Life on lava: How microbes colonize new habitats

Life has a way of bouncing back, even after catastrophic events like forest fires or volcanic eruptions. While nature's resilience to natural disasters has long been recognized, not much is known about how organisms colonize brand-new habitats for the first time. A new study led by a team of ecologists and planetary scientists from the University of Arizona provides glimpses into a poorly understood process. 

The team conducted field research in Iceland following a series of eruptions of the Fagradalsfjall volcano, located on the southwestern tip of the island. The volcano erupted for a total of three times over the course of the study period, from 2021 until 2023. With each eruption, lava flows blanketed the tundra around the volcano, in some places even covering lava deposits from the previous year.

"The lava coming out of the ground is over 2,000 degrees Fahrenheit, so obviously it is completely sterile," said Nathan Hadland, a doctoral student in the U of A Lunar and Planetary Laboratory and first author of a paper published in Nature Communications Biology. "It's a clean slate that essentially provides a natural laboratory to understand how microbes are colonizing it."

To untangle the ecological dynamics involved in that process, Hadland and his team searched for clues about where the microbes that colonize fresh lava come from. They collected samples from a variety of different potential sources, including lava that had solidified mere hours before, rainwater, and aerosols – particles floating in the air. For context, they sampled soil and rocks from surrounding areas.

The researchers then extracted DNA from these samples and used sophisticated statistical and machine learning techniques to identify the organisms present on freshly imposed lava flows, the composition of these micro-habitats and where they originated.

While Iceland receives a considerable amount of precipitation, freshly deposited lava rocks don't hold much water and contain little to no organic nutrients, Hadland explained. To thrive in that scarce environment, organisms have to deal with very low amounts of water and nutrients.

"These lava flows are among the lowest biomass environments on Earth," said co-author Solange Duhamel, associate professor at the U of A's Department of Molecular and Cellular Biology, in the College of Science, as well as LPL. "They are comparable to Antarctica or the Atacama Desert in Chile, which is not that surprising considering they start out as a blank slate. But our samples revealed that single-celled organisms are colonizing them pretty quickly."

As microbes colonized the new habitat, biodiversity increased over the course of the first year following an eruption. But after the first winter, diversity "tanked," according to Hadland, probably because the seasonal shifts in environmental conditions were selecting for a specific subset that could survive those conditions. With each subsequent winter, the analyses revealed less turnover and showed that diversity stabilized over time. With all these data, a picture began to emerge.

'Badass microbes' move in first

"It appears that the first colonizers are these 'badass' microbes, for lack of a better term, the ones that can survive these initial conditions," Hadland said, "because there's not a lot of water and there's very little nutrients. Even when it rains, these rocks dry out really fast."

Over the next several months and seasonal shifts, the study revealed, the microbial community begins to stabilize, as more microbes are added with rainwater and "moved in" from adjacent areas.

A major finding of the study pointed to rainwater playing a critical role in shaping microbial communities on freshly deposited lava, according to the researchers.

"Early on, it appears colonizers are mostly coming from soil that is blown onto the lava surface, as well as aerosols being deposited," Hadland said. "But later, after that winter shift in diversity we observed, we see most of the microbes are coming from rainwater, and that's a pretty interesting result."

Scientists have long known that rainwater is not sterile; microbes in the atmosphere, either free floating or attached to dust particles, can even function as cloud condensation nuclei, which are microscopic particles that offer water vapor a surface to latch on to and grow into tiny droplets. In other words, tiny, invisible creatures may play outsized roles in weather and climate phenomena.

"Seeing this huge shift after the winter was pretty amazing," Duhamel said, "and the fact that it was so replicable and consistent over the three different eruptions – we were not expecting that."

While previous studies have looked at how organisms colonize habitat, most of them focus on secondary ecological succession – the technical term for organisms reclaiming disturbed habitat – and macro ecology, in other words, plants and animals. But the research in this paper is the first in-depth look at primary succession by microbes – organisms moving into new habitat as it is being formed, according to the authors. And unlike previous research based on samples collected months after a volcanic eruption, Hadland's team sampled lava flows as soon as they cooled. Finally, because the eruptions were going on over three years, the team was able to piece together an ecological picture with unprecedented resolution.

"The fact that we were able to do this three times – following each eruption in the same area – is what sets our project apart," Hadland said. "In science, we want to measure things three times – what we call a 'triplicate,' if possible, and that is very rare in a natural environment. For this study, nature essentially is giving us a triplicate."

From Arizona to Iceland to Mars

"For the first time, we are beginning to gain a mechanistic understanding of how a biological community established over time, from the very beginning," Duhamel said, adding that one of the study's implications is to potentially inform the habitability on other worlds such as Mars.

Most of the Martian surface is basaltic and has been modified by volcanic processes just like Earth, Duhamel explained, even though volcanism has quieted down considerably on Mars.

"Volcanic activity injects a lot of heat into the system, and it releases volatile gases, it can melt frozen water beneath the surface," Duhamel said. "We can observe these widespread, large volcanic terrains on Mars with remote sensing, and so the idea is that past volcanic eruptions could have created transient periods of habitability."

How microbes could potentially colonize new environments and unraveling their spatial distribution patterns is a first step toward probing the potential of life on other planets. Earlier this year, Duhamel was part of a team of U of A researchers selected for the inaugural "Big Idea Challenge" award, administered by the Office of Research and Partnerships. Finalist teams will receive $250,000 over two years and strategic guidance to support transformative research that seeks novel solutions to grand challenges.

"We can begin to tackle questions like, 'How does volcanism influence habitability?' 'How do microbes take advantage of those types of environments?' and apply the answers to similar types of systems that we have observed on Mars." Duhamel said. "Understanding how life could establish itself on a new lava flow on the surface of Mars, or at least how it could have done so in the past and knowing what kinds of biosignature we should look for and could potentially retrieve is a crucial step in that direction."

Co-authors on the paper include Christopher Hamilton, U of A associate professor in the Department of Planetary Sciences, and Snædís Björnsdóttir with the University of Iceland in Reykjavik.