Corals are more than just colorful marine structures, they are complex living organisms teeming with microscopic life. At the heart of this intricate web of relationships is Symbiodiniaceae, a tiny algae that lives within coral tissue, providing energy through photosynthesis. But it turns out that these algae aren’t acting alone. A groundbreaking study by Matthews et al. suggests that bacteria living in their microscopic environment, the phycosphere, a mucus-like layer surrounding Symbiodiniaceae, could be shaping coral evolution in ways we are only just beginning to understand.
The research explores how bacteria influence the growth, metabolism, and even the genetic makeup of Symbiodiniaceae. By altering the bacterial composition of free-living Symbiodiniaceae, before they settle within coral hosts, the study revealed that the algae’s development is directly affected by the type and abundance of bacteria present. The results suggest a deep biochemical connection, with bacteria helping to regulate essential exchanges of carbon and nitrogen, two key ingredients for life. This complex relationship hints at something even more profound: a long history of co-evolution. While scientists have long known that corals and Symbiodiniaceae are deeply intertwined, this study suggests a third crucial player in the mix. It paints a picture of a three-step domino effect, the bacteria influence Symbiodiniaceae, which in turn affects coral health and survival. The unseen bacterial community may be a silent architect of coral reef ecosystems.
The research also uncovers evidence of horizontal gene transfer, where genetic material is exchanged between bacteria and Symbiodiniaceae, suggesting that microbes might even be contributing to the genetic evolution of these algae. This could mean that bacteria aren’t just passive passengers but active participants in shaping the evolution of coral symbionts.
Intriguingly, Symbiodiniaceae seem to be selective about which bacteria they associate with, subtly adjusting the microbial mix in their phycosphere. This suggests a finely tuned relationship that has evolved over time, reinforcing the idea that corals, their algae, and their bacteria are not separate entities but part of a single, interconnected system. As coral reefs face mounting threats from climate change, understanding these hidden relationships could be crucial. If bacteria play a key role in coral resilience, perhaps it could be used to help them survive in a rapidly changing ocean environment.
You can find the full paper here:
Matthews, J.L., Khalil, A., Siboni, N., Bougoure, J., Guagliardo, P., Kuzhiumparambil, U., DeMaere, M., Le Reun, N.M., Seymour, J.R., Suggett, D.J. and Raina, J.B., 2023. Coral endosymbiont growth is enhanced by metabolic interactions with bacteria. Nature Communications, 14(1), p.6864.
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