Hawaiian Lava Caves Are Full of 'Dark Matter' Bacteria

Hawaii’s volcanic environment contains a mysterious variety of microbes, new research has discovered this week. Scientists say that the island’s lava caves and other structures created by volcanic activity have unique, diverse, and still-living bacterial communities within them. The findings suggest that much remains to be learned about life in some of the most extreme conditions on Earth.

Researchers at several universities and NASA collaborated for the study, which was published Thursday in Frontiers in Microbiology. They studied samples collected from 70 sites along the Big Island of Hawaii, the largest island in the Hawaiian archipelago. These sites include caves, tubes, and fumaroles, which are openings or vents through which volcanic gases and water can escape. They analyzed and sequenced the RNA found in the samples, making it possible to create a rough map of the bacterial community living there.

Stalactite formations in the 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 some of the most inhospitable places in the world, as they are extremely hot and filled with chemicals that are toxic to most living things. So the research team hopes to find relatively little variation of life lying within sites that have these extreme conditions. The older caves and tubes formed more than 500 years ago, the researchers found, did have a greater diversity of bacteria. But to their surprise, even active geothermal vents are teeming with all sorts of bacteria. And compared to other sites, the bacterial communities in these harsher habitats also appear to be more complex in how they interact with one another.

“This leads to the question, do extreme environments help create 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 was it about the extreme environment that helped create this?

Thick microbial mats hang under stone ledges in steam vents that run along the East Rift Zone. (Image: Jimmy Saw)

The bacteria found at this site also rarely overlap, meaning that these environments appear to host their own unique microbial world, with at least thousands of unknown species left to identify. One group of bacteria in particular, known as the Chloroflexi, may be particularly influential, as they are commonly found in distinct volcanic areas and appear to interact with many other organisms. And they may well be examples of “hub species” – microbes that are essential to the structure and function of their communities.

“This study suggests the possibility that more ancient bacterial lineages, such as the phylum Chloroflexi, may have had an important ‘job,’ or ecological role,” Prescott said. “Chloroflexors are a very 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 do in this community. Some scientists call such groups ‘microbe dark matter’ – microorganisms that are invisible or unstudied in nature.”

This kind of genetic sampling study can provide a broad view of the world of bacteria found in a given place, but not more detailed information about individual species or the role they play in their small environment. So scientists say that more research is needed to unravel the mystery of this volcano’s inhabitants. In time, what we learn may be relevant to our understanding of how life began on Earth or even on Mars, as these environments may be the closest analogues to what the planets looked like in the past.

#Hawaiian #Lava #Caves #Full #Dark #Matter #Bacteria