The scientists, led by Sergei Bulat of the genetics laboratory at the Saint Petersburg Institute of Nuclear Physics, reported Thursday that the bacteria was discovered in a water sample taken from Lake Vostok, which sits under more than two miles of Antarctic ice.
Bulat said the new bacterium was found to have DNA that was less than 86 percent similar to previously identified organisms on Earth. A level of 90 percent usually means that the organism is unknown.
He said they ran the bacteria's composition through a global database and were not able to find anything similar to its type. Scientists couldn't even figure out the bacteria's descendents.
This raised the possibility that such isolated bodies of water might host microbial life forms new to science.
"After putting aside all possible elements of contamination, DNA was found that did not coincide with any of the well-known types in the global database," said Bulat, of the genetics laboratory at the St Petersburg Institute of Nuclear Physics.
"We are calling this life form unclassified and unidentified," he added.
The team of researchers is now awaiting more samples from Lake Vostok to continue their analysis. Bulat noted that the drill team headed back to Antarctica in January and should arrive home in May with more deep-core samples to analyze.
Researchers have been studying samples brought up from Vostok, the largest sub-glacial lake in Antarctica, since it was drilled last year. The freshwater lake has likely been buried, unaltered, under the ice for the past million years.
The drilling project took years to plan and implement. The lake's location in the heart of the East Antarctic Ice Sheet, makes it one of the most inhospitable environments on the planet.
It is the place where thermometers recorded the lowest ever temperature on Earth of 128 degrees below zero (Fahrenheit) on 21 July 1983.
Vostok Station was set up by the Russians in 1956, and their seismic soundings soon suggested there was an area of liquid underneath all the ice.
However, it was only in the 1990s that British scientists, with the help of radar, were able to determine the full extent of the sub-glacial feature.
U.S. researchers recently broke through into another Antarctic lake known as Whillans. They have also reported the discovery of microbial life in the lake waters.