Probiotics could help save overheated coral news and research

Probiotics could help save overheated coral news and research

Sarah Vitak: This is Scientific American’s 60 seconds of science. I’m Sarah Vitak.

Charles Darwin’s famous voyage on the HMS Beagle is best known for bringing us the concept of evolution. But Darwin also did research on coral reefs and their formation. One thing about reefs in particular really puzzled him: That conundrum became known as Darwin’s reef paradox. The paradox is this:

Voolstra: How can you find this lush, teeming life in the otherwise nutrient-poor ocean.

Vitak: That’s Dr. Christian Voolstra, a professor at the University of Konstanz in Germany.

Voolstra: And the trick is symbiosis. Corals are basically sedentary organisms or animals, so they basically pick a place and they sit and then they can’t move. So the way they make a living is that they interact with microalgae in the tissues. And these are essentially small plants that do photosynthesis. And this photosynthesis generates sugars. And these sugars will essentially be supplied to the corals.

Vitak: These little critters around the world are in great danger, great danger. According to a report by the Global Coral Reef Monitoring Network published in October 2021, we have lost 14% of the world’s coral reefs in the past decade. This was mainly due to large scale bleaching events. Coral bleaching is caused by changes in the coral’s environment, including increased temperature, sunlight, or pollutants. But what exactly does it mean that coral is bleached?

Voolstra: The color of corals comes from the photosynthetic pigments of the algae. So once this algae is out, the coral will look white. So what happens in bleaching is that these symbiotic algae or small plant cells are expelled from the coral tissue.

If the environmental conditions actually get better again, they can actually take up their algae again and it’s good. So this is a transition state. But in reality, if environmental conditions persist, the coral will literally starve to death.

Vitak: dr. Voolstra and his team were very interested in researching a new approach to help corals cope with elevated ocean temperatures: treating them with probiotics. [Christian R. Voolstra et al., Extending the natural adaptive capacity of coral holobionts]

Voolstra: TThe general consumer knows that you can buy yogurt with probiotic cultures, right? There are bacteria that are good for your gut.

Vitak: Like humans, coral has a microbiome; a community of microorganisms that live on or in them. Previous work had shown that strengthening the coral’s bacterial microbiome by giving them doses of probiotics helped them survive challenging conditions. The process is similar to how we work with microbiomes and probiotics in humans.

Voolstra: You extract microbes from these highly resilient individuals, and then you literally transplant them or offer them to less resilient individuals of the same coral species. So it’s not like you’re putting something in there that wasn’t there, but it’s really like these human fecal transplants. You have a healthy donor and you offer these bacteria to an affected recipient.

Vitak: This had already been demonstrated in previous research as proof of concept. But dr. Voolstra and his team wanted to dig deeper and understand it a little better.

To conduct the experiment, they worked in what they call “mesochosms” — sort of a sweet spot between a sterile isolated lab environment and an entirely wild reef environment. Basically, they had aquariums with multiple types of corals and some other critters. This allowed them to keep the conditions under control, but also gave them a slightly more realistic result.

One very useful thing about working with coral is that they are colonial organisms.

Voolstra: That means they consist of repetition of the same building blocks. From one colony you can generate many fragments or pieces that all have the exact same genotype with the exact same environmental history. And then you can put them in different conditions.

Vitak: Once they had their fragments, they treated some with a mixture of bacteria that they had carefully isolated, selected and grown from resilient coral — and of course they wanted to be in control of their experiment too, so they gave some placebo saline.

Finally, they slowly ramped up the heat to simulate ocean warming.

Voolstra: And this was a very long experiment that essentially lasted over 75 days.

Vitak: What they found was fascinating. All the coral showed signs of fading as the temperature increased, but the probiotic-treated coral recovered more quickly. And they were 40% more likely to survive.

Voolstra: Okay, as a coral biologist, or as a biologist, in general, I think you’re usually really happy when you have a 5% effect or something observable that you can count with reasonable numbers. This is huge. I mean, if you almost double the chance of survival, this is huge.

Vitak: The team also looked at how adding this probiotic cocktail changed the coral’s microbiome and how it changed the coral itself. Adding the probiotic changed the composition of the coral’s microbiome.

Voolstra: It also caused a change in the expression of certain genes in the coral host. And those genes were really kind of go-to genes that you’d bet on if this is for more recovery.

Vitak: So basically: things like repair genes, immunity genes, and stress response genes.

Voolstra: So this is kind of the cliffhanger of this study, you actually change things in the host. And in the correlated host, and we don’t know how long these changes will last. Of course, if those changes can be maintained over the long term, you don’t need to keep this probiotic treatment going all the time, right?

Vitak: Which would be great to translate this to the real world.

Voolstra: I mean, there’s 300,000 square miles of coral reef. There are billions of coral. So if you want to submerge a small potion and inoculate every coral, this becomes unmanageable. No organism lives in isolation. And I think we’re starting to understand this more and more.

Vitak: Thanks for listening. For Scientific American’s 60 Second Science, I’m Sarah Vitak.

[The above text is a transcript of this podcast.]

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