Deep-sea sensor reveals corals produce reactive oxygen species

Just like us, corals breathe oxygen and eat organic carbon. And just like us, as a byproduct of energy and oxygen conversion in the body, corals produce reactive oxygen species (ROS), a family of chemical compounds that are naturally made by cells during cell division, while fighting pathogens and performing other physiological tasks. functions.

But until now, it was unclear whether healthy deep-sea corals produce a particular type of ROS, called superoxide (O₂^•-). Superoxide is a highly reactive ROS known to influence ocean ecology, organismal physiology, and ocean chemistry, including carbon degradation and the bioavailability of metals and nutrients.

A recent study published in Nexus PNAS reveals, for the first time, that deep-sea corals and sponges produce ROS superoxide, meaning that these chemicals have a range of previously unknown effects on ocean life and deep-sea chemistry. The authors prove that ROS are not only produced as a response to stress, but as a fundamental part of its functioning.

In the study, the authors took direct measurements of superoxide in the water closely surrounding the corals, by introducing a first-of-its-kind chemiluminescent sensor called SOLARIS, into the ocean more than 2,000 meters deep, on board of the Alvin submersible.

“These are the first measurements ever made of this chemical in the deep sea,” said Colleen Hansel, senior scientist in marine chemistry and geochemistry at Woods Hole Oceanographic Institution (WHOI) and lead author of the study.

Detecting superoxide in the ocean is a particularly difficult task that required collaborative expertise, from chemistry to physics to engineering. As a highly reactive compound, superoxide lasts only a few seconds in water. WHOI engineers Jason Kapit, co-author of the paper, and William Pardis, along with Hansel and associate scientist Scott Wankel, developed the SOLARIS system as a robot-controlled instrument capable of sucking water directly on the surface of the coral.

Water enters the sensing wand and mixes inside a chamber, where a chemical reaction with the superoxide produces light that can be measured in real time. During this expedition, the wand’s movements were controlled by Alvin’s mechanical arms, with Kapit and Hansel being part of the three-person team diving inside Alvin.

“A fantastic aspect of this particular project is that it combines science and engineering in a way that is unique to WHOI,” Kapit said.

The first dives with SOLARIS took place in October 2019 in the Monterey Bay National Marine Sanctuary off the coast of California, where they discovered large, healthy corals living in a protected ocean environment. This helped eliminate the possibility that superoxide was produced solely in response to stress.

According to Hansel, the corals they measured produced superoxide with an enzyme, called NOX, that converts oxygen to superoxide outside of cells, meaning it is likely a fundamental building block of their usual vital functions, whether it is its growth or its production to stun their prey. . The deep-sea corals studied do not have algal symbionts like shallow-water corals, which are already known to produce extracellular ROS and have long been assumed to originate from symbiotic algae.

These results exclude algae as a source of superoxide and instead indicate that the coral animal itself or its bacterial symbionts are the sources. Without further research, the authors cannot completely rule out that bacteria may play a role in ROS production, but they believe this is unlikely due to the presence of NOX in the corals studied here.

“Over the past decade, in particular, many studies have begun to identify how the production of extracellular ROS like superoxide can have beneficial facets for an organism,” said Lina Taenzer, joint program student, chemistry and geochemistry. marines, and lead author of the study. study, who joined Hansel’s lab at WHOI in 2019. She also dove at Alvin to measure superoxide with SOLARIS.

“It is fascinating that corals can regulate ROS to transmit signals to other cells and change how they function and respond to the environment,” Taenzer said. “It’s also interesting in terms of the cellular defense mechanism.” For example, if an organism is invaded by a pathogen, it can produce a strong oxidative burst. This acts as a kind of chemical warfare to protect itself. On the other hand, overproduction of superoxide can have detrimental effects on an animal, degrading the body’s essential proteins and breaking down DNA.

Species diversity was also significant. During his dive at Alvin, Taenzer happened to measure various species, including sponges and starfish.

“There was an aspect of exploration, and the fact that we were using a new instrument that we had never used before made it really exciting and rewarding,” Taenzer said.

Although there is still much to know about how deep-sea corals function and respond to their environments, this study helps shed light on the fundamental controls of coral health and activity. And the more scientists understand and share, the more accurately they will be able to predict how coral ecosystems will respond to warming seas and climate change.

“It’s difficult to model how corals will respond to changing ocean conditions if we don’t understand how they currently perform under reference conditions,” Hansel said. “We need to understand what healthy coral looks like, what sick coral looks like, and what some of the factors are that control the health and physiology of these organisms.”

The long-term goal is to use SOLARIS to measure corals, deep-sea sponges, and other ROS-producing organisms in other regions of the world to get a more complete picture of how life marine influences ocean chemistry.

“The discovery of these highly reactive compounds in the deep ocean could also impact the carbon cycle, the metal cycle and microbial ecology, to name a few. This is a complete unknown to this stage, but it’s exciting to think about it on a broader scale,” Hansel said. said.