溫度逆境下為萼形柱珊瑚接種內生桿菌之影響

Abstract

珊瑚礁是地球上十分重要的生態系之一，近年來，大量人為活動及氣候變遷使珊瑚白化事件愈趨嚴重。面對珊瑚白化的困境， Peixoto等人於2017年提出了新名詞：珊瑚有益微生物 (beneficial microorganisms for corals, BMC)，假設透過BMC的接種可以幫助珊瑚渡過環境逆境，且目前也有數篇研究證實了BMC具有幫助珊瑚渡過熱逆境的潛力。作為許多健康珊瑚的核心菌群，有研究指出內生桿菌 (Endozoicomonas) 可以執行許多維持珊瑚健康的重要功能，例如: 參與醣循環、DMSP代謝、活性氧物質清除等，具有作為BMC的潛力。因此，本研究以台灣北海岸的萼形柱珊瑚 (Stylophora pistillata) 為對象，設計了為期18天的珊瑚升溫及內生桿菌接種實驗，分別測試了四株可培養且具不同代謝功能的內生桿菌：E. montiporae CL-33、E. acroporae Acr-14、E. penghunesis 4G、E. ruthgatesiae 8E，於實驗期間透過珊瑚共生藻光化學效能 (Fv/Fm) 測定、珊瑚影像紀錄、珊瑚菌相分析，評估熱逆境下接種內生桿菌對珊瑚的影響。並假設在升溫逆境下接種內生桿菌的珊瑚相較以過濾人工海水 (filtered-artificial sea water, FASW) 處理的珊瑚可以有較好的生理表現。經實驗發現，升溫逆境下接種內生桿菌對珊瑚沒有影響。熱逆境下四株內生桿菌處理組及FASW處理組的珊瑚共生藻光化學效能 (Fv/Fm) 表現都會下降 (Fv/Fm <0.6)，且珊瑚在各組都出現不同程度的組織脫落或死亡，實驗中觀察到的不同熱壓力反應主要都來自珊瑚群體差異。而根據細菌16S rRNA 基因 V6-V8定序結果分析，四株內生桿菌都可以在接種的珊瑚中被偵測到，但接種內生桿菌對珊瑚菌相沒有明顯影響。本研究是首次對內生桿菌進行溫度逆境下作為珊瑚有益菌之潛力測試，經實驗發現接種內生桿菌並不會對珊瑚造成影響，未來需要更進一步的實驗證實本次實驗所觀察到的結果。

Coral reefs are among of the most important ecosystems on Earth. In recent years, human activities and global warming have resulted in sever coral bleaching. In response to this challenge, Peixoto et al. (2017) proposed the concepta “Beneficial Microorganisms for Corals (BMC) ”, which suggests that microbiome manipulation can improve coral fitness under environmental stresses. To date, several studies have confirmed that BMCs can benefit corals under thermal stresses. Endozoicomonas is a core member of coral microbiomes and plays many crucial roles in coral holobiont such as carbon cycle, DMSP metabolism, and ROS scavenging, making it a potential BMC. In this study, we conducted an 18-day Endozoicomonas inoculation and heating experiment on the coral, Stylophora pistillata, from the northern coast of Taiwan. Four Endozoicomonas strains (E. montiporae CL-33, E. acroporae Acr-14, E. penghunesis 4G, and E. ruthgatesiae 8E) were selected to examine their influences on coral response to the thermal stress. Heat stress drove decreases in coral symbiotic algae photosynthetic efficiency in all Endozoicomonas-inoculation and control (filtered-artificial seawater, FASW) groups. In addition, different levels of coral tissue loss and mortality were also observed disregarding the treatment. Sequencing of bacterial 16S rRNA gene V6-V8 hypervariable regions detected all four Endozoicomonas strains in inoculated corals. However, the inoculation didn’t significantly change the overall structure of coral microbiomes. This study is the first to test the potential of Endozoicomonas as a BMC for thermal stresses. We found that Endozoicomons inoculation do not affect coral under thermal stresses, but further experiment are required to confirm the phenomenon we observed.