“Just 30 years ago, biologists didn’t really consider how large organisms – ‘macro-organisms’ like ourselves – are intimately linked to the microbial world”, explains Rebecca Vega Thurber, professor of microbiology at Oregon State University. Chief scientist on the leg between the Solomon Islands and Papua New Guinea, she is about to finish her second voyage aboard Tara. Passionate about her research subject, Rebecca also has the ability to make things easy to understand. “Now we know that every macro-organism on the planet has evolved in the presence of bacteria, viruses and other micro-organisms. We are now calling this community the “microbiome” of those animals.” The Tara Pacific expedition is focusing on the invisible microbial world that lives around and inside corals.
Human beings live with a multitude of invisible organisms
The microbiome of human beings is everywhere, but we mainly think it’s inside our guts. Our microbiome is very important in stimulating our immune system, allowing us to develop properly and providing natural antibiotics to prevent infections of foreign agents that can enter our bodies and provoke diseases. Our microbiomes are essential to everyday human life!
Can we use the words “collaboration” and “symbiosis” to explain this relationship between micro-organisms and their hosts?
There’s definitely a collaboration between our bodies and the millions of microbes living on and inside us. Microbes are also very important for the survival and health of corals across the planet, and they are thought to be involved in the metabolism of vital nutrients. They are also thought to protect corals from foreign agents. They perform like soldiers in the field, protecting the corals from any invader (such as bacteria) that might try to infect the colony. Some of these bacteria produce antibiotics, and sometimes they just occupy the physical space on the coral, preventing foreign bacteria from invading.
What is the purpose of microbiome studies aboard Tara?
We study how the microbiome changes in the 3 species we’re sampling across the entire region of the Pacific, from Panama all the way to China. Across this huge seascape, we can see differences in the composition and diversity of these bacteria within a coral host. This may tell us something about how responsive these bacteria are to the environment. So that’s really the third question: what are the bacteria providing to the coral that allows them to resist threats like climate change, pollution, and overfishing? Do they provide some extra genetic material, via the collaboration between animal and coral, that protects them from bleaching and disease?
Do you already have some ideas about the answers to these questions?
Yes, my laboratory and others have been looking at corals from all around the world and trying to describe what kind of bacteria they have. My lab is really interested in pollution. We’ve shown that in polluted waters, the coral microbiome shifts quite dramatically. It goes from a very stable community, one that’s very resistant to change, to one that’s very stochastic or sporadic. And we think this is a really important predictor of what the coral microbiome might look like in the future. It might just become less stable, and like in humans, if our bacterial community becomes unstable, we’re susceptible to things like diseases, increasing temperatures and other viruses and agents.
What is the research protocol?
Aboard Tara, our research involves collecting the same 3 species across the entire Pacific range. We then use meta-barcoding of the 16S gene, a single gene that every bacterium has. Then we compare the composition of those genes across all of the corals we’ve collected, essentially creating a catalogue of all the different types of bacteria in every single sample. After that, we can compare the catalogue from place to place. We can see – for example like here in Papua New Guinea – that corals seem to have done very well. The scientific community has observed a world bleaching event that lasted almost 2 years across the entire planet, caused from climate change and El Nino. A lot of reefs have died, for example in Samoa, where Tara witnessed the phenomenon. So one of our questions is: why have the corals done well in some places and not others? Maybe it’s something about the composition of the animal and its microbiome. If we see a unique microbiome signature here in Papua New Guinea, that might give us an understanding of why the corals are doing so well here, why they are resistant. Perhaps it’s something that the corals are providing – certain components or metabolites.
Could it be the linked to the evolution of coral here in the Triangle of Coral, which some scientists consider to be the birth place of all corals?
Absolutely, these corals have evolved here, under different conditions, which are warmer, sometimes in shallow places. So they may have evolved resistance. They have been adapting over evolutionary time to the conditions here. But conditions are changing so rapidly due to climate change, that one question is: can corals themselves adapt fast enough to outpace climate change? Corals are slow to reproduce – they are very long-lived animals. So they may be using their microbiome to help resist climate change, because bacteria can rapidly adapt and evolve. Their lifetimes are very short, therefore they evolve very, very quickly. They can also pick up genes from the environment, unlike their coral hosts.
What is the lifespan of a bacteria?
When we talk about E. coli, which is the model system for understanding bacteria, the lifespan would be 20 minutes, under the right conditions. But it’s probably a few hours or days for most bacteria. The coral we saw today at Kimbe Island was somewhere between 300 and 800 years old! So imagine how many generations of bacteria have lived with it. Billions and billions, many, many orders of magnitude more. By studying together the rapid evolution of the bacteria and the slow evolution of the host, hopefully we’ll get an idea of what combination is right for resisting climate change and other threats like pollution.
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