Methionine Transport in Chlorella vulgaris

Absorption of ³⁵S-l-methionine by Chlorella vulgaris was measured at concentrations that ranged from 0.1 to 10.0 μmoles/ml. A brief, rapid phase of uptake was followed by a more prolonged, slower phase that was linear only at the lowest concentrations. The radioactivity accumulated by the end of 1 hour's incubation at an exogenous level of 0.1 μmole/ml was retained by the cells despite the inclusion of 10 μmoles/ml of nonradioactive methionine in the rinse medium. As the exogenous concentration was raised, the ratio of intracellular soluble radioactivity to exogenous radioactivity decreased. Analysis of the accumulated, soluble radioactivity showed that 90% was in the form of methionine and that about 10% had been converted to a compound with properties of S-adenosylmethionine. Azide and ethionine were the most effective of the inhibitors tested.     

Sulfite: Preferential sulfur source and modifier of CO2 fixation in Chlorella vulgaris

Sulfite was added at the time of inoculation to a standard and to a sulfate deficient medium of Chlorella vulgaris. It was not only used as a sulfur source, but besides this, at concentrations <1.0 mmol l^–1, the growth yield was enhanced up to 30% compared to sulfate saturated conditions. Higher sulfite concentrations increasingly inhibited cell growth. Growth rate determinations indicated that the enhancement, and the inhibition respectively, were confined to the very beginning of culture growth; the time period during which the sulfite was not yet oxidized (5–10 h). In contrast, an increased CO₂ fixation rate/unit of protein, occurring up to 5.0 mmol l^–1 sulfite and a shift towards the -carboxylation pathway, are persisting at least during the growth period of 4 days. The preferential uptake of sulfite, also indicated by a marked increase in methionine content of algal protein, presumably causes an increase in thylakoidal sulfolipids, and is such modifying the CO₂ fixation.Abbreviations PGA 3-phosphoglyceric acid - APS adenosine 5-phosphosulfate - PEP phosphoenolpyruvate     

Gold uptake by Chlorella vulgaris

This paper describes a study on the uptake of gold (III) ions by viable and treated cells of the unicellular alga, Chlorella vulgaris. Inactivating the algal cells by various physical/chemical treatments resulted in a considerable enhancement in the uptake capacity over the pristine cells. X-ray Photoelectron Spectroscopy (XPS) analyses confirmed the deposition of elemental gold, Au (O), on the cell surface, indicating that a reduction process has taken place. XPS results also suggested an increase in the oxidized carbon species, carboxyl species in particular, on the surfaces of the treated cells. FTIR spectroscopy results revealed that the carboxyl group was involved mainly in the binding of the gold on the surface of both the viable and treated cells.     

Metabolism of Urea by Chlorella vulgaris

Urea metabolism was studied with nitrogen-starved cells of Chlorella vulgaris Beijerinck var. viridis (Chodat), a green alga which apparently lacks urease. Incorporation of radioactivity from urea-(14)C into the alcohol-soluble fraction was virtually eliminated in cell suspensions flushed with 10% CO(2) in air. This same result was obtained when expected acceptors of urea carbon were replenished by adding ornithine and glucose with the urea. Several carbamyl compounds, which might be early products of urea metabolism and a source of the (14)CO(2), were not appreciably labeled. If cells were treated with cyanide at a concentration which inhibited ammonia uptake completely and urea uptake only slightly, more than half of the urea nitrogen taken up was found in the medium as ammonia. Cells under nitrogen gas in the dark were unable to take up urea or ammonia, but the normal rate of uptake was resumed in light. Since 3-(3,4-dichlorophenyl)-1,1-dimethylurea did not selectively inhibit this uptake, an active respiration supported by light-dependent oxygen evolution in these cells was ruled out. A tentative scheme for urea metabolism is proposed to consist of an initial energy-dependent splitting of urea into carbon dioxide and ammonia. This reaction in Chlorella is thought to differ from a typical urease-catalyzed reaction by the apparent requirement of a high energy compound, possibly adenosine triphosphate.     

小球藻的玻璃化超低温保存法

先用含0.5 m01·L-1甘油和0.4 mol·L-1蔗糖的预处理液处理20min,然后用含30%蔗糖 15%乙二醇 10%二甲基亚砜 BBMG培养液的玻璃化液处理,在0℃下预冻60min后,将小球藻投入液氮.此法存活率较高,可达到60.14%,小球藻种质保存效果较好.通过试验初步建立了小球藻玻璃化法超低温保存的技术程序.     

Formation of Thiosulfate from Sulfite by Desulfovibrio vulgaris

Crude extracts of Desulfovibrio vulgaris reduced sulfite to sulfide. Ammonium sulfate fractionation of crude extracts separated a thiosulfate-forming system from sulfite- and thiosulfate-reductase activities. Further purification by sucrose density centrifugation separated the thiosulfate-forming system into two components, both of which were required for the reaction. In addition to these two components, cytochrome c₃, ferredoxin, and hydrogenase were required to form thiosulfate from sulfite. By absorption spectra and from the effect of pH and substrate concentration, the ionic species acting as the substrate for thiosulfate-formation was concluded to be bisulfite.     

Flocculation of Chlorella vulgaris by Lactobacillus casei

Summary The flocculation of Chlorella vulgaris by Lactobacillus casei was studied to determine whether the latter could act as a suitable flocculant for the removal of Chlorella from algal ponds. The flocculating activity of the Lactobacilli was caused by the bacterial cells themselves, and not by diffusible products of bacterial metabolism. Diffusible products of algal metabolism inhibited flocculation. For algae resuspended in water, the best flocculation occurred at pH values less than 3.5 where the charges on the bacterial and algal cells were opposite. For flocculation at least one bacterium was required for every algal cell; in terms of cell concentrations,10 mg/l of bacteria were required to flocculate an algal suspension of 1,000 mg/l. The mechanism of flocculation implied by the results is that positively charged cells of L. casei adsorb to the surface of negatively charged cells of C. vulgaris neutralizing the charge and thus destabilizing the algal suspension. Because of the low pH required and because diffusible products of algal metabolism inhibit the flocculation, it is unlikely that L. casei could be usefully employed as a flocculant of Chlorella from algal ponds.     

The Assimilation of Acetate by Chlorella vulgaris

The acetate metabolism of autotrophically grown, acetate-adaptedand acetate-grown cells is compared. All oxidize acetate rapidlyand assimilate about half of the acetate added in short-termexperiments. Kinetic analysis of the incorporation of ¹⁴C-acetatereveals citrate as a primary product of acetate assimilationin all cells in darkness. Malate formed from acetate-I-¹⁴C byacetate-grown cells is asymmetrically labelled in a manner consistentwith a primary incorporation of acetate into malate by a malatesynthase reaction. The chief difference between autotrophic and acetate-grown cellsis the faster rate at which the latter incorporate acetate carboninto compounds outside the tricarboxylic acid cycle. In particular,incorporation into protein and carbohydrate is much faster inacetate-grown cells and it is suggested that enzymes catalysingreactions leading away from the tricarboxylic acid cycle mayincrease in activity in acetate-grown cells. Light greatly stimulates acetate incorporation into lipide andalso increases the synthesis of protein and carbohydrate.     

Electrotransformation of Chlorella vulgaris

Using hygromycin B resistance as a marker for selection, we have established the conditions required for the transformation of Chlorella vulgaris. The exponentially grown C. vulgaris cells were transformed by electroporation with plasmid pIG121-Hm, and transformants were selected with hygromycin B at a concentration of 50 μg/ml. Cell extracts prepared from the late-log cultures of the transformants exhibited glucuronidase activities as conferred by the gus gene on pIG121-Hm. The maintenance of plasmid in the algal cells seemed to be transient as many cultures derived from the hygromycin B-resistant colonies gradually lost the hygromycin resistance upon prolonged growth. The result of Southern blotting of the genomic DNAs prepared from transformant cultures exhibiting persistent hygromycin resistance showed that integration of part of the plasmid DNA into the host chromosome had taken place. Received: 19 December 1997 / Revision received: 5 October 1998 / Accepted: 27 October 1998     

活性小球藻对铅离子的吸附与解吸特征研究

研究了活性小球藻对Pb^2＋的生物吸附、解吸及其机理。结果表明,培养至指数生长期的小球藻对Pb^2＋的吸附能力最强,吸附率可达75％。吸附液的pH值在7左右,小球藻对Pb^2＋有较好的吸附作用,吸附率可达80％。吸附的动力学实验表明,在小球藻对Pb^2＋吸附的起始阶段,吸附速度较快,10min即可达到平衡。研究还表明,加强光照可以促进小球藻对Pb^2＋的吸附在一定的浓度范围内,小球藻对Pb^2＋的吸附符合Freundlich等温吸附模型。在解吸实验中,用EDTA和HCI作为解吸剂的解吸率可分别达到近80％和60％,可以有效解吸被吸附的Pb^2＋。     

Hexose-transport-deficient mutants of Chlorella vulgaris

Autotrophically grown cells of Chlorella vulgaris show a strong increase in the uptake rates for hexoses and for seven amino acids when incubated in the presence of hexoses. This increase is due to de-novo synthesis of three transport proteins: one forhexoses and two for amino acids. Mutants deficient in hexose transport were obtained after treatment of wild-type cells with acridine orange, followed by a selection procedure using the toxic hexose analogue, 2-deoxy-D-glucose. Moreover, the two amino-acid-transport systems could not be induced in these mutants by hexoses. The capacity to phosphorylate hexoses was identical in mutants and in the wild-type strain. The loss of transport activities can be correlated with the loss of certain radiolabeled protein bands on fluorograms of sodium dodecylsulfate-polyacrylamide gels. These proteins are assumed to be responsible for the different transport systems in the wild-type strain. With the help of additional mutants defective in one or two of the different aminoacid-transport systems, it has been attempted to assign the different transport activities to individual protein bands on the gel.Abbreviations AUP arginine-uptake-defective mutant - 2-DG 2-deoxy-D-glucose - 6-DG 6-deoxy-D-glucose - HUP hexose-uptake-defective mutant - PUP^- proline-uptake-defective mutant - SDS sodium dodecyl sulfate - WT wild type     

Biotransformation and Bioconcentration of Steroid Estrogens by Chlorella vulgaris

The biotransformation and bioconcentration of natural and synthetic steroid estrogens by Chlorella vulgaris were investigated by using batch-shaking experiments with incubation for 48 h in the light or dark. Estradiol and estrone were interconvertible in both light and dark conditions; however, this biotransformation showed a preference for estrone. In the light, 50% estradiol was further metabolized to an unknown product. Apart from biotransformation, estrone, as well as hydroxyestrone, estriol, and ethinylestradiol, was relatively stable in the algal culture, whereas estradiol valerate was hydrolyzed to estradiol and then to estrone within 3 h of incubation. All of the tested estrogens exhibited a degree of partitioning to C. vulgaris; however, the concentrations of estriol, hydroxyestrone, ethinylestradiol, and estradiol valerate were always below the quantification limits. For estradiol and estrone, the partitioning of these estrogens in the algal extracts to the filtrates was <6% of the total amount present. The average concentration factor for estrone was ca. 27; however, the concentration factor for estradiol was not reported since no equilibrium was reached between the aqueous solution and that within the cells due to continuing biotransformation.     

Biotransformation and bioconcentration of steroid estrogens by Chlorella vulgaris

The biotransformation and bioconcentration of natural and synthetic steroid estrogens by Chlorella vulgaris were investigated by using batch-shaking experiments with incubation for 48 h in the light or dark. Estradiol and estrone were interconvertible in both light and dark conditions; however, this biotransformation showed a preference for estrone. In the light, 50% estradiol was further metabolized to an unknown product. Apart from biotransformation, estrone, as well as hydroxyestrone, estriol, and ethinylestradiol, was relatively stable in the algal culture, whereas estradiol valerate was hydrolyzed to estradiol and then to estrone within 3 h of incubation. All of the tested estrogens exhibited a degree of partitioning to C. vulgaris; however, the concentrations of estriol, hydroxyestrone, ethinylestradiol, and estradiol valerate were always below the quantification limits. For estradiol and estrone, the partitioning of these estrogens in the algal extracts to the filtrates was <6% of the total amount present. The average concentration factor for estrone was ca. 27; however, the concentration factor for estradiol was not reported since no equilibrium was reached between the aqueous solution and that within the cells due to continuing biotransformation.     

Removal and biodegradation of nonylphenol by immobilized Chlorella vulgaris

The removal and biodegradation of nonylphenol (NP) by alginate-immobilized cells of Chlorella vulgaris were compared with their respective free cultures. The effects of four cell densities of 10(4) per algal bead were investigated, as were the four algal bead concentrations, with regard to the removal and biodegradation of NP. Although immobilization significantly decreased the growth rate and NP's biodegradation efficiency of C. vulgaris, NP removal over a short period was enhanced. The NP removal mechanism by immobilized cells was similar to that by free cells, including adsorption onto alginate matrix and algal cells, absorption within cells and cellular biodegradation. The optimal cell density and bead concentration for the removal and biodegradation of NP was 50-100×10(4) cells algal bead(-1) and 2-4 beads ml(-1) of wastewater, respectively. These results demonstrated that immobilized C. vulgaris cells under optimal biomass and photoautotrophic conditions are effective in removing NP from contaminated water.     

内陆水体盐度升高对小球藻生理特性的影响

全球气候变化引起内陆水体盐度缓慢升高,对浮游植物造成显著影响。为了探究水体盐度升高对浮游植物生理特性的影响,以普通小球藻为试验对象,在原水和不同盐度（1、3、5 g·L^-1）条件下研究普通小球藻生长增殖情况,分析其抗氧化酶活性及对光合作用的生理响应。结果显示,盐度升高会抑制普通小球藻生长,当达到3 g·L^-1以上时抑制作用明显,细胞分裂增殖指标均明显下降,叶绿素a合成速率衰减,藻细胞膜损坏严重,同时其光合活性显著降低。这表明过高盐度（>3 g·L^-1）极有可能破坏藻细胞的生理结构和抗氧化能力,导致其生长增殖受到抑制。研究结果从细胞增殖和生理特性角度分析了水体盐度变化对水体浮游藻类的影响,以期为保护内陆水体生物多样性提供参考。