The search for life on Mars is not an easy task. Not only is the red planet difficult to get to, it is also extremely inhospitable to life as we know it.
However, there are places on Earth that can show us how life could have survived on Mars – if not now, then at some other point during the 4.5 billion years of the planet’s history. Places are like deserts, you might think, and you would be right; but there is more to Mars than deserts.
Scientists have studied microbes that somehow survive in one of the most inhospitable places on Earth: a hot, toxic, acidic lake in a volcanic crater in Costa Rica. How these extremophile microbes adapt to their hellish environment could show us how microbes could once live on a younger, wetter, more volcanic Mars.
“One of our key findings is that in this extreme volcanic lake, we have found only a few types of microorganisms, but a potential multitude of ways in which they can survive,” said astrobiologist Justin Wang of the University of Colorado Boulder.
“We believe they do this by surviving on the outskirts of the lake when eruptions occur. That’s when it would be useful to have a relatively broad set of genes.”
The lake is known as Laguna Caliente (literally “hot lake”) and is located in the crater of the active volcano Poas in Costa Rica. It is one of the most acidic lakes in the world, with a layer of liquid sulfur floating along the bottom and often causing localized acid rain and fog. In addition, the water is saturated with toxic metals. It’s not exactly teeming with life.
However, it is not completely uninhabited. In 2013, a research team led by the University of Colorado at Boulder found that a single species of microbe survived in the lake. acidophiliaor “acid lovers”, who live in an acidic environment and have a number of genes that allow them to do so.
The Poas volcano continued to rumble, and in 2017 there was an explosive eruption. Naturally, the research team decided to revisit Laguna Caliente to see how the ongoing volcanic activity might have affected the microbial community they discovered in 2013, especially since the volcanic eruptions may have sterilized the lake.
The researchers took samples from the lake, sulfur lumps and sediments at the bottom of the lake and subjected them to gene sequencing and a metagenomic shotgun to identify any organisms that might be lurking in it. Amazing but not only acidophilia was still present, as were a small number of other microbial species.
acidophilia was the dominant species living in the lake, but they all had significant adaptations for survival. The team found that the bacteria have genes that can confer acid resistance, as well as heat tolerance genes, which are vital in environments that can reach boiling temperatures.
In addition, organisms have a large number of genes that allow them to metabolize various substances that may be toxic to others. These substances include sulfur, iron and arsenic. They also have carbon fixation genes, which allows plants to convert carbon into organic compounds; and appear to be able to process both simple and complex sugars, as well as bioplastic pellets that can be used in times of energy and carbon shortages.
“We expected a lot of the genes we found, but we didn’t expect that many given the lake’s low biodiversity,” Wang said. “It was quite unexpected, but it is absolutely elegant. It makes perfect sense that this is how life adapted to life in an active volcanic crater lake.”
Hydrothermal environments are of increasing interest to astrobiologists. Organisms that manage to thrive in these extreme locations often don’t rely on sunlight to survive, but use chemical reactions to produce energy. This means they could offer a counterpart to ecosystems found elsewhere far from the Sun, such as the hidden oceanic icy moons of Saturn and Jupiter.
But scientists also believe that life on Earth may have originated in a deep hydrothermal environment, since it would have been shielded from the young Sun’s harsh ultraviolet radiation but contained all the ingredients necessary for life to emerge. Perhaps when Mars was younger, wetter, and more volcanically active, the hydrothermal environment could also have ignited life.
“Our study provides insight into how ‘terrestrial life’ could exist in a hydrothermal environment on Mars,” Wang said.
“But whether life ever existed on Mars and whether it is similar to the microorganisms we have here is still a big question. We hope our research will steer the conversation toward looking for signs of life in these environments.”
The team’s research was published in Frontiers in astrobiology.