Hawaiʻi’s volcanic habitats are rich in bacterial diversity, including many yet-to-be-discovered species, a new study shows. These lava caves and geothermal vents are similar to what might have existed on Mars, and the bacterial communities living there provide clues about how life can exist in extreme environments. This work also suggests that there is still much to learn about 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 represent how life might have existed on Mars and early Earth in the past, and this study explores the diversity and interactions within these microbial ecosystems. Surprisingly, the results revealed that a group of bacteria called Chloroflexi tend to be “core” species, meaning they are connected to many other species and often 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 study points to the possibility that older lineages of bacteria, such as the phylum Chloroflexi, may have important ecological ‘jobs’ or functions,” said first author Dr. Rebecca D Prescott of NASA’s Johnson Space Center and the University of Hawaii at Mānoa. in the 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 these groups ‘microbial dark matter’ “: the invisible or unstudied microorganisms in nature”.
Invisible volcanic life
To get a sense of how bacterial communities might develop over time, Prescott and his collaborators collected 70 samples from a variety of sites, including active geothermal vents (fumaroles), as well as lava tubes and caves.” younger’ and ‘old’, which were under 400 years and between 500 and 800 years, respectively. By sequencing the samples’ ribosomal RNA, they could measure the diversity and abundance of the bacterial classes in each sample. The networks formed by coexisting bacteria also provided clues about how these microbes might interact with each other.
The research team expected that harsher conditions, geothermal sites, might have lower diversity than more established, habitable lava tubes. While it was true that diversity was lower, the team was surprised to find that interactions within these communities were more complex than in more diverse locations.
“This leads to the question: do extreme environments help create more interactive microbial communities, with microorganisms more dependent on each other?” Prescott said. “And if so, what about the extreme environments that help create it?”
Because 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 at different sites showed great variation in the diversity and complexity of microbial interactions. Counterintuitively, the most abundant groups, Oxyphotobacteria and Actinobacteria, were often not “core” species, suggesting that their roles may be less important to overall community structure.
More questions than answers
The current study, based on partial sequencing of one gene, cannot precisely determine the species of microbes or their “jobs” in the community. Therefore, more studies are needed to help reveal the individual species present, as well as to better understand the role of these bacteria in the environment.
“Overall, this study helps illustrate how important it is to study microbes in co-culture, rather than growing them alone (as isolates),” Prescott said. “In the natural world, microbes don’t 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 work in the community”.
Beyond insights into past, or even future, life on Mars, bacteria from volcanic environments may also be useful for understanding how microbes turn volcanic rock (basalt) into soils, as well as bioremediation, biotechnology and the sustainable management of resources.
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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