Ice-olated Bacteria Still Viable after 2,800 years!

Lake Vida is a hyper-saline Antarctic lake discovered in 2002. It has been the subject of research due to being fully endoheric, it is encapsulated by a year-round 15.8m ice cover, with an underlying 800-970m of permafrost. The temperature of the lake was recorded at -13°C but stays as liquid water due to its extremely high salinity, it is slightly acidic at pH6.2. This fully encapsulated lake has no inflow of energy in any form, however viable and actively metabolising bacteria have been found, which have been locked in the ice and isolated from the outside world for ~2,800 years.

Originally, when first discovered, these bacteria were thought to have been frozen in the ice and accidentally thawed and reanimated upon extraction, however in this study it is concluded that the bacteria have been viable for the full ~2,800 years of isolation, living on a maintenance level metabolism, without any forms of obvious energy input from the sun due to the think ice cap above or from ground heat/water due to the underlying permafrost. The paper aims to find out what, exactly, the bacteria are using as an energy source and how they obtain nutrients.

A variety of biochemical tests were performed on extracted ice cores and brine samples to determine oxygenicity, dissolved organic carbon levels, mineral levels (N₂O, Fe, S) and methane levels. Scanning electron microscopy was used to visualise cells.

The author states early on in the article that even though the lake has no energy source, the ecosystem would still be expected to contain life. However it was predicted that the system would be primarily methanogenesis, as expected in the final stages of decomposition. The results, in contrast, showed that a complex geochemistry with enormous amounts of various chemicals needed to sustain several types of metabolism were present. The range of compounds found include dissolved metals, inorganic and organic carbon, N₂O, H₂, as well as large amounts of both reduced and oxidized forms of dissolved nitrogen. This suggests that, together with the microbial assemblage that is potentially capable of metabolisms ranging from denitrification to chemolithoautotrophy and fermentation, a complex and adaptive ecosystem is capable of lasting ~2,800 years and more, as the author states that with the current DOC level the lake may last for a “far more prolonged period”. This gives arise to the speculation that life may still yet exist in similar situations on Mars, Europa and Enceladus, and if so, may tell us more about the origin of life on Earth (proving or disproving the Panspermia hypothesis).

 Initially it was speculated that a coupled Iron(III)-Sulphate reduction cycle metabolism was the predominant feature which allowed the constant turnover of energy, however this was rejected due to a high DOC concentration in the brine. Instead the research explains a system where the brine reacts with the surrounding serpentinite rock, to release H₂ and N₂O into the water, which is subsequently used by the bacteria. 16S rRNA gene sequence analysis showed that several species present (Phyla Firmicutes and Bacteroidetes) are able to metabolise H₂ as an energy source to prevent depurinisation and racemization. These speculations are supported by the autochthonous carbon inventory (the carbon originally isolated with the lake) only decreasing by 0.002%, however this equation assumes the respiration is equal to production.

Whilst this paper suggests some interesting and unique concepts, one problem which the authors glance over is predominantly worrying. Lake Vida has been an enclosed and isolated ecosystem for nearly 3,000 years, a pristine example of a system completely devoid of human interference. By taking samples the researchers may have contaminated the lake and no description is given to any aseptic technique, apart from detailing the method used to store the samples/cores. However, even with this nagging sense of human destruction, this paper makes for an interesting read, and the promise of potentially finding life in similar ecosystems on other planets is particularly enticing.