Green Alga Scenedesmus Obliquus Research Articles

Evidence for a dual function of the herbicide-binding D1 protein in photosystem II

The LF-1 mutant of the green alga Scenedesmus obliquus is completely blocked on the oxidizing (water-splitting) side of photosystem II (PS II) while the reaction center and reducing side remain functional. A 34-kDa protein found in the PS II reaction center core complex of wild-type cells is replaced by a 36-kDa protein in the mutant cells. Both of these proteins are labeled by azido[ 14C]atrazine and are recognized by polyclonal antibodies raised against the herbicide-binding, D1 protein of Amaranthus hybridus. The data provide a new perspective on the role of the D1 protein by implying that it affects the oxidizing side of PS II in addition to performing its well established function on the reducing side.

The nucleotide sequence of Scenedesmus obliquus chloroplast elongator methionine-accepting tRNA.

The chloroplast elongator methionine-accepting tRNA from the green alga Scenedesmus obliquus was purified and and its nucleotide sequence determined. The sequence does not bear close homology to higher-plant chloroplast tRNAMetm species, nor to the chloroplast tRNAMetm species from Euglena gracilis. This tRNA is unique among all tRNAs in having pseudouridine at position 8, and this has implications with regard to the proposed interaction of aminoacyl-tRNA synthetases with their cognate tRNAs at this position. The primary sequence of the tRNA is: pG-C-C-U-G-C-U-psi-A-G-C-U-C-A-G-U-D-Gm- G-C-C-A-G-A-G-C-A-U-C-C-G-psi-psi-U-C-A-U-m2A-C-G-C-G-G-A-A-A- m7G-D-C-A-C-U-A-G-T-psi-C-G-A-A-U-C-U-A-G-U-A-G-C-A-G-G-C-A-C-C-A-OH.

Culture and nitrite uptake in immobilized Scenedesmus obliquus

The green alga Scenedesmus obliquus was immobilized in Ca-alginate beads. The cell growth after immobilization was studied by cell counting. The nitrite uptake was not affected by immobilization, except that a longer lag phase was observed in immobilized cells than in free ones. That result could be due to a barrier effect of the matrix against nitrite diffusion inside the beads. The treatment of cells by glycerol prior to their immobilization in a batch reactor induced an increase of nitrite uptake by the cells. This effect disappeared after a few runs. The glycerol effect on specific rates seemed also to decrease when the number of immobilized cells increased. This decrease can be related to the decrease of light efficiency as well as substrate accessibility when a high cell concentration was used. Several alternating runs of Tris-HCl buffer containing nitrite growth medium depleted in combined nitrogen were tested. Cellular growth occurred inside the beads up to a maximum followed by a decrease of cell number in the beads.

Bleomycin-Iron Complex and Oxygen Activate Algal Ribonucleotide Reductase

Abstract Ribonucleotide reductase of green algae (Scenedesmus obliquus) is a radical-containing enzyme which rapidly loses activity under anaerobic conditions. Reactivation in the presence of air is enhanced by 10 μᴍ iron(II)-bleomycin chelate. The reaction lends new biochemical potential to the antibiotic and should be valuable in mechanistic studies of ribonucleotide reduction.

Cadmium effects on photosynthesis and nitrate assimilation in Scenedesmus obliquus. A potentiometric study in an open CO 2-system

A potentiometric titration method was used to study nitrate assimilation and photosynthetic carbon uptake in suspensions of the green alga Scenedesmus obliquus. CO 2 with a known partial pressure was bubbled continuously through the system, and photosynthesis and nitrate assimilation were calculated from changes in pH and alkalinity. The inhibitory effect on these processes caused by the free Cd 2+-ion as well as by Cd(II) in complex with Cl − and with the organic chelator EDTA was further studied. In short term experiments Cd-toxicity was found to increase in the series Cd(EDTA) 2− < CdCl + < Cd 2+_. Photosynthesis was less inhibited than nitrate assimilation at [Cd(II)] < 10 −6 M.

Modification of ultraviolet sensitivity of the green alga Scenedesmus obliquus (Turpin) Kuetzing by acriflavine

AbstractThe effect of pre‐ and post‐irradiation treatments with acriflavine on the kinetics of ultraviolet inactivation of the green alga Scenedesmus obliquus (Turpin) Kuetzing has been studied. Acriflavine is found to modify the UV‐doses. Pre‐irradiation treatment of the alga lessens but post‐irradiation treatment adds to the extent of UV‐inactivation. Incorporation of the dye in the algal suspension during irradiation also elicits a protective effect against UV‐inactivation. The observations are suggestive of an instantaneous uptake and incorporation of the dye in UV‐sensitive components of algal cells‐resulting in altered response of the pre‐, during‐, and post‐irradiation dye‐treated alga to UV and provide evidence for the operativity of two repair system, i.e. light‐independent and light‐dependent repair of the lesions in this alga.

The nucleotide sequences of a cytoplasmic and a chloroplast tRNATyr from Scenedesmus obliquus.

The nucleotide sequences of two species of tyrosine accepting tRNA from the eukaryotic green alga Scenedesmus obliquus have been determined. The sequence of the cytoplasmic tRNATyr is: (sequence in text) This is the first chloroplast tRNATyr species to be sequenced.

Purification and structural analysis of aromatic-amino-acid-accepting tRNA species from the green alga Scenedesmus obliquus

Purification and structural analysis of aromatic-amino-acid-accepting tRNA species from the green alga <i>Scenedesmus obliquus</i>

Purification and characterization of thioredoxin from the N2-fixing cyanobacterium Anabaena cylindrica.

Thioredoxin has been purified to homogeneity from the cyanobacterium Anabaena cylindrica. The protein consists of a single polypeptide chain with a relative molecular mass of about 11 680 which has two cysteine residues (residues 31 and 34) in the sequence-Cys-Gly-Pro-Cys- and an isoelectric point at pH 4.55. The N-terminal amino acid sequence of 39 residues shows distinct homologies with the sequences of Escherichia coli and Corynebacterium nephridii thioredoxins. Anti-(A. cylindrica thioredoxin) antiserum was used to quantify the thioredoxin which constituted about 0.22% of the soluble protein in cell-free extracts of N2-fixing, NO3- -grown or NH4+-grown A. cylindrica. Activation of fructose-1,6-bisphosphatase of A. cylindrica, activation of glutamine synthetase and NADP+-dependent malate dehydrogenase of the green alga Scenedesmus obliquus but not of A. cylindrica, and deactivation of glucose-6-P dehydrogenase of the cyanobacterium Anabaena variabilis were all achieved using the same thioredoxin species. No other thioredoxin species were detected in extracts of A. cylindrica when examined for the activation of these enzymes.

Biotechnology and exploitation of the green alga Scenedesmus obliquus in India

The Governments of India and West Germany have initiated and supported a joint microalgae research project in India from 1973 to 1981. Data are presented about the green alga Scenedesmus obliquus, pertaining to its cultivation, processing, chemical composition, nutritional and toxicological properties. Optimal growth rates were obtained from algae supplied with CO 2 and molasses as carbon sources. Various analyses showed a nutritionally excellent composition of the alga. Among the different processing methods tested, drum-drying gave the best results which could be confirmed by nutritional evaluations such as PER (Protein Efficiency Ratio), NPU (Net Protein Utilization), BV (Biological Value) and DC (Digestibility Coefficient). Preliminary toxicological studies with rats did not show any adverse symptoms or indications which would limit the utilization of Scenedesmus as a supplement in food and feed.

A precise potentiometric method for determination of algal activity in an open CO2 system

Abstract. The activity of the green alga Scenedesmus obliquus was studied in simplified nutrient solutions (20 mol m−3 NaNO3, 20 mol m−3 NH4C1, 20 mol m−3 NH4NO3, and 20 mol m−3 NaCl, respectively) at 25 °C. The experiments were performed under welldefined incident photon density fluxes ranging from 10 to 200 μmol m2 s−1, Light‐dependent changes in pH and alkalinity (A) were followed by means of a potentiometric method using a glass electrode. In the experiments, carbon dioxide with known partial pressure was bubbled through the algal suspension, and during dark periods ul intervals of 1 h, the solution was allowed to equilibrate with the gas phase. This technique was applied to calculate equilibrium values of pH and alkalinity at regular intervals during a 12‐h period. Results obtained in NaNO3, solution show a linear increase in A with time, at each level of illumination studied. After an initial drop, A also increases in NH4NO3, solution in a similar way to that in NaNO3 solution. The change in A with time was also found to increase linearly with the photon density flux studied and no saturation level could be defined. In experiments in NaCl solution, no changes in A were registered while measurements in NH4Cl solution showed a decrease in A with time.

PHYSICAL AND CHEMICAL PROPERTIES OF CHLOROPHYLL RCI EXTRACTED FROM PHOTOSYSTEM I OF SPINACH LEAVES AND FROM GREEN ALGAE

Abstract— A new chlorophyll, designated chlorophyll RCI (Chi RCI), with absorption and fluorescence properties different to other known chlorophylls, has been extracted from photosystem I (PSI) sub‐chloroplast particles of the green alga Scenedesmus obliquus; it was suggested that this chlorophyll is either the chromophore ofP–700 or the chromophore of another holochrome associated in a 1:1 molar ratio withP–700. We now report the extraction and isolation of a chlorophyll from PSI particle preparations from spinach leaves with properties identical to those of Chi RCI from Scenedesmus. Its molar ratio toP–700 measured in vivo is again approximately 1:1. Chlorophyll RCI is further characterized by its fluorescence characteristics and redox behaviour. Molecular weight determinations show that Chi RCI has a mol wt 35 units higher than that of chlorophyll a (Chi a).

Preferential distribution of excitation energy into photosystem I of desiccated samples of the lichen Cladonia impexa and the isolated lichen‐alga Trebouxia pyriformis

Abstract The effect of desiccation on distribution of excitation energy between the two photosystems has been studied in the lichen Cladonia impexa Harm., in the green alga Trebouxia pyriformis Archibald, isolated from Cladonia squamosa; and in the non‐lichen green alga Scenedesmus obliquus, strain D3. The method used was to compare the low temperature fluorescence emission of samples equilibrated with air with different humidity prior to freezing in liquid nitrogen.Desiccation of Cladonia and Trebouxia caused a pronounced increase of the height of the far red fluorescence emission band, F 715, over the short wave bands, F685 and F697; the ratio between the two short wave bands remained essentially constant. Upon rewetting, these species regained normal fluorescence emission properties, indicating that they are desiccation‐tolerant. Scenedesmus, which was used as a desiccation intolerant species, also showed an increase of the far red fluorescence band over the two short wave bands upon desiccation, but the original fluorescence spectrum was not restored upon rewetting.These results are interpreted as showing that desiccation of tolerant species such as Cladonia and Trebouxia causes a preferential energy distribution into photosystem I. We tentatively believe that desiccation induces conformational changes within the chloroplast thylakoids, thereby controlling distribution of energy between the two photosystems. Furthermore, this change in energy distribution may be of ecological significance as the mechanism by which desiccated lichens or algae avoid photo‐dynamic destruction of the photosynthetic apparatus when photosynthesis is inhibited under dry conditions. By a preferential distribution of absorbed energy into photosystem I, the organisms avoid the formation of strong, harmful oxidants in photosystem II when photosynthesis is inhibited. It is suggested that β‐carotene associated with the far red‐absorbing chlorophyll a fraction of the reaction center antenna of photosystem I is the final sink for excess excitation energy in dry, desiccation‐tolerant lichens and algae.

31] Carotenoid biosynthesis by cultures and cell-free preparations of Flavobacterium R1560

This chapter describes carotenoid biosynthesis by cultures and cell-free preparations of Flavobacterium R1560. Flavobacterium strain R1560 is an orange-yellow, Gram-negative bacterium that produces a high yield of the carotenoid zeaxanthin (β,β-carotene-3,3′-diol). It is also one of the few bacteria to incorporate mevalonic acid efficiently into carotenoids and other isoprenoids, such as ubiquinone. These features make R1560 very effective for the preparation of radioactive zeaxanthin for use as substrate in feeding experiments with marine animals in the studies of astaxanthin (3,3′-dihydroxy-β,β-carotene-4,4′-dione) formation. Flavobacterium R1560 is also an ideal source of cell-free enzyme systems for the studies of carotenoid biosynthesis. The carotenoids synthesized are identified by their chromatographic properties, light absorption spectra, and if possible, mass spectra. Suitable mixtures of authentic carotenoids for use as unlabeled carriers may be obtained from tomatoes or from pigment mutants of the green alga Scenedesmus obliquus. The carotenoids are assayed for radioactivity by liquid scintillation counting; either the colored samples are bleached before counting or corrections are made for color quenching.

The synthesis and properties of 4,5-dioxov aleric acid, a possible intermediate in the biosynthesis of 5-aminolaevulinic acid, and its in vivo formation in Scenedesmus obliquus

The formation of 5-aminolaevulinic acid for chlorophyll biosynthesis in the pigment mutant C-2A′ of the unicellular green alga Scenedesmus obliquus occurs via two pathways: the first and major pathway uses glycine and succinyl-CoA as precursors and the second, the C-5 pathway, uses the intact five C-atom skeleton of either glutamate or 2-oxoglutarate. The intermediates in this latter pathway of 5-aminoalevulinic acid biosynthesis are still a matter of controversy and discussion but, in this paper, we have demonstrated in this Scenedesmus mutant that 4,5-dioxovaleric acid occurs in the cells when illuminated in the presence of laevulinic acid and the amount of 4,5-dioxovaleric acid formed is dependent on the period of illumination. In a preliminary experiment we have shown, under similar conditions, the labelled 4,5-dioxovaleric acid can be obtained from both dl-[1- 14C]glutamate and [2- 14C]glycine. This suggests that 4,5-dioxovaleric acid is formed enzymically from the five C-atom skeleton of glutamate but may also arise from the deamination of ALA formed by the condensation of succinyl-CoA and glycine by the 5-aminolaevulinic acid synthase pathway. To obtain positive identification the naturally occurring, and also the labeled, 4,5-dioxovaleric acid were isolated as the more stable benzoquinoxaline derivative by condensation with 2,3-diaminonaphthalene and identified by comparison with the benzoquinoxaline derivative of an authentic sample of 4,5-dioxovaleric acid prepared by the hydrogenation of ozonide of benzylidene laevulinic acid. The structures of the authentic sample of 4,5-dioxovaleric acid and its benzoquinoxaline derivative were confirmed by NMR and mass spectroscopy and both further characterized by TLC and by infrared, ultraviolet and fluorescence spectroscopy.

The influence of pentachlorophenol on the biosynthesis of 5-aminolevulinic acid and chlorophyll

1. 1. Pentachlorophenol (PCP) markedly inhibited the light-dependent formation of chlorophyll and 5-aminolevulinic acid (ALA) in a parallel fashion in the pigment mutant C-2A' of the unicellular green alga Scenedesmus obliquus. 2. 2. This indicates that the site of inhibition of chlorophyll formation occurs at or before the synthesis of ALA. The ALA-forming enzyme, 5-aminolevulinic acid synthetase, was not inactivated by PCP. The formation of ALA synthetase however, was inhibited by PCP to the same extent as ALA biosynthesis. 3. 3. PCP also inhibited total protein formation and the activity of structurally-bound photosystem II of photosynthesis. Respiration was stimulated at lower concentrations of PCP, suggesting that it has uncoupling activity. 4. 4. From our experiments we suggest that the inhibiting effect of PCP may be due to a general and far-reaching effect on metabolism, possibly by modifying membrane structure or formation.

Two biosynthetic pathways to 5-aminolevulinic acid in algae

1. 1. In the X-ray induced mutant C-2A' of the green alga Scenedesmus obliquus, the formation of 5-aminolevulinic acid (LALA) is light dependent. ALA so formed arises by the classical ALA synthetase pathway involving glycine and succinate as substrates and also by the C-5 pathway using the intact 5-carbon skeleton of glutamate or 2-keto-glutarate as precursors. The ALA synthetase and also the enzymes of the C-5 pathway have been measured in crude cell-free homogenates prepared from cells taken at various stages during greening. 2. 2. We have shown that 4,5-dioxovaleric acid (DOVA) occurs in the Scenedesmus mutant and that 14C-labelled DOVA is formed from 14C-labelled glutamate when cultures of etiolated, dark-grown cells are illuminated in the presence of levulinic acid (LA).

Plutonium uptake by Scenedesmus obliquus as a function of isotope and oxidation state

Uptake of 238Pu 4+, 238Pu 6+, 239Pu 4+ and 239Pu 6+ by the green alga Scenedesmus obliquus (Türp) Kütz was studied to determine whether isotope or oxidation state differences affect Pu uptake from aqueous medium by algal cells. At equivalent 238Pu and 239Pu concentrations, even when initial oxidation states differed, accumulations of these isotopes by S. obliquus were not significantly ( p>0.05) different. Plutonium accumulation by S. obliquus was log-linear.

Observations on the photohydrogen producing activity during the synchronous cell cycle of Scenedesmus obliquus

In anaerobically adapted samples of synchronized cultures of the unicellular green alga Scenedesmus obliquus it was observed that both the rate and the maximum volume of hydrogen produced in the light changed in a parallel fashion over the life cycle. These two parameters of cells of the 16th h were 3 times greater than the comparable values for cells of the 8th h. Although both photosystems are involved in photohydrogen production the patterns seen over a complete life cycle (24 h) for hydrogen metabolism was inverse to that noted for changes in the photosynthetic capacity. The provision of either glucose, ethanol or acetate to 8th and 16th h cultures enhanced photohydrogen production of the 8th to the same level as the 16th h. From these findings, and also from the observation that the starch content is low at the 8th but 4 fold at the 16th h, it is apparent that in autotrophic cultures an endogenous organic compound, and not water, serves as the electron donor for photohydrogen production. Since free glucose was not detected the natural substrate is most likely starch. From experiments with monochromatic light and observations on the inhibitory action of DCMU and DBMIB on photohydrogen production we conclude that the major portion of the machinery for photohydrogen production in Scenedesmus requires both PS I and PS II participation and the input of electrons from the natural substrate proceeds through PS II.The alternate possibility that glucose, acetate and ethanol also act as inhibitors of reactions, most probably photophosphorylation, which compete with photohydrogen production was suggested by some experiments. The subsequent modulation of hydrogenase activity was discussed as a possible reason for the enhancement of photohydrogen production.

Two Biosynthetic Pathways to δ-Aminolevulinic Acid in a Pigment Mutant of the Green Alga, Scenedesmus obliquus

Pigment mutant C-2A' of the unicellular green alga Scenedesmus obliquus develops only traces of chlorophyll and has no detectable amount of delta-aminolevulinic acid (ALA) when grown in the dark. In light it develops ALA and in the presence of levulinic acid (LA), a competitive inhibitor of ALA dehydratase, it accumulates 0.18 mmoles of ALA per 10 microliters of packed cell volume per 12 hours. This amount could be increased up to 15 times by feeding precursors and cofactors.Incubation with [U-(14)C]glutamate, [1-(14)C]glutamate, and [2-(14)C]glycine yielded significantly labeled ALA, whereas [1-(14)C]glycine did not label the ALA specifically. Thus, two pathways using either glycine/succinyl-coenzyme A or incorporating the whole C-5-skeleton of glutamate into ALA are present in this alga. The efficiency of the glycine/succinyl-coenzyme A pathway seems to be three times higher than that of the glutamate pathway. Incubation with [5-(14)C]2-ketoglutarate, which can serve both pathways as a precursor, resulted in radioactivity of ALA as high as the sum of both labeling with [1-(14)C]glutamate and [2-(14)C]glycine.Since the newly synthesized chlorophyll was radioactive regardless of labeled substrate employed, both pathways culminate in chlorophyll formation.