利用穩定碳同位素組成解析混合微生物與沉積物之胺基酸來源

Source discrimination in microbial mixtures and sediments by carbon isotopic compositions of amino acids

鄭雅方(Ya-Fang Cheng)

指導教授 ： 王珮玲

國立臺灣大學/理學院/海洋研究所/碩士(2019年)

https://doi.org/10.6342/NTU201900542

摘要

胺基酸的穩定碳同位素組成與生物體合成胺基酸之路徑有關，因此代謝胺基酸路徑類似之生物在統計上具有共有特徵性的胺基酸穩定碳同位素組成樣式，近年來在生態學與生物地球化學研究中被利用於追蹤有機物的來源，並具有探索微生物在沉積物內活動伴隨再利用現地有機物，並新生成胺基酸的能力。然而，目前使用胺基酸碳同位素組成估計有機物的組成來源的能力仍不足，且前人在估計沉積物有機物組成時並未對微生物活動及代謝多樣性探討。
本研究分析已知組成之混合微生物的胺基酸碳同位素組成，透過已知菌株源在線性區別分析中求得的特徵胺基酸，利用混合模型估計混合物中胺基酸的來源。無論三端源或二端源的混合物，利用胺基酸碳同位素值估計而得的來源組成與已知組成有良好的正相關性，然而利用標準化的胺基酸碳同位素值估計三端源混合物時，發現未能有效的還原混合比例，這可能是由於其中一端源之特徵未能與另兩個端源有良好的分離，且在標準化過程中受同位素值差異大影響造成基準值偏移。此外，基準值飄移也對二端源混合物的端源辨識有所影響，只有在二端源混合之胺基酸碳同位素值基準值相近的情況下，能透過標準化的胺基酸碳同位素值還原出相關性較高並與已知組成接近的估計。
此外，本研究分析關渡濕地沉積物之胺基酸碳同位素組成，發現在同一根岩心中之胺基酸碳同位素組成有差異，而由混合模型推估沉積物之有機物來源主要為微型藻類及陸生植物，次要則源自微生物的貢獻。在此河岸濕地沉積物之微生物貢獻並無隨深度增加的趨勢，但樣品間有所差異，與前人的地化剖面資料相比較，此處胺基酸組成可能由強烈的微生物活動分層主導，不只有異營微生物貢獻，還包括其他多樣的微生物族群。

關鍵字

胺基酸 ； 穩定碳同位素組成 ； 微生物 ； 濕地

並列摘要

The stable carbon isotopic compositions of amino acids (δ13CAA) are associated with the biosynthetic pathways in organisms, leading to the statistically isotopic compositional characteristics of the organisms with similar amino acids metabolism. In recent years, the δ13CAA patterns have been applied on tracing the sources of organic matter in ecological and biogeochemical studies; also, they can be used to explore the microbial activities and resynthesis of organic matter in the sediment. However, quantitative estimation of the contributing sources in organic matter by δ13CAA patterns remains a great challenge, and the estimation usually ignores the diversity of microbial metabolism during degradation.
This study analyzed the δ13CAA values of microbial mixtures with known contributions of certain amino acid metabolisms, and the contributions of each sources was estimated using the informative amino acids derived from linear discriminant analysis of the source cultures by the Bayesian mixing model. The estimates based on δ13CAA values in both two and three-source mixtures showed strong positive correlations with the estimates based on cell densities. While the estimates based on the normalized δ13CAA values showed misleading results in three-source mixtures due to the low discrepancy of the δ13CAA patterns for one of the source cultures and the distinct mean δ13CAA values. Moreover, the shift of baseline for the source cultures with distinct δ13CAA values might also be the reason for the worse estimates of two-source mixtures; otherwise, the two-source mixtures with a similar range of δ13CAA values of the source cultures demonstrated better correlations between estimates by the δ13CAA value and cell-counting.
In addition, the δ13CAA patterns of sediments from Guandu wetland were examined, and the differences in the δ13CAA patterns among the samples within a sediment core were observed. The estimates by the Bayesian mixing model suggested that the major contribution of amino acids was microalgae and terrestrial plants and a minor contribution was microorganisms in most sediment samples. The contributions of microorganisms were not increased with depth, which may infer a strong influence of microbial activities including heterotrophic bacteria and other microbes related to the biogeochemical zonation in riverine wetlands.

並列關鍵字

amino acids ； stable carbon isotopic composition ； microbes ； wetland

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