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Molecular mechanisms of extreme desiccation tolerance in the terrestrial cyanobacterium

陆生蓝藻极端干燥耐受性的分子机制

基本信息

批准号：
18608001
负责人：
SAKAMOTO Toshio
金额：
$ 2.5万
依托单位：
Kanazawa University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2006
资助国家：
日本
起止时间：
2006 至 2007
项目状态：
已结题

项目摘要

We investigated changes of trehalose level in field-isolated, natural colonies of the terrestrial cyanobacterium Nostoc commune responding to desiccation. No detectable trehalose was found in fully hydrated N. commune colonies; however, trehalose accumulation occurred in response to water loss during desiccation and high levels of trehalose were detected in the air-dried colonies. The three genes for trehalose metabolism, treZ (maltooligosyltrehalose trehalohydrolase, Mth), treY (maltooligosyltrehalose synthase, Mts), and treH (trehalase), were found as a gene cluster, and the mRNAs for these genes were detectable at similar levels during desiccation. Trehalase of N. punctiforme was heterologously expressed in E. coli cells in an active form with a molecular mass of 52kDa. Trehalase activity was strongly inhibited in the presence of 10mM NaCl while trehalose synthesis activity remained active in the presence of salt. These data suggest that the rate of trehalose production exceeds that of trehalose hydrolysis under water-stress conditions characterized by increased cellular solute concentrations. The terrestrial cyanobacterium N. commune forms a visible colony in which the cells are embedded in extracellular polysaccharides (EPSs), which play a crucial role in the extreme desiccation tolerance of this organism. The activities that hydrolyse glycoside bonds were examined using artificial nitrophenyl-linked sugars as substrates. Aβ-D-glucosidase, with a molecular mass of20kDa, was resistant to20min of boiling and was identified as a cyanobacterial fasciclin protein based on its N-terminal amino-acid sequence. The36-kDa major protein (WspA) showed heat-resistantβ-D-galactosidase activity.

我们调查了海藻糖水平的变化，在现场隔离，天然菌落的陆地蓝藻地木耳响应干燥。在完全水合的N.公社殖民地;然而，海藻糖的积累响应于干燥过程中的水分损失而发生，并且在空气干燥的菌落中检测到高水平的海藻糖。海藻糖代谢的三个基因，treZ（麦芽寡糖基海藻糖海藻水解酶，Mth），treY（麦芽寡糖基海藻糖合酶，Mts），和treH（海藻糖酶），被发现作为一个基因簇，这些基因的mRNA在干燥过程中以相似的水平检测。海藻糖酶; punctiforme在E.大肠杆菌细胞中的活性形式，分子量为52 kDa。海藻糖酶活性在10 mM NaCl存在下被强烈抑制，而海藻糖合成活性在盐存在下保持活性。这些数据表明，海藻糖的生产率超过海藻糖水解的水分胁迫条件下，其特征在于增加细胞溶质浓度。陆生蓝藻N.在这种情况下，一种名为“commune”的微生物形成了一个可见的菌落，其中细胞嵌入在胞外多糖（EPS）中，胞外多糖在这种生物体的极端干燥耐受性中起着至关重要的作用。水解糖苷键的活动进行了检查，使用人工硝基苯连接的糖作为底物。β-D-葡萄糖苷酶分子量为20 kDa，耐煮沸20 min，根据其N端氨基酸序列鉴定为蓝藻fasciclin蛋白。36-kDa的主要蛋白（WspA）具有耐热β-D-半乳糖苷酶活性。