Scientists Develop the First Stable Coral Cell Cultures

By Robert LeaApr 27 2021

A new era of biological research could be on the horizon thanks to new research that reveals a method to culture coral cells.

Earth’s coral reefs are under severe threat due in no small part to the effects of climate change with rising ocean temperatures causing coral bleaching events in record numbers. As major bleaching events become more frequent, less time exists between them to allow corals to recover. 

The net effect of this is the estimated loss of 50% of the planet’s corals over the last 30 years with recent estimates saying that even if the Paris Agreement’s target of 1.5⁰C temperature rise is met up to 70% of coral reefs could still be wiped out in the not-too-distant future.

Fortunately, corals could be about to receive a vital lifeline thanks to new research from a team of Japanese researchers. These scientists have successfully established sustainable cell lines in coral. 

Cultures were seeded from Acropora tenuis — a bushy purple or blue coral found in the Red Sea, areas of the Indian Ocean, and the Pacific Ocean — with seven out of eight continuously proliferating for almost a year.

“Establishing stable cell lines for marine organisms, especially coral, has proven very difficult in the past. This success could prove to be a pivotal moment for gaining a deeper understanding of the biology of these vitally important animals.”

Professor Noriyuki Satoh, head of the Okinawa Institute of Science and Technology Graduate University’s (OIST) Marine Genomics Unit

The research could be vital to conservation efforts.

The coral the team cultured is part of the Acroporide family, not just one of the most common types of these ocean dwellers, but is also one that plays a significant structural role in the formation of coral reefs thanks to the speed at which it grows.

Acropora corals also happen to be particularly vulnerable to changes in ocean conditions such as rises in temperature and acidification and as such suffer significantly from bleaching events.

“Establishing knowledge about the basic biology of these corals through cell lines could one day help protect them against climate change,” adds Satoh. 

Alongside Professor Kaz Kawamura, an expert in developing and maintaining cell cultures of marine organisms from Kochi University, Satoh is the senior author of a paper documenting the research published in the latest edition of the journal Marine Biotechnology.

Get Some Culture

In order to develop their cultures and create their cell lines, the researchers used coral larvae, something that helps avoid cross-contamination from the wealth of organisms that make adult coral their home. 

There is another advantage delivered by the use of coral larvae in experiments such as this, however. Larvekl cells divide more easily than adult cells, meaning they are easier to use to build cultures. 

The team isolated eggs and sperm from coral specimens fertilizing the eggs and developing the resultant larval cells in separate Petri dishes. The team’s initial attempts were, unfortunately, met by failure. 

“Small bubble bodies appeared and then occupied most of the petri dish. We later found that these were the fragments of dying stony coral cells.”

Professor Kaz Kawamura, Kochi University

The team tackled these initial disappointments by adding a protease called plasmin — an enzyme that breaks the peptide bonds of proteins — to the beginning stages of culture growth. This addition allowed the continued growth of the stony coral cells and prevented them from dying.

After a period of around three weeks, the team found their larval cells had developed into eight distinct cell types with a variety of colors, gene activity, and forms. 

Though varied, there was one exciting thing that some of the corals did have in common. The researchers discovered that some of the cell lines were similar in both form and gene activity to an inner layer of cells that forms shortly after coral eggs are fertilized.

It is this layer — the endoderm — that hosts the algae which form a symbiotic relationship with the coral, photosynthesizing and providing it with sustaining nutrients.

Professor David Miller, a leading coral biologist who was not involved with the study, explains the importance of this symbiotic relationship to corals, and how understanding could be the key to conservation efforts. 

“At this point in time, the most urgent need in coral biology is to understand the interaction between the coral animal and its photosynthetic symbiont at the cellular level, and how this relationship collapses under stress, leading to coral bleaching and death,” says Miller, who hails from James Cook University, Australia. “Subject to confirmation that these cells in culture represent coral endoderm, detailed molecular analyses of the coral/photosymbiont interaction would then be possible — and from this, real advances in understanding and perhaps preventing coral bleaching could be expected to flow.”

Coral Research Enters a New Era

The aspect of the study that interests Satoh also concerns the relationship between the corals and their symbiotic tenants. The researcher aims to discover how these photosymbiotic algae cells initially enter the corals. 

“The algae are incorporated into the coral cells around a week after the larvae first develop,” says Satoh. “But no one has yet observed this endosymbiotic event on a single-cell level before.”

Excitingly the team’s research also led to a development that should help labs across the globe study coral cell lines. The team found that their cultures were still viable after being frozen with liquid nitrogen. This means they could be frozen and shipped to other labs, allowing other teams to thaw out the cell lines and conduct their own studies.

It is likely that other teams will take advantage of this transportation opportunity to study how single coral cells respond to stressors such as pollution and high temperatures. Research teams could also defrost these cell cultures and use them to investigate how corals produce the calcium carbonate they use to build their exoskeletal structures. 

For the researchers who led this study, their next focus will be the establishment of genetically identical cell lines. “This will give us a much clearer idea of exactly which coral cell types we are growing, for example, gut-like cells or nerve-like cells, by looking at which genes are switched on and off in the cells,” concludes Satoh.

The team’s research coupled with some of the follow-up studies could ultimately help ecologists understand how corals develop giving us a better idea of how they can be farmed. 

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