Volcanic habitats in Hawaii are rich in bacterial diversity, including many as yet undiscovered species, a new study shows. These lava caves and geothermal vents are similar to what may have once existed on Mars, and the bacterial communities that coexist there provide clues to how life might exist in extreme environments. This work also suggests that there is much more to learn about the as-yet-unknown bacteria here on Earth.
Lava caves, lava tubes and geothermal vents on the Big Island of Hawaii have greater bacterial diversity than scientists expected, reports a new study in Frontiers in Microbiology. These habitats show how life may have existed on Mars and early Earth in the past, and this study examines the diversity and interactions in these microbial ecosystems. Surprisingly, the results revealed that a group of bacteria called Chloroflexi are often “hub” species, meaning they are associated with many other species and typically play key ecological roles in the community. Little is known about many species of Chloroflexi and further study will reveal previously undiscovered species as well as what role these species play in these extreme environments.
“This research points to the possibility that more ancient lineages of bacteria, such as the phylum Chloroflexi, may have important ecological ‘jobs’ or roles,” said first author Dr. Rebecca D Prescott of NASA’s Johnson Space Center and the University of Hawaii at Manoa. , in USA. “Chloroflexi are an extremely diverse group of bacteria, with many different roles, found in many different environments, but they are not well studied and so we do not know what they do in these communities. Some scientists call such groups ‘microbial dark matter’ – the unseen or unstudied microorganisms in nature.”
Unseen volcanic life
To get a sense of how bacterial communities might evolve over time, Prescott and her collaborators collected 70 samples from a variety of locations, including active geothermal vents (fumaroles) as well as “younger” and “older” lava tubes. and caves that were less than 400 years old and between 500 and 800 years old, respectively. By sequencing the ribosomal RNA in the samples, they could measure the diversity and abundance of the bacterial classes in each sample. The networks formed by co-occurring bacteria also provided clues to how these microbes might interact with each other.
The research team had expected that the harshest conditions—geothermal sites—might have less diversity than the more established and habitable lava tubes. While it was true that diversity was less, the team was surprised to see that interactions within these communities were more complex than in places with greater diversity.
“This raises the question, do extreme environments help create more interactive microbial communities, with microorganisms more dependent on each other?” Prescott said. “And if so, what is it about extreme environments that helps create that?”
Since Chloroflexi and another class called Acidobacteria were present at almost all sites, they may play an important role in these communities. But these were not the most abundant bacteria, and individual communities from different sites showed wide variation in the diversity and complexity of microbial interactions. Counterintuitively, the most abundant groups, Oxyphotobacteria and Actinobacteria, were often not “central” species, suggesting that their roles may be less important to overall community structure.
More questions than answers
The current research, based on the partial sequencing of a single gene, cannot pinpoint the types of microbes or their “work” in the community. Therefore, further studies are needed to reveal the individual species that are present, as well as to better understand the role of these bacteria in the environment.
“Overall, this study helps illustrate the importance of studying microbes in co-culture rather than growing them alone (as isolates),” Prescott said. “In the natural world, microbes do not grow in isolation. Instead, they grow, live, and interact with many other microorganisms in a sea of chemical signals from those other microbes. This can then alter their gene expression, affecting their performance in the community.
In addition to insights into past or even future life on Mars, bacteria from volcanic environments may also be useful for understanding how microbes transform volcanic rocks (basalt) into soils, as well as bioremediation, biotechnology, and sustainable resource management.
Reference: Prescott RD, Zamkovaya T, Donachie SP et al. Islands within islands: bacterial phylogenetic structure and consortia in Hawaiian lava caves and fumaroles. In front. Microbiol. 13:934708. doi: 10.3389/fmicb.2022.934708.
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