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Of 7 green algae, Chlorella fusca var. vacuolata removed about 23% of 2,4-dichlorophenol (DCP) at 10-80 microM after 4 d when grown photoautotrophically. Removal of DCP was growth-dependent and was suppressed dose-dependently by the photosynthesis inhibitor, 3-(3,4-dichlorophenyl)-1,1-dimethyl urea.
The requirement of metabolic energy for the interaction of polyene macrolide antibiotics with eukaryotic organisms remains a controversial subject (for review see ref. 1) It has been claimed that the lethal binding of these antibiotics to the sterol target component of the hydrophobic core of the membrane, in accordance with the model of de Kruijff and Demel, is an energy-dependent process. When energy production is reduced by removal of all metabolisable substrates or by adding metabolic inhibitors, polyene binding and antifungal effects are also reduced. Metabolic energy may be required to maintain binding site accessibility or to move antibiotic molecules to the active site. The interaction is also restricted at low temperatures, possibly because of the reduced thermal mobilities of the groups concerned with antibiotic uptake. However, it should be emphasised that the interaction of polyene macrolides with artificial lipid membranes is a purely physicochemical process, although the type of permeability pathways induced are similar to those observed in natural membranes. Using Chlorella vulgaris as a model organism, we demonstrate here that the interaction of polyene macrolides with sensitive cells and the induction of lethal membrane permeability changes are energy-dependent processes or purely physicochemical phenomena, depending on the structure of the antibiotic used.
Nine strains of Chlorella protothecoides and 43 strains representing the five species of Prototheca were screened in flask culture for their ability to synthesize L-ascorbic acid (AA). Ascorbic acid was detected in all strains, ranging from 4.8 to 0.38 mg AA g x (-1) of dry cells. Organisms selected for further study grew well and maintained their AA productivity above a pH of 3.5. They can produce AA using a variety of carbon and nitrogen sources. Aerobic fermentation of selected strains resulted in extracellular accumulation of AA up to 76 mg x l(-1). By classical mutagenesis and selection methods, we created mutants of Prototheca moriformis ATCC 75669 that produced greater quantities of AA than the wild-type strain (78.4 vs 21.9 mg AA g x (-1) of cells). A process based on extracellular production could greatly reduce the cost of AA manufacture by eliminating the need for extraction of the AA from the cells.
Carbon dioxide (CO(2)) is a colorless gas that exists at a concentration of approximately 330 ppm in the atmosphere and is released in great quantities when fossil fuels are burned. The current flux of carbon out of fossil fuels is about 600 times greater than that into fossil fuels. With increased concerns about global warming and greenhouse gas emissions, there have been several approaches proposed for managing the levels of CO(2) emitted into the atmosphere. One of the most understudied methods for CO(2) mitigation is the use of biological processes in engineered systems such as photobioreactors. This research project describes the effectiveness of Chlorella vulgaris, used in a photobioreactor with a very short gas residence time, in sequestering CO(2) from an elevated CO(2) airstream. We evaluated a flow-through photobioreactor's operational parameters, as well as the growth characteristics of the C. vulgaris inoculum when exposed to an airstream with over 1850 ppm CO(2). When using dry weight, chlorophyll, and direct microscopic measurements, it was apparent that the photobioreactor's algal inoculum responded well to the elevated CO(2) levels and there was no build-up of CO(2) or carbonic acid in the photobioreactor. The photobioreactor, with a gas residence time of approximately 2 s, was able to remove up to 74% of the CO(2) in the airstream to ambient levels. This corresponded to a 63.9-g/m(3)/h bulk removal for the experimental photobioreactor. Consequently, this photobioreactor shows that biological processes may have some promise for treating point source emissions of CO(2) and deserve further study.
Whole cells of the microalga Chlorella sorokiniana were evaluated in the oxidation of prochiral thioethers as regards conversion, enantiomeric excess and enantioselectivity.
The amino acid sequence of the plastocyanin from the green alga Chlorella fusca was determined. The protein consists of a single polypeptide chain of 98 residues, and was determined by characterization of chymotryptic and thermolysin peptides. The amino acid sequence shows considerable similarity to that of higher plant plastocyanins. The protein contains a single cysteine, and the sequence in the vicinity of this residue is similar to that around the cysteine residue of bacterial azurins. The plastocyanin contains some uncharacterized carbohydrate. Detailed evidence for the sequence of the protein has been deposited as Supplementary Publication SUP 50 036 (17pp., 1 microfiche) at the British Library (Lending Division) (formerly the National Lending Library for Science and Technology), Boston Spa, Yorks. LS23 7BQ, U.K., from whom copies may be obtained on the terms given in Biochem. J. (1973) 131, 5.
1. Isocitrate lyase activity was measured in non-induced Chlorella fusca var. vacuolata cells. 2. During exponential autotrophic growth about 1-2 molecules of the enzyme per cell were present. 3. In light-limited cultures the amount of the enzyme increased to 10-20 molecules/cell. 4. When autotrophic cultures were placed in the dark, the basal activity of isocitrate lyase increased after a 2h lag so that after 8h in the dark there was a 500-fold increase in activity. 5. When isocitrate lyase was induced (by addition of acetate and removal of illumination) in autotrophic cultures which had been growing exponentially, the full induced rate of enzyme synthesis was obtained after 70-80min. 6. When light-limited autotrophic cultures were induced, the rate of isocitrate lyase synthesis was maximal after only 40-50min. 7. These data are consistent with a catabolite-repression control co-ordinated with photosynthetic activity,which may be independent of the specific inducing effect of acetate.
The rate of increase of isocitrate lyase activity was measured in darkened Chlorella fusca var. vaculoata cultures in the presence and absence of acetate and compared with the rate of incorporation of [35S]methionine into isocitrate lyase enzyme protein under the same conditions. Isocitrate lyase enzyme protein was isolated for this purpose by specific immunoprecipitation and sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. After 4h in the dark, in the presence of acetate the rate of increase of isocitrate lyase activity was 75 times that in the absence of acetate. Incorporation of [35S]methionine into isocitrate lyase was 140 times greater in the presence of acetate. Incorporation of [35S]methionine into the trichloroacetic acid-insoluble fraction overall was about five times as fast in the presence of acetate. These data are not consistent with an increased turnover of isocitrate lyase enzyme molecules, sufficient to account for the low rate of increase of isocitrate lyase activity in the absence of acetate. The greater rate of enzyme synthesis in the presence of acetate must therefore be due to some effect of this metabolite on the processing or translation of isocitrate lyase mRNA.
Two different molecular forms of flavodoxin from the green alga Chlorella fusca have been purified to homogeneity and their properties compared. The molecular masses are 22 kDa (flavodoxin I) and 20 kDa (flavodoxin II). Western blots of axenic crude extract show the two bands. Both are single polypeptide chains and their N-terminal sequences differ but are very similar. Each form contains 1 mol of FMN/mol of apoprotein, exhibits a typical flavodoxin u.v.-visible absorption spectrum and does not contain covalently bound phosphate. The oxidation-reduction properties of the FMN in the flavodoxins differ considerably. Redox potentials of flavodoxin I at pH8 are -240 mV for the oxidized/semiquinone couple and -350 mV for the semiquinone/hydroquinone couple. Flavodoxin II gives more electronegative values: -278 mV and -458 mV respectively. Flavodoxin II fulfils better the redox requirements for photosynthetic electron transport and, as expected, it is more efficient at mediating NADP+ photoreduction in the photosynthetic electron flow. A new h.p.l.c. method for flavodoxin purification is described, which is useful for the isolation of very similar anionic proteins.
A prokaryotic biotin acceptor domain was fused to the carboxy terminal end of the Chlorella hexose-proton symporter. The plant symporter is biotinylated in vivo when expressed in Schizosaccharomyces pombe. The extended biotinylated transport protein is fully active, catalyzes accumulation of D-glucose analogs and restores growth of a glucose-uptake-deficient yeast strain. Crude membranes were solubilized with octyl-beta-D-glucoside in the presence of Escherichia coli L-alpha-phosphatidylethanolamine. Biotinylated symporter was purified to homogeneity by biotinavidin affinity chromatography. The symporter protein was reconstituted together with cytochrome-c oxidase prepared from beef heart mitochondria into proteo-liposomes. Cytochrome-c oxidase is a redox-driven H(+)-pump generating a proton motive force (inside negative and alkaline) while transferring electrons from cytochrome-c to oxygen; this energy is used by the symporter to accumulate D-glucose at least 30-fold. In the absence of the driving force the transport protein facilitates diffusion of D-glucose until the concentration equilibrium is reached. It was shown that maximal transport activity depends highly on the amount of co-reconstituted cytochrome-c oxidase and that the symporter possesses 10% of its in vivo turnover number under optimized in vitro transport conditions.
The hypothesis that the Delta9 desaturase of Chlorella vulgaris might operate by a synchronous mechanism has been tested using a kinetic isotope effect (KIE) approach. Thus the intermolecular primary deuterium KIE on the individual C-H bond cleavage steps involved in Delta9 desaturation have been determined by incubating growing cultures of C. vulgaris (strain 211/8K) with mixtures of the appropriate regiospecifically deuterated fatty acid analogues. Our analysis shows that the introduction of a double bond between C-9 and C-10 occurs in two discrete steps as the cleavage of the C9-H bond is very sensitive to isotopic substitution (kH/kD = 6.6 +/- 0.3) whereas a negligible isotope effect (kH/kD = 1.05 +/- 0.05) was observed for the C10-H bond-breaking step. Similar results were obtained for linoleic acid biosynthesis (Delta12 desaturation). These data clearly rule out a synchronous mechanism for these reactions.
This research describes the identification of three new high molecular weight polysaccharide preparations isolated from food-grade microalgae that are potent activators of human monocytes/macrophages: "Immulina" from Spirulina platensis, "Immunon" from Aphanizomenon flos-aquae, and "Immurella" from Chlorella pyrenoidosa. These polysaccharides are structurally complex and have estimated molecular weights above ten million daltons. All three polysaccharides are highly water soluble and comprise between 0.5 % and 2.0 % of microalgal dry weight. Immunostimulatory activity was measured using a transcription factor-based bioassay for nuclear factor kappa B (NF-kappa B) activation in THP-1 human monocytes/macrophages. Using this system the EC(50) values for these microalgal polysaccharides are between 20 and 110 ng/ml (about 10pM). THP-1 activation was confirmed by measuring immune cytokine mRNA induction using reverse transcriptase-polymerase chain reaction (RT-PCR). Each polysaccharide substantially increased mRNA levels of interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha). These polysaccharides are between one hundred and one thousand times more active for in vitro monocyte activation than polysaccharide preparations that are currently used clinically for cancer immunotherapy.
Oral administration of dry powder of Chlorella vulgaris (CVP) showed clear prophylactic effects in water-immersion restraint stress-induced and in cysteamine-induced peptic ulcer models, but not in Shay's rat model. Drugs that enhance the protective factors of ulcer formation are effective in the first two models. CVP may prevent ulcer formation mainly through the "immune-brain-gut" axis and protection of gastric mucosa by its own characteristics.
An active substance with antitumor activity (ARS2) was purified from the culture media of Chlorella vulgaris and found to be a glycoprotein with a molecular weight of 63,100 amu, as determined by matrix-assisted laser desorption/ ionization (MALDI) mass spectrometry. ARS2 contains 66.9% carbohydrate, mainly D-galactose, and 35.2% protein. The carbohydrate moiety has a beta-1,6-D-galactopyranose backbone, as determined by methylation analysis and 13C-NMR. Apparently, the protein moiety, whose 15 amino acid sequence at the NH2-terminus, we determined as DVGEAFPTVVDALVA, is necessary for the antitumor activity, as assessed by hydrazinolysis, periodate oxidation, and proteolysis.
At the level of the central nervous system an aqueous extract of the marine microalga Chlorella stigmatophora (Butcher) (Chlorophyceae) showed anti-dopaminergic-type activity in assays of its effects on spontaneous motor response, rectal temperature, motor coordination, amphetamine-induced hypermotility, exploratory conduct, muscle relaxation, catalepsy, conditioned avoidance responses, oxotremorine-induced cholinergic syndrome, and pentylenetetrazole-induced convulsions.
The light-induced increases of the effective fluorescence yield in Chlorella are too slow to be primary processes in photosynthesis. The fast transient state (risetime 25 nsec, limited to the first flash) is attributed to a priming reaction for the photosystem that makes oxygen. The slower cyclical process (risetime 3 musec, decay time 200 musec and 2 msec) is attributed to the dark reactions that make oxygen after photoexcitation of this system. The slower cyclical process is also distinguished by a narrower emission spectrum that peaks at a shorter wavelength than the dark adapted or fast transient state. A minimum of six different fluorescent states are required to explain the data. In addition to the usual assumption about changing quantum yield of fluorescence in these processes, the data suggest that changes in cross section of optical absorption must also be considered. The slowest relaxation times observed (0.2-2 msec) are well correlated with the slow steps detected in evolution of oxygen.
The multicellular obligately photoautotrophic alga Volvox is composed of only two types of cells, somatic and reproductive. Therefore, Volvox provides the simplest model system for the study of multicellularity. Metabolic labeling experiments using radioactive precursors are crucial for the detection of stage- and cell-type-specific proteins, glycoproteins, lipids, and carbohydrates. However, wild-type Volvox lacks import systems for sugars or amino acids. To circumvent this problem, the hexose/H+ symporter (HUP1) gene from the unicellular alga Chlorella was placed under the control of the constitutive Volvox beta-tubulin promoter. The corresponding transgenic Volvox strain synthesized the sugar transporter in a functional state and was able to efficiently incorporate 14C from labeled glucose or glucosamine. Sensitivity toward the toxic glucose/mannose analogue 2-deoxy-glucose increased by orders of magnitude in transformants. Thus we report the successful transformation of Volvox with a gene of heterologous origin. The chimeric gene may be selected for in either a positive or a negative manner, because transformants exhibit both prolonged survival in the dark in the presence of glucose and greatly increased sensitivity to the toxic sugar 2-deoxyglucose. The former trait may make the gene useful as a dominant selectable marker for use in transformation studies, whereas the latter trait may make it useful in development of a gene-targeting system.
The complete nucleotide sequence of the chloroplast genome (150,613 bp) from the unicellular green alga Chlorella vulgaris C-27 has been determined. The genome contains no large inverted repeat and has one copy of rRNA gene cluster consisting of 16S, 23S, and 5S rRNA genes. It contains 31 tRNA genes, of which the tRNALeu(GAG) gene has not been found in land plant chloroplast DNAs analyzed so far. Sixty-nine protein genes and eight ORFs conserved with those found in land plant chloroplasts have also been found. The most striking is the existence of two adjacent genes homologous to bacterial genes involved in cell division, minD and minE, which are arranged in the same order in Escherichia coli. This finding suggests that the mechanism of chloroplast division is similar to bacterial division. Other than minD and minE homologues, genes encoding ribosomal proteins L5, L12, L19, and S9 (rpl5, rpl12, rpl19, and rps9); a chlorophyll biosynthesis Mg chelating subunit (chlI); and elongation factor EF-Tu (tufA), which have not been reported from land plant chloroplast DNAs, are present in this genome. However, many of the new chloroplast genes recently found in red and brown algae have not been found in C. vulgaris. Furthermore, this algal species possesses two long ORFs related to ycf1 and ycf2 that are exclusively found in land plants. These observations suggest that C. vulgaris is closer to land plants than to red and brown algae.