THE EFFECT OF CERTAIN RESPIRATORY INHIBITORS ON THE RESPIRATION OF CHLORELLA

Chlorella, when made heterotrophic by means of certain sugars, respires like other heterotrophic cells when subjected to the respiratory inhibitors, hydrocyanic acid, hydrogen sulfide, and carbon monoxide. Whether the case of Chlorella is typical for green cells in general remains to be seen. Experiments with various other green organisms are being carried out, in hope of settling this point.     

STEROLS OF CHLORELLA. I. THE NATURALLY OCCURRING STEROLS OF CHLORELLA VULGARIS, C. ELLIPSOIDEA, AND C. SACCHAROPHILA

The characteristics of the sterols naturally occurring in threespecies of Chlorella were examined. The algae were grown heterotrophicallyon glucose. Sterols were extracted and isolated from the lipidfraction and were characterized by means of chemical and physicaltests. Chlorella vulgaris contained three sterols. Only the principalone, chondrillasterol, was identified. Chondrillasterol hasbeen isolated previously from the genus Scenedesmus. Chlorella ellipsoidea and Chlorella saccharophila were foundto contain sterols with ß-oriented alkyl groups atC-24 in contrast to the -oriented groups commonly found in higherplants. Poriferasterol was identified as the principal sterolof both algae. Clionasterol and 22-dihydrobrassicasterol wereidentified as the two secondary sterols present. None of thesesterols have previously been reported to occur in plants. Theisolation of 22-dihydrobrassicasterol has not been previouslyreported from any natural source. ¹Scientific Article A1153, Contribution No. 3623 of the Universityof Maryland Agricultural Experiment Station. ²This work has been supported in part by a grant from the NationalAeronautics and Space Administration.     

pH对小球藻Chlorella sp. XQ-200419光合作用、生长和产油的影响

以一种生长快、油脂含量高的小球藻(Chlorella sp. XQ-200419)为实验材料, 利用测定净光合放氧速率的方法研究了pH对其光合作用的影响; 使用改良的BG-11培养基在微藻环形培养池模拟系统中进行分批培养, 培养周期为8d, 培养过程中使用 pH控制仪在线监测藻液的pH, 根据pH变化, 自动接通、关闭CO2通气管道, 将藻液pH分别控制在5.06.0, 7.08.0, 8.09.0, 9.010.0, 10.011.0内, 研究pH对生长速率、生物质面积产率、总脂含量和总脂面积产率的影响。主要结果如下: 藻液pH对小球藻Chlorella sp. XQ-200419光合放氧、生长速率、生物质产率、总脂含量和产率都有显著影响, 适宜的pH范围是7.09.0, 在此范围内, 光合放氧、生长速率、生物质产率、总脂含量和产率均保持较高水平, 且pH的影响不显著; pH低于7.0, 高于9.0, 其光合放氧、生长速率、生物质产率、总脂含量和产率都显著降低。这表明pH对小球藻Chlorella sp. XQ-200419光合作用的影响和对生长、产油的影响是一致的。pH 7.08.0, 小球藻的生物质平均面积产率和总脂平均面积产率都达到最大值, 分别是8.9 g/(m2d)和2269.5 mg/(m2d); 当藻液pH超过10.0, 生物质平均面积产率和总脂平均面积产率分别降低42.1%和60.0%。适合于小球藻生长的pH也有利于其积累油脂, 所以, pH对小球藻产油的影响是一种适宜模式, 而非胁迫模式。规模化培养小球藻Chlorella sp. XQ-200419, 通过补充CO2将藻液pH控制在7.09.0内, 可以获得高生物质产率和总脂产率。研究结果反映出pH对小球藻光合作用、生长和产油影响的规律, 也为规模化培养小球藻生产微藻油脂过程中合理控制藻液pH提供了依据。       

THE EFFECT OF CULTURE CONDITIONS ON THE HYDROCARBON CONTENT OF CHLORELLA VULGARIS12

Cultures of Chlorella vulgaris were grown aulo-trophically under fluorescent light and heterotrophically on glucose and inorganic salts. Hydrocarbons were extracted and analyzed by gas-liquid chromatography, molecular sieve separations, and silicic acid-AgNO₃ chromatography. Chlorella vulgaris grown under both culture conditions contained a series of saturated n-paraffins ranging from 17 to 36 carbon atoms in length. This is in contrast to reports in the early literature which indicated that the hydrocarbon fraction of algae was composed of only 1 or 2 specific hydrocarbons. Only under heterotrophic conditions, however, did C. vulgaris produce 1-penta-cosene and 1-heptacosene as the primary components of the hydrocarbon mixture. Other Chlorella species were examined, but only C. vulgaris produced significant quantities of these compounds.     

THE EFFECT OF THE H ION CONCENTRATION ON THE AVAILABILITY OF IRON FOR CHLORELLA SP

The data obtained in these experiments indicate clearly that unless the necessary precautions are taken to keep the iron of the culture medium in solution the results obtained by varying the H ion concentration will not represent the true effect of this factor on growth. The availability of iron in nutrient solutions has been the subject of numerous recent investigations and it is now known that iron is precipitated at the lower hydrogen ion concentrations, that the iron of certain iron salts is less likely to be precipitated than that of others, and that certain salts of organic acids tend to keep the iron in solution. In general, ferric citrate seems to be the most favorable source of iron. In addition to chemical precipitation, however, it is also possible for the iron to be removed by adsorption on an amorphous precipitate such as calcium phosphate. As this precipitate is frequently formed when nutrient solutions are made alkaline, this may account for the discordant results reported in the literature as to the availability of certain forms of iron. By omitting calcium from the culture solution iron can be maintained in a form available for growth in alkaline solutions by the addition of sodium citrate. In such solutions the maximum growth of Chlorella occurred at pH 7.5. The alkaline limit for growth has not been established as yet. In investigating the availability of iron at varying concentrations of the hydrogen ion, changes in the pH value of the solution during the course of an experiment should also be taken into account. This is especially important in unbuffered solutions. The differential absorption of the ions of ammonium salts may cause a marked increase in the hydrogen ion concentration, which in turn will cause an increase in the solubility of iron. In strongly buffered solutions as used in these experiments this effect is slight.