Thousands of unknown bacterial species have been discovered living within the otherworldly lava caves beneath Hawaiʻi. Here, amid the oddly greenish-purple dripping rocks, scientists are hoping to gain some rare insights into so-called “microbial dark matter” and pick up some knowledge about how life might have once lived elsewhere in the solar system.
The microbial life found inside the bizarre ancient lava caves was recently explored for a new study published in the journal Frontiers in Microbiology. Researchers from the University of Hawai‘i at Mānoa collected dozens of ribosomal RNA genetic samples from active geothermal vents, as well as a variety of lava tubes and caves ranging between 400 to 800 years old in age.
As expected, the geothermally active sites held less microbial diversity and a lower abundance, likely owing to the harshness of the conditions. However, to their surprise, these more extreme sites also feature communities of bacteria that displayed significantly more complex interactions with one another.
One of the most interesting discoveries was bacteria known as Chloroflexi. The researchers explain that these bacteria appear to serve as “hub” organisms that play an integral role in the interdependent network of other microbial species. Chloroflexi, as well as another “hub” organism called Acidobacteria, were found at nearly all of the locations, highlighting how important they must be to the wider system. However, it’s still unclear what their “job” or role actually entails.
“This study points to the possibility that more ancient lineages of bacteria, like the phylum Chloroflexi, may have important ecological ‘jobs,’ or roles,” Dr Rebecca D Prescott, first author from NASA Johnson Space Center and University of Hawaiʻi at Mānoa, said in a statement.
“The Chloroflexi are an extremely diverse group of bacteria, with lots of different roles found in lots of different environments, but they are not well studied and so we don’t know what they do in these communities. Some scientists call such groups ‘microbial dark matter’ – the unseen or un-studied microorganisms in nature.”
“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.”
All of this could have implications for the search for ancient life on Mars. Volcanic systems in Hawai‘i are geologically similar to those on ancient Mars, which had active volcanoes and geothermal vents. Given that microbial life can thrive in the bizarre environment beneath Hawai‘i, it’s not a huge jump to say similar organisms could have once lived on Mars
“With these geological similarities, Hawaiian volcanic environments can provide some insight into the possibility of life on Mars in its ancient past and how microbial communities could survive today on Mars in lava caves, or if introduced from Earth,” the study authors write in the conclusion of their paper.