温度和干旱对生物结皮中2优势藻种胞外多糖分泌的影响机制

The produce and release of Extracellular polysaccharides (EPS) is one of the important adaptive mechanisms of cyanobacteria evolved to face severe environment. Nowadays, the synthetic mechanism of EPS is still unclear. In this study, two dominant species in biological soil crusts, Microcoleus vaginatus FACHB 896 and Nostoc sp. FACHB 892 will be selected as research objects. They will be cultivated under different temperature and desiccation, to study the changes of extracellular EPS secretion and intracellular glycogen, intracellular total sugar, soluble sugar and soluble protein other physiological indexes as well as their correlations. And the expression of EPS synthesis protein gene exoD and EPS export protein gene epsB will also be studied by fluorescence quantitative PCR technology. The mechanism of EPS secretion will be uncovered by a combination of morphology, physiological and molecular methods. These results can improve existing knowledge on the adaptation mechanism of desert cyanobacteria to temperature and desiccation, and can provide theory for the mechanism of crust formation and the desertification control by use of desert cyanobacteria.

胞外多糖(EPS)是结皮蓝藻适应多种严酷环境的生命保障系统，其分泌的机制一直是土壤生态系统修复学研究的核心论题。然而，目前关于结皮蓝藻EPS分泌的机制尚不清楚。本研究拟选取生物结皮中2种优势藻种(具鞘微鞘藻和念珠藻)为研究对象，研究它们在不同温度和干旱条件下胞外EPS的分泌与细胞内糖原、细胞内总糖、可溶性糖和可溶性蛋白等生理指标的变化规律及其相互关系；并利用实时荧光定量PCR技术探讨EPS合成基因exoD和EPS转运基因epsB的表达变化。通过形态、生理和分子相结合的方法，揭示结皮蓝藻EPS分泌的规律与内在机理，从而有利于进一步理解结皮蓝藻适应温度和干旱的机制，并为探讨生物结皮的形成机理和荒漠化治理提供科学依据。

胞外多糖(EPS)是生物结皮蓝藻适应多种严酷环境的生命保障系统。然而，目前关于结皮蓝藻EPS分泌的机制尚不清楚。本研究通过形态、生理和核糖核酸测序（RNA-Seq）技术探究藻EPS分泌的规律与内在机理。研究发现长期干旱、低温、高温、高光强促进念珠藻 EPS的分泌，这表明藻细胞通过分泌EPS来抵抗逆境环境。高温和干旱抑制具鞘微鞘藻EPS的分泌，细胞通过储存碳能量来维持生存。通过京都基因与基因组百科全书(KEGG)通路富集分析，处理组基因富集的显著性主要是核糖体、核糖体的生物发生的代谢途径中，预测该功能基因通过调控合成抗胁迫的酶等蛋白来抵御逆境。同时，我们分析了与胞外脂多糖合成相关基因的转录表达情况，发现处理组基因KdsD和KpsF明显下调。总之，两藻种EPS分泌的本质是胞内碳氮代谢不平衡的产物。藻类可能通过下调基因KdsD和KpsF来抑制EPS合成。这些结果为探讨生物结皮的形成机理和荒漠化治理提供科学依据。