Steve Smith in a Hawaiian cave passage filled with roots of the Kaʻu district on the Island of Hawai`i. Credit: Kenneth Ingham
Centuries-Old Lava Caves of Hawaiʻi Island Contain Thousands of Unknown Bacterial Species
Higher bacterial diversity than scientists expected has been uncovered in the lava caves, lava tubes, and geothermal vents on the big island of Hawaiʻi. The findings have been 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
“This study points to the possibility that more ancient lineages of bacteria, like the phylum Chloroflexi, may have important ecological ‘jobs,’ or roles,” said first author Dr. Rebecca D Prescott of 
Thick microbial mats hang under a rock ledge in steam vents that run along the Eastern Rift Zone on Hawaiʻi Island. Credit: Jimmy Saw
The harshest conditions—the geothermal sites—were expected to have lower diversity than the more established and habitable lava tubes. While the diversity was indeed found to be lower, the team of researchers was surprised to discover that the interactions within these communities were more complex than in locations with higher diversity.
“This leads to the question, do extreme environments help create more interactive microbial communities, with microorganisms more dependent on each other?” said Prescott. “And if so, what is it about extreme environments that helps to create this?”
Since Chloroflexi, and another class called Acidobacteria, were present at nearly all of the locations, they may play essential roles in these communities. However, these were not the most abundant bacteria, and the individual communities from the different sites showed large variations in the diversity and complexity of the microbial interactions. Counterintuitively, the most abundant groups, Oxyphotobacteria and Actinobacteria, were not often ‘hub’ species, suggesting that their roles may be less important to the overall structure of the community.
More questions than answers
Since the current study was based on the partial sequencing of one gene, 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 that are present, as well as to better understand these bacteria’s roles in the environment.
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. Credit: Kenneth Ingham
“Overall, this study helps to illustrate how important it is to study microbes in co-culture, rather than growing them alone (as isolates),” said Prescott. “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 then can alter their gene expression, affecting what their jobs are in the community.”
Beyond the insights about past, or even future, life on Mars, bacteria from volcanic environments can also be useful in understanding how microbes turn volcanic rock (basalt) into soils, as well as bioremediation, biotechnology, and sustainable resource management.
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 S. G. Chain and Penelope J. Boston, 21 July 2022, Frontiers in Microbiology.
DOI: 10.3389/fmicb.2022.934708
Funding: NASA Headquarters, George Washington University