It’s life, but not as we know it

The deserts of Antarctica are one of the most extreme environments on earth. While it was once believed that the harsh conditions precluded life, we now know that terrestrial Antarctica hosts a surprising diversity of microbial taxa.

Chris Greening from the Centre for Geometric Biology  and colleagues (Sean Bay, Thomas Lines and John Beardall) from the School of Biological Sciences have been working with researchers from a range of institutions to investigate how microbes can exist despite freezing temperatures, strong UV radiation, frequent freeze-thaw cycles and limited carbon, nitrogen and water availability.

Soil samples from three arid Antarctic sites were found to have low concentrations of organic carbon, nitrogen and moisture content and a low proportion of phototrophs (organisms able to use light to create energy)  – findings incompatible with observed bacterial diversity.

Adams Flat: one of the arid, Antactic sampling sites with surprisingly high microbial diversity.

The researchers used a range of techniques to help them understand the possible alternative energy sources that microbial communities are using to support their maintenance energy and carbon needs.

Shotgun DNA sequencing identified a large number of taxa and also genes that suggested that the Antarctic microbial communities are able to scavenge H2/CO2 and CO from the atmosphere to use as energy and carbon sources. These findings were followed up by further experimental work to test the hypothesis that microbial communities are, in fact, using atmospheric trace gases for carbon and energy sources.

In laboratory microcosms, the research team found that soil communities aerobically oxidised atmospheric H2 and CO.  What’s more, when 14C-labelled CO2 was added to microcosms, H2 addition caused a significant increase in CO2 fixation in the dark but not the light.  These findings are consistent with the hypothesis that energy needs are being met via chemosynthetic and not photosynthetic CO2 fixation.

The arid and nutrient starved surface soils from Antarctica are the first ecosystem described to date that appears to use atmospheric trace gases to drive primary production.  But it may not be the last; possibly this process also dominates other arid desert systems and provides a mechanism to explain high microbial diversity in nutrient starved environments as well as opening the door to the possibility that atmospheric gases could support life on other planets.