This week a pioneering study published in the Proceedings of the National Academy of Science< (PNAS) reveals, for the first time, a viable community of bacteria that survives and ekes out a living in a dark, salty and subfreezing environment beneath nearly 20 meters of ice in one of Antarctica’s most isolated lakes.
The study, lead by Dr Alison Murray and Dr Christian Fritsen of Nevada’s Desert Research Institute (DRI) USA, included Dr Ashley Townsend from the UTAS Central Science Laboratory as part of a multi-national team that also included Dr Ross Edwards, a past UTAS graduate (now at Curtin University).
Lake Vida, the largest of several unique lakes found in the McMurdo Dry Valleys, contains no oxygen, is mostly frozen and possesses the highest nitrous oxide levels of any natural water body on Earth. A briny liquid that is approximately six times saltier than seawater percolates throughout the icy environment that has an average temperature of minus 13.5 degrees centigrade.
“This study provides a window into one of the most unique ecosystems on Earth,” said Murray, the report’s lead author.
“Our knowledge of geochemical and microbial processes in lightless icy environments, especially at subzero temperatures, has been mostly unknown up until now. This work expands our understanding of the types of life that can survive in these isolated, cryoecosystems and how different strategies may be used to exist in such challenging environments.”
Despite the very cold, dark and isolated nature of the habitat, the report finds that the brine harbors a surprisingly diverse and abundant assemblage of bacteria that survive without a present-day source of energy from the sun. Previous studies of Lake Vida dating back to 1996 indicate that the brine and its’ inhabitants have been isolated from outside influences for more than 3,000 years.
The team developed stringent protocols and specialised equipment for their 2005 and 2010 field campaigns to sample the lake brine while avoiding contaminating the pristine ecosystem. To sample the unique environment researchers worked under secure, sterile tents on the lake’s surface to keep the site and equipment clean as they drilled ice cores, collected samples of the salty brine residing in the lake ice and then assessed the chemical qualities of the water and its potential for harboring and sustaining life, in addition to describing the diversity of the organisms detected.
Back in their laboratories at either end of the country, the two Australian researchers Townsend and Edwards determined the composition of the lake’s brine by reducing the salty water to its constituent atoms using instrumentation called Inductively Coupled Plasma Mass Spectrometry – a technique that breaks down samples using a hot plasma at temperatures like that of the sun. Determining the mass of the atoms revealed their identities (mass spectrometry). Townsend said that this was analytically challenging work.
"Looking for the presence and concentration of trace elements in brine solutions is like looking for "a needle in a haystack".
"You need to measure the presence of an analyte, while at the same time, not contaminating the sample."
Such geochemical analyses suggest that chemical reactions between the brine and the underlying iron-rich sediments generate nitrous oxide and molecular hydrogen. The latter, in part, may provide the energy needed to support the brine’s diverse microbial life.
“It’s plausible that a life-supporting energy source exists solely from the chemical reaction between anoxic salt water and the rock,” explained Fritsen.
“If that’s the case,” said Murray. “This gives us an entirely new framework for thinking of how life can be supported in cryoecosystems on earth and in other icy worlds of the universe.”
This research was supported jointly by NSF and NASA, while the CSLs ICP-MS infrastructure was purchased with support from ARC LIEF and UTAS funds.