By Robert Cooke
The first member of a new family of ultra-tiny microbes, smaller than known bacteria, was recently captured in scalding-hot water jetting up through the sea floor near Iceland, scientists said. It is unlike any other creature known.
What the German research team is calling "a new, nano-sized hyperthermophilic archaeon" is tinier than the smallest known living organisms, mycoplasma.
Still, it is larger than those semi-living things, the viruses. So it seems to represent a class of its own.
Because it has only about half a million links in its chain of genetic material, the researchers said, the new microbe "is close to the theoretical minimum genome size for a living being".
At a mere 400 millionths of a millimetre across, more than 6million would fit on the head of a pin.
The microbes are classified as Archaea - one of the three giant branches of life that also include bacteria and eukaryotes, organisms with cell nuclei.
Archaea are genetically different from bacteria and many are "extremophiles" that live in the most extreme environments on Earth.
But although Archaea include some very strange primitive life forms, the new group is odder than anything found before and thought to comprise a new category within the domain.
The discovery was announced by Harald Huber, Karl Stetter and their colleagues at the University of Regensburg, Germany, and Verena Wimmer at the Max Planck Institute in Heidelberg, Germany, in the journal Nature.
The new creature, named Nanoarchaeum equitans, seems to be primitive indeed. The researchers said the bug's need for high temperatures and no oxygen "correlates with probable early environmental conditions" when life was first forming on Earth.
This suggests, they said, "that the Nanoarchaeota are possibly still a primitive form of microbial life" that arose very early in evolution, when life was just getting going on this planet.
Although it was found living on larger microbes, it is not yet clear whether it is a parasite, or lives there symbiotically.
Yan Boucher and Ford Doolittle, biologists at Dalhousie University in Nova Scotia, say the organism "is an exciting new creature ... that is as worthy of our attention" as any living fossil discovered, such as the big coelacanth fish. It also has "a genome begging to be sequenced", meaning studied in molecular detail.
Such discoveries, they said, raise "a lingering suspicion - or romantic hope - that there might be even weirder organisms hiding out there".