like bacteria, archaea are single-celled organisms found in large habitats. They are found living in extreme conditions, such as in high salt concentrations, pressures and temperatures. Some species also live in human bodies but unlike bacteria, they do not cause any disease.

Archaea have a spiral-shaped filament-like structure called archaellum for locomotion. Some species are able to propel themselves at high speeds by rotating the archaellum. These filaments have intracellular motors that are responsible for rotating these extracellular filaments. The motors use ATP (Adenosine Tri-Phosphate) source of energy for the process.

Methanocaldococcus villosus is a species of archaea found near underwater volcanoes off Iceland. Here, the water temperature can reach up to 80 degrees celsius. They cultured them in nitrogen, carbon dioxide, sodium sulphide and adjusted pH.

“M. villosus swims at a speed of about 500 body lengths per second,” said Dr Lavinia Gambelli, a biologist at the University of Exeter. “Considering that the tiny cell is only about one micrometre in size, this means half a millimeter in one second. At first glance, this does not seem much. But in comparison, a cheetah achieves only 20 body lengths per second, so if an M.villosus cell had the size of a cheetah, it would swim at approximately 3000 kilometers per hour. The incredible speed that M. villosus can achieve makes it one of the fastest organisms on the planet.”

Biologists used the cryo-electron microscope to observe the archae. This microscope can determine cell size whose width is small like hydrogen atoms. Further, they kept the resolution power at 3.8 Å to observe their structure.

“At this resolution, we can see the very fabric of life and study fundamental biological processes at atomic detail,” said Dr Bertram Duam, a Senior biologist at the University. “In this study, we were able to look closely at the smallest propeller in the world, to find more about its shape and how it works. As well as teaching us more about these fascinating organisms, this could have implications for human health and technology.”

Previously, biologists discovered only a single protein in the filament called archaellins. But, the new study found that the filament or archaellum used by M. villosus had thousands of copies of two alternating proteins.

The research indicated that the genetic structure and assembly of the filament were more complex than assumed before. The biologists also found two structural elements that helped archae move the filament and propel cells at high speed.