Studies of polysaccharides from three edible species of Nostoc (cyanobacteria) with different colony morphologies: Structural characterization and effect on the complement system of polysaccharides from Nostoc commune

The cyanobacterium Nostoc commune Vaucher produces quite complex extracellular polysaccharides. The cyanobacterium is nitrogen fixing, and on growing the cyanobacterium in media with and without nitrogen, different types of extracellular polysaccharides were obtained. These were also different from the polysaccharides present in N. commune collected in the field. High pH anion exchange chromatography (HPAEC) of weak acid hydrolysates of the culture-grown material demonstrated that, in this case, HPAEC was useful for comparison of the different polymers. The main differences between the polymers from the field group and the culture-grown samples were the presence of substantial amounts of arabinose, 2-O-methylglucose, and glucuronic acid in the latter. Methylation studies also revealed a difference in the branching points on the glucose units between the field and cultured samples, being 1,4,6 for the first and 1,3,6 for the latter. The field acidic fraction gave, on weak acid hydrolysis and separation on BioGel P2 and HPAEC, 12 oligosaccharide fractions that were isolated and studied by different mass spectroscopy techniques. The structures of the oligosaccharides were determined, and two different series that can originate from two repeating pentamers were identified: GlcAl-4/6GlcM1-4Ga11-4Glc1-4Xyl and GlcAl-4/6Glc1-4Ga11-4Glc1-4Xyl. The difference between these oligosaccharides lies in the methyl substituent on carbon 2 of the glucose unit next to the nonreducing glucuronic acid unit. The polysaccharides from field material were shown to have a strong effect on the complement system.

Chemical Constituents of a Marine-Derived Endophytic Fungus Penicillium commune G2M

Cultivation of the endophytic fungus Penicillium commune, which was isolated from the semi-mangrove plant Hibiscus tiliaceus, afforded one new compound 1-O-(2,4-dihydroxy-6-methylbenzoyl)-glycerol (1) along with thirteen known products, including 1-O-acetylglycerol (2), N-acetyltryptophan (3), 3-indolylacetic acid methyl ester (4), 1-(2,4-dihydroxy-3,5-dimethylphenyl)ethanone (5), 2-(2,5-dihydroxyphenyl)acetic acid (6), (4R,5S)-5-hydroxyhexan-4-olide (7), thymidine (8), uracil (9), thymine (10), ergosterol (11), beta-sitosterol (12), beta-daucosterol (13), and ergosta-7,22-dien-3 beta,5 alpha,6 beta-triol (14). The structures of these compounds were established by detailed NMR spectroscopic analysis, as well as by comparison with literature data or with authentic samples.

内蒙古草原地耳和发菜的固氮特性及在氮素循环中的作用

以内蒙古干旱半干旱草原上的固氮蓝藻－普通念珠藻和发状念珠藻为研究对象，对其分布、生态特点、形态结构、生物量及不同条件下的固氮活性进行了研究，并根据降水与气温状况对其年固氮量进行了估算。结果表明：同发状念珠藻相比，普通念珠藻的分布更为广泛，其形态也有较大的差异。普通念珠藻的生物量在以禾本科为主的退化草场和沙地上较大，在pH值偏碱、含水量300％和温度30℃的情况下，其固氮活性较高，达2500nmolC2H2/g•h（干重）以上，年固氮量也高达4.19kg/h.m2，占草原氮素总输出的10％左右。由此可见，在维持干旱半干旱草原与荒漠草原生态系统的氮素平衡中，固氮蓝藻这类低等固氮植物可能起着重要作用。

3种念珠藻多糖对自由基的清除作用

研究了地木耳(Nostoc commune)、葛仙米(N.sphaeroides)和发菜(N.flagelliform e)3种念珠藻多糖对自由基的清除作用。结果表明,3种念珠藻多糖对超氧阴离子自由基和羟自由基具有很强的清除作用,且呈量效关系,地木耳清除超氧自由基作用最强,最高清除率达72.3%,葛仙米和发菜分别为46.7%、35.5%;发菜清除羟自由基效果最强,最高清除率达74.3%,葛仙米和地木耳清除率分别为49.0%、46.7%;3种念珠藻多糖对DPPH自由基的清除作用不显著。

Mutations stabilize small subunit ribosomal RNA in desiccation-tolerant cyanobacteria Nostoc

The ribosomal RNA molecule is an ideal model for evaluating the stability of a gene product under desiccation stress. We isolated 8 Nostoc strains that had the capacity to withstand desiccation in habitats and sequenced their 16S rRNA genes. The stabilities of 16S rRNAs secondary structures, indicated by free energy change of folding, were compared among Nostoc and other related species. The results suggested that 163 rRNA secondary structures of the desiccation-tolerant Nostoc strains were more stable than that of planktonic Nostocaceae species. The stabilizing mutations were divided into two categories: (1) those causing GC to replace other types of base pairs in stems and (2) those causing extension of stems. By mapping stabilizing mutations onto the Nostoc phylogenetic tree based on 16S rRNA gene, it was shown that most of stabilizing mutations had evolved during adaptive radiation among Nostoc spp. The evolution of 16S rRNA along the Nostoc lineage is suggested to be selectively advantageous under desiccation stress.

Studies on polysaccharides from three edible species of Nostoc (Cyanobacteria) with different colony morphologies: Comparison of monosaccharide compositions and viscosities of polysaccharides from field colonies and suspension cultures

Hot water-soluble polysaccharides woe extracted from field colonies and suspension cultures of Nostoc commune Vaucher, Nostoc flagelliforme Berkeley et Curtis, and Nostoc sphaeroides Kutzing. Excreted extracellular polymeric substances (EPS) were isolated from the media in which the suspension cultures were grown. The main monosaccharides of the field colony polysaccharides from the three species were glucose, xylose, and galactose, with an approximate ratio of 2:1:1. Mannose was also present, but the levels varied among the species, and arabinose appeared only in N. flagelliforme. The compositions of the cellular polysaccharides and EPS from suspension cultures were more complicated than those of the field samples and varied among the different species. The polysaccharides from the cultures of N. flagelliforme had a relatively simple composition consisting of mannose, galactose, glucose, and glucuronic acid, but no xylose, as was found in the field colony polysaccharides. The polysaccharides from cultures of N. sphaeroides contained glucose (the major component), rhamnose, fucose, xylose, mannose, and galactose. These same sugars were present in the polysaccharides from cultures of N. commune, with xylose as the major component. Combined nitrogen in the media had no qualitative influence on the compositions of the cellular polysaccharides but affected those of the EPS of N. commune and N. flagelliforme. The EPS of N. sphaeroides had a very low fetal carbohydrate content and thus was not considered to be polysaccharide in nature. The field colony polysaccharides could be separated by anion exchange chromatography into neutral and acidic fractions having similar sugar compositions. Preliminary linkage analysis showed that 1) xylose, glucose, and galactose were 1-->4 linked, 2) mannose, galactose, and xylose occurred as terminal residues, and 3) branch points occurred in glucose as 1-->3,4 and 1-->3,6 linkages and in xylose as a 1-->3,4 linkage. The polymer preparations from field colonies had higher kinematic viscosities than those from corresponding suspension cultures. The high viscosities of the polymers suggested that they might DE suitable for industrial uses.

中国竹材腐朽真菌多样性初步研究

生物多样性是人类赖以生存的物质基础，菌物多样性是生物多样性的重要组成。我国位于亚太竹区，是世界竹类的分布中心之一，有着极为丰富的竹种资源，并孕育着丰富的菌物资源。近年来，我国对木材腐朽菌，特别是多孔菌进行了广泛深入的研究，发表了许多新种和中国新记录种，但是对生于竹材上的腐朽菌却少见报道。因此，开展竹材腐朽真菌种类的研究对深入认识腐朽菌物种多样性，积极利用这些菌物资源，防治竹类病害以及竹材保藏都具有重要意义。 本论文按照多孔菌现代分类学方法对采集自我国10省市18个自然保护区、森林公园和林场的竹材腐朽真菌标本进行了初步的研究。对11种重要的竹材腐朽菌进行详细的描述和显微结构绘图，记载了每种的寄主、国内分布，并对每种与其相似种的联系和区别以及腐朽类型进行了讨论。 研究结果显示，我国范围内共记录及描述竹材腐朽真菌从5属增加到28属，新增属分别为：假芝属、薄孔菌属、小薄孔菌属、蜡孔菌属、拟蜡孔菌属、小集毛孔菌属、囊孔菌属、浅孔菌属、圆齿菌属、产丝齿菌属、耙齿菌属、容氏孔菌属、锐孔菌属、多年卧孔菌属、木层孔菌属、硬孔菌属、中国干腐菌属、干皮孔菌属、褶菌属、栓孔菌属、附毛孔菌属、孢孔菌属和中国记录属拟浅孔菌属 (Grammotheloposis)，其中广义多孔菌有20属，革菌2属，齿菌1属；有15属为白腐菌，1属褐腐。 新增竹材腐朽真菌19种，其中多孔菌有15种，革菌1种，齿菌1种，褶菌2属。相似干朽菌(Serpula similis)和棕榈浅孔菌（Grammothele fuligo）竹区分布较多，前者是腐朽病原菌，后者腐朽作用不强，但影响竹材美观。二者在中国南方竹区广泛分布，是对竹材危害较严重的种类。而长江以北分布极少。另外有药用菌4种，分别为浅黄囊孔菌（Flavodon flavus）、宽棱木层孔菌(Phellinus torulosus)、裂褶菌(Schizophyllum commune)和灵芝(Ganoderma lucidum)。待定种1种(Grammotheloposis sp.)。