Two Russian scientists claim to have found a new type of bacteria in a lake buried under 3.5 kilometres of ice in Antarctica, even though the head of a lab involved in the analysis has cast doubt over the results.

The Arctic and Antarctic Research Institute, an agency of the ministry of natural resources of the Russian Federation, issued a news release Monday saying that the evidence for a new microbe comes from a more comprehensive analysis of DNA in the samples taken from the surface of Lake Vostok in February 2012.

That analysis, conducted in a genetics lab at the St. Petersburg Nuclear Physics Institute, compared the DNA to a database of known bacteria and found only an 86 per cent match with known species, said the release from Sergei Bulat and Valery Lukin.

The scientists issued the release roughly a month after U.S. scientists with a competing scientific project announced that they had found live bacteria in clean samples from another Antarctic subglacial ice stream called Whillans, which is buried under 800 metres of ice.

The Russian study was originally presented at a scientific conference in Moscow dealing with astrobiology — the study of how we might find life on other planets, which often looks at organisms found in extreme environments on Earth that may resemble extraterrestrial environments.

However, following media reports about Bulat's and Lukin's announcement last week, Vladimir Korolyov, head of the genetics lab where the analysis was done, cast doubt on the findings in an interview with the Russian news agency Interfax.

Korolyov told Interfax that most of the bacteria found in the samples are thought to be contaminants from the kerosene used in the drilling, from human bodies or from the lab itself.

"There was one strain of bacteria which we did not find in the drilling liquid, but the bacteria could in principle use kerosene as an energy source," Korolyov was quoted as saying. That suggested that even the unknown organism might not come from the Lake Vostok, but from the ice or the drill.

Korolyov added that pure samples would be collected from the lake next year.

"For now, we 'd rather not say something," he said.

The news release acknowledged that the sample used in the analysis was lake water mixed with jet fuel and Freon drilling fluid and was "very dirty." However, it said that the researchers worked hard to process and analyze the water.

Lyle Whyte, a scientist at McGill University in Montreal who holds a Canada Research Chair in environmental microbiology, said Bulat and Lukin present an interesting result, but further analysis of clean samples would be needed to justify their conclusions.

Whyte, who studies microbes in Canada's High Arctic, added that it's not unusual for organisms found in the Arctic and Antarctic to show only 80 to 90 per cent similarity with known microbes.

Lake Vostok has been buried beneath kilometres of ice and cut off from the rest of the world for millions of years. Scientists have speculated that it may therefore contain very unique ecosystems. Russian scientists began drilling toward the surface of the lake in 1990 from the Vostok research station and finally broke through 13 months ago.