DEOXYRIBONUCLEIC ACID CONTENT OF THE THREE CELL TYPES OF PHAEODACTYLUM TRICORNUTUM BOHLIN1

There is no significant difference in the DNA content of the oval, fusiform, and triradiate cell types of Phaeodactylum tricornutum, suggesting that they do not represent an alternation of haploid and diploid generations. The triradiate cells have a shorter generation time than the oval or fusiform cells.     

CALCIUM DEFICIENCY CAN INDUCE THE TRANSITION FROM OVAL TO FUSIFORM CELLS IN CULTURES OF PHAEODACTYLUM TRICORNUTUM BOHLIN1,2

The diatom Phaeodactylum tricornutum Bohlin is known to be pleomorphic. Previously it was considered that growth on medium solidified with agar produced ovate cells, whereas growth in liquid medium gave rise to fusiform cells. We have shown that ovate cells can be propagated in liquid medium if the calcium content of the medium is below 15 mg/liter. If the concentration of calcium is raised, fusiform cells develop.     

UPTAKE OF GUANINE BY THE DIATOM,PHAEODACTYLUM TRICORNUTUM1

Nitrate-cultured cells of Phaeodactylum tricornutum Bohlin lack the ability to take up guanine but can do so after a period of nitrogen deprivation, i.e. photosynthesis in nitrogen-free medium. Maximum rate of uptake occurred after 24 h of nitrogen deprivation. The development of ability to take up guanine required CO₂ fixation and was prevented by cycloheximide, ammonium or nitrate. The guanine taken up accummulated in the cells almost entirely as a compound which is probably methylated hypoxanthine. Guanine uptake was dependent upon metabolism and exhibited Michaelis-Menten like kinetics with a half-saturation value of 0.48 ± 0.05 μM guanine and a maximum uptake rate for guanine of ca. 200 nmol · 10^?8 cells · h^?1. Rate of uptake increased hyperbolically with Na⁺ concentration, with 8.25 mM Na⁺ supporting half-maximal rate, and it was inhibited by K⁺ ions.     

ON PIGMENTS,GROWTH, AND PHOTOSYNTHESIS OF PHAEODACTYLUM TRICORNUTUM12

A maximum growth rate with doubling time of 18 hr at 18 C could be maintained. Continuous cultures at about half maximum growth rate provided cells for study of pigments and photosynthesis. The light intensity curve of photosynthesis had no unusual features and showed light-saturated rates of 30-35 μl O₂/mrn³-hr at 18 C. Pigment analysis showed chlorophylls a and c (a/c ratio = 4), fucoxanthin, β-carotene, and diadinoxanthin. Growth under red light (±660 mμ) altered pigments only by decrease in chlorophyll c to about one-half the content obtained under clear tungsten lamps. The large and anomalous spectral shift in fucoxanthin following organic solvent extraction runs confirmed, but efforts to isolate a native fucoxanthin were unsuccessful. Spectral analysis of acetone extracts and sonicated cell preparations allowed estimate of fractional absorption by each component pigment. The analysis shows that chlorophyll a and fucoxanthin are the principal light absorbing pigments and that absorption by other carotenoids is very small.     

三角褐指藻产油突变株的筛选

能源短缺和原油价格上涨是全球关注的问题之一, 生物柴油作为一种优质的替代液体燃料越来越受到重视。以油料作物、废食用油和动物脂肪为原料生产生物柴油已远远不能满足需求。相比而言, 产油微藻具有光合效率高、生物量大、油含量高、生长速率快、不受季节的限制及不占用耕地等优势15, 被认为是制备生物柴油燃料的更有潜力的原料。由于目前微藻生物柴油生产成本过高, 尚未获得商业化生产。       

THE METABOLISM OF GUANINE BY THE DIATOM PHAEODACYLUM TRICONUTUM BOHLIN1

Guanine taken up by intact cells of Phaeodactylum tricornutum Bohlin was rapidly converted to allantoin which accumulated in the cells; the earleir view that the compound which accumulated was a methylahypoxanthine is shown to be erroneous. In contrast, cells of P. tricornutum, after premeabilisation with toluene, converted guanine only to xanthine, the reaction presumably being catalysed by guanine diaminase. Freshly harvested N-replete cells contained substantial guanine deaminase activity (ca. 200 nmol (10⁸ cells h)^?1); this activity doubled during 5 hours of N-deprivation. During the same period, the ability to take up guanine, which was initially low, increased by about 25x.     

ULTRASTRUCTURE OF A CHAIN-FORMING DIATOM PHAEODACTYLUM TRICORNUTUM1

The ultrastructure of a chain-forming clone of the polymorphic diatom Phaeodactylum tricornutum Bohlin has been studied by scanning and transmission electron microscopy. Both fusiform and tri-radiate cells are capable of forming chains. The cells, lacking any silica shell, are attached to each other at the central region of the theca, leaving the arms free. Neither homogenization nor sonication completely disrupts the chains. The attachment is due to fusion of the cell wall in the central region of the cell during cell wall deposition. This fusion results from failure of the cytoplasmic cleavage furrow to separate the plasma membranes of the two daughter cells sufficiently so that a single wall is deposited instead of two separate walls. Possible explanations for this are discussed.     

解淀粉芽孢杆菌对三角褐指藻的化感作用研究

实验研究不同剂量(100、500和1000μL)的解淀粉芽孢杆菌菌液、解淀粉芽孢杆菌代谢产物和解淀粉芽孢杆菌(Bacillus amyloliquefaciens)及代谢产物混合液3种组合对三角褐指藻(Phaeodactylum tricornutum)生长的影响.结果表明,解淀粉芽孢杆菌、其代谢产物和两种的混合液对三...     

THE POLYMORPHIC DIATOM PHAEODACTYLUM TRICORNUTUM: ULTRASTRUCTURE OF ITS MORPHOTYPES1,2

The ultrastructure of the oval, fusiform and triradiate morphotypes of Phaeodactylum tricornutum Bohlin is described. The organization and structure of the cytoplasmic organelles is similar in all three morphotypes, except that the vacuoles occupy the extra volume created by the arms of the fusiform and triradiate cells. The frustule in fusiform and triradiate cells is organic; in the oval type it may be organic or one of the valves may have a silica frustule surrounded by an organic wall. In all cells, the organic cell wall has up to 10 silica bands (13 nm wide) embedded in its surface in the girdle region, lacks girdle bands, and has an outer corrugated cell wall layer, except in the girdle region. Cell division, organic wall formation and silica deposition are described in detail. Four types of oval cells are also described. The relation to other diatoms is discussed.     

CHANGES IN CELL COMPOSITION AND LIPID METABOLISM MEDIATED BY SODIUM AND NITROGEN AVAILABILITY IN THE MARINE DIATOM PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE)1

The effects of nitrogen starvation in the presence or absence of sodium in the culture medium were monitored in batch cultures of the marine diatom Phaeodactylum tricornutum Bohlin. During nitrogen starvation in the presence of sodium, cell nitrogen and chlorophyll a decreased, mainly as a consequence of continued cell division. These decreases were accompanied by decreases in the rates of photosynthesis and respiration. There was no change in either cell volume or carbohydrate, but both carbon and lipid increased. During nitrogen starvation in the absence of sodium, cell division ceased. Cell nitrogen and chlorophyll a remained constant, and respiration did not decrease, but the changes in the photosynthetic rate and the lipid content per cell were similar to cultures that were nitrogen-starved in the presence of sodium. The carbon-to-nitrogen ratio increased in both cultures. Nitrogen, in the form of nitrate, and sodium were resupplied to cultures that had been preconditioned in nitrogen- and sodium-deficient medium for 5 d. Control cultures to which neither nitrate or sodium were added remained in a static state with respect to cell number, volume, and carbohydrate but showed slight increases in lipid. Cells in cultures to which 10 mM nitrate alone was added showed a similar response to cultures where no additions were made. Cells in cultures to which 50 mM sodium alone was added divided for 2 d, with concomitant small decreases in all measured constituents. Cell division resumed in cultures to which both sodium and nitrate were added. The lipid content fell dramatically in these cells and was correlated to metabolic oxidation via measured increases in the activity of the glyoxylate cycle enzyme, isocitrate lyase. We conclude that lipids are stored as a function of decreased growth rate and are metabolized to a small extent when cell division resumes. However, much higher rates of metabolism occur if cell division resumes in the presence of a nitrogen source.     

FIRST INSIGHTS INTO IMPROVEMENT OF EICOSAPENTAENOIC ACID CONTENT IN PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE) BY INDUCED MUTAGENESIS1

A strain improvement program was initiated based on mutagenesis with the goal of commercial production of eicosapentaenoic acid (EPA)from EPA-overproducing microalgal strains. Two rounds of mutation and selection were conducted using Phaeodactylum tricornutum Bohlin UTEX #640 as the parent strain. After the first round of mutagenesis, a putative mutant (provisionally labeled 114) was obtained. The EPA content (% of dry weight) of this mutant strain was 37% higher than that of the wild type. 114 was further mutated and another putative mutant (provisionally called II242) was isolated, the EPA content of which was 44% higher than that of the wild type. When cultured with aeration in 1-L flasks, EPA content of the wild type and putative mutants 114 and II242 was, 17.3 mg · g^?1, 31.5mg · g^?1, and 38.6 mg · g^?1 dry biomass, respectively. EPA productivity was 3.48 mg · L^?1· d^?1 4.01 mg · L^?1· d^?1, and 4.98 mg · L^?1· d^?1 respectively. These figures compare favorably with many other promising EPA-producing microorganisms and suggest that the use of a single methodology such as mutation and selection is a way to improve the polyunsaturated fatty acid content of microalgae and other microorganisms.     

CHANGES IN ABSORBANCE SPECTRUM OF THE DIATOM PHAEODACTYLUM TRICORNUTUM UPON MODIFICATION OF PROTEIN STRUCTURE1,2

Changes in the absorbance spectrum, of the diatom Phaeodactylum tricornutum which are brought about by heat, urea, stilt, and formaldehyde have been studied. The changes brought about by all agents are similar. Each converts cell suspensions from orange-brown to yellow-green. This color change results from an increase in absorbance in the blue and a decrease in absorbance in the green. All agents, except salt, also bring about an increase in absorbance in the red at wavelengths below that of the red peak of chlorophyll, and a decrease in absorbance at longer wavelengths. On heating cells, the absorbance change in the green occurs more rapidly than the changes in the blue and red. The converse is true when cells are treated with 4 M NaCl. Heat or formaldehyde treatments chemically modify chlorophyll pigments which are present in untreated cells. The change in absorbance in the green is probably due to changes in the molecular environment of fucoxanthin which, results from protein modification. The changes in the blue and red are at least partly due to chemical changes in chlorophylls, but may also be due, in part, to protein modification.     

酵母全细胞苯丙氨酸鲜氨酶（PAL）活性的紫外分光光度测定法

本文报告以L-苯丙氨酸 (L-phe) 为底物,酵母全细胞作酶源,酶促生成产物反式-肉桂酸 (t-Ca)测定苯丙氨解氨酸 (PAP,EC_(4.3.1.5) 活性的紫外分光光度法。测定程序包括标准物质t-Ca的加样试验,绝对回收率试验,线性回归分析的整套定量分析研宄步骤,建立了一套经过修改的Kalghatgi和Subba Rao(1975) PAL 活性测定法。此法具有良好的准确度和精密度,已经用于评价具有PAL活性的酵母菌株在液体培养物中细胞生长和PAL活性形成的时间过程研究。     

LIGHT DEPENDENCE OF GROWTH AND PHOTOSYNTHESIS IN PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE)1

Phaeodactylum tricornutum Bohlin was maintained in exponential growth over a range of photon flux densities (PFD) from 7 to 230 μmol·m^?2s^?1. The chlorophyll a-specific light absorption coefficient, maximum quantum yield of photosynthesis, and C:N atom ratio were all independent of the PFD to which cells were acclimated. Carbon- and cell-specific, light-satuated, gross photosynthesis rates and dark respiration rates were largely independent of acclimation PFD. Decreases in the chlorophyll a-specific, gross photosynthesis rate and the carbon: chlorophyll ratio and increases of cell- or carbon-specific absorption coefficients were associated with an increase in cell chlorophyll a in cultures acclimated to low PFDs. The compensation PFD for growth was calculated to be 0.5 μmol·m^?2s^?1. The maintenance metabolic rate (2 × 10^?7s^?1), calculated on the basis of the compensation PFD, is an order of magnitude lower than the measured dark respiration rate(2.7 × 10^?6mol O₂·mol C^?1s^?1). Maintenance of high carbon-specific, light-saturated photosynthesis rates in cells acclimated to low PFDs may allow effective use of short exposures to high PFDs in a temporally variable light environment.     

三角褐指藻岩藻黄素-叶绿素蛋白复合体的分离纯化和功能研究

通过改进硅藻主要捕光天线(FCP)的分离和提取方法, 得到高纯度、高均一性的三角褐指藻FCP蛋白,并通过电泳、液相色谱、质谱和吸收荧光光谱学等手段研究三角褐指藻FCP的氨基酸序列、色素组成和捕光特点等, 初步预测三角褐指藻的结构和功能特点。结果表明三角褐指藻FCP含有198个氨基酸, 与高等植物LHCII的序列Identity约为24%。三维结构预测显示FCP具有与LHCII相似的三次跨膜螺旋框架结构, 但跨膜螺旋较短, 且无膜表面螺旋结构。FCP中主要结合了叶绿素a、叶绿素c、岩藻黄素, 不含叶绿素b, Chl. a/c为3.0。光谱学分析表明岩藻黄素可以在水下弱光环境中有效地捕获绿光, 并高效地传递至叶绿素。而岩藻黄素在400-500 nm区域吸收的光能, 向叶绿素传递效率较低, 预示着岩藻黄素在强光下也有一定的光保护功能。FCP中有4个叶绿素结合的保守氨基酸位点, 可能是其叶绿素结合位置, 但岩藻黄素的结合位置因其结构和结合位点的变化而无法预测。研究为进一步探索FCP的结构和功能特性奠定了基础。     

剪切应力对毛细血管内皮细胞代谢的影响

建立的平行平板流协腔装置适用于研究血管内皮细胞代谢对剪切流场的响应。将培养的人胚肾小球血管单层内皮细胞置于剪应力分别为５＊１０＾－５Ｎ／ｃｍ＾２,１＊１０＾－４Ｎ／ｃｍ＾２和１．５＊１０＾－４Ｎ／ｃｍ＾２的定常层流中剪切２５小时。