Hawaii’s lava caves are teeming with bacterial ‘dark matter’

Thurston Lava Tube in Hawaii Volcano National Park, Big Island

Thurston Lava Tube in Hawaii Volcano National Park, Big Island
Photo: Shutterstock (Shutterstock)

Hawaii’s volcanic environments contain a rich array of mysterious microbes, new research this week has found. Scientists say the islands’ lava caves and other structures created by volcanic activity harbor unique, diverse and as yet uncharacterized communities of bacteria. The results indicate that there is still much to learn about life in some of the most extreme conditions on Earth.

Researchers from several universities and NASA collaborated on the study, which was published Thursday in Frontiers in Microbiology. They studied samples taken from 70 sites along the Big Island of Hawaii, the largest island in the Hawaiian archipelago. These sites included caves, tubes and fumaroles, which are openings or vents where volcanic gases and water can escape. They analyzed and sequenced the RNA found in the samples, creating a rough map of the bacterial communities living there.

A stalactite formation in a Hawaiian cave system from this study with copper minerals and white microbial colonies.

A stalactite formation in a Hawaiian cave system from this study with copper minerals and white microbial colonies.
Photo: Kenneth Ingham

Some of these areas, especially those with ongoing geothermal activity, are the most inhospitable places on earth, as they are incredibly hot and filled with chemicals toxic to most living things. The research team therefore expected to find relatively little variety of life nested in sites that exhibited these extreme conditions. Older caves and tubes that formed more than 500 years ago, the researchers found, had greater bacterial diversity. But to their surprise, even the active geothermal vents were filled with a wide variety of bacteria. And compared to the other sites, the bacterial communities in these more hostile habitats also appeared to be more complex in their interaction with each other.

“This brings us to the next question: do extreme environments contribute to creating more interactive microbial communities, with microorganisms more dependent on each other?” said study author Rebecca Prescott, a researcher at NASA’s Johnson Space Center and the University of Hawaii, in a statement. “And if so, what is in the extreme environments that contributes to creating this?

Thick microbial mats hang below a rocky ledge in steam vents that run along the eastern rift zone.

Thick microbial mats hang below a rocky ledge in steam vents that run along the eastern rift zone.
Image: jimmy saw

The bacteria found in these sites also rarely overlapped, meaning these environments appear to host their own unique microbial worlds, with at least thousands of unknown species yet to be identified. One group of bacteria in particular, known as Chloroflexi, could however be particularly influential, as they were commonly found in different volcanic areas and appeared to interact with many other organisms. And it’s possible that they are an example of a “central species” – microbes vital to the structure and functioning of their communities.

“This study indicates the possibility that older bacterial lineages, such as the phylum Chloroflexi, may have important ‘jobs’ or ecological roles,” Prescott said. “Chloroflexi are an extremely diverse group of bacteria, with many different roles found in many different environments, but they are not well studied so we don’t know what they are doing in these communities. Some scientists call these groups “dark microbial matter” – the invisible or unstudied microorganisms in nature. »

These types of genetic sampling studies can provide a broad view of the bacterial world found in a particular location, but not more detailed information about individual species or the roles they play in their little quarters. Scientists therefore say that more research is needed to decipher the mystery of these volcanic inhabitants. Over time, what we learn may be relevant to our understanding of how life began on Earth or even Mars, since these environments may be the closest extant analog to what planets looked like there. for a long time.

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