盐生隐杆藻胞外多糖的粘度特性

盐生隐杆藻(Aphanothece halophytica Fremy)属蓝藻门(Cynnophyta)色球藻目(Chroococales),具有很强的耐盐性,在其生长过程中释放粘性多糖.该多糖粘度较大,可作为增稠剂、润滑剂、乳化剂和保湿剂等,应用于食品、医药和化妆品工业.为进一步开发利用,对该多糖的粘度进行了测定和分析.     

盐生隐杆藻胞外多糖(EPAH)抗衰老的实验研究

通过检测实验小鼠血清中的SOD、CAT、MDA、GSH的活性,同时检测肝、脑中脂褐素(Lf)的量以及胸腺系数和脾系数等多项指标,研究了盐生隐杆藻胞外多糖抗衰老活性,并通过耐力实验研究了盐生隐杆藻胞外多糖对小鼠增强耐力的作用.结果显示EPAH能明显降低老龄小鼠肝、脑脂褐素的含量,降低老龄小鼠血清中MDA的含量,增强老龄小鼠血浆中SOD、GSH、CAT的生物学活性,同时增强抗应激能力,提示EPAH有提高小鼠抗衰老的作用.     

嗜盐隐杆藻胞外多糖的分离、纯化及理化特性

嗜盐隐杆藻（Ａｐｈａｎｏｔｈｅｃｅ ｈａｔｏｐｈｙｔｉｃａ）培养液经离心,浓缩、透析、有机溶剂沉淀得胞外多糖（Ｅｘｏｐｏｌｙｓａｃｃｈａｒｉｄｅｓ,ＥＰＳ）粗品,经ＤＥＡＥ－纤维素二次柱层析纯化得ＥＰＳ精品。葡聚糖Ｇ－２００凝胶过滤表明其为单一组份。对其进行理化测试并对各组分进行定量分析,多糖、已糖醛酸、硫酸根含量分别为４０．９６％２３．２７％和３４．４６％,元素分析你测得Ｃ、Ｈ、Ｎ、Ｓ含量分别为     

营养盐浓度对航天搭载盐藻生长及胞外多糖含量的影响

比较了培养液中不同营养盐浓度对“神舟5号”搭载盐藻(Dunaliella salina)和非搭载盐藻的生长及胞外多糖积累的影响,发现经“神舟5号”搭载后盐藻最适营养盐浓度发生了变化。非搭载盐藻培养液中最佳单因子组合为:CaC l2200 mg/L、MgC l2500 mg/L、KNO31 000 mg/L、KH2PO455 mg/L。搭载盐藻培养液中最佳单因子组合为:CaC l2250 mg/L、MgC l2500 mg/L、KNO31 000 mg/L、KH2PO415 mg/L。搭载和非搭载盐藻胞外多糖累积的最佳单因子组合相同:CaC l2、MgC l2、KNO3、KH2PO4分别为250、2 000、500、15 mg/L,但搭载盐藻胞外多糖的分泌明显高于非搭载盐藻。     

罗伦隐球酵母胞外多糖的研究I．发酵条件

研究了罗伦隐球酵母(Cryptococcus laurentii)产生胞外多糖的适宜条件。培养基组成(g／L)：葡萄糖80.00,酵母膏1.25,KH2PO4 3.00,MgSO4·7H2O 0.05,CaCO3 10.00,pH6.0。在30℃,旋转式摇床(200r／min)上培养6天。胞外多糖产量最高可达17.38g／L,对底物的转化率为21.725％。     

罗伦隐球酵母胞外多糖的研究 Ⅰ.发酵条件

研究了罗伦隐球酵母(cryptococcus laurentii)产生胞外多糖的适宜条件。培养基组成(g/L):葡萄糖80.00,酵母膏1.25,KH_2PO_3.00,MgSO_4·7H_2O0.05,CaCO_3 10.00,pH6.0。在30℃,旋转式摇床(200r/min)上培养6天。胞外多糖产量最高可达17.38g/L,对底物的转化率为21.725％。     

地生枝顶孢(AT01)胞外多糖发酵条件的研究

研究地生枝顶孢AT01菌株胞外多糖发酵工艺,主要内容包括碳源、氮源、起始pH及接种量等.AT01胞外多糖的最佳培养基组成白砂糖4%,黄豆粉3%,磷酸氢二钾0.5%,氢氧化钙O.3%,MgSO4·7H2O O.05%,pH自然(6.7).最佳培养条件接种量为1O%,起始pH为6.7,装液量为100mL/250mL.     

根瘤菌属胞外多糖的研究

本文研究了豌豆根瘤菌(Rhizobum Leguminosarum),苜蓿根瘤菌(R. meliloti),三叶草根瘤菌(R. trifolii),菜豆根瘤菌(R. phaseoli),豇豆根瘤菌(Rradyrhizobium sp.(Vigna))和大豆根瘤菌(R. Japonicum)产生的胞外多糖化学组分的差异,结果表明,不同种的根瘤菌能产生具有不同组分的胞外多糖,其多糖组分的差异主要表现在糖醛酸和甘露糖的含量。豌豆根瘤菌、三叶草根瘤菌,菜豆根瘤菌产生的胞外多糖含有糖醛酸,大豆根瘤菌和苜蓿根瘤菌产生的胞外多糖一般不含有糖醛酸。根瘤菌有快生型和慢生型之别,这种差异也可由其产生的胞外多糖组分看到,一般快生型根瘤菌:豌豆根瘤菌,苜蓿根瘤菌,菜豆根瘤菌,三叶草根瘤菌,(包括最近证明的快生型大豆根瘤菌)的胞外多糖中甘露糖所占百分比较低(低于20％),葡萄糖所占的百分比较高(高于60％),而慢生型根瘤菌:大豆根瘤菌和豇豆根瘤菌的胞外多糖中甘露糖所占百分比较高(高于36％),葡萄糖所占的百分比较低(低于50％)。     

Molecular characterization of DnaK from the halotolerant cyanobacterium Aphanothece halophytica for ATPase,protein folding,and copper binding under various salinity conditions

Previously, it was found that the dnaK1 gene of the halotolerant cyanobacterium Aphanothece halophytica encodes a polypeptide of 721 amino acids which has a long C-terminal region rich in acidic amino acid residues. To understand whether the A. halophytica DnaK1 possesses chaperone activity at high salinity and to clarify the role of the extra C-terminal amino acids, a comparative study examined three kinds of DnaK molecules for ATPase activity as well as the refolding activity of other urea-denatured proteins under various salinity conditions. DnaK1s from A. halophytica and Synechococcus sp. PCC 7942 and the C-terminal deleted A. halophytica DnaK1 were expressed in Escherichia coli and purified. The ATPase activity of A. halophytica DnaK1 was very high even at high salinity (1.0 M NaCl or KCl), whereas this activity in Synechococcus PCC 7942 DnaK1 decreased with increasing concentrations of NaCl or KCl. The salt dependence on the refolding activity of urea-denatured lactate dehydrogenase by DnaK1s was similar to that of ATPase activity of the respective DnaK1s. The deletion of the C-terminal amino acids of A. halophytica DnaK1 had no effect on the ATPase activity, but caused a significant decrease in the refolding activity of other denatured proteins. These facts indicate that the extra C-terminal region of A. halophytica DnaK1 plays an important role in the refolding of other urea-denatured proteins at high salinity. Furthermore, it was shown that DnaK1 could assist the copper binding of precursor apo-plastocyanin as well as that of mature apo-plastocyanin during the folding of these copper proteins.     

Purification and Characterization of Nitrate Reductase from the Halotolerant Cyanobacterium <Emphasis Type="Italic">Aphanothece halophytica</Emphasis>

Summary Factors affecting the activity of nitrate reductase (E.C.1.7.7.2) from the halotolerant cyanobacterium Aphanothece halophytica were investigated. Cells grown in nitrate-containing medium exhibited higher nitrate reductase activity than cells grown in medium in which nitrate was replaced by glutamine. When ammonium was present in the medium instead of nitrate, the activity of nitrate reductase was virtually non-detectable, albeit with normal cell growth. The enzyme was localized mainly in the cytoplasm. The enzyme was purified 406-fold with a specific activity of 40.6 μmol/min/mg protein. SDS-PAGE revealed a subunit molecular mass of 58 kDa. Gel filtration experiments revealed a native molecular mass of 61 kDa. The K _m value for nitrate was 0.46 mM. Both methyl viologen and ferredoxin could serve as electron donor with K _m values of 4.3 mM and 5.2 μM, respectively. The enzyme was strongly inhibited by sulfhydryl-reactive agents and cyanide. Nitrite, the product of the enzyme reaction, showed little inhibition. Chlorate, the substrate analog, could moderately inhibit the enzyme activity. NaCl up to 200 mM stimulated the activity of the enzyme whereas enzyme inhibition was observed at ≥300 mM NaCl.     

Ion metabolism in a halophilic blue-green alga,Aphanothece halophytica

The intracellular ion content of the halophilic blue-green alga, Aphanothece halophytica was studied as a function of age, external sodium and external potassium concentration. Intracellular Na⁺ was found to be about 0.38 millimoles/g dry mass. Intracellular K⁺ concentrations were as high as 1 M and varied directly with external salinity. Intracellular Ca⁺⁺ and Mg⁺⁺ were in the range previously reported for fresh water blue-green algae despite their extremely high extracellular concentrations. Average cell size is consistent at room temperature with two exceptions. When the outside K⁺ is lower than 6.5 mM the cells tend to be smaller with less intracellular K⁺ and high Ca⁺⁺. In stationary phase cultures the cells are larger with high intracellular Mg⁺⁺ and low K⁺.     

Plasma membrane lipid composition of the halophilic cyanobacterium Aphanothece halophytica

The plasma membrane from Aphanothece halophytica was isolated using both glycerol and sucrose gradient centrifugation. The isolated membrane was characterized for lipid content by TLC and isolated lipids were quantified by chemical analysis. The plasma membrane of A. halophytica was composed of MGDG, DGDG and PG. The sulfur containing lipid SQDG was not detected. The mole percent of each lipid in the plasma membrane varied with the external salinity of the media. MGDG was the most abundant lipid in the plasma membrane of cells grown at one molar external NaCl. At three molar external NaCl, PG was the most abundant lipid. The ratio of uncharged to charged lipids comprising the plasma membrane decreased as the external salinity increased. It is possible that the alteration in lipid composition is of major importance in the adaptation of A. halophytica to changing external salinity.Abbreviations TLC Thin-layer chromatography - MGDG momogalactosyldiacylglycerol - DGDG digaloctosyldiacylglycerol - PG phosphatidylglycerol - SQDG sulphoquinovosyldiacylglycerol     

A glycine betaine transport system in Aphanothece halophytica and other glycine betaine-synthesising cyanobacteria

Uptake of exogenous ¹⁴C-glycine betaine has been followed in the cyanobacterium Aphanothece halophytica and other species able to synthesise glycine betaine in response to osmotic stress. At 1 mmol dm^–3 uptake was rapid (flux rate=29.50 nmol m^–2 s^–1), equilibrating at an internal concentration of 120 mmol dm^–3 within 30 min. This rapid uptake, coupled with high internal accumulation, was characteristic of glycine betaine-synthesising cyanobacteria only. The ¹⁴C-glycine betaine transported was not catabolised. Kinetic studies indicated a Michaelis-Menten type relationship (K _m=2.0 mol dm^–3, V _max=45 nmol min^–1 mm^–3 cell volume), with a pH optimum of 8.0–8.5. Darkness dramatically decreased the flux rate. Higher ¹⁴C-glycine betaine levels occurred in cells growth in medium of elevated osmotic strength, and glycine betaine uptake was sensitive to changes in external salinity. A relationship between Na⁺ availability and glycine betaine uptake was observed, with >80 mmol dm^–3 Na⁺ required for optimal stimulation of uptake in seawater-grown cells. Severe hyperosmotic stress (1000 mmol dm^–3 NaCl) reduced the rate of glycine betaine uptake but increased internal glycine betaine concentration at equilibrium. Hypo-osmotic stress caused a decline in the internal glycine betaine concentration due to an increased rate of loss, indicating that the efflux system was also sensitive to ambient salinity changes. It is envisaged that this active transport system may be an adaptive mechanism in halophilic glycine betaine-synthesising cyanobacteria.     

Accumulation of glycinebetaine and its synthesis from radioactive precursors under salt-stress in the cyanobacterium Aphanothece halophytica

Growth in salt-stressed (2.0 M NaCl) Aphanothece halophytica was initially delayed during the first two days of cultivation and eventually attained the same growth rate as the control (0.5 M NaCl) cells. Glycinebetaine accumulation increased slightly in control cells but a dramatic increase of glycinebetaine occurred in salt-stressed cells during a growth period of six days. There was no apparent increase in the synthesis of [¹⁴C] glycinebetaine in the control cells, in contrast to the marked increase in its synthesis in the salt-stressed cells. Increasing NaCl concentration in the growth medium induced both the accumulation and the synthesis of glycinebetaine. Time course experiments provided evidence that [¹⁴C] choline was first oxidized to [¹⁴C] betaine aldehyde which was further oxidized to [¹⁴C] glycinebetaine in A. halophytica. The supporting data for such a pathway were obtained from the presence of choline and betaine aldehyde dehydrogenase activities found in the membrane and cytoplasmic fractions, respectively. The activities of these two enzymes were also enhanced upon increasing NaCl concentration in the growth medium from 0.5 M to 2.0 M. Under this condition an increaseof approximately 1.5-fold was observed for choline dehydrogenase activity as compared to 2.5-fold for betaine aldehyde dehydrogenase activity, suggesting a preferable induction of the latter enzyme by salt stress. A. halophytica was able to utilize [¹⁴C] ethanolamine and [¹⁴C] glycine for the synthesis of [¹⁴C] glycinebetaine. This revised version was published online in August 2006 with corrections to the Cover Date.