July 5, 2013
Subglacial Life Found In Ice Cores From Lake Vostok, Antarctica
Lawrence LeBlond for redOrbit.com - Your Universe Online
Lake Vostok, the largest of some 400 subglacial lakes scattering Antarctica's frozen depths, has been the subject of ambitious research for at least the past 15 years. Lying more than 2 miles below the surface, the lake was first drilled in 1998 by a team of Russian, French and American scientists.
But such was not the case. A research team led by Dr. Scott Rogers, a Bowling Green State University professor of biological sciences, has been busy revealing a surprising variety of life forms living, thriving and reproducing in one of the most extreme environments on planet Earth.
A paper on the thousands of species so far identified from Lake Vostok is published in the June 26 issue of PLoS ONE.
Rogers explained this is the fourth article he and his team have published on their investigations of Lake Vostok. The work has been supported by several grants, which include those from the National Science Foundation, the USDA and the BGSU Faculty Research Committee.
Finding unique life forms is only one amazing aspect of this remote region. Lake Vostok is the fourth-deepest lake on Earth and is the largest of all subglacial lakes known in Antarctica. The ice that is covering the lake has done so for the past 15 million years, creating tremendous pressure on the subglacial body of water. The weather in the region is so harsh and unpredictable that scientists must utilize special gear and undergo survival training just to visit the site.
As for the existence of life in such inhospitable conditions, Rogers and colleagues thought the environment would be too harsh for such a discovery. However, upon studying the core samples removed from the deep layer of ice accreted from lake water that froze where glacier meets water, Rogers and colleagues discovered samples teeming with life.
The samples of ice examined were as clear as diamonds, forming in the relatively warm temperatures of the lake, due to the intense pressure from the ice above. Two separate core samples from different areas of the lake have showed similar finds.
"We found much more complexity than anyone thought," Rogers said. "It really shows the tenacity of life, and how organisms can survive in places where a couple dozen years ago we thought nothing could survive."
The team used DNA and RNA sequencing of the ice core samples to identify thousands of bacteria, including some that are commonly found in the digestive systems of fish, crustaceans and annelid worms, as well as in fungi. Other species discovered are associated with habitats of lake and ocean sediments.
The team also found psychrophiles, or organisms associated with extreme cold, along with thermophiles. The existence of thermophiles, organisms that prefer heat, suggests to the team there may be hydrothermal vents deep in the lake, keeping these organisms alive. As well, the presence of both freshwater and marine water species suggests the lake was once connected to the ocean and freshwater may have been deposited in the lake by the glacier.
Of the two areas studied, the southern embayment region of the lake has produced the largest number of species, including many that are common to freshwater environments. They also found more psychrophiles and thermophiles in this sampling. The team believes the embayment area appears to contain much of the biological activity in the lake.
"Many of the species we sequenced are what we would expect to find in a lake," Rogers said. "Most of the organisms appear to be aquatic (freshwater), and many are species that usually live in ocean or lake sediments."
BGSU Doctoral student Yury Shtarkman said, "It's a very challenging project and the more you study, the more you want to know. Every day you are discovering something new and that leads to more questions to be answered. In studying the environmental DNA and RNA, we ask how similar are these sequences to those of sequences from organisms already identified in national databases. We are tracing the evolution and the ecology of the lake itself. "
The climate of Antarctica was not always frozen. Before 35 million years ago, the climate was rather diverse with many plants and animals. Then about a million years later, a "huge drop in temperature occurred" and ice covered the lake, when it was probably still connected to the Southern Ocean. The sea ice then lowered by as much as 300 feet, cutting the lake off from the ocean. Then about 14 million years ago a second big temperature drop occurred and sea levels dropped even farther.
As ice built up over the lake, it was plunged deeper into darkness and became isolated from the atmosphere. As the ice cover grew, so did the pressure. While many species would have vanished from the lake, it seems many more survived, according to the study results.
Rogers said the team had been working on the samples for years, but it was a very slow process. To help move the process along, he said they started thinking of going about the process in a different manner.
Instead of culturing living organisms, the team concentrated on sequencing DNA and RNA in the ice. Using metagenomics and metatranscriptomics, the team produced thousands of sequences at a time and analyzed them with "Big Data" methods via computer. This process quickly outpaced the older method, which would have taken years to generate enough cultured organisms to get just a few dozen sequences.
However, this strategy did pose a problem. The team went from having too few sequences to having too many to analyze. But after two long years of analysis, the final results showed Lake Vostok contains a diverse set of microbes and multicellular organisms.
While the new method has been proven much more efficient, Rogers was cautious in giving it a 100-percent approval rating. Despite this, he feels there's a multitude of organisms in the ice core samples, many from the lake itself, that warrant additional research.
The DNA sequences produced by Rogers' research, have been deposited in the National Center for Biotechnology GenBank database, and will be available to other researchers for further study.
Researchers from another group said they had found organisms from ice core samples taken from Lake Vostok earlier this year, but later retracted that finding, reporting their equipment was contaminated with drilling oil.