Ancient lava caves in Hawaii teem with mysterious lifeforms

Microbes are the smallest living organisms known on Earth and can be found just about everywhere, even in cold, Martian-like conditions in lava caves.

On the island of Hawaii, scientists recently discovered an impressive array of new microbes thriving in geothermal caves, lava tubes, and volcanic vents.

These underground structures formed 65 and 800 years ago and receive very little sunlight. It can also contain metals and toxic gases. However, microbial mats are a common feature of Hawaiian lava caves.

Samples of these mats, taken between 2006 and 2009 and then again between 2017 and 2019, reveal more unique life forms than expected. When the researchers sequenced 70 samples for a single RNA gene, which is commonly used to determine bacterial diversity and abundance, they were unable to match any results with known genera or species, at least not with high confidence.

“This indicates that caves and fumaroles are diverse, poorly explored ecosystems,” the study authors wrote.

Microbes, after plants, represent most of our planet’s biomass and nearly all of the biomass in the Earth’s interior. However, because these creatures are so small and live in such harsh environments, they have historically been ignored by scientists.

In recent years, underground microbes have received more attention because they are found in environments very similar to those on Mars. But there is still a long way to go.

Recent estimates suggest that 99.999 percent of all types of microbes remain unknown, leading some to refer to them asdark matter”.

New research from Hawaii underscores just how mysterious these life forms are.

Diversity of diversity between sites. Ancient lava tubes, which are between 500 and 800 years old, either hosted more diverse microbial populations from thermally active sites or were less than 400 years old.

While these ancient sites were more diverse, those of the smaller and more active samples had more complex microbial interactions, likely due to the lower diversity. Microbes may have to work together to survive better.

Researchers believe that the microbes take some time to colonize the volcanic basalt, and as the environment around them changes, so does their community structure. In cooler caves, for example, Proteobacteria and Actinomyces are more prevalent.

“This leads us to the question, do extreme environments help create more interactive microbial communities, with microorganisms more dependent on each other?” asks microbiologist Rebecca Prescott of the University of Hawaii at Manoa.

“And if so, what about the harsh environments that help create this?”

In smaller lava caves, microbes tend to be more closely related. This indicates that competition is a stronger force in harsher environments, which reduces the chance of closely related species living side by side.

The formation of stalactites in a Hawaiian cave with white microbial colonies. (Kenneth Ingham)

Several classes of bacteria, such as Chloroflexi and Acidobacteria, are present in almost all sites, regardless of age.

These microbes appear to play a major role in their communities. The authors call them the “pivotal” species because they bring other microbes together.

It is possible that Chloroflexi microbes may provide carbon sources to the ecosystem by harnessing light energy in relatively dark conditions.

But for now, that’s just a guess. Because only one gene was partially sequenced in the study, Prescott and her colleagues cannot determine the role of a specific microbe in their underground community.

“Overall, this study helps illustrate how important it is to study microbes in the co-culture, rather than growing them alone (as isolate),” Prescott says.

“In the natural world, microbes do not grow in isolation. Instead, they grow, survive 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 functions in society. .”

The study was published in Frontiers in Microbiology.

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