Researchers in Germany have found a remarkable new type of microbe so small that dozens could cluster on the back of a regular bacterium, writes Dick Ahlstrom
Scientists have discovered a "new" form of life that could date back billions of years to when the earliest life forms evolved on Earth. The heat-loving bacteria are so tiny that six million of them would easily fit on the head of a pin.
The newcomer was recovered from the bottom of the Atlantic off Iceland, 120 metres down in the 90 degree heat of a volcanic undersea vent. Its genetic blueprint is close to the smallest yet discovered for a living organism. It is a genome that suits their minute size, just 400 millionths of a millimetre across.
The organisms are so small and so very different from anything seen before that the genetic probes usually used to detect life just didn't work, according to Prof Karl Stetter and his colleagues at the University of Regensburg and the Max Planck Institute for Medical Research, both in Germany. The researchers describe their unusual find in the journal Nature.
The organism represents a new phylum of the Archaea, one of the three giant branches of life along with "regular" bacteria and Eukaryotes, which includes us. Its remarkable size prompted the scientists to name the phylum Nanoarchaeota, and this particular species is called Nanoarchaeum equitans.
Another surprising aspect of the new bug is that it lives on the back of another newly discovered heat-loving archaeic bacteria. It is no parasite and seems to enjoy a symbiotic lifestyle with the much larger organism, Ignicoccus, recovered from the same deep-sea vent.
N equitans doesn't seem to be able to survive on its own, although the researchers admit they know very little so far about this unusual form of life and don't know how Ignicoccus helps it to live.
They have established, however, that it has a very small genome of just 500,000 steps, "close to the theoretical minimum genome size calculated for a living being". In comparison, the human genome has billions of steps.
It lives in near-boiling temperatures in the absence of oxygen, probably dining on sulphur, although this remains uncertain. These conditions nicely mimic those thought to have existed on the young Earth more than three billion years ago, when scientists believe primitive life forms first evolved.
The research team can't say that N equitans has been around from the very beginning; "however, its high growth temperature and anaerobic mode of life correlates with probable early environmental conditions, which suggest that the Nanoarchaeota are possibly still a primitive form of microbial life".