Rising Temperatures Put Coral Reefs at Risk
Global warming is heating the world’s oceans, and coral ecosystems are among the most vulnerable victims. When water temperatures climb beyond a coral’s comfort zone, the delicate symbiosis between the animal and its photosynthetic partners breaks down, often leading to bleaching and disease. Yet not all corals succumb equally; some display a surprising tolerance to extreme heat. Recent research from NYU Abu Dhabi sheds light on an unexpected ally that may explain this disparity.
The Hidden Helpers: Endozoicomonas Bacteria
Scientists have long known that healthy corals host a diverse community of microbes, but the functional role of many of these microorganisms remained a mystery. The study, published in Nature Microbiology, focuses on a group called Endozoicomonas, which is found in reefs worldwide. By examining samples of the reef-building species Acropora pharaonis from the Arabian Gulf—where summer water can exceed 34 °C—the researchers discovered that these bacteria produce hormones traditionally associated with vertebrate reproduction, namely testosterone and progesterone.
Why Hormones Matter for Coral Immunity
Corals, like many organisms, rely on a suite of chemical signals to regulate their immune defenses. Under heat stress, the coral’s own capacity to synthesize such hormones diminishes, weakening its ability to fend off pathogens and cellular damage. The bacterial partners step in, synthesizing testosterone and progesterone from cholesterol supplied by the host. Laboratory experiments confirmed that different bacterial strains convert cholesterol into one or both hormones, and that the output varies with temperature, suggesting a finely tuned response to environmental conditions.
Experimental Proof of Concept
To test whether the bacterial hormones actually bolster coral defenses, the team exposed fragments of another coral species, Acropora downingi, to 33 °C water. Some fragments received supplemental testosterone or progesterone, while control fragments did not. Gene‑expression analysis revealed that hormone‑treated corals activated a suite of immune‑related genes far more robustly than untreated ones. In particular, genes involved in protecting cells from oxidative stress and preventing programmed cell death were up‑regulated, indicating a heightened state of resilience.
Implications for Reef Conservation
This discovery opens new avenues for mitigating climate‑induced coral loss. If specific bacterial strains can be cultured and re‑introduced to vulnerable reefs, they might act as a biological buffer, supplying essential hormones when the coral’s own production falters. Moreover, the findings underscore the importance of preserving the microbial diversity that naturally inhabits healthy reefs, as these microscopic allies could become a cornerstone of future restoration strategies.
While much work remains to translate laboratory insights into field applications, the study provides a compelling example of how symbiotic relationships can evolve to meet the challenges of a warming planet.
Source: https://scientias.nl/sommige-bacterien-helpen-koralen-met-het-overleven-van-hittestress/
