歐亞大陸中陸域泥火山之微生物的生物地理學模式

Microbial Biogeographic Patterns of Terrestrial Mud Volcanoes across Eurasian Continent

陳俐陵(Li-Ling Chen)

指導教授 ： 王珮玲

共同指導教授 ： 林立虹

國立臺灣大學/理學院/海洋研究所/碩士(2017年)

https://doi.org/10.6342/NTU201702623

摘要

相較於其他沉積物生態系，陸域泥火山之間的流體流通性取決於下方流體通道，因此微生物的播遷途徑受限於有限的流體交換；另外，還原性流體接觸到大氣，使得其中絕對厭氧的群集更難以遷徙。本研究假設在播遷極度困難、化學梯度變化劇烈的歐亞大陸陸域泥火山中，微生物的生物地理學模式將由環境中的物理化學因子為主導。藉由分析環境物理化學因子及微生物群集的水平距離變化，以探究各樣點之內的群集多樣性及分布、不同樣點之間的群集多樣性差異大小，並以中性理論或環境因子解釋陸域泥火山的分布結果。
本研究利用過去蒐集橫跨歐亞大陸9000公里，分布於義大利、喬治亞、伊朗、中國、緬甸及台灣之陸域泥火山共14根岩心，分析結果顯示，於岩芯尺度僅有5個普遍種。大部分微生物群集的Bray-Curtis相異度在樣本及岩芯尺度皆大，僅義大利泥火山具有較相似的群集組成。地理距離及環境物理化學因子，與不同尺度的陸域泥火山生態系之微生物生物地理學模式相關。於中性理論的地理距離分析中，隨著物種相對豐度增加、物種出現的最大距離也增加，樣本尺度的斜率為4.014e-04 %/公里，岩芯尺度斜率則為4.069e-04 %/公里，證明Abundance-range relationship的存在。另外，隨著棲地間的距離增加，群集的相似度降低，樣本尺度的斜率為 4.033e-02，岩芯尺度斜率則為2.533e-01，證明Distance-decay relationship的存在。另一方面，環境物理化學因子對於整體生物群集中的解釋度僅9.9 %，若針對特定代謝作用的生物與此代謝作用相關的化學因子分析，則可產生不等程度的相關性。例如，Thiobacillus可氧化元素硫、硫代硫酸鹽或多硫代硫酸鹽作為能量來源，代謝後產生硫酸鹽，其豐度與硫酸根離子呈現正相關。Thiohalorhabdus為極端嗜鹽菌，其豐度與氯離子具有高度正相關。此結果並不完全支持本研究最初的假設－在播遷極度困難、化學梯度變化劇烈的陸域泥火山中，微生物生物地理學模式主要與環境中的物理化學因子有關。僅有特定物種的分布與特定的化學因子有高度相關，此結果可能肇因於有限的儀器分析靈敏度，更反映了我們對物種生理代謝特徵的有限認識。而中性理論則較能描述整體陸域泥火山微生物生物地理學的分布模式，顯示微生物群集的播遷能力對於群集的組成與多樣性扮演了重要的角色。

關鍵字

微生物生物地理學 ； 歐亞大陸 ； 陸域泥火山 ； 中性理論 ； 環境物理化學因子

並列摘要

Terrestrial mud volcanoes represent the surface expression of conduits tapping fluid and gas reservoirs in deep subsurface environments. Whether dispersal of microbial communities could proceed in such habitat depends significantly on the connectivity of the subsurface fluid conduits along long distance. While most terrestrial mud volcanoes are hydrologically isolated from each other and strictly obligatory anaerobes inherited in mud volcanoes would be limited upon the exposure to the atmosphere, microbial dispersal would be restricted. This study hypothesized that the physiochemical factors in mud volcanoes is highly correlated with microbial community structure. With this, we analyzed microbial community structure of terrestrial mud volcanoes using samples collected from Italy, Georgia, China, Myanmar, Iran, and Taiwan. We conducted various analyses to test the validity of distance and physiochemical factors in explaining biogeographic pattern.
Our analyses demonstrated that most communities varied significantly between samples or cores (with Bray-Curtis dissimilarity > 0.7). Exceptions (with Bray-Curtis dissimilarity = 0.69) occurred for core pairs from Italy but could be categorized in accordance with their geological backgrounds. Among more than 100,000 OTUs, no cosmopolitan could be found. However, five cosmopolitans belong to Proteobacteria, Bacteroidetes, and Methanosarcina in all cores. The slope parameters of positive abundance-range and distance-decay relationships were generally greater than or comparable with those for marine seafloor sediments, and cold seeps, suggesting the effects of dispersal capability on community diversity. For comparison, the nine physiochemical parameters (including methane, chloride, sulfate, total nitrogen, total sulfur, total inorganic carbon and total organic carbon) only explained 9.9% of community variance, and specific geochemical parameters were correlated with specific taxa. For example, Thiobacillus and sulfate were positivity correlated with a Pearson coefficient of 0.86. Since this genus could oxidize sulfide, thiosulfate or polythionates to produce sulfate for energy acquisition. Their high relatedness suggests a strong control of geochemical context on population distribution. Overall, our results did not support the original hypothesis we proposed. Physiochemical parameters could be correlated to limited taxa possibly due to the lack of understanding of the physiological characteristics for communities. Instead, the neutral theory can better account for the biogeographic pattern in terrestrial mud volcanoes.

並列關鍵字

microbial biogeography ； Eurasian continent ； terrestrial mud volcanoes ； neutral theory ； physiochemical factors

參考文獻

邱怡萍. (2015). 義大利西西里島泥火山之微生物族群組成與甲烷循環. (碩士學位論文), 臺灣大學.

Button, D., Robertson, B. R., Lepp, P. W., & Schmidt, T. M. (1998). A small, dilute-cytoplasm, high-affinity, novel bacterium isolated by extinction culture and having kinetic constants compatible with growth at ambient concentrations of dissolved nutrients in seawater. Applied and Environmental Microbiology, 64(11), 4467-4476.

Pimenov, N., Savvichev, A., Rusanov, I., Lein, A. Y., & Ivanov, M. (2000). Microbiological processes of the carbon and sulfur cycles at cold methane seeps of the North Atlantic. Microbiology, 69(6), 709-720.

Martiny, J. B. H., Bohannan, B. J., Brown, J. H., Colwell, R. K., Fuhrman, J. A., Green, J. L., Horner-Devine, M. C., Kane, M., Krumins, J. A., & Kuske, C. R. (2006). Microbial biogeography: putting microorganisms on the map. Nature Reviews Microbiology, 4(2), 102-112.

Alam, M., Alam, M. M., Curray, J. R., Chowdhury, M. L. R., & Gani, M. R. (2003). An overview of the sedimentary geology of the Bengal Basin in relation to the regional tectonic framework and basin-fill history. Sedimentary Geology, 155(3), 179-208.