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PubMed2005

Chlorella virus-encoded deoxyuridine triphosphatases exhibit different temperature optima.

A putative deoxyuridine triphosphatase (dUTPase) gene from chlorella virus PBCV-1 was cloned, and the recombinant protein was expressed in Escherichia coli. The recombinant protein has dUTPase activity and requires Mg(2+) for optimal activity, while it retains some activity in the presence of other divalent cations. Kinetic studies of the enzyme revealed a K(m) of 11.7 microM, a turnover k(cat) of 6.8 s(-1), and a catalytic efficiency of k(cat)/K(m) = 5.8 x 10(5) M(-1) s(-1). dUTPase genes were cloned and expressed from two other chlorella viruses IL-3A and SH-6A. The two dUTPases have similar properties to PBCV-1 dUTPase except that IL-3A dUTPase has a lower temperature optimum (37 degrees C) than PBCV-1 dUTPase (50 degrees C). The IL-3A dUTPase differs from the PBCV-1 enzyme by nine amino acids, including two amino acid substitutions, Glu81-->Ser81 and Thr84-->Arg84, in the highly conserved motif III of the proteins. To investigate the difference in temperature optima between the two enzymes, homology modeling and docking simulations were conducted. The results of the simulation and comparisons of amino acid sequence suggest that adjacent amino acids are important in the temperature optima. To confirm this suggestion, three site-directed amino acid substitutions were made in the IL-3A enzyme: Thr84-->Arg84, Glu81-->Ser81, and Glu81-->Ser81 plus Thr84-->Arg84. The single substitutions affected the optimal temperature for enzyme activity. The temperature optimum increased from 37 to 55 degrees C for the enzyme containing the two amino acid substitutions. We postulate that the change in temperature optimum is due to reduction in charge and balkiness in the active cavity that allows more movement of the ligand and protein before the enzyme and substrate complex is formed.

Amino Acid Motifs↗
PubMed1986

DNA methyltransferase induced by PBCV-1 virus infection of a Chlorella-like green alga.

A DNA methyltransferase was isolated from a eucaryotic, Chlorella-like green alga infected with the virus PBCV-1. The enzyme recognized the sequence GATC and methylated deoxyadenosine solely in GATC sequences. Host DNA, which contains GATC sequences, but not PBCV-1 DNA, which contains GmATC sequences, was a good substrate for the enzyme in vitro. The DNA methyltransferase activity was first detected about 1 h after viral infection; PBCV-1 DNA synthesis and host DNA degradation also began at about this time. The appearance of the DNA methyltransferase activity required de novo protein synthesis, and the enzyme was probably virus encoded. Methylation of DNAs with the PBCV-1-induced methyltransferase conferred resistance of the DNAs to a PBCV-1-induced restriction endonuclease enzyme described previously (Y. Xia, D. E. Burbank, L. Uher, D. Rabussay, and J. L. Van Etten, Mol. Cell. Biol. 6:1430-1439). We propose that the PBCV-1-induced methyltransferase protects viral DNA from the PBCV-1-induced restriction endonuclease and is part of a virus-induced restriction and modification system in PBCV-1-infected Chlorella cells.

Cell Transformation, Viral↗
PubMed2002

Increased pigment and lipid content, lipid variety, and cell and population size of the microalgae Chlorella spp. when co-immobilized in alginate beads with the microalgae-growth-promoting bacterium Azospirillum brasilense.

Three strains of the freshwater microalgae used for wastewater treatment, Chlorella vulgaris and Chlorella sorokiniana co-immobilized separately in alginate beads with the microalgae-growth-promoting bacterium Azospirillum brasilense Cd, resulted in significant changes in microalgal-population size, cell size, cell cytology, pigment, lipid content, and the variety of fatty acids produced in comparison with microalgae immobilized in alginate without the bacterium. Cells of C. vulgaris UTEX 2714 did not change in size, but the population size within the beads significantly increased. On the other hand, C. vulgaris UTEX 395 cells grew 62% larger, but their numbers did not increase. The population of C. sorokiniana UTEX 1602 increased, but not their cell size. The content of pigments chlorophyll a and b, lutein, and violoaxanthin increased in all microalgal species. The lipid content also significantly increased in all three strains, and the number of different fatty acids in the microalgae increased from four to eight. This study indicates that the microalgae-growth-promoting bacterium induced significant changes in the metabolism of the microalgae.

Alginates↗
PubMed1986

Replication of the algal virus PBCV-1 in UV-irradiated Chlorella.

The large dsDNA algal virus, PBCV-1, replicates in UV-irradiated Chlorella, albeit more slowly and with a smaller burst size than in untreated Chlorella. Irradiated cells are unable to form colonies, and endogenous RNA and DNA synthesis are reduced to background levels. Thus a fully function host nucleus is not required for PBCV-1 replication.

Chlorella↗
PubMed1984

Intracellular infection of aposymbiotic Hydra viridis by a foreign free-living Chlorella sp.: initiation of a stable symbiosis.

An aposymbiotic strain of Hydra viridis became infected with free-living Chlorella sp. A stable symbiosis formed that differed in its characteristics from other known Chlorella/Hydra symbioses. The algae reproduced and formed clusters in host endodermal cells, inside large vacuoles filled with an electron-dense substance. A few algae were found to be digested by the hydra, but the apparently uncontrolled reproduction rate of the algae more than compensated for this loss. Surplus algae were expelled into the coelenteron and eventually into the surrounding medium. The expelled algae were repeatedly re-engulfed by the hydra during its feeding, forming a process of continuous reinfection. We suggest that such repeated reinfection of the hydra by the expelled algae provides the host with an endless number of Chlorella from which it might in time select a suitable adapted, controllable symbiont. The present newly formed symbiosis might serve as a model for the study of evolution of algal endosymbioses.

Animals↗
PubMed1986

The cell cycle of symbiotic Chlorella. IV. DNA content of algae slowly increases during host starvation of green hydra.

The distribution of DNA content of symbiotic Chlorella algae freshly isolated from green hydra was compared with that of cultured Chlorella of the NC64A strain, using flow cytometry. In nonlogarithmic cultures of NC64A most cells had accumulated in G1 phase, while in logarithmic cultures a peak containing cells in S phase and mitosis could be distinguished from the larger G1 peak. However, symbiotic algae showed a single broad peak in which there was no clear distinction between G1 and S phase/mitosis. When hydra were starved for a prolonged period, inhibiting host cell and algal division, the DNA content of the symbiotic algae slowly increased, and the number of daughter cells produced after a single feeding increased with the length of the preceding period of starvation. This suggests that symbiotic algae are able to cycle slowly through S phase, but unless the host is fed they cannot traverse into mitosis and complete the cell division cycle. No significant difference in cell size was found between algae producing either four or eight daughter cells after 1-day- or 22-day-starved hydra were fed, suggesting that algal cell size did not determine the number of daughter cells produced. Instead, this may be dependent upon the length of time the cell had spent in S phase prior to receiving the, as yet unknown, stimulus to enter into mitosis.

Animals↗
PubMed1993

Widespread distribution of Chlorella viruses in Japan.

An extensive survey for Chlorella viruses was done across Japan and in nine countries of Asia, Europe, North America, and South America. Of 150 fresh-water samples collected from 77 distinct areas in Japan, 29 showed plaques on a lawn of Chlorella sp. (strain NC64A). Typically, 10 to 1000 PFU/ml of viruses were present at sampling sites located throughout Japan. Viruses were also detected in two samples from Brazil and China but not from other countries where water samples were screened. Several representatives of these viruses including ones isolated from Brazil and China were compared with respect to genome size, genome structure, and protein components. It was found that these viruses should belong to the same virus group consisting of large icosahedral particles with linear dsDNA genomes. Physiological and ecological factors affecting virus distribution are discussed.

Chlorella↗
PubMed1999

Asymmetric reduction of ethyl 2-methyl 3-oxobutanoate by Chlorella.

Chlorella pyrenoidosa Chick reduced ethyl 2-methyl 3-oxobutanoate to the corresponding alcohols with the diastereomer (anti/syn) ratio of 53/47. The enantiomer excesses of anti-(2S, 3S)- and syn-(2S, 3R)-hydroxy esters were 89 and > 99ee% respectively. C. vulgaris and C. regularis afforded predominantly the syn-isomer, contrary to C. pyrenoidosa. The differences in the activity of reducing ethyl 2-methyl 3-oxobutanoate were observed among three strains of Chlorella. Addition of 2% metal salts slightly increased the chemical yield of the hydroxy ester.

Butyrates↗
PubMed2000

Cryoprotective activities of group 3 late embryogenesis abundant proteins from Chlorella vulgaris C-27.

The nucleotide sequence of hiC12, isolated as a cDNA clone of hardening-induced Chlorella (hiC) genes, was identified. The clone encodes a late embryogenesis abundant (LEA) protein having six repeats of a 11-mer amino acid motif, although in a slightly imperfect form. To overexpress the hiC61) and hiC12 genes, their coding regions were PCR amplified and subcloned into a pGEX-1lambdaT vector. The HIC6 and HIC12 proteins were expressed as GST fusion proteins in E. coli, then purified. The two HIC proteins were found to be effective in protecting a freeze-labile enzyme, LDH, against freeze-inactivation. On a molar concentration basis, they were about 3.1 x 10(6) times more effective in protecting LDH than sucrose and as effective as BSA. Cryoprotection tests with five kinds of chain-shortened polypeptides, synthesized based on the 11-mer amino acid motif of the HIC6 protein showed that the cryoprotective activity decreased with a decrease in the repeating units of the 11-mer motif. In fact, cryoprotective activities of three kinds of single 11-mer amino acids were very low even at high concentrations. All the results suggested that the sufficiently repeated 11-mer motif is required for the cryoprotective activities of Chlorella LEA proteins.

Amino Acid Sequence↗
PubMed2005

Biodegradation of bisphenol A and disappearance of its estrogenic activity by the green alga Chlorella fusca var. vacuolata.

Bisphenol A (BPA) is known as an endocrine disruptor and often is found in landfill leachates. Removal of BPA by green alga, Chlorella fusca, was characterized, because we previously found that various phenols were well removed by this strain, including BPA. Chlorella fusca was able to remove almost all BPA in the concentration range from 10 to 80 microM for 168 h under continuous illumination at 18 W/m2. At the low light intensity of 2 W/m2, 82% of 40 microM BPA was removed, and only 27% was removed in the dark. Moreover, C. fusca could remove 90% of 40 microM BPA under the 8:16-h light:dark condition, which was almost as high as that under the continuous-light condition. The amount of BPA contained in the cells was less than the amount of BPA removed from the medium. Monohydroxybisphenol A was detected as an intermediate of BPA degradation. Moreover, estrogenic activity that originated from BPA in the culture medium also completely disappeared. Based on these results, BPA was finally degraded to compounds having nonestrogenic activity. Therefore, C. fusca can be considered a useful organism to remove BPA from landfill leachates.

Benzhydryl Compounds↗
PubMed2005

Toxicity, biotransformation, and mode of action of arsenic in two freshwater microalgae (Chlorella sp. and Monoraphidium arcuatum).

The toxicity of As(V) and As(III) to two axenic tropical freshwater microalgae, Chlorella sp. and Monoraphidium arcuatum, was determined using 72-h growth rate-inhibition bioassays. Both organisms were tolerant to As(III) (72-h concentration to cause 50% inhibition of growth rate [IC50], of 25 and 15 mg As[III]/L, respectively). Chlorella sp. also was tolerant to As(V) with no effect on growth rate over 72 h at concentrations up to 0.8 mg/L (72-h IC50 of 25 mg As[V]/L). Monoraphidium arcuatum was more sensitive to As(V) (72-h IC50 of 0.25 mg As[V]/L). An increase in phosphate in the growth medium (0.15-1.5 mg PO4(3-)/L) decreased toxicity, i.e., the 72-h IC50 value for M. arcuatum increased from 0.25 mg As(V)/L to 4.5 mg As(V)/L, while extracellular As and intracellular As decreased, indicating competition between arsenate and phosphate for cellular uptake. Both microalgae reduced As(V) to As(III) in the cell, with further biological transformation to methylated species (monomethyl arsonic acid and dimethyl arsinic acid) and phosphate arsenoriboside. Less than 0.01% of added As(V) was incorporated into algal cells, suggesting that bioaccumulation and subsequent methylation was not the primary mode of detoxification. When exposed to As(V), both species reduced As(V) to As(III); however, only M. arcuatum excreted As(III) into solution. Intracellular arsenic reduction may be coupled to thiol oxidation in both species. Arsenic toxicity most likely was due to arsenite accumulation in the cell, when the ability to excrete and/or methylate arsenite was overwhelmed at high arsenic concentrations. Arsenite may bind to intracellular thiols, such as glutathione, potentially disrupting the ratio of reduced to oxidized glutathione and, consequently, inhibiting cell division.

Arsenic↗
PubMed1990

Oral administration of Chlorella vulgaris augments concomitant antitumor immunity.

Chlorella vulgaris, an unicellular green algae, or its acetone-extract (Ac-Ex) were administered orally to Meth A tumor bearing BALB/c or (BALB/c x DBA/2)F1 (CDF1) mice. When CDF1 mice were fed daily with 10% dried powder of Chlorella vulgaris (CVP) containing diet before and after Meth A tumor inoculation, the growth of rechallenged Meth A tumor was significantly suppressed in an antigen-specific manner. Augmentation of antitumor resistance was exhibited also by Winn assay using lymph node cells of tumor-bearing mice orally administered with CVP or Ac-Ex. Antigen-specific concomitant immunity in these mice were mediated by cytostatic T cells but not by cytotoxic T cells. Natural killer cells seemed not to contribute in antitumor resistance in this system.

Adjuvants, Immunologic↗
PubMed2001

Hypocholesterolemic effect of indigestible fraction of Chlorella regularis in cholesterol-fed rats.

The effects of Chlorella regularis powder (CP) and Chlorella regularis indigestible fraction (CIF) on serum and liver lipid concentrations and on fecal steroid excretion were estimated in rats fed diets containing 5 g/kg cholesterol and 2.5 g/kg sodium cholate. The ingestion of 12.7% CP or 5.3% CIF did not influence food intake or growth. CP and CIF decreased the levels of serum cholesterol, but had no effect on the levels of serum triacylglycerol and phospholipid. Liver cholesterol contents were lower in the CP and CIF groups than in the control group, but CP and CIF did not affect liver triacylglycerol content. CP and CIF increased the total amount of fecal neutral steroids excreted, but did not modify the total bile acid excretion. However, the soluble bile acid concentrations of reconstituted fecal water in the rats fed CP and CIF diets were lower than the control value. Moreover, CP and CIF had a high bile acid binding capacity in vitro. These results indicated that CIF had a hypocholesterolemic effect and enhanced fecal neutral steroid excretion while decreasing the soluble fecal bile acid concentration.

Animals↗
PubMed1979

Uptake of uranium by various cell fractions of Chlorella regularis.

To know what kinds of the cell components of Chlorella regularis are concerned with uranium binding, uptake of uranium by various cell fractions was examined. The uptake value (microgramU/mg starting dry cells) of the hot water-treated cells was almost the same as that of the starting dry Chlorella cells, showing that the cell components extracted with hot water were not so concerned with uranium binding. The cell components extracted with dilute alkali seemed to play an important role in uranium binding, and those extracted with chloroform-methanol seemed to be partly concerned with uranium binding. The cellulose fraction of the cells was scarcely concerned with uranium binding. In the dry cells, 34% of uranium taken up existed in the cell walls. However, in the living cells, 85% existed in the cell walls. The above results showed that the dry or the hot water-treated cells are the most convenient for uranium recovery from the aqueous systems.

Chlorella↗
PubMedDate not supplied

GC-MS analysis of fatty acids in phospholipids from Chlorella vulgaris cultivated synchronously in the presence of propranolol.

Changes in the content and composition of fatty acids in phospholipids were determined to estimate the effect of propranolol on the growth of unicellular green algae Chlorella vulgaris cultivated synchronously. The general biological activity of the cells and the division coefficient (DC) as well as the cell synchronisation were disturbed by propranolol in a concentration dependent manner. Also, the effect of propranolol on the fatty acids content of Chlorella vulgaris phospholipids was proportional to its concentration.

Anti-Arrhythmia Agents↗
PubMedDate not supplied

[Photoinduced reactivation of photosystem II in Chlorella after prolong incubation without light].

The light-dependent reactivation of photosystem II in Chlorella pyrenoidosa Chick, CALU-175 cells, inactivated with supraoptimal temperatures (40-43 degrees C) in the dark or during heterotrophic growth was studied. It was shown that the inactivation of photosystem II after incubation in the dark at 41-42 degrees C, which showed up in the suppression of relative yield of variable chlorophyll fluorescence Fv due to an increase in yield F0 could be completely reversed by light. The inactivation of photosystem II at 43 degrees C in the dark could not be reversed by subsequent irradiation. In this case, the suppression of Fv/Fm was related not only to the growth of F0 but also with the decrease in Fm. The light dependences of the rate and extent of reactivation of yield Fv after heterotrophic growth or incubation of chlorella at 41 degrees C in the dark completely coincided. The full light-induced reactivation of photosystem II took place as the rate of photoinduced electron transport reached the rate of nonphotochemical reduction of plastoquinone in the dark. These results suggest that the light-reversed inactivation of photosystem II after heterotrophic growth or incubation at 41 degrees C in the dark is due to the redox-interaction of the primary quinone acceptor with plastoquinone reduced by the electron flux from the substrates of chlororespiration.

Chlorella↗
PubMedDate not supplied

Fatty acid composition of Chlorella and Spirulina microalgae species.

Two New Age foods which contain high concentrations of whole food nutrients are the single-celled microalgae Chlorella and Spirulina. They are accepted as functional foods, which are defined as products derived from natural sources, whose consumption is likely to benefit human health and enhance performance. These foods are used as a supplement/ingredient or as a complete food to enhance the performance and state of the human body, or improve a specific bodily function. Functional foods are used mainly as products to nourish the human body after physical exertion or as a preventive measure against ailments. We determined the fatty acid compositions, particularly polyunsaturated fatty acid compositions, of Chlorella and Spirulina by capillary column-gas chromatography. The data obtained show that Spirulina contains unusually high levels of gamma-linolenic acid, an essential polyunsaturated fatty acid.

Bacterial Proteins↗
PubMed1970

The influence of spaceflight on Chlorella.

Three strains of Chlorella were investigated following spaceflight aboard Zond-5. Synchronized suspensions of Chlorella cells were grown in special containers. Each of these contained 0.1 X 10(6) cells. In the laboratory the strains LARG-1 and LARG-3 were examined microscopically. Nearly all the cells were in an autospore stage (94-98% for LARG-1 and 96-98% for LARG-3). Space effects on survival, mutation and cell development were studied. During the study of cell sporulation dynamics, the number of autospores resulting from the first sporulation was estimated. Percentage survival of the exposed cells is lower than that of the control. In the experimental material development of cells has been delayed and the percentage of visible mutations has been increased.

Chlorella↗