Written by Carly E. Karrick
Teamwork makes the dream work, especially when that dream is building a coral reef. Corals that build reefs have a lot of microbes that live in and on them. These microbes include everything from algae, to bacteria, to viruses [1]. Recent studies are beginning to explore how these microbes interact with each other and corals, and what that means for coral reefs.
Many microbes live in and on coral, but we don’t know much about viruses
Coral microbes change how corals interact with their environment. Perhaps the most famous microbe living in coral are tiny algae that provide food for the coral in exchange for nutrients and shelter [2]. There are many different types of these algae, and certain types can withstand higher seawater temperatures [2]. This influences the ability of coral to live in a warming ocean. More recently, scientists have begun to understand how bacteria also influence coral [3]. However, we don’t know as much about viruses associated with coral. Viruses infect both corals and their associated microbes, and they can have positive, neutral, and negative impacts on coral health [4]. Viruses infecting bacteria (phages) are interesting because they can control bacterial communities, even potentially protecting corals against disease [5]. However, there are a lot of challenges with studying phages. In 2024, a group of researchers from the University of Miami (Florida, USA) tackled these challenges to understand how phages interact with bacteria and coral.
How can we study viruses anyway?
You’re probably familiar with the idea of scientists using DNA for biological studies (think Human Genome Project). While this method can be used to study single organisms, scientists can also identify entire communities of organisms in a sample or environment by studying the DNA of all the organisms. This method, called metagenomics, is really useful for studying microbes. Microbial DNA can be used to identify microbes and to get an idea of what they could be doing. However, some microbes are easier to identify with this method than others. A study led by Bailey Wallace at the University of Miami used a new technique to make it easier to find viruses in metagenomic data. The researchers used this technique to identify phages in publicly available data and corals they collected in Curaçao. So, which phages are present in corals, which bacteria do they infect, and what does this mean for coral reefs?
Viruses, bacteria, and coral are really connected!
The researchers found that certain phages and bacterial hosts were more common in corals. Importantly, they also found unique functions of these phages. The figure shown below represents how phages and bacteria are highly connected, with phages changing how bacteria use nutrients and interact with other organisms. For example, if certain bacteria are infected by certain phages, they could start causing coral disease, even if they didn’t before being infected.
The researchers studied how phages and bacteria are connected. They created this interaction network to show these connections. Each green circle is a virus, each blue circle is a bacterium, each orange diamond is a piece of viral DNA that changes how bacteria process nutrients, and each pink diamond is a piece of viral DNA that changes how bacteria interact with other organisms. If any of these features are joined by a line, they are connected. “Keystone viruses” that are most connected to other phages, bacteria, and phage DNA are circled in yellow. This network shows that viruses and bacteria are highly connected in coral because phages can change how bacteria process nutrients and interact with other organisms.
The connections between different microbes and coral change our understanding of coral health
This study shows that interactions between different microbes can change how they affect corals. This is really important to better understand coral health. For example, as we think about whether a microbe is good or bad for a coral, we might need to consider other microbes as well to complete the puzzle of coral health. This is true for other organisms as well. For example, the soil is really hot in Yellowstone National Park (Montana, USA) due to geothermal activity. A grass can grow in the hot soil when it has a fungus that is infected with a virus, but not if the fungus isn’t infected [6]. After the COVID-19 pandemic, I know I can appreciate how microbes influence my own health. Beyond pandemic-causing viruses, I’ve seen so much information about how microbes living in my gut are important for my health, too. All of that to say, microbes in corals are fascinating, important, apparently really connected to each other, and not all bad.
Read the full article here: Wallace, B.A., Varona, N.S., Hesketh-Best, P.J., Stiffler, A.K., and Silveira, C.B. (2024). Globally distributed bacteriophage genomes reveal mechanisms of tripartite phage-bacteria-coral interactions. The ISME Journal, 18(1), wrae132. https://doi.org/10.1093/ismejo/wrae132
References
[1] Blackall, L.L., Wilson, B., and van Oppen, M.J.H. (2015). Coral–the world’s most diverse symbiotic ecosystem. Molecular Ecology, 24(21), 5330-5347. https://doi.org/10.1111/mec.13400
[2] Baker, A.C. (2003). Flexibility and specificity in coral-algal symbiosis: diversity, ecology, and biogeography of Symbiodinium. Annual Review of Ecology, Evolution, and Systematics, 34, 661-689. https://doi.org/10.1146/annurev.ecolsys.34.011802.132417
[3] Bourne, D.G., Morrow, K.M., and Webster, N.S. (2016). Insights into the coral microbiome: underpinning the health and resilience of reef ecosystems. Annual Review of Microbiology, 70, 317-340. https://doi.org/10.1146/annurev-micro-102215-095440
[4] Vega Thurber, R., Payet, J.P., Thurber, A.R., and Correa, A.M.S. (2017). Virus-host interactions and their roles in coral reef health and disease. Nature Reviews Microbiology, 15, 205-216. https://doi.org/10.1038/nrmicro.2016.176
[5] Vega Thurber, R.L., Silva, D., Speare, L., Croquer, A., Veglia, A.J., Alvarez-Filip, L., Zaneveld, J.R., Muller, E.M., and Correa, A.M.S. (2024). Coral disease: direct and indirect agents, mechanisms of disease, and innovations for increasing resistance and resilience. Annual Review of Marine Science, 17, 227-255. https://doi.org/10.1146/annurev-marine-011123-102337
[6] Márquez, L.M., Redman, R.S., Rodriguez, R.J., and Roossinck, M.J. (2007). A virus in a fungus in a plant: three-way symbiosis required for thermal tolerance. Science, 315(5811), 513-515. https://doi.org/10.1126/science.1136237
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