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CUHK reveals coral’s ‘best allies’
Denitrifying specialist bacteria help corals survive in polluted waters
A research team from the School of Life Sciences at The Chinese University of Hong Kong (CUHK) has discovered that the secret behind corals’ ability to endure “toxic waters” lies in certain “denitrifying specialist bacteria” living inside them. These bacteria can efficiently remove nitrate pollution caused by sewage and agricultural activities, helping corals withstand environmental stress and acting as their “best allies” in polluted waters. The research findings have been published in the internationally renowned journal Nature Communications.
Rising ocean temperatures are widely known to harm corals, but nitrate pollution caused by sewage and agricultural activities is a hidden threat that has received relatively little attention. Nitrate enrichment makes corals more vulnerable to heat, accelerating the decline of coral reefs. The nitrate concentration in Hong Kong’s western waters ranks as one of the highest among the world’s coral reef areas. Although most coral species cannot survive in such harsh environments, a few resilient varieties have managed.
The research team, led by Professor Luo Haiwei, Associate Professor of the CUHK’s School of Life Sciences and Director of the Simon F.S. Li Marine Science Laboratory, together with Post-doctoral Fellow Dr Xiang Nan, developed an innovative population-genomic framework to study changes in the microbial communities inside corals across waters with varying levels of nutrient pollution. The study results show that corals growing in severely nitrate-polluted waters contain large numbers of a helpful group of bacteria that can efficiently remove excess nitrate. In contrast, these bacteria are relatively scarce in cleaner waters. The study also showed that, under conditions simulating real coral reef environments, these bacteria remove nitrate far more efficiently than other similar bacteria.
Conventional microbial surveys have shown little difference in the types of nitrate-removing bacteria found in corals from clean versus polluted waters. However, in Hong Kong’s western waters, where nitrate levels are severely elevated, the corals that survive are associated with a group of particularly effective bacteria with exceptionally high nitrate-removal capacity. These denitrification experts remove nitrate at speeds far exceeding those of ordinary denitrifying bacteria. In other words, what determines coral survival is not the broad category of bacteria they host but whether they harbour these specialist bacteria capable of clearing pollution. This hidden microbial teamwork mechanism can be overlooked in conventional surveys, yet it plays an important role in helping corals survive harsh conditions. Professor Luo said: “This precise method for identifying functional microbial specialists can be applied to any ecosystem, opening a new pathway for using microbial therapies to enhance ecosystem resilience.” Other team members include Professor Christian R. Voolstra from the University of Konstanz, Professor Benoit Thibodeau and Professor Shelby E. McIlroy from CUHK.
The CUHK Microbial Evolution and Ecology Laboratory was established in 2015 by Professor Luo, focusing on evolutionary genetics and population genomics of bacterial lineages that are relevant to biogeochemical cycles of carbon and nitrogen, coral conservation and crop productivity. The laboratory has produced multiple breakthrough results, including the development of new methods to estimate the age of bacterial groups, correlating bacterial evolution with host evolution and the planet’s evolution, discovering new mechanisms of bacterial speciation, revisiting the role of natural selection in bacterial adaptive evolution and developing novel, evolution-guided probiotics for long-term host persistence in marine conservation. This project was funded by the Hong Kong Research Grants Council General Research Fund and the Marine Conservation Enhancement Fund, and also received support from the CUHK Research Committee Postdoctoral Fellowship Scheme, the Simon F.S. Li Marine Science Laboratory and CUHK’s Institute of Environment, Energy and Sustainability.
The full research article is available here: https://www.doi.org/10.1038/s41467-026-72571-w
The CUHK research team has discovered that “denitrifying specialist bacteria” living inside corals can help them withstand environmental stress and act as their “best allies” in polluted waters. The photo shows Oulastrea crispata, the coral species studied by the CUHK team, surviving in the highly nitrate-polluted western waters of Hong Kong.
Photo credit: Dr Inga Conti-Jerpe
Oulastrea crispata is also found in the cleaner eastern waters of Hong Kong.
Photo credit: Dr Philip Thompson
CUHK researchers showed that specialised bacteria, commonly found in western Hong Kong corals in Hong Kong’s western waters, are especially efficient at removing nitrate under conditions similar to natural coral reef environments.
Professor Luo Haiwei (left) and Dr Xiang Nan (right) at the Simon F.S. Li Marine Science Laboratory.
Photo credit: Cheung Kwok-chu
