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At least 217 records · Page 12Linked to original sources
PubMed2000

Isolation and characterization of nitrite-reductase-deficient mutants of Chlorella sorokiniana (strain 211-8k).

A method is presented to isolate mutants of Chlorella sorokiniana with defects in NO3- metabolism. Three nitrite-reductase (NIR; E.C.1.7.7.1)-deficient mutants were obtained from 500 pinpoint-colony-forming clones. The final screening was performed using NO3-, NO2- or NH4+ as N-source. The mutants isolated absorb NO3- with rates close to those measured for the wild type and they excrete NO2- into the medium. The ratio between NO3- uptake and NO2- excretion was 1:1. The sensitivity of NO3- uptake to NH4+ was reduced in the mutant strains as it was in the N-starved wild type of Chlorella. Nitrate reductase (NR; EC 1.6.6.1) expression and NR activity were slightly reduced compared to the wild type due to feedback regulation in the mutant strains. No NIR protein was found in the three mutants. However, NIR activity was obtained (50% of the wild-type) for one mutant strain. The NIR-deficient mutants and the already available NR-deficient mutants will be promising tools for investigations of the nitrate assimilation pathway on the molecular level and for studies searching for signaling of C and N metabolism by inorganic N-compounds.

Ammonia↗
PubMed2006

Purification and characterization of a novel haemagglutinin from Chlorella pyrenoidosa.

We previously identified a strong haemagglutination activity in the freshwater unicellular green alga, Chlorella pyrenoidosa. Here, we sought to purify and characterize the haemagglutinin associated with this activity. Ammonium sulfate precipitation, gel filtration on sephacryl S-200 and DEAE-Sepharose ion-exchange chromatography were used to purify the haemagglutinin, which was designated CPH (Chlorella pyrenoidosa haemagglutinin). The molecular weight of CPH was estimated as 58 kDa by SDS-PAGE and 60 kDa by gel filtration of the native protein, indicating that this haemagglutinin exists as a monomer. The haemagglutinin activity of CPH was inhibited by glycoproteins, especially yeast mannan, but not by monosaccharides or disaccharides, indicating that CPH is carbohydrate-specific. In addition to the composition of CPH shown to be rich in glycine and acidic amino acids, heamagglutinating activity of CPH was insensitive to variations in pH or the presence of divalent cations, and atomic force microscopy revealed that the protein is rod-shaped. These results indicate that the characteristics of CPH are consistent with its identification as a haemagglutinin, and suggest that CPH may be a viable candidate for applications in a variety of biomedical fields.

Biotechnology↗
PubMed1998

A gas chromatographic-mass spectrometric method using a PoraPLOT column for the detection of hydroperoxide lyase in Chlorella pyrenoidosa.

A gas chromatographic-mass spectrometric (GC-MS) method using a PoraPLOT Q column was developed for the analysis and identification of the volatile products produced by the action of hydroperoxide lyase (HPLS) upon 13-hydroperoxylinoleic or 13-hydroperoxylinolenic acids. The developed procedure required no derivatization, was not affected by the presence of water, did not require cryogenic conditions to be maintained during injection, and allowed for the quantitation of most products. An acetone powder preparation of Chlorella pyrenoidosa cells was triturated with borate buffer pH = 8.0, and the mixture centrifuged at 12,000 x g. The supernatant and pellet were assayed for HPLS activity by GC-MS analysis of the volatile products given by linoleic acid hydroperoxide. The data showed that the majority of HPLS activity resides in the pellet fraction, and that the primary volatile component was pentane, with smaller amounts of 2-(Z)-pentene and 1-pentene being produced. The fact that HPLS activity resides in the water-insoluble fraction of the acetone powder suggests that HPLS from Chlorella is a membrane-associated enzyme. This investigation also determined that a spectrophotometric assay using alcohol dehydrogenase for measuring HPLS activity was not specific, but measured enzymatic activity other than HPLS.

Aldehyde-Lyases↗
PubMed1984

Purification and properties of L-alanine:4,5-dioxovalerate aminotransferase from Chlorella regularis.

The enzyme L-alanine:4,5-dioxovalerate aminotransferase (EC 2.6.1.43), which catalyzes the synthesis of 5-aminolevulinic acid, was purified 161-fold from Chlorella regularis. The enzyme also showed L-alanine:glyoxylate aminotransferase activity (EC 2.6.1.44). The activity of glyoxylate aminotransferase was 56-fold greater than that of 4,5-dioxovalerate aminotransferase. The ratio of the two activities remained nearly constant during purification, and when the enzyme was subjected to a variety of treatments. 4,5-Dioxovalerate aminotransferase activity was competitively inhibited by glyoxylate, with a Ki value of 0.5 mM. Double-reciprocal plots of velocity versus 4,5-dioxovalerate with varying L-alanine concentrations indicate a ping-pong reaction mechanism. The apparent Km values for 4,5-dioxovalerate and L-alanine were 0.12 and 3.5 mM, respectively. The enzyme is an acidic protein having an isoelectric point of 4.8. The molecular weight of the enzyme was estimated to be 126,000, with two identical subunits. These results suggest that, in Chlorella, as in bovine liver mitochondria and Euglena, both 4,5-dioxovalerate and glyoxylate aminotransferase activities are associated with the same protein. From the activity ratio of transamination and catalytic properties, it is concluded that this enzyme does not function primarily as a part of the 5-carbon pathway to 5-aminolevulinic acid synthesis.

Catalysis↗
PubMed1980

A study of dark luminescence in Chlorella. Background luminescence, 3-(3,4-dichlorophenyl)-1,1-dimethylurea-triggered luminescence and hydrogen peroxide chemiluminescence.

Dark luminescence, defined as the ability of completely relaxed (dark-adapted) photosynthetic systems to emit light, has been studied in Chlorella. Three main effects have been demonstrated. 3-(-3,4-Dichlorophenyl)-1,1-dimethylurea elicits a weak emission LD of very long lifetime (several minutes); it is believed to result from a negative shift of redox potential of the secondary System II electron acceptor B producing in some centers a state Q- (reduced primary acceptor), as postulated by Velthuys and Amesz ((1974 Biochim. Biophys. Acta 333, 85--94), which can recombine with an oxidizing equivalent in a state S2 present in very small amount. As in photoinduced luminescence, this recombination excites chlorophyll which then emits light. A much stronger emission LH is observed after injection of H2O2. Both signals are modified or suppressed by treatments specific of the oxygen emission system, such as: thermal denaturation at 50 degrees C, NH2OH, etc. In addition, a weak, permanent background luminescence L0 has been observed; like LD and and LH, it is a System II property and requires the integrity of the oxygen-evolving system. It is believed to reflect a very slow back flow of electrons from an endogeneous reductant pool to oxygen through part of the photosynthetic chain. Using flash preillumination, it is demonstrated that H2O2 is able to oxidize S0 into S2, the latter giving rise to LH; H2O2 does not act on S1 (or much less). The reactive site of H2O2 seems to be the same as the binding site of NH2OH. Evidence is given that the strong LH signal in particular reveals a stable, low pH of the intrathylakoid phase in Chlorella.

Chlorella↗
PubMed1996

Novel amplification of non-photochemical chlorophyll fluorescence quenching following viral infection in Chlorella.

In higher plants non-photochemical dissipation of excess light, trapped by the pigment pool of photosystem II, prevents photodamage to the photosynthetic apparatus. We report here that an algal virus infecting Chlorella strain Pbi induces non-photochemical quenching of photosystem II fluorescence, indicating enhanced loss of absorbed light energy from photosystem II. This phenomenon occurs soon after the establishment of the virus infection cycle and is observed at low irradiance (20 micromol quanta m-2 s-1). At low light, infection associated non-photochemical quenching is not linked to extensive conversion of violaxanthin to antheraxanthin and zeaxanthin. However, such conversion occurs rapidly (2-10 min) in infected cells under conditions of high irradiance (100-300 micromol quanta m-2 s-1). Under similar conditions uninfected Chlorella cells do not display significant changes in non-photochemical quenching.

Carotenoids↗
PubMed1985

Trichothecene structure and toxicity to the green alga Chlorella pyrenoidosa.

Using the paper-disk method with Chlorella-seeded agar plates, 15-acetoxyscirpenol, HT-2 toxin, acetyl T-2 toxin and neosolaniol inhibited growth at a concentration of 1 mg/ml, whereas verrucarol, T-2 tetraol, nivalenol, fusarenon-X, deoxynivalenol and 3-acetyldeoxynivalenol were inactive. Taking into account that verrucarin A, roridin A, T-2 toxin and diacetoxyscirpenol had previously been found to strongly inhibit Chlorella growth, esterification at R15 appears to be important for growth inhibitory activity. The most active agents are also esterified at R4. Inhibition of protein synthesis appears to be involved in the toxicity.

Chlorella↗
PubMed1990

Cloning and sequencing the cytosine methyltransferase gene M. CviJI from Chlorella virus IL-3A.

The Chlorella virus IL-3A gene encoding the DNA methyltransferase M.CviJI, which methylates the internal cytosine in (G/A)GC(T/C/G) sequences, was cloned and expressed in Escherichia coli. The region containing the M.CviJI gene was sequenced and a single open reading frame of 1101 bp was identified that could code for a polypeptide of 367 amino acids with a predicted molecular weight of 41,864. M.CviJI contained regions of amino acids which were similar to bacterial cytosine methyltransferases. Eighteen other Chlorella viruses, of 36 tested, contained DNA sequences which hybridized to the M.CviJI gene; DNA from some, but not all, of these 18 viruses also contained 5-methylcytosine in (G/A)GC(T/C/G) sequences.

Amino Acid Sequence↗
PubMed1990

5-Azacytidine-resistant mutants of Chlorella virus IL-3A.

Many dsDNA-containing viruses which infect the unicellular, eukaryotic Chlorella-like green alga strain NC64A encode for DNA methyltransferases and DNA site-specific (restriction) endonucleases. We have hypothesized that these endonucleases help degrade host DNA permitting deoxynucleotides to recycle into virus DNA. This hypothesis was tested by isolating deletion mutants of Chlorella virus IL-3A lacking functional genes for the cytosine methyltransferase M.CviJI and the cognate site-specific endonuclease CviJI. The growth and burst sizes of the mutants and parent virus were identical. Also host nuclear and chloroplast DNAs disappeared from infected cells at the same rates. Thus M.CviJI and CviJI activities are not required for IL-3A replication and CviJI activity is not essential for host DNA degradation.

Azacitidine↗
PubMed1991

The termini of the chlorella virus PBCV-1 genome are identical 2.2-kbp inverted repeats.

The Chlorella virus PBCV-1 genome is a linear nonpermuted 333-kbp dsDNA molecule with covalently closed hairpin termini. The termini (minus the hairpin) are identical inverted repeats of at least 2185 bases after which the sequence diverges. The inverted repeats contain two small potential open reading frames and several direct repeats. However, neither the open reading frames nor the remainder of the inverted repeats are transcribed during PBCV-1 replication. Twenty-nine other Chlorella virus DNAs, of 36 tested, hybridized to the PBCV-1 terminal fragments.

Amino Acid Sequence↗
PubMed1992

The DNA polymerase gene from chlorella viruses PBCV-1 and NY-2A contains an intron with nuclear splicing sequences.

The deduced amino acid sequences of two eukaryotic chlorella virus (PBCV-1 and NY-2A) DNA polymerases are 90% identical and contain amino acid motifs typical of alpha-like (Family B) DNA polymerases. The open reading frames of both PBCV-1 and NY-2A DNA polymerases are interrupted by an identically located, small (101 or 86 nucleotides, respectively) intron that resembles eukaryotic nuclear-spliced messenger RNA introns. This discovery suggests that chlorella virus replication has a nuclear phase.

Amino Acid Sequence↗
PubMed1989

Coenzyme non-specific glutamate dehydrogenase from Chlorella pyrenoidosa 82T: electron microscopic studies.

The constitutive coenzyme non-specific glutamate dehydrogenase (GDH) from Chlorella pyrenoidosa 82T was purified to homogeneity by column immunoaffinity chromatography and examined by an electron microscope. The enzyme molecule was found to be a hexameric oligomer composed of monomers arranged in three 2-point group symmetry in two layers slightly twisted round the 3-fold axis. The molecule is 8 +/- 1 nm in diameter and 10 +/- 1 nm in height. The enzyme molecules appear both to dissociate into trimers and to associate along the 3-fold axis forming linear aggregates under certain conditions. A tentative model of the Chlorella GDH molecule is proposed, which is very similar to those described for bovine liver GDH and GDH from Clostridium symbiosum.

Chlorella↗
PubMed1990

Characterization of nuclear DNA in 12 species of Chlorella (Chlorococcales, Chlorophyta) by DNA reassociation.

Strains of 12 different species of the genus Chlorella were analyzed for amount, reiteration frequency and kinetic complexity of chromosomal DNA components by C0t analysis. The resulting C0t curves reveal at least two different DNA components consisting of single copy DNA (up to 95%) and of repetitive DNA with complexities of 4.1 x 10(3) base pairs (bp) to approximately 11.7 x 10(3) bp and a reiteration frequency of 100-760. The total amount of repetitive DNA is less than 9% of the nuclear genome and similar in all strains studied. In contrast, the total kinetic complexity varies in a wide range from 1.26 x 10(7) bp to 8.08 x 10(7) bp which is mainly due to differences in the size of single copy DNA. The genome sizes in Chlorella seem not to be correlated with biochemical and physiological characteristics and therefore are unlikely to be useful as a taxonomical marker. A comparison of thermal denaturation profiles showed that the melting points of repetitive and single copy DNA differ by approximately 7 degrees C which may result from base mismatch and/or from a distinct base composition of the repetitive DNA.

Cell Nucleus↗
PubMed1994

A group-I self-splicing intron in the nuclear small subunit rRNA-encoding gene of the green alga, Chlorella ellipsoidea C-87.

We report the presence of a 442-bp group-I self-splicing intron in the nuclear small subunit (SSU) rRNA-encoding gene (rDNA) of the unicellular green alga, Chlorella ellipsoidea C-87 (C. saccharophila 211-1a). The intron was found to be inserted at a position within the highly conserved helix 48 that was close to the 3' terminus of the SSU rRNA. The position was exactly the same as previously identified for the Pneumocystis carinii intron. A secondary structure model for the C. ellipsoidea intron contained all P1-P10 motifs of the group-I introns. Although the overall secondary structure of the C. ellipsoidea intron was substantially different from that of the intron in the nuclear large subunit rDNA of Tetrahymena thermophila, the nucleotide (nt) sequences constituting the catalytic core were strikingly conserved between the two; only three of 48 nt were different. The C. ellipsoidea intron was autocatalytically excised from the transcript in vitro via the group-I mechanism under somewhat unique conditions. No SSU rDNA intron was found in six other Chlorella species, including C. fusca var. vacuolata, C. kessleri, C. minutissima, C. protothecoides, C. sorokiniana and C. vulgaris.

Animals↗
PubMed1974

Effect of dynamic factors of space flights on the green alga Chlorella vulgaris.

The biological effects of vibrational and linear acceleration on the alga Chlorella vulgaris were studied. Periodic vibration in the frequency range of 4-4000 Hz with vibrational acceleration up to 16 g did not affect the survival and mutability of Chlorella cells and did not modify the effects of acute gamma-radiation. However, random vibration similar to that occurring during launch of spaceships, combined with linear acceleration increased the radiation damage to algae produced by acute gamma-radiation at a dose of 10000 r. This effect is seen only in cells at the beginning of the G1 stage, which precedes DNA synthesis.

Acceleration↗
PubMed1980

Biological studies of Chlorella pyrenoidosa (strain LARG-1) cultures grown under space flight conditions.

This paper reports data from an electron microscopic analysis of Chlorella pyrenoidosa (LARG-1) cultures after five days of growth in the dark on a semiliquid mineral/glucose medium in the IFS-2 device on board the Soyuz 27-Salyut 6-Soyuz 28 orbital research complex (Soviet-Czechoslovak experiment "Chlorella-1"). For space flight of five days duration the ultrastructural cellular organization of the flight and control cultures were similar. This testifies to normal cell function.

Cell Size↗
PubMed2005

Chlorella dichloromethane extract ameliorates NO production and iNOS expression through the down-regulation of NF kappa B activity mediated by suppressed oxidative stress in RAW 264.7 macrophages.

BACKGROUND: It has been proposed that chlorella extracts have antioxidative and anti-inflammatory effects. METHODS: RAW 264.7 murine macrophage cell line was preincubated with various concentrations (0-100 mug/ml) of chlorella dichloromethane extract (CDE) and stimulated with lipopolysaccharide (LPS) to induce oxidative stress and inflammation. RESULTS: Treatments of CDE reduced thiobarbituric acid-reactive substances (TBARS) accumulation, enhancing glutathione level and activities of antioxidative enzymes including superoxide dismutase (SOD), catalase, glutathione peroxidase (GSH-px), and glutathione reductase in LPS-stimulated macrophages than LPS-only treated cells. Nitric oxide (NO) production was significantly suppressed in a dose-dependent manner (p<0.05) with an IC(50) of 30.5 microg/ml. Treatment of CDE at 50 microg/ml suppressed NO production to 6% of LPS-control. Treatment with CDE suppressed the levels of inducible nitric oxide synthase (iNOS) protein and mRNA expressions. The specific DNA binding activities of nuclear factor kappa B (NF kappa B) on nuclear extracts from CDE treatments were significantly suppressed with an IC(50) of 62.7 mug/ml in a dose-dependent manner. CONCLUSIONS: CDE ameliorates NO production and iNOS expression through the down-regulation of NF kappa B activity, which may be mediated by attenuated oxidative stress in RAW 264.7 macrophages.

Animals↗
PubMed2005

Synchronous-scan fluorescence spectra of Chlorella vulgaris solution.

The characterization of the Chlorella vulgaris solution was carried out using synchronous-scan spectroscopy. The range of concentration of algae and Fe(III) in aqueous solutions were 5 x 10(8)-8 x 10(9) cells l(-1) and 10-60 microM, respectively. Effective characterization method used was synchronous-scan fluorescence spectroscopy. The wavelength difference (Deltalambda) of 90 nm was maintained between excitation and emission wavelengths; 90 nm was found to be the best Deltalambda for effective characterization of Chlorella vulgaris solution with or without quencher species (e.g., Fe(III), humic acid (HA)) for the first time. The peak was observed at about EX 236.6 nm/EM 326.6 nm for synchronous-scan fluorescence spectra. The fluorescence quenching of algae in system of algae-Fe(III)-HA was studied using synchronous-scan spectroscopy for the first time. Fe(III) was clearly the effective quencher. The relationship between I0/I (quenching efficiency) and c (concentration of Fe(III) added) was a linear correlation for the algae solution with Fe(III). Also, Aldrich humic acid was found to be an effective quencher. pH effect on synchronous-scan fluorescence intensity of algal solution with Fe(III) and/or HA was evident.

Chlorella vulgaris↗