釀酒酵母(Saccharomyces cerevisiae)為單細胞的生物，但後來發現部分的釀酒酵母會呈現聚集生長，像是在釀酒工業中會因為發酵後期發酵槽的醣源不足而促使細胞在細胞膜上分泌絮凝劑(flocculant)，促使細胞跟細胞之間產生表面黏附力而聚集，這個現象被稱之為絮凝現象(flocculation)，目前研究大多證實絮凝現象能夠提高釀酒酵母的環境適應力，像是提供營養分配作用、抗逆境性等。但除了絮凝以外，還有另外一種聚集是釀酒酵母在出芽生殖時，由於子母細胞進行染色質分離時初級的幾丁質隔膜沒有正常分解而造成子細胞持續依附在母細胞上，最終形成聚集體，這種聚集被命名為鏈狀聚集現象(Chain-formation)，但奇特的是鏈狀聚集不同於絮凝現象，目前只被發現在單套體釀酒酵母中，在雙套體釀酒酵母並不會出現，因此，本篇研究的主題是希望能探討鏈狀聚集現象對於釀酒酵母單套體的意義為何?是否和絮凝現象一樣是為了增加對環境適應力，或者是其他的因素?而我為了確認鏈狀聚集是否和釀酒酵母的環境適應力有關，首先，我統整了關於野生型釀酒酵母RM11與RM11-1a的基因表現量差異的文獻，找出造成兩者不同表型的關鍵基因-AMN1基因，並利用基因工程的技術調控細胞內AMN1基因表現量，成功的製造出不聚集的野生型單套體突變株與具有聚集表型的雙套體釀酒酵母菌株，而後，我將聚集與不聚集的酵母菌兩兩分組，並藉由共培養在營養環境、6%乙醇環境與38oC熱環境下比較兩者之間生存競爭能力的差異，結果證實不論在怎樣的環境下，野生型雙套體中不聚集的RM11都比聚集的突變株RM11/pTEF AMN1具有更佳的環境適應力，而野生型單套體則相反，聚集的RM11-1a比不聚集的突變株RM11-1a/ΔAMN1具有更佳的環境適應力，因此單套體呈聚集表型，雙套體呈非聚集表型的原因不僅僅是為了因應環境需求，單套體的聚集可能是為了在環境中進行性別轉變後更快速的進行交配，重新回到雙套體世代，而雙套體世代因為不需要進行這個，所以皆為非聚集生長，而本篇的研究證明了釀酒酵母的鏈狀聚集是受到分子機制所調控的，但並非如同絮凝現象主要是因為受到環境因素，更有可能是為了讓單套體的釀酒酵母重新回到較穩定的雙套體世代。

Saccharomyces cerevisiae is a single cell organism. However, it is frequently observed that yeast cells tend to clump together into the aggregation phenotype. The most common type of yeast aggregation is flocculation. It is a reversible cell-cell aggregation phenomenon, and caused by the interaction between specific flocculation proteins of cell surface. Other than flocculation, chain-forming is another aggregation phenotype. It is due to the failure of separation between mother cells and daughter cells, and is regulated by AMN1 genes. In our laboratory, it is observed that the chain-forming aggregation phenotype only occurs in haploid yeast cells but not in diploid yeast cells. However, flocculation phenomenon occurs in both haploid and diploid yeast cells. In order to explore this issue, I tested the fitness effect of the aggregation phenotype in haploid and in diploid yeast cells to check whether aggregation phenomenon affect the yeast adaption. My data showed that the aggregation phenotype increases the fitness of haploid cells under several environmental conditions but not for the diploid cells. Therefore, I concluded that the haploid yeast cells need the aggregation phenotype but not the diploid yeast cells, and it is not subject to environment.

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