Extremophiles are well-adapted to a volcanic lake

Microbes living in one of the most hostile habitats on the planet – in the crater lake of a volcano – might guide our search for ancient life on Mars, according to new research.

The lake is nestled in the 2,697-metre Poás Volcano, in Costa Rica. It’s filled with ultra-acidic water – 10 million times more acidic than tap water – with a high toxic metal content. Magma channels running under the lake can trigger geyser-like eruptions of steam, ash and rock, and within a few hours water temperatures can swing from comfortable to boiling.

But despite it all, microbes from a single ‘extremophile’ genus are thriving. In a new paper published in Frontiers in Astronomy and Space Science, researchers found out how.

According to Justin Wang, lead researcher from the University of Colorado Boulder, US, the team found only a few types of microorganisms, but a “potential multitude” of ways for them to survive.

“We believe they do this by surviving on the fringes of the lake when eruptions are occurring,” he explains. “This is when having a relatively wide array of genes would be useful.”

In 2013, researchers first found a single microbial type in the crater lake: Acidiphilium. This type of bacteria also commonly found in toxic drainage from coal mines and other hydrothermal systems, where water is heated by the Earth’s processes such as volcanism of hot magma beneath the crust. These bacteria are generally known to have multiple genes that help them better survive their surroundings.

Now, this latest study has sequenced the DNA of the bacteria in the crater lake to find that they have a range of biochemical ‘tools’ to tolerate extreme and changing conditions. This includes the potential to create energy from a range of things including sulphur, iron, arsenic, carbon fixation, simple and complex sugars, and bioplastic granules.

“We expected a lot of the genes that we found, but we didn’t expect this many given the lake’s low biodiversity,” says Wang. “This was quite a surprise, but it is absolutely elegant. It makes sense that this is how life would adapt to living in an active volcanic crater lake.”

Life on Earth is thought to have arisen in hydrothermal systems like these, as they provide the key ingredients of heat, water and energy. Studying modern-day systems can give scientists glimpses into our own origins – as well as an idea of how life could exist on other planets like Mars.

“Our research provides a framework for how ‘Earth life’ could have existed in hydrothermal environments on Mars,” explains Wang. “But whether life ever existed on Mars and whether or not it resembles the microorganisms we have here is still a big question.”

He suggests that while previous searches for life on the Red Planet have focused on streambeds and river deltas, we should perhaps pay more attention to ancient hot springs that existed on Mars billions of years ago. In these early days, volcanism was rampant, creating hot, volatile, mineral-rich pools of water.

Despite the seemingly lethal conditions of these environments, the bacteria studied in this new paper show that organisms can adapt by creating energy from all kinds of minerals.

The team even has some ideas of where on Mars to look for these hot springs.

“There are some good targets on the crater rim of Jezero Crater, which is where the Perseverance rover is right now,” Wang says.