Occurrence of poly-beta-hydroxybutyrate in Spirulina species.

Several strains of photoautotrophically grown Spirulina spp. contained poly-beta-hydroxybutyrate (PHB) at concentrations never exceeding a few milligrams per gram of dry weight. Under mixotrophic growth conditions in the presence of acetate, PHB reached values greater than 2.5% of dry weight. With pyruvate, no significant effect on PHB accumulation was obtained.     

钝顶螺旋藻富集转化硒及硒在藻体中的分布

钝顶螺旋藻在４℃、避光、隔离空气条件下,对硒的吸附量死体显著高于活体。藻体对硒的最大富集量为６２７．４μg.g^-1(DW),培养基中硒浓度在３００μg.ml^-1以下时有机硒转化率大于８０％。藻体中的硒主要分布在水溶性组化率大于８０％。藻体中的硒主要分布在水溶性组分中,占总硒的６５％以上,蛋白质硒占有机硒的７１．９％,多糖、核酸也有一定量硒分布。     

Accumulation of selenium in mixotrophic culture of Spirulina platensis on glucose

Accumulation of Se in mixotrophic culture of Spirulina platensis was investigated in this study. Results indicated that glucose was better than acetate as an organic carbon source for mixotrophic culture of S. platensis. Supplementation of glucose (2 gL(-1)) significantly enhanced the biomass concentration (2.57 gL(-1)) and the production of phycocyanin (0.279 gL(-1)) and allophycocyanin (0.126 gL(-1)) in S. platensis, which were much higher than those of photoautotrophic culture (1.08 gL(-1), 0.119 gL(-1) and 0.042 gL(-1), respectively). Stepwise addition of Se during the growth phase avoided the inhibitory effect of high Se concentration on the growth of S. platensis. The Se enrichment favored the production of phycocyanin and allophycocyanin in the algal cells. The highest Se yield (1033 microgL(-1)) was obtained at an accumulative Se concentration of 250 mgL(-1), with organic Se percentage, biomass concentration, phycocyanin and allophycocyanin yields of 92.3%, 2.55 gL(-1), 0.295 gL(-1) and 0.153 gL(-1), respectively. These results indicated that the application of mixotrophic culture S. platensis with stepwise addition of Se to the medium could offer an effective and economical way for the production of high Se-enriched algal products.     

The Effect of Selenite Ions on Growth and Selenium Accumulation in Spirulina platensis

Selenium accumulation and the growth of cyanobacterium Spirulina platensis (Nordst.) Geitl. were studied in a culture with sodium selenite-supplemented nutritional medium. Selenite concentrations below 20 mg/l did not inhibit the growth of S. platensis. The addition of 30 mg/l of this salt somewhat decreased the growth rate during the linear growth phase, induced the earlier suspension transition to the steady-state phase, and substantially lowered the highest optical density of the suspension. However, even at 170 mg/l Na₂SeO₃, the culture still demonstrated a capacity for growth. The content of selenium in the cells depended directly on its concentration in the medium, up to the lethal level. At high selenium concentrations (100–170 mg/l), S. platensis reduced Se(IV) up to Se(0). The latter was secreted onto the cell surface and into the cultural medium. The high concentrations of Na₂SeO₃ acidified the cytoplasmic pH as was measured by ³¹P-NMR spectroscopy. At the same time, the content of protein on a dry weight basis decreased and that of carbohydrates and lipids somewhat increased, just as was observed in S. platensis cells under other stress factors. In the presence of 20 mg/l Na₂SeO₃, the selenium content in the biomass increased by 20000 times as compared to that in the control cells, whereas the biochemical composition of biomass did not change. In this case, the selenium was incorporated almost completely in the protein fraction. The selenium concentration in this fraction increased more significantly when the sulfur content was lowered in the medium.     

Osmotic adjustment in Spirulina platensis

Unilateral irradiation of maize (Zea mays L.) seedlings results in a fluence-rate gradient, and hence below saturation, a gradient of the far-red-absorbing form of phytochrome (Pfr). The Pfr-gradients established by blue, red and far-red light were spectrophotometrically measured in the mesocotyl. Based on these Pfr-gradients and the fluence-response curves of phytochrome photoconversion the fluence-rate gradients were calculated. The fluence-rate gradient in the blue (460 nm) was steeper than that in the red (665 nm), which in turn was steeper than that in the far-red light (725 nm). The fluence-rate ratios front to rear were 1:0.06 (460 nm), 1:0.2 (665 nm), and 1:0.33 (725 nm). The assumption that phytochrome-mediated phototropism of maize mesocotyls is caused by local phytochrome-mediated growth inhibition was tested in the following manner. Firstly, the Pfr response curve for growth inhibition was calculated; these calculations were based on measurements of Pfr-gradients and data from red-light-induced phototropism. Secondly, the Pfr response curve for growth inhibition was used as a basis for calculating fluence-response curves for blue-and far-red-light-induced phototropism. Finally, these calculated results were compared with experimental data. It was concluded that the threshold for phytochrome-mediated phototropism of maize mesocotyls reflects the apparent photoconversion cross section of phytochrome whereas the maximal inducable curvature depends on the steepness of the light (Pfr) gradient across the mesocotyl.Abbreviations Pfr far-red-absorbing form of phytochrome - Ptot total phytochrome - Fr far-red light     

A new restriction endonuclease from Spirulina platensis.

Three restriction endonucleases, Sp1I, Sp1II and Sp1III have been purified partially from Spirulina platensis subspecies siamese and named. Sp1I cleaves bacteriophage lambda DNA at one site, phi X 174 RF DNA at two sites, but does not cleave pBR322 DNA. This enzyme recognizes the sequence 5'CGTACG3' 3'GCATCG5' and cuts the site indicated by the arrows. Sp1II is an isoschizomer of Tth111I and Sp1III is an isoschizomer of HaeIII.     

Two tuf genes in the cyanobacterium Spirulina platensis.

Probes derived from the tufA gene of Escherichia coli have been utilized to detect homologous sequences on Spirulina platensis DNA. A 6-kilobase-pair fragment of S. platensis DNA appears to contain two sequences homologous to the E. coli gene. Thus, as reported for gram-negative bacteria, the cyanobacterium presumably contains two tuf genes.     

Accumulation of poly-beta-hydroxybutyrate in cyanobacterium Synechocystis sp. PCC6803

Accumulation of poly-beta-hydroxybutyrate (PHB) by photoautotrophic microorganisms makes it possible to reduce the production cost of PHB. The Synechocystis sp. PCC6803 cells grown in BG11 medium under balanced, nitrogen-starved or phosphorus-starved conditions were observed by transmission electron microscope. Many electron-transparent granules in the nitrogen-starved cells had a diameter up to 0.8 micron. In contrast, the number of granules in the normally cultured cells decreased obviously and only zero to three much smaller granules were in each cell. These granules were similar to those in bacteria capable of synthesizing PHB. They were proved to be PHB by gas chromatography after subjecting the cells to methanolysis. Effects of glucose as carbon source and light intensity on PHB accumulation in Synechocystis sp. PCC6803 under nitrogen-starved cultivation were further studied. Glucose and illumination promoted cell growth but did not favor PHB synthesis. After 7 days of growth under nitrogen-starved photoautotrophic conditions, the intracellular level of PHB was up to 4.1% of cellular dry weight and the PHB concentration in the culture broth was 27 mg/l.     

Lead removal by Spirulina platensis biomass

In this investigation, we report on the biosorption of Pb (II) from aqueous solutions by the nonliving biomass of the micro-alga (cyanobacterium) Spirulina platensis. Propagation of the micro-alga was carried out in outside oblong raceway ponds. The biomass was cleaned, dried and used for the investigation. The effects of pH, adsorbent dose, temperature, initial concentration of Pb (II), and contact time on the adsorption of lead by the dry biomass were studied. The experiments were carried out in 250 ml conical flasks containing 100 ml of test solutions using an orbital incubator at 150 rpm. Concentrations of the metal before and after the experiments were measured using Atomic Absorption Spectrophotometer. Very high levels of Pb (II) removal (>91%) were obtained. The optimum conditions for maximal adsorption by S. platensis were found to be pH 3; 2 g of adsorbent dose; incubation at 26°C; 100 mg/l of lead initial concentration and 60 minutes of contact time. The experimental data fitted well with Freundlich isotherm equation with R² values greater than 0.97. Based on our results, we recommend the utilization of S. platensis biomass for heavy metal removal from aqueous solutions.     

Cadmium biosorption on Spirulina platensis biomass

Dry biomass of Spirulina platensis re-hydrated for 48 h was employed as a biosorbent in tests of cadmium(II) removal from water. Various concentrations of biomass (from 1 to 4 g l⁻¹) and metal (from 100 to 800 mg l⁻¹) were tested. Low biomass levels (X_o  2 g l⁻¹) ensured metal removal up to 98% only at Cd₀= 100 and 200 mg l⁻¹, while X_o  2.0 g l⁻¹ were needed at Cd₀ = 400 mg l⁻¹ to achieve satisfactory results. Whereas X_o = 4.0 g l⁻¹ was effective to remove up to Cd₀ = 500 mg l⁻¹, a further increase in metal concentration (Cd₀ = 600 and 800 mg l⁻¹) led to progressive worsening of the system performance. At a given biomass levels, the kinetics of the process was better at low Cd²⁺ concentrations, while, raising the adsorbent level from 1.0 to 2.0 g l⁻¹ and then to 4.0 g l⁻¹, the rate constant of biosorption increased by about one order of magnitude in both cases and the adsorption capacity of the system progressively decreased from 357 to 149 mg g⁻¹.     

Action of Spirulina platensis on bacterial viruses

The impact of the biomass of the blue-green microalga (cyanobacterium) S. platensis on bacteriophage T4 (bacterial virus) has been evaluated. The study revealed that the addition of S. platensis biomass into the agar nutrient medium, followed by sterilization with 2% chloroform and thermal treatment, produced an inhibiting or stimulating effect on the reproduction of the bacteriophage in Escherichia coli B cells, depending on the concentration of S. platensis and the multiplicity of phage infection, as well as on the fact whether the microalgae were added during the first cycle of the development of the virus. The reproduction of the bacteriophage in E. coli B was influenced by the method and duration of the sterilization of the nutrient medium with S. platensis.     

A new model of phycobilisome in Spirulina platensis

Phycobilisomes (PBS) were isolated from blue-green algaSpirulina platensis. Scanning tunneling microscope was used to investigate the three-dimensional structure of PBS deposited on freshly cleaved highly oriented pyrolytic graphite (HOPG) in ambient condition at room temperature. The results showed that the rods of PBS radiated from the core to different directions in the space other than arrayed in one plane, which was different from the typical hemi-discoidal model structure. The diameter of PBS was up to 70 nm, and the rod was approximately 50 nm in length. Similar results were observed in Langmuir-Blodgett (LB) film of PBS. The dissociated PBS could reaggregate into rod-like structures and easily form two-dimensional membrane while being absorbed on HOPG, however, no intact PBS was observed. The filling-space model structure of PBS inSpirulina platensis with STM from three-dimensional real space at nanometer scale was found, which showed that this new structural model of PBS surely exists in blue-green algae and red algae. The function of this structural model of PBS was also discussed.     

Isolation and Photosynthesis of Spheroplasts in Spirulina platensis

Spirulina platensis is a nonheterocystic filamentous blue-green alga (cyanobacterium). Large quantity of highly qualified spheroplasts were obtained by improved isolation method. The spheroplast has a wrinkled and porous surface. Their diameter ranged from 3.8 btm to 4. 6 μm. The activity of photosynthetic oxygen evolution in the spheroplasts was about 40 % of the intact cell. The absorption spectra of the filaments and spheroplasts at room temperature revealed that they had the same pigments, Chla, PC, PEC and carotenoid. In spheroplasts the relative content of PC and carotenoid decreased, and that of PEC increased. It implicated that the light absorption of Spirulina platensis could be influenced by the cell wall. Some differences existed between the original cells and spheroplasts in the low temperature fluorescence emission spectra. F757 of spheroplasts excited by 436 nm was reduced obviously and that excited by 580 nm was disapeared. F728/F685 and F640/F685 enhanced, and F693/F685 was reduced. F728/F640 was lower than that of the original cells. These results indicated that removing the cell wall may inhibit the PS Ⅱ activity and influence the F695 from core antenna pigment system.     

钝顶螺旋藻富硒培养条件的优化

硒是人和动物必需的微量元素 ,补硒可以防治多种疾病。有机硒具有低毒、高生物利用度的优点 ,目前主要寄希望于生物转化的途径来获得有机硒[1 ] 。植物对硒的生物有机化作用已有综述[2 ] ,并开发有富硒酵母[3 ] 、富硒菇类[4] 、富硒大蒜、富硒黄芪、富硒西洋参、富硒麦芽、富硒茶以及富硒鸡蛋、富硒牛奶等[5] 。螺旋藻是一种很有开发利用前景的藻类 ,但其含硒量极微 ,实验报道富硒螺旋藻对60 Ｃｏ γ射线胸部照射大鼠诱发肺炎和早期肺、肝纤维增生有防治作用[6] 。在培养液中添加亚硒酸钠可以实现藻类对硒的富集和转化 ,而且螺旋藻对无机硒…     

A new model of phycobilisome in Spirulina platensis

Phycobilisomes (PBS) were isolated from blue-green alga Spirulina platensis. Scanning tunneling microscope was used to investigate the three-dimensional structure of PBS deposited on freshly cleaved highly oriented py-rolytic graphite (HOPG) in ambient condition at room temperature. The results showed that the rods of PBS radiated from the core to different directions in the space other than arrayed in one plane, which was different from the typical hemi-discoidal model structure. The diameter of PBS was up to 70 nm, and the rod was approximately 50 nm in length. Similar results were observed in Langmuir-Blodgett (LB) film of PBS. The dissociated PBS could reaggregate into rod-like structures and easily form two-dimensional membrane while being absorbed on HOPG, however, no intact PBS was observed. The filling-space model structure of PBS in Spirulina platensis with STM from three-dimensional real space at nanometer scale was found, which showed that this new structural model of PBS surely exists in blue     

Computer control of carbon-nitrogen ratio in Spirulina platensis

An on-line computer was used to control the ratio of carbon to nitrogen in algal biomass. An indirect method of growth and biomass estimation was utilized. This was based on balancing the amount of CO(2) carbon in and out of the algal bioreactor. It was shown that growth conditions govern the morphology and composition of Spirulina platensis. Cells grown under light limitation were narrower, had high levels of phycocyanin pigments, and were packed full of small lipid granules. Whereas cells grown under nitrogen limitation lost their characteristic blue-green color, had reduced levels of phycocyanin, were fatter, and were packed full of larger lipid granules.