Cyclic Beta Glucans of the Rhizobiaceae

9505706米勒氏革兰氏阴性菌在其周质区室中积累高水平的寡糖。 这些低聚糖的生物合成受到严格的酶调节，当细胞在低渗培养基中生长时，周质浓度可达到大于100 mM的水平。 这些分子的积累已被证明代表了在低渗环境中生长的适应性策略，并且据信这种积累为细胞提供了调节周质体积的机制。 在拟议的研究计划中，苜蓿根瘤菌将被用作模式细菌，直接研究周质寡糖在低渗适应过程中的作用。 提出了三个主要目标：1）识别新的R.苜蓿周质寡糖合成缺陷突变体;苜蓿周质寡糖突变体的低渗生长、周质体积和细胞表面性质;苜蓿（渗透调节和运输）。 拟议中的研究将提供重要的洞察力的微生物周质的性质，在根际生物多样性和生态系统稳定性的互动动态，涉及基本的微生物/植物宿主/寄生虫的关系。 由于生物膜可以自由渗透水，所有活细胞都必须科普其环境中水的可用性变化。 这对于直接遇到宽范围的渗透强度环境（例如，从非常稀到高盐条件）。 某些细菌进一步受到渗透胁迫的挑战，因为它们含有称为周质的外部细胞区室。 隔室与许多基本的细胞过程（包括营养获取、蛋白质输出和运动性）整体相关，并且可占总细胞体积的高达40%。 尽管如此，对周质的了解还是非常有限的。 最近，研究表明，在稀释环境中生长期间，多种多样的细菌在其周质隔室内积累高浓度的结构独特的寡糖（一类碳水化合物）。 此外，已经表明，在细菌中已经进化出多种生物合成途径，以确保周质寡糖的合成和积累。虽然周质寡糖的确切功能尚未确定，但通常认为，当细胞受到应激时，它们的积累为细胞调节周质体积提供了一种机制。 在本研究计划中，R.苜蓿属（meliloti）是一种重要的农业土壤细菌，将被用作模式微生物，以直接研究周质寡糖在植物胁迫环境中生长期间的作用。 这项研究的结果将提供有关的结构和功能的周质，一个动态的隔间连接到几个重要的细胞过程的重要信息。 ***

9505706 Miller Gram-negative bacteria accumulate high levels of oligosaccharides within their periplasmic compartments. The biosynthesis of these oligosaccharides is strictly osmoregulated, and periplasmic concentrations may reach levels greater than 100 mM when cells are grown in hypoosmotic media. The accumulation of these molecules has been shown to represent an adaptive strategy for growth in hypoosmotic environments, and it is believed that this accumulation provides a mechanism for the cell to regulate periplasmic volume. In the proposed research program, Rhizobium meliloti will be used as a model bacterium to directly investigate the roles of the periplasmic oligosaccharides during hypoosmotic adaptation. Three major objectives are proposed: 1) identification of new classes of R. meliloti mutants defective for periplasmic oligosaccharide biosynthesis; 2) characterization of R. meliloti periplasmic oligosaccharide mutants (hypoosmotic growth, periplasmic volume, and cell surface properties); 3) further characterization of periplasmic oligosaccharide biosynthesis by R. meliloti (osmotic regulation and transport). The proposed studies will provide important insight concerning the nature of the microbial periplasm in the interactive dynamics of biological diversity of the rhizosphere and ecosystem stability involving essential microbe/plant host/parasite relationships. %%% Because biological membranes are freely permeable to water, all living cells must cope with changes in the availability of water in their environment. This is particularly a problem for bacterial cells which directly encounter wide ranges of osmotic strength environments (e.g., from very dilute to hypersaline conditions). Certain bacteria are further challenged by osmotic stress because they contain an outer cellular compartment called the periplasm. The compartment is integrally linked to many fundamental cellular processes (including nutrient acquisition, protein export, and motility) and may represent up to 4 0% of the total cellular volume. Nonetheless, understanding of the periplasm is surprisingly limited. Recently, it was shown that a great diversity of bacteria accumulate high concentrations of structurally unique oligosaccharides (a class of carbohydrate) within their periplasmic compartments during growth in dilute environments. Furthermore, it has been shown that a variety of biosynthetic pathways have evolved among bacterial to insure the synthesis and accumulation of periplasmic oligosaccharides. Although the precise functions of the periplasmic oligosaccharides remain undefined, it is generally believed that their accumulation provides a mechanism for the cell to regulate periplasmic volume when cells are stressed osmotically. In the proposed research program, R. meliloti, an agriculturally important soil bacterium, will be used as a model microbe to directly investigate the roles of the periplsmic oligosaccharides during growth in osmotically stressed environments. The results of this study will provide important information concerning the structure and function of the periplasm, a dynamic compartment linked to several important cellular processes. ***