Bacteria rule: Life found deep beneath Antarctic ice!

ENLARGE

Electron microscope image showing a coccoid shaped microbial cell attached to a larger sediment particle from sub-glacial Lake Whillans.

Photo: Trista Vick-Majors

The temperature hovers at freezing. The water is super-pressurized and pitch black. But a lake 800 meters below the West Antarctic ice sheet is brimming with microbial life. That’s according to a new study that documented 3,931 types of bacteria and Archaea (an even more ancient group of organisms) in sub-glacial Lake Whillans.

Using great care to avoid contamination from surface microbes, a team led by Brent Christner, an associate professor of biological sciences at Louisiana State University, used a hot-water drill to reach the lake in January, 2013. In this week’s Nature, Christner and colleagues described how they put samples of water and sediment through gene-recognition technology.

The resulting biodiversity was surprising, Christner says. “One primary reason I got into the ecology of extreme environments was the thought that when the level of stress went up, diversity would go down, and you would have fewer species.” The idea that an extreme ecosystem would be provide an easy answer to basic ecological questions, “is one idea that I might have to abandon. This is anything but simple.”

WIS = Whillans Ice Stream; SLW = Sub-glacial Lake Whillans; hydropotential = water pressure at base of ice sheet; grounding line is where the ice sheet begins to float on the ocean.

Courtesy Brent Christner, LSU

Previous reports of microbes from other lakes under the Antarctic ice have met skepticism, due to the possibility of contamination by surface microbes. To avoid that problem while melting through 800 meters of ice required “a significant effort,” Christner says.

Keeping it clean

To feed uncontaminated water to the hot-water drill, a 40-foot shipping container held a water purification system with filters down to 0.2 microns and then a high-intensity ultraviolet lamp “that blasted any organisms that were still present,” Christner says. “That water was comparable to pharmaceutical grade water.”

The few cells present in drilling water came from the ice that was melted while drilling, Christner says, but the concentration of microbes was thousands of times higher inside the lake.

The vast majority of DNA sequences were related to known organisms, but it was not surprising that others were not, Christner says. “Just about every study that uses these tools will detect organisms we have never seen before.”

Christner confirms that some of those microbes are now being grown in the lab.

The picture that emerged from Christner’s research, which was sponsored by the National Science Foundation, is anything but simple. Some microbes release energy as they metabolize iron or sulfur — they “eat rock,” as geomicrobiologist Martyn Tranter of the University of Liverpool put it in a commentary in Nature. Some microbes in the lake extract carbon — a necessity for life — from carbon dioxide, performing the same service that green plants do through photosynthesis. These microbes also transform nitrogen into the bio-available forms nitrate and ammonium.

A careful drilling process was necessary to avoid contamination with microbes from the surface. Rollover image to see muddy sediment retrieved from Sub-glacial Lake Whillans.

Both photos Reed Scherer, Northern Illinois University

So what?

It’s hard to imagine liquid water in a place as frigid as Antarctic, but due to heat from the earth and friction against the base of the ice, 55 percent of the West Antarctic ice sheet actually rests on water. Lake Whillans was slightly more than 2 meters deep at the borehole, and may reach a depth of 10 meters or so. The lake has emptied periodically into the ocean, which is located about 100 kilometers away.

Where do you call home, microbe?

We asked Tranter to speculate about the source of the microbes, and he suggested they may have reached their present home at least half a million years ago, when the ice sheet was much smaller. Microbes could have fallen from the air onto exposed rock, or rained from the ocean onto submerged areas that now underlie glaciers.

In either case, as the ice grew, these microbes would have remained alive even as the sediment and lake were buried under ice. “It seems completely wacky that organisms would be okay living in the cold, beneath a kilometer or so of ice,” Tranter admits. “But if you think about deep sea sediments, the water column over them is on the order of one, two, even five kilometers, and a lot of ocean bottom water is 2°C, not much different from the 0°C under the West Antarctic ice sheet. So it’s not too much of a stretch of the imagination to think that those sediments would still contain microorganisms that essentially don’t care if a big column of sea-water, or ice, is above them.”

We suggested that, given the documented flow of water beneath the ice sheet, perhaps sub-glacial rivers carried in the microbes, and Tranter responded, “People would have laughed at you a decade ago, but there is a river system under the ice sheet. Just how that system flows, whether the flow is constant, these are the sort of things that are going to grab the imagination of the next generation of polar scientists.”

The current paper, Tranter says, “will stimulate all sorts of activity on the sub-glacial environment.”