Coral microbiome essential for surviving climate change, new study finds
UNIVERSITY PARK, Pa. – Coral microbiomes – which include bacteria, fungi and viruses – play an important role in the ability of corals to tolerate rising ocean temperatures, according to new research from Penn State. The team also identified several genes within certain corals and the symbiotic photosynthetic algae that live inside their tissues that may play a role in their response to heat stress. The findings could inform current coral reef conservation efforts, for example, by highlighting the potential benefits of modifying coral reefs with microbes found to enhance coral responses to heat stress.
“Prolonged exposure to heat can cause ‘bleaching’ in which photosymbionts (symbiotic algae) are dropped from the coral animal, causing the animal to die,” said Monica Medina, professor of biology at Penn State. “We found that when certain corals experience heat stress, their microbiomes can protect them from bleaching. In addition, we can now identify specific genes in coral animals and their photosymbionts that could be involved in this heat stress response. “
Viridiana Avila-Magaña, a former student at Penn State and currently a postdoctoral researcher at the University of Colorado at Boulder, said: Now know that the entire holobiont – the coral animal, the photosymbiont and the microbiome – is involved in the response to stress.
In their study, published today (September 30) in Nature Communications, the researchers focused on three species of coral: mountain star coral (Orbicella faveolata), gnarled brain coral (Pseudodiploria clivosa) and starlet coral. shallow waters (Siderastrea radians) – which are known to differ in their sensitivity to heat stress. Collected near Puerto Morelos, Mexico, each species of coral harbors a unique set of photosymbionts and microbiomes. The team’s objective was to study the different metabolic contributions of each member of the holobiont to the overall stress tolerance of corals and to identify the differences in the expression patterns of the genes linked to these metabolic activities. .
Medina explained that metabolism is the process of converting food into energy. For corals, she said, this process is strongly stimulated by photosymbionts, which through photosynthesis provide coral animals with at least 90% of their energy needs. But, until now, the contributions of microbiomes have not been well understood.
“We know that heat stress resulting from climate change can disrupt coral metabolism and lead to bleaching,” Medina said. “Therefore, it is important to understand the different contributions of holobiont members and how these metabolic activities change in response to heat stress.”
The researchers performed a controlled heat stress experiment in which they kept the three coral species in a tank for nine days at 93 degrees F (34 degrees C), which is 11 degrees (6 degrees C) higher than the average temperature normally encountered by these corals. Scientists sequenced the RNA of coral holobionts – including coral animals, photosymbionts and members of microbiomes – after the nine-day period and a control group not exposed to heat stress, with the aim of detecting changes in the gene expression. that affect the heat stress response of the holobiont. Specifically, they used the gene expression data to estimate the metabolic activities of each member of the holobiont.
Next, the team used a type of phylogenetic ANOVA technique, called Expression Variance and Evolution Model, to examine changes in heat stress-related gene expression that occurred during evolution.
“In collaboration with Professor Rori Rohlfs of San Francisco State University, who is co-author of this study, we developed a method based on a phylogenetic ANOVA that allowed us to follow the genes whose expression has already diverged between species in response to a given stimuli. – in our case, heat stress, ”said Viridiana Avila-Magaña. “This approach is becoming particularly relevant for coral reef research given recent debates on the adaptive potential of different coral holobionts in the face of climate change threats. With this approach in mind, we were able to understand why different corals have unique physiological responses to heat stress, and how changing gene expression has shaped their different susceptibilities.
Avila-Magaña explained that corals have experienced episodes of high temperatures during evolution and understanding how gene expression has evolved in response to these events can inform coral responses to current and future warming events.
“Our goal with this research was to determine whether there had been any lineage-specific innovations for heat stress in corals and their algal photosymbionts, as well as whether all members, including bacterial communities, contribute differently. to the robustness of holobionts, ”she said.
Gene expression data revealed that the three coral holobionts did indeed differ in their responses and metabolic capacities under high temperature stress. The team also found that members of each holobiont had unique responses that influenced the holobiont’s overall ability to cope with heat stress.
“We have discovered more genes associated with a heat stress response in coral holobionts than previous studies, and we also show that changes in the expression of these genes have occurred during evolution,” said Medina.
Interestingly, the scientists concluded that the greater thermal tolerance observed in some coral holobionts, such as the starlet coral, may be due, in part, to a higher number and diversity of thermally tolerant microbes in their microbiomes, this which provides redundancy in key metabolic pathways. that protect against heat stress.
“We have discovered that certain corals harbor a stable and diverse microbiome resulting in a wide range of metabolic abilities that we believe remain active during the thermal challenge,” said Avila-Magaña. “In contrast, we found that the less thermally tolerant species had reduced bacterial activity and diversity. “
Medina noted that the results underscore the importance of comparative approaches across a wide range of species to better understand the various responses of corals to increasing sea surface temperatures.
Medina and Avila-Magaña said: “Corals have been strongly affected by climate change, and the methods we developed in our study represent an excellent tool for scientists trying to understand the adaptation potential of populations and populations. cash.
Other authors on the paper include Susana Enríquez, professor, Universidad Nacional Autónoma de México; Bishoy Kamel, Assistant Research Professor of Biology, University of New Mexico and Joint Genome Institute, Michael DeSalvo, University of California Merced; Roberto Iglesias-Prieto, professor of biology, Penn State; Kelly Gómez-Campo, graduate student in biology, Penn State; Hiroaki Kitano, professor, Systems Biology Institute Japan; and Rori Rohlfs, assistant professor of biology, San Francisco State University.
The National Science Foundation and the Joint Genome Institute (Department of Energy) supported this research.