Ancient Microbial ‘Dark Matter’ – Thousands of Unknown Bacterial Species Discovered in Hawaiian Lava Caves


Steve Smith in a root-filled Hawaiian cave passage in the Kaʻu district of the island of Hawai`i. 1 credit

Age-old lava caves on the island of Hawaii contain thousands of unknown bacterial species

Higher bacterial diversity than scientists expected has been found in lava caves, lava tubes, and geothermal vents on the Big Island of Hawaii. The findings were reported in a new study published today (July 21, 2022) in the journal Frontiers in microbiology.

This research investigates the variety and interactions within these microbial ecosystems, which illustrate how life may have existed on " data-gt-translate-attributes="[{" attribute="">March and the primitive Earth in the past. Surprisingly, the results showed that a class of bacteria known as Chloroflexi are often “central” species, meaning they are related to many other species and usually play crucial ecological roles in the community. Many species of Chloroflexi are poorly understood, and further research will reveal previously unknown species, as well as information about the role these species play in these extreme environments.

“This study indicates the possibility that older bacterial lineages, such as the phylum Chloroflexi, may have important ‘jobs’ or ecological roles,” said first author Dr. Rebecca D Prescott of " data-gt-translate-attributes="[{" attribute="">Nasa Johnson Space Center and University of Hawaii in Manoa, USA. “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. »

Unseen Volcanic Life

Prescott and his colleagues collected 70 samples from a variety of locations, including active geothermal vents (fumaroles), as well as “younger” and “older” lava tubes and caves, which were less than 400 years old and between 500 and 800 years, respectively, to get an idea of ​​how bacterial communities might change over time. They were able to determine the diversity and abundance of bacterial classes in each sample by sequencing the ribosome RNA present in the samples. Co-occurring bacterial networks also provided insights into possible interactions between these microorganisms.

Eastern Rift Zone Hawaii Microbial Mats

Thick microbial mats hang below a rocky ledge in steam vents that run along the Eastern Rift Zone on the island of Hawaii. 1 credit

The harshest conditions – geothermal sites – were expected to have lower diversity than more established and habitable lava tubes. While diversity was indeed found to be lower, the research team was surprised to discover that interactions within these communities were more complex than in places with higher diversity.

“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 Prescott. “And if so, what’s in the extreme environments that contribute to creating this?”

Since Chloroflexi and another class called Acidobacteria were present at almost all sites, they may play a vital role in these communities. However, they are not the most abundant bacteria, and individual communities from different sites showed wide variations in the diversity and complexity of microbial interactions. Unexpectedly, 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

Because the current study was based on partial gene sequencing, it cannot accurately determine the species of microbes or their “jobs” in the community. Therefore, further research is needed to help reveal the individual species present, as well as to better understand the roles of these bacteria in the environment.

Hawaiian Cave Microbial Colonies

A stalactite formation in a Hawaiian cave system from this study with copper minerals and white microbial colonies. Despite the fact that copper is toxic to many organisms, this formation hosts a microbial community. 1 credit

“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 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 the expression of their genes, affecting their jobs in the community.

Beyond information about past and possibly future life on Mars, bacteria from volcanic environments may also be useful in understanding how microbes transform volcanic rock (basalt) into soils, as well as bioremediation, biotechnology and management. resource sustainability.

Reference: “Islands within Islands: Bacterial Phylogenetic Structure and Consortia in Hawaiian Lava Caves and Fumaroles” by Rebecca D. Prescott, Tatyana Zamkovaya, Stuart P. Donachie, Diana E. Northup, Joseph J. Medley, Natalia Monsalve, Jimmy H. Saw, Alan W. Decho, Patrick SG Chain and Penelope J. Boston, July 21, 2022, Frontiers in microbiology.
DOI: 10.3389/fmicb.2022.934708

Funding: NASA Headquarters, George Washington University


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