Probiotics can help save overheated coral news and research

Sarah Vitak: This is Scientific American’s 60-second science. I’m Sarah Vitak.

Charles Darwin’s famous journey on the HMS Beagle is primarily known for giving us the concept of evolution. But Darwin also examined coral reefs and their formation. One thing about reefs in particular really confused him – that mystery became known as Darwin’s reef paradox. The paradox is this:

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

Thin: This is Dr. Christian Voolstra, professor at the University of Konstanz in Germany.

Voolstra: And the trick is symbiosis. Corals are basically attached organisms or animals, so they basically choose a place and they sit and then they can not move. So the way they support themselves is that they cooperate with microalgae inside the tissues. And these are mainly small plants that do photosynthesis. And this photosynthesis generates sugars. And these sugars will mainly be delivered to the coral animals.

Thin: These small animals all over the world are in great danger of much danger. According to a report from the Global Coral Reef Monitoring Network published in October 2021, we lost 14% of the world’s coral reefs in the last decade. This was mostly due to large-scale bleaching events. Coral bleaching is triggered by changes in the coral’s environment – including increased temperature, sunlight or pollution. But exactly what does it mean for corals to fade?

Voolstra: The color of the corals comes from the photosynthetic pigments of the algae. So the minute these algae are out, the coral looks white. So what happens when bleached is that these symbiotic algae or small plant cells are driven out of the coral tissue.

If the environmental conditions actually get better again, they can actually pick up their algae again and they feel good. So this is a transient state. But in reality, if the environmental conditions remain, the coral will literally starve to death.

Thin: Dr. Voolstra and his team were really interested in research that took a new approach to helping corals cope with rising sea 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 some bacteria that are good for your gut.

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

Voolstra: Microbes are extracted from these highly resistant individuals, and then literally transplanted or offered to less resistant individuals of the same coral species. So it’s not like you’re putting something there that was not there, but it’s really like this human fecal transplant. You have a healthy donor and you offer these bacteria to an affected recipient.

Thin: This had already been shown as a proof of concept in previous research. But Dr. Voolstra and his team wanted to drill down and understand it a little better.

To do the experiment, they worked in what they call “mesochosms” – a kind of sweet spot between a sterile isolated lab environment and a completely wild reef environment. Basically, they had aquariums with several types of corals and some other animals. This allowed them to control the conditions but also get a slightly more real result.

One very convenient thing about working with corals is that they are colonial organisms.

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

Thin: Once they had their fragments, they treated some of them with a mixture of bacteria that they had carefully isolated, selected and grown from resilient corals – and of course they wanted control of their experiment as well, so they gave some a placebo salt solution.

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

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

Thin: What they found was fascinating. All corals showed signs of fading as the temperature rose, but the corals treated with probiotics 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 are usually very happy if you have a 5% effect or something observable that you can count on reasonable numbers. This is massive. I mean, if you almost double the survival, this is huge.

Thin: The team also looked at how the addition of this probiotic cocktail changed the coral’s microbiome and how it changed the coral itself. Addition of probiotics altered the composition of the coral microbiome.

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

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

Voolstra: So this is kind of a cliffhanger in this study, you’re actually changing things in value. And in correlate values, and we do not know how long these changes will continue. Of course, if these changes can be sustained in the long run, you would not have to continue with this probiotic treatment, right?

Thin: Which would be great when it comes to translating this into the real world.

Voolstra: I mean, there are 300,000 square kilometers of coral reefs. There are billions of corals. So if you want to bring a little magic potion underwater and inoculate each coral, this becomes unmanageable. No organism feeds in isolation. And I think we’re just getting better at understanding this.

Thin: Thank you for listening. For Scientific Americans 60 Second Science, I’m Sarah Vitak.

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

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