Interactions between coral and their associated microbes for adaptive potential under environmental change

Abstract

Coral reefs are known as rainforest in the ocean that fosters various marine lives. However, coral reefs are declining rapidly in recent years due to global warming, overfishing, ocean acidification etc. Coral associated microbes are indispensable in coral reef ecosystems. Coral symbiotic algae (Symbiodiniaceae) provide coral hosts with oxygen via photosynthesis. Some coral associated bacteria can help with energy cycle in coral reef ecosystems and defend the hosts against pathogens. In the study of Symbiodiniaceae community from corals in different geographical regions in the South China Sea, coral-algal symbiosis was found to be highly flexible in both Galaxea fascicularis and Montipora spp. Temperature served as a major environmental factor shaping the diversity and specificity of Symbiodiniaceae, shuffling coral-algal symbiosis in congeneric scleractinian corals. These results suggest that scleractinian corals may have the ability to regulate Symbiodiniaceae community structures under different temperatures and thus be able to adapt to gradual climate change. When examining coral-algal symbiosis under nutrient stress at transcriptomic level, coral larvae exhibited highly stress response, and Symbiodiniaceae maintained ATP generation as well as coral-algal symbiosis via photosystem adjustment. Significantly correlated coral/algal transcripts were mainly related to energy consumption, nitrogen compound metabolism and stress response, suggesting coral-algal symbiosis was critical for coral meta-organism adaptation under eutrophication. By researching on interactions among coral associated prokaryotic microbial communities, Symbiodiniaceae and the environments, several prokaryotic microbes with ecological functions of photosynthesis and nitrogen fixation were detected to be correlated with potential stress-resistant Symbiodiniaceae. Prokaryotic microbial communities in Porites lutea were predicted to have higher photosynthesis functions under higher temperature than those in Montipora spp. Considering higher resistance of P. lutea in Hong Kong, these indicate that algal-microbial partnership had the potential to provide a compensation mechanism allowing coral hosts to adapt to higher temperatures. Furthermore, estimation of coral-microbial associations was expanded at larger evolutionary scale including both deep sea and shallow water corals. Different microbial genera were found to be phylogenetically conserved in certain coral lineages, indicating a microbial community acclimatization during coral evolution. Besides, different genes of bacteria-origin were detected in different coral lineages, with a number of genes shared by close lineages, suggesting horizon gene transfer (HGT) was occurred during coral evolution for coral adaption potentially. The central interest of this thesis work is the coral adaptive potentials under different environments from coral microbiology perspective, especially under the background of ongoing climate change. By studying the coral-microbial associations (including coral-algal symbiosis) under different environmental conditions and potential gene transfers between coral hosts and microbes, I’d like to provide more theoretical basis for coral conservation and coral distribution in the future

Date of Award	2020
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology