Sunday, November 27, 2022

What a mysterious green slime discovered in lava caves tells us about life on other planets

Within the lava caves of Hawaii, microbial life thrives. In fact, a recent study found that life within caves is made up almost entirely of unknown species.

More surprisingly, the researchers found that microbial life was structured in complex networks of species that depended on one another. Within these networks were ‘hub species’, with so many links with other species that if they were removed, it could lead to ecological collapse.

We spoke to Dr. Rebecca Prescott and Dr. Stuart Donachi, microbiologists at the University of Hawaii at Manoa and the study’s authors.

How did you discover life in these lava caves?

Dr. Rebecca Prescott: We had 70 samples of microbial mats [layers of microbes that live on surfaces] Which we saw from different volcanic environments of different ages. The atmosphere consisted of lava tubes, geothermal caves and steam vents.

To identify the microbes, we looked at a gene called the ’16S rRNA gene’. It is like a small tag which helps us in identification. To try to better understand the structure of these communities, we also looked at which microbes were ‘moving out’ together.

Tell us more about this technology.

Dr. Stuart Donachi: Before 1986, microbiologists could only identify microbes they had grown in the laboratory. Everything we knew about microbial diversity—meaning how many species there are—was based only on what we could grow in a petri dish. It gave us a narrow perspective, but it was the best we could do at the time.

In 1986, a method was developed that involved sequencing [the 16S rRNA gene], This method is based on extracting as much DNA as possible from a sample of the environment and then making copies of this particular gene. Once this method was applied to the environment, we detected bacteria that had never been observed before.

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RP: There are a lot of microbes in the environment that have never been cultivated. Most of them haven’t. We saw a lot of microbial groups [in the volcanic samples] What we call ‘hub species’, which means that they are closely related to other species of bacteria in these networks. If you want to remove them, you can see that a lot of them have broken connections. Therefore they may have important ecological roles.

What kind of things do these hub germs do?

RP: I can only speculate here. I want to emphasize that we do not know what their function is. But an example of a hub species would be the Chloroflexi bacteria we found in a volcanic environment. Some Chloroflexi can photosynthesize at low light levels. They may be able to carry carbon in the system. Other organisms around them may not actually have the ability to photosynthesize in low light.

SD: anywhere you find these photosynthesizing organisms [such as Chloroflexi]They take inorganic carbon and form organic molecules from it. But they are like leaky cells – they emit other biological molecules into the environment. They die too. Their cells break down and this releases the contents of the cells into the environment, and this allows other organisms to grow that require pre-formed organic molecules.

RP: I study ‘quorum sensing’, which is bacteria talking to each other via chemicals. When they do this, they can respond as a group to something in the environment.

One of the reasons we wanted to understand these network structures is because we see really high levels of quorum-sensing genes in a lot of caves, and I don’t have a good explanation for why you’d see that. So this is another possibility as to why you might see a particular organism as the hub species in the network – it could be that it is doing something and then communicating with others.

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Could it tell us more about microbes in other extreme environments?

SD: I don’t know if we necessarily addressed this in this study, but as a personal observation, [research like this demonstrates] importance of water. I went to maybe 20 caves in the Kilauea caldera between 2006 and 2009. And some of them are completely dry and have a regular temperature. It was a challenge to identify anything organic, except the roots of the plants coming from the roof.

But in others, the cave was hot and overly humid. I think the relative humidity was 102 percent. It’s like being in a sauna. Rain water was dripping from the ceiling from the ground above, then flowing over the walls of the cave and dripping onto the floor. The floor was hot – we checked the temperature in the ground and it was like 90 degrees celsius down a few inches.

The water that was coming from the ceiling was dripping on the floor and getting converted into steam. So you get this kind of circulation of rain water becomes groundwater, and then gets converted into steam. And that’s where we saw the richest, thickest, green microbial mats, indicating the importance of water.

That’s why we always say that where there is water, there is life. Life, at least as we know it, needs water. That’s why we’re looking for liquid water on other planets or any other body, because it’s the first thing we know that’s essential for life.

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