Researchers find assortment of new microbes in Hawaii lava caves | Science

Between 2006 and 2009 and between 2017 and 2019, US researchers took about 70 samples from lava caves, lava tunnels and geothermal or fumarole vents — openings in the Earth’s crust from which warm to very hot water vapors and volcanic gases escape.

When the researchers sequenced those samples for a single RNA gene, which is commonly used to identify microbial diversity and abundance, they were unable to link any results to known genuses or species, at least not with great fidelity. “This suggests that caves and fumaroles are underexplored ecosystems,” the researchers write.

These underground structures were formed 65 to 800 years ago and receive little or no sunlight. They may also harbor toxic minerals and gases. Still, microbial mats are a common feature of lava caves in Hawaii. Microbes, after plants, make up the majority of our planet’s biomass and nearly all of the biomass in the Earth’s deep subsurface. But because these organisms are so small and live in such extreme environments, scientists have so far overlooked them.

In recent years, there has been a growing interest in subterranean microbes because they live in environments that are harshly similar to those on Mars, but there is still a long way to go. According to recent estimates, 99.999% of all microbe species would remain unknown, leading some to call them “dark matter”.

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The new research from Hawaii shows how obscure these life forms are. The diversity between the locations varied. Older lava tubes, which are between 500 and 800 years old, harbor more diverse microbe populations than geothermal active sites or sites less than 400 years old. While these older sites were more diverse, the younger and more active sites showed more complex interactions between microbes, likely due to the lower diversity. The microbes may need to work together to better survive.

Researchers suspect that it takes time for microbes to colonize volcanic basalts, and as the environment around them changes, so does their community structure. In cooler caves, for example, Proteobacteria and Actinobacteria are more abundant. “This raises the question of whether extreme environments contribute to the emergence of more interactive microbial communities, with microorganisms more dependent on each other?” wonders microbiologist Rebecca Prescott of the University of Hawaii in Mānoa. “And if so, what is it about extreme environments that this helps create?”

In younger lava caves, the microbes were found to be further apart. This suggests that competition is a stronger force in harsher environments, a force that reduces the likelihood of closely related species living side-by-side.

Different types of bacteria, such as Chloroflexi and Acidobacteria, were found in almost all sites, regardless of age. These microbes appear to be key players in their communities. The researchers call them “hub” species because they bring other microbes together.

It is possible that Chloroflexi microbes are sources of carbon in the ecosystem by using light energy in relatively dark conditions, but for now that is just speculation. Because only one gene was partially sequenced in the study, Prescott and her colleagues can’t say what a particular microbe’s role is in their underground community.

“This study illustrates the importance of studying microbes in co-culture, rather than just growing them as isolates,” says 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 can then alter their gene expression, affecting what their roles are in the community,” she concludes.

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