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PubMed1998

Alteration of substrate affinities and specificities of the Chlorella Hexose/H+ symporters by mutations and construction of chimeras.

The cDNAs HUP1 and HUP2 of Chlorella kessleri code for monosaccharide/H+ symporters that can be functionally expressed in Schizosaccharomyces pombe. By random mutagenesis three HUP1 mutants with an increased Km value for D-glucose were isolated. The 40-fold increase in Km of the first mutant is due to the amino acid exchange N436I in putative transmembrane helix XI. Two substitutions were found in a second (G97C/I303N) and third mutant (G120D/F292L), which show a 270-fold and 50-fold increase in Km for D-glucose, respectively. An investigation of the individual mutations revealed that the substitutions I303N and F292L (both in helix VII) cause the Km shifts seen in the corresponding double mutants. These mutations together with those previously found support the hypothesis that helices V, VII, and XI participate in the transmembrane sugar pathway. Whereas for most mutants obtained so far the Km change for D-glucose is paralleled by a corresponding change for other hexoses tested, the exchange D44E exclusively alters the Km for D-glucose. Moreover the pH profile of this mutant is shifted by more than 2 pH units to alkaline values, indicating that the activity of the transporter may require deprotonation of the corresponding carboxyl group. Chimeric transporters were constructed to study the 100-fold lower affinity for D-galactose of the HUP1 symporter as compared with that of the HUP2 protein. A crucial determinant for the differential D-galactose recognition was shown to be associated with the first external loop. The effect could be pinpointed to a single amino acid change: replacement of Asn-45 of HUP1 with isoleucine, the corresponding amino acid of HUP2, yields a transporter with a 20 times higher affinity for D-galactose. The reverse substitution (I47N) decreases the affinity of HUP2 for D-galactose 20-fold.

Amino Acid Sequence↗
PubMed2003

Paramecium bursaria Chlorella virus 1 encodes two enzymes involved in the biosynthesis of GDP-L-fucose and GDP-D-rhamnose.

At least three structural proteins in Paramecium bursaria Chlorella virus (PBCV-1) are glycosylated, including the major capsid protein Vp54. However, unlike other glycoprotein-containing viruses that use host-encoded enzymes in the endoplasmic reticulum-Golgi to glycosylate their proteins, PBCV-1 encodes at least many, if not all, of the glycosyltransferases used to glycosylate its structural proteins. As described here, PBCV-1 also encodes two open reading frames that resemble bacterial and mammalian enzymes involved in de novo GDP-L-fucose biosynthesis. This pathway, starting from GDP-D-mannose, consists of two sequential steps catalyzed by GDP-D-mannose 4,6 dehydratase (GMD) and GDP-4-keto-6-deoxy-D-mannose epimerase/reductase, respectively. The two PBCV-1-encoded genes were expressed in Escherichia coli, and the recombinant proteins had the predicted enzyme activity. However, in addition to the dehydratase activity, PBCV-1 GMD also had a reductase activity, producing GDP-D-rhamnose. In vivo studies established that PBCV-1 GMD and GDP-4-keto-6-deoxy-D-mannose epimerase/reductase are expressed after virus infection and that both GDP-L-fucose and GDP-D-rhamnose are produced in virus-infected cells. Thus, PBCV-1 is the first virus known to encode enzymes involved in nucleotide sugar metabolism. Because fucose and rhamnose are components of the glycans attached to Vp54, the pathway could circumvent a limited supply of GDP sugars by the algal host.

Animals↗
PubMed2004

Copper-induced oxidative stress in the chlorophycean microalga Chlorella vulgaris: response of the antioxidant system.

A concentration dependent increase in lipid peroxidation, carotenoid content and activity of superoxide dismutase was observed in the green microalga Chlorella vulgaris following copper exposure. In contrast, activities of catalase, ascorbate peroxidase and glutathione reductase, and the cellular GSH, ascorbate and K+ pool depicted a reverse trend. However, a significant rise in intracellular proline content was also evident in copper supplemented cultures. Though this study depicted the malfunction of the major antioxidant system of C. vulgaris under copper stress the test organism was found to survive and grow even at 3.0 microg mL(-1) of Cu treatment (32% growth). Further study is needed to establish the role of proline in metal toxicity regulation.

Ascorbate Peroxidases↗
PubMed2005

Effect of illumination of nitrate and phosphate removal by coimmobilized Chlorella pyrenoidosa and activated sludge.

Chlorella pyrenoidosa and activated sludge were co-immobilized with simplifying modified PVA-sulfate method. Effects of light intensity and light:dark ratio on the growth of co-immobilized algae cells and removal of nitrate and phosphate were studied. The results indicate that the growth rate of co-immobilized algae cells reduces when light intensity is decreased from 4000 Lux to 1000 Lux, while optimal light:dark ratio for algal growth is 16:8. The influence of illumination on nitrate removal is so weak that the removal percentage can reach 90 approximately 100% within 12 approximately 24 h during the experimental periods in spite of changing illumination conditions. On the other hand, phosphate removal efficiency reduces when light intensity or light:dark ratio is decreased. The highest phosphate removal percentage is 99.6% under the circumstances of 4000 Lux and full-time illumination in our experiment, while the average phosphate removal is about 78%. The change of pH value in water samples is also observed. When water sample is treated by the co-immobilized system, pH value increases in light and decreases in dark. Microorganisms' physiological action is considered as the main mechanism that leads to the change of pH value.

Cells, Immobilized↗
PubMed2002

Effect and mechanism of inorganic carbon on the biodegradation of dimethyl phthalate by Chlorella pyrenoidosa.

The effect and mechanism of inorganic carbon (IC) on the biodegradation of dimethyl phthalate (DMP) by a green microalga Chlorella pyrenoidosa was investigated. It was indicated that DMP could be used as the sole carbon source to support the slow heterotrophic growth of C. pyrenoidosa, but both the growth of C. pyrenoidosa and the biodegradation rate of DMP were obviously increased when initial inorganic carbon concentration (IC) was increased from 0.6 to 23.7 mg/l. Phthalic acid (PA) was found to be an intermediate product of DMP biodegradation and accumulated in the culture solution, which caused a sharp decrease in pH of medium and inhibited both the growth of alga and the biodegradation of DMP. The role of IC for improving the biodegradation of DMP was both to supply a favorite carbon source to support the rapid growth of alga and to mitigate the decrease of pH because of the production of PA. A suggested second-order kinetic equation of organic pollutant biodegradation by microalgae (-dC/dt = KNr) fitted well with the experimental data and the correlation coefficients were all above 0.9. The second-order constant (K) apparently declined with the increase of initial IC because lower ratio between organic carbon from DMP and IC was used to support the growth of alga when initial IC increased.

Biodegradation, Environmental↗
PubMed2001

Effects of the green algae Chlorella vulgaris on the response of the host hematopoietic system to intraperitoneal ehrlich ascites tumor transplantation in mice.

Chlorella vulgaris extract (CVE) was examined for its effects on the Ehrlich ascites tumor-induced suppression in the numbers of bone marrow and spleen granulocyte-macrophage progenitor cells (CFU-GM) in mice. No effects on bone marrow and spleen CFU-GM, as compared to controls, were observed in normal mice given 50, 100 and 200 mg/kg CVE orally for 5 days. In tumor-bearing mice, myelosuppression concomitant with increased number of spleen CFU-GM were observed. The number of CFU-GM in the bone marrow was restored to control levels after the administration of CVE (50, 100 and 200 mg/kg) to tumor-bearing mice, and a slight reduction in spleen colony formation was observed in these animals. In addition, CVE significantly prolonged the survival of mice inoculated with the Ehrlich ascites tumor. These results suggest a protective antitumor effect of CVE which might be attributable, at least in part, to the stimulation of the production and, possibly, maturation of granulocytes and macrophages.

Administration, Oral↗
PubMed2001

Population growth of Euchlanis dilatata (Rotifera): combined effects of methyl parathion and food (Chlorella vulgaris).

In the present work, the combined impact of four concentrations (0, 0.0625, 0.125, and 0.25 mg/L) of methyl parathion and three densities (0.5 x 10(6), 1.0 x 10(6), and 2.0 x 10(6) cells/mL) of the green alga Chlorella vulgaris on the population growth of Euchlanis dilatata was studied. In general, regardless of the food level, an increase in the concentration of methyl parathion resulted in a significant reduction of the maximal population density and rate of population increase. The population growth rate in the controls ranged from 0.248 to 0.298; rates were lower in the presence of the pesticide. At any toxicant concentration, rotifers fed higher algal density showed significantly higher population growth compared with those at lower food levels. An interaction between toxicant and food level was evident on the population growth of E. dilatata. Results have been discussed in light of the protective role of algal density on the toxic effects of insecticides on rotifers and the differences in susceptibility to toxicants between planktonic and littoral rotifers.

Animals↗
PubMed2003

Temporal changes in the toxicity of pentachlorophenol to Chlorella pyrenidosa algae.

The toxicity of pentachlorophenol (PCP) on Chlorella pyrenidosa algae was investigated with specific attention given to possible variation of toxic effects with time. A concentration-effect relationship was observed in which there was significant inhibition of PCP on cell density and chlorophyll A content. The inhibition rate of PCP on cell density was dependent on exposure time. The IC50 values after exposure times of 2, 4 and 6 days for cell growth were 4.18 +/- 0.49, 3.49 +/- 0.40 and 3.30 +/- 0.26 mg/L, respectively. There was also inhibition of chlorophyll A production, which appeared to increase marginally with exposure time for a given concentration of PCP. The corresponding IC50 values on day 2, 4 and 6 were 2.30 +/- 0.12, 2.63 +/- 0.38 and 3.30 +/- 0.34 mg/L, respectively. The effect of PCP on nitrate reductase (NR), was first stimulation followed by an inhibition phase. It is postulated that the observed temporal changes in the activity of nitrate reductase (NR) may occur through the addition or loss of phosphorus in the NR protein.

Biomass↗
PubMed1954

The identity of the fluorescent and delayed light emission spectra in Chlorella.

1. The delayed light emission of Chlorella pyrenoidosa over the wave length range 400 to 950 mmicro has been investigated. 2. Emission of delayed light is confined to the range 600 to 800 mmicro. 3. To the precision with which the low light intensities involved can be measured with the apparatus in these experiments, the emission spectrum of the delayed light is the same as the spectrum of the fluorescent light. 4. Thus the delayed light must come from excited chlorophyll.

Chlorella↗
PubMed1956

The effects of some inhibitors on the rates of photosynthesis and respiration by Chlorella.

The effects of several inhibitors on the rates of photosynthesis and of respiration by Chlorella pyrenoidosa have been studied. The inhibitors used in this study include potassium cyanide, hydroxylamine hydrogen chloride, dinitrophenol,and sodium azide. Each inhibitor seems to have its own characteristic action in photosynthesis and in respiration. With the exception of hydroxylamine, all the inhibitors show a stimulation of respiration at low concentrations of the inhibitors. Only dinitrophenol inhibits respiration to a marked extent. Potassium cyanide, hydroxylamine, and dinitrophenol are about equally effective in inhibiting photosynthesis, but sodium azide is nearly ten times as effective.

Cell Respiration↗
PubMed1957

The course of respiration during the life cycle of Chlorella cells.

Endogenous and glucose respiration were studied during the life history of Chlorella pyrenoidosa. A generalized picture of the course of respiration during the life cycle is suggested. At the liberation of daughter cells from the wall of the mother cell, or soon after, the respiration rate reaches its lowest level. If the daughter cells are placed in light the respiration rate rapidly increases with time, soon reaches a maximum, and then declines slowly. Two factors are important in the initial increase-the early developmental stage of the cells and the influence of light. In autotrophically developing algae the parts played by developmental processes and by light have not been separated. Direct activation of respiratory enzymes by light, in addition to the level of respiratory substrate, cannot be excluded. The decline of respiration rate over most of the cell history seems to have no connection with light and is probably bound to the developmental processes per se. Darkening the suspension interrupts growth and induces liberation of daughter cells, with concomitant faster decrease in respiration rate. The rate of respiration of small daughter cells decreases in darkness only slowly with time. Illumination seems necessary to bring these cells back to a high level of respiratory activity.

Cell Respiration↗
PubMed1985

DNA methylation of viruses infecting a eukaryotic Chlorella-like green alga.

The genomic DNAs of the eukaryotic Chlorella-like green alga, strain NC64A, and eleven of its viruses all contain significant levels of 5-methyldeoxycytidine. In addition, the host DNA as well as six of the viral DNAs also contain N6-methyldeoxyadenosine. At least some of the methylated bases in the host reside in different base sequences than the methylated bases in the viruses as shown by differential susceptibility to restriction endonuclease enzymes. This suggests that the viruses encode for DNA methyltransferases with sequence specificities different from that of the host enzyme.

Base Composition↗
PubMed1987

IL-3A virus infection of a Chlorella-like green alga induces a DNA restriction endonuclease with novel sequence specificity.

A type II restriction endonuclease, named CviJI, was isolated from a eukaryotic Chlorella-like green alga infected with the dsDNA containing virus IL-3A. CviJI is the first restriction endonuclease to recognize the sequence PuGCPy; CviJI cleaves DNA between the G and C. Methylation of the cytosine in PuGCPy sequences prevents cleavage by CviJI. CviJI cleaved DNA into smaller but defined fragments in the presence of ATP. This "star" activity was stimulated by dithiothreitol and/or S-adenosylmethionine but did not occur under conditions which favor "star" activity of other restriction endonucleases.

Adenosine Triphosphate↗
PubMed1988

A site-specific single strand endonuclease activity induced by NYs-1 virus infection of a Chlorella-like green alga.

A site-specific endonuclease was isolated from a eukaryotic Chlorella-like green alga infected with the dsDNA-containing virus NYs-1. The enzyme recognizes the sequence 5'-CC-3' and cleaves 5' to the first C. It cleaves 5'-CmC-3' sequences but not 5'-mCC-3' sequences. The enzyme creates breaks in dsDNA whenever two 5'-CC-3' sequences on opposite strands are close enough for the two strands to separate; when the 5'-CC-3' sequences on opposite strands are further apart only a portion of the strands separate. Consequently, NYs-1 endonuclease does not produce a completely stable DNA digestion pattern. The enzyme probably does not cleave ssDNA and definitely does not cleave ssRNA or dsRNA.

Chlorella↗
PubMed1996

Molecular cloning of the three base restriction endonuclease R.CviJI from eukaryotic Chlorella virus IL-3A.

R.CviJI is unique among site-specific restriction endonucleases in that its activity can be modulated to recognize either a two or three base sequence. Normally R.CviJI cleaves RGCY sites between the G and C to leave blunt ends. In the presence of ATP R.CviJI* cleaves RGCN and YGCY sites, but not YGCR sites. The gene encoding R.CviJI was cloned from the eukaryotic Chlorella virus IL-3A and expressed in Escherichia coli. The primary E.coli cviJIR gene product is a 278 amino acid protein initiated from a GTG codon, rather than the expected 358 amino acid protein initiated from an in-frame upstream ATG codon. Interestingly, the 278 amino acid protein displays the normal restriction activity but not the R.CviJI* activity of the native enzyme. Nine restriction and modification proteins which recognize a central GC or CG sequence share short regions of identity with R.CviJI amino acids 144-235, suggesting that this region is the recognition and/or catalytic domain.

Amino Acid Sequence↗
PubMed1998

Mutational analysis of Chlorella virus DNA ligase: catalytic roles of domain I and motif VI.

A conserved catalytic core of the ATP-dependent DNA ligases is composed of an N-terminal domain (domain 1, containing nucleotidyl transferase motifs I, III, IIIa and IV) and a C-terminal domain (domain 2, containing motif VI) with an intervening cleft. Motif V links the two structural domains. Deletion analysis of the 298 amino acid Chlorella virus DNA ligase indicates that motif VI plays a critical role in the reaction of ligase with ATP to form ligase-adenylate, but is dispensable for the two subsequent steps in the ligation pathway; DNA-adenylate formation and strand closure. We find that formation of a phosphodiester at a pre-adenylated nick is subject to a rate limiting step that does not apply during the sealing of nicked DNA by ligase-adenylate. This step, presumably conformational, is accelerated or circumvented by deleting five amino acids of motif VI. The motif I lysine nucleophile (Lys27) is not required for strand closure by wild-type ligase, but this residue enhances the closure rate by a factor of 16 when motif VI is truncated. We find that a more extensively truncated ligase consisting of only N-terminal domain 1 and motif V is inert in ligase--adenylate formation, but competent to catalyze strand closure at a pre-adenylated nick. These results suggest that different enzymic catalysts facilitate the three steps of the DNA ligase reaction.

Adenosine Triphosphate↗
PubMed1984

DNA polymerases of Chlorella. II. Characterization to distinguish the two enzymes.

Previously, we reported two DNA polymerases (DPols), Pol I and Pol II, in the unicellular green alga, Chlorella (Aoshima, J., Nishimura, T., & Iwamura, T. (1982) Cell Struc. Funct. 7, 71-86). Changes in their activities during the cell cycle either in the normal and drug-inhibited courses indicated that Pol I and Pol II functioned to replicate nuclear and chloroplast DNAs, respectively. In the present work, we have examined their enzymic properties to characterize and distinguish them further. A number of inhibitors commonly used for such studies were also tested to determine their effects and the results were analyzed by use of the simple and useful "Tamiya plot." We have also analyzed the data obtained in inhibitor studies on various eukaryotic DPols in the literature using the Tamiya plot, and the results will be presented elsewhere (Iwamura, T. & Aoshima, J. (1984) J. Biochem. in press). Comparisons of the algal DPols with mammalian enzymes as regards enzymic properties and inhibition modes have led us to conclude that: [1] the algal two DPols are significantly different from each other, despite having many similarities to each other: [2] they are related in properties to any of the three mammalian DPols-alpha, -beta, and -gamma; Pol I (n-DPol) was a little more like alpha than Pol II (ch-DPol), which in turn more akin to gamma. This feature was quantitized by using vectors in a three-dimensional alpha-beta-gamma-space. Another peculiar feature derived from the Tamiya plot of the inhibitions by araCTP and aphidicolin (both being competitive with cCTP) has led us to propose a specific allosteric role of cCTP in the reaction mechanism besides its role as one of the substrates.

Cations, Divalent↗
PubMed2005

The formation of Zn-Chl a in Chlorella heterotrophically grown in the dark with an excessive amount of Zn2+.

Chlorella, when heterotrophically cultivated in the dark, is able to grow with Zn2+ at 10-40 mM, which is 10 times the concentration lethal to autotrophically grown cells. However, the lag phase is prolonged with increasing concentrations of Zn2+; for example, in this study, 1 d of the control lag phase was prolonged to about 16 d with Zn2+ at 16.7 mM (x2,000 of the control). Once the cells started to grow, the log phase was finished within 4-6 d regardless of Zn concentration, which was almost the same as that of the control. The photosysystem I reaction center chlorophyll, P700, and the far-red fluorescence were detected only after the late log phase of the growth curve, suggesting that chlorophyll-protein complexes can be organized after cell division has ceased. Interestingly, at more than 16.7 mM of Zn2+, Zn-chlorophyll a was accumulated and finally accounted for about 25% of the total chlorophyll a in the late stationary phase. We found that the Zn-chlorophyll a was present in the thylakoid membranes and not in the soluble fractions of the cells. The rather low fluorescence yield at around 680 nm in the stationary phase suggests that Zn-chlorophyll a can transfer its excitation energy to other chlorophylls. Before accumulation of Zn-chlorophyll a, a marked amount of pheophytin a was temporally accumulated, suggesting that Zn-chlorophyll a could be chemically synthesized via pheophytin a.

Cell Division↗