龜山島珊瑚群聚與淺海熱泉之好氧甲烷氧化活性

Abstract

甲烷是三大主要溫室氣體之一，其全球暖化潛勢為二氧化碳的28-34倍。甲烷遍佈全球，在自然環境中如海洋、濕地都可發現其存在。海洋中的甲烷可由甲烷氧化菌進行分解，其中好氧甲烷氧化菌可利用甲烷單氧化酶 (pMMO) 將甲烷分解成甲醇並進入下一步的分解作用。此外，在淺層海洋底泥的相關研究中也有發現好氧甲烷氧化菌的蹤跡。龜山島作為本次研究的主要地點，是個同時具有淺海熱泉及珊瑚群聚的一個特殊海域；在龜首的部分具有淺海熱液噴口聚集地，而在另一側龜尾的部分則有豐富生態的珊瑚群聚。龜山島的特殊地理環境能提供我們探討並比較兩種生態的甲烷氧化潛力及甲烷氧化菌相組成之間的差異。本研究利用甲烷培養實驗及次世代定序技術，分析龜山島淺海熱泉及珊瑚群聚底泥中甲烷氧化潛力及甲烷氧化菌相，同時也分析位於台灣南部的墾丁及綠島的珊瑚礁底泥，進一步探討珊瑚群聚的甲烷消耗能力。實驗結果顯示，龜山島珊瑚群聚的底泥相對於淺海熱泉的底泥具有較高的甲烷氧化潛力，且甲烷氧化菌所擁有的功能基因 (pmoA) 的豐度的結果及甲烷氧化菌的菌相組成，推測珊瑚群聚的甲烷氧化潛力可能比淺海熱泉高。另外，墾丁和綠島的珊瑚礁底泥結果也與龜山島珊瑚群聚呈現一樣的趨勢。本研究結果同時展示珊瑚群聚底泥與淺海熱泉底泥的甲烷氧化的能力，提供未來探討這兩種生態的甲烷氧化菌在甲烷循環過程中，所扮演的角色及甲烷減排可能貢獻。此外，通過在龜山島的近海熱泉的甲烷氧化能力及甲烷氧化菌組成，可以預測未來海洋酸化對海洋環境的甲烷氧化活動所造成的影響及菌相的變化。

Methane is a powerful greenhouse gas with 28-34 times greater global warming potential than carbon dioxide. However, methane has a shorter atmospheric lifetime, which means that reducing methane emissions could slow down the rate of global warming, faster than reducing carbon dioxide. Ocean is one of the natural methane budgets and in shallow layer marine sediment, aerobic methanotrophs which can consume methane to methanol through enzyme pMMO were found. Kueishan Island, our study site is a special geological area that has a shallow-water hydrothermal vent at the front of Kueishan Island (Head) and the coral community located behind Kueishan Island (Tail), which allowed us to compare both methanotrophic activity and aerobic methanotrophs composition in two ecosystem’s sediments. Here we show that sediments of two different ecosystems had different methane oxidation rate. At the Tail site (coral community), the methane-oxidation rate was higher than at the Head site (hydrothermal vent) and the pmoA gene copy number showed the same trend. The microbiome composition results showed that coral community had aerobic methanotrophs and the abundance changed after methane incubation. In sum, the coral community had a higher methane-consuming ability and the presence of aerobic methanotrophs, compared to the shallow hydrothermal vent in Kueishan Island; the outcome in other coral reef (Kenting and Lyudao) also supported the results shown in Kueishan Island. Our results provided insight into the ability of coral community sediments to methane consuming. The aerobic methanotrophs and their roles played in the ocean methane cycle need to be further explored in the future. In addition, we could predict the future of methanotrophic activity and change in microbiome composition under the ocean acidification and global change based on the results of shallow-water hydrothermal vent in Kueishan Island.