Climate change is wiping out rare bacteria in Antarctic soil

Antarctica’s cold, dry soils are teeming with microbial life, but we know remarkably little about how its microorganisms are affected by climate change.

New Australian research has begun to fill in these gaps, focussing on a specific type of microbe – chemotrophs.

These use trace gases in the atmosphere – such as hydrogen, methane, and carbon monoxide – as an energy source in a process known as chemosynthesis. Phototrophic microbes, on the other hand, use visible light as an energy source through photosynthesis.

The research revealed that chemotrophs declined in Antarctic soil over a 14 year period from 2005 to 2019.

“Until recently, climate predictions were made without really looking at the role of microbes,” says Belinda Ferrari, a professor in the School of Biotech & Biomolecular Science at the University of New South Wales, and who is senior author of the new paper in Conservation Biology.

“We still don’t even really know exactly what these microbes are doing – most of them haven’t even been cultured in the lab.

“We think it’s important to monitor changes to the abundance of these bacteria as it could have significant effects on climate and environment.”

Ferrari and collaborators looked at data from soil samples collected in 2005 on the Windmill Islands in eastern Antarctica.

They then employed a technique known as “gradient forest modelling,” which is usually used to project animal and plant species’ survival into the future, based on changing environmental parameters.

“We analysed 17,000 species at once, and we looked at over 70 different environmental parameters,” says Ferrari.

“There were different things we measured in the soil, like how much carbon, the pH, moisture, things like that, and used that to predict where you might get a tipping point that will lead to a change in community structure.”

The model suggested that, as the Antarctic desert gets less arid and soil moisture increases with climate change, changing conditions would favour phototrophic microbes over chemotrophic ones.

“These bacteria are really rare. They’re the ones that live on trace gases in the atmosphere, but in Antarctica they’re actually the dominant microbes,” says Ferrari.

Testing their projections against a second set of soil samples, collected 14 years later in 2019, revealed a decline in the abundance of these rare chemotrophic taxa.

“We predicted at about 10 to 12% moisture in the soil, we’d get a shift from those chemotrophs to the phototrophs. And that’s exactly what we found,” says Ferrari.

The possible effects of this shift in the composition of microbial populations could have a knock-on effect on the Antarctic ecosystem.

Chemotrophs play a role in carbon sequestration by removing hydrogen, carbon monoxide and carbon dioxide from the atmosphere and storing it in organic compounds. If they were to disappear completely, it could affect greenhouse gas concentration and may even accelerate the warming of the local climate.

The researchers call for further research and say that “better understanding of such threshold tipping points will aid conservation efforts.

“It is crucial that long-term monitoring of these sites is established for the protection of Antarctic desert ecosystems.”