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PubMed2004

Evolutionary trade-off between defence against grazing and competitive ability in a simple unicellular alga, Chlorella vulgaris.

Trade-offs between defence and other fitness components are expected in principle, and can have major qualitative impacts on ecological dynamics. Here we show that such a trade-off exists even in the simple unicellular alga Chlorella vulgaris. We grew algal populations for multiple generations in either the presence ('grazed algae') or absence ('non-grazed algae') of the grazing rotifer Brachionus calyciflorus, and then evaluated their defence and competitive abilities. Grazed algae were better defended, yielding rotifer growth rate 32% below that of animals fed non-grazed algae, but they also had diminished competitive ability, with a growth rate under nutrient-limiting conditions 28% below that of non-grazed algae. Grazed algae also had a smaller cell size and were more concentrated in carbon and nitrogen. Thus, C. vulgaris genotypes vary phenotypically in their position along a trade-off curve between defence against grazing and competitive ability. This genetic variation underlies rapid algal evolution that significantly alters the ecological predator-prey cycles between rotifers and algae.

Animals↗
PubMed1989

Mutual exclusion occurs in a Chlorella-like green alga inoculated with two viruses.

Progeny viruses resulting from dual inoculations with different and near-isogenic viruses of a Chlorella-like green alga were distinguished by immunoblotting. Plaques arising from single cells inoculated with two viruses usually contained only one of the viruses. Thus the viruses mutually exclude one another. In some combinations the ratio of viruses (as infective centres) recovered differed significantly from the input ratio.

Adhesiveness↗
PubMed1986

Estimation of the Mr of isocitrate lyase messenger RNA from Chlorella fusca.

The mRNA for the adaptive enzyme isocitrate lyase (ICL) from Chlorella fusca has been identified by fractionation of total poly(A)-containing RNA and in vitro translation followed by immune precipitation. The Mr of ICL mRNA was approximately 8.0 X 10(5), which is in good agreement with a previous estimate obtained by in vivo double-labelling.

Chlorella↗
PubMed1976

Inhibition of RNA synthesis in Chlorella pyrenoidosa and Bacillus megaterium by the pine-blight toxin, dothistromin.

Dosthistromin, an anthraquinone derivative produced by the pine-blight fungus, Dothistroma pini, inhibits the growth of Chlorella pyrenoidosa and Bacillus megaterium. At growth inhibitory concentrations, dothistromin strongly inhibits incorporation of [3H]uridine into RNA of both species. With B. megaterium, marked inhibition of [3H]uridine incorporation is apparent within 5 min of addition of dothistromin, but only a slight inhibition of [3H]thymidine incorporation into the DNA-containing fraction or of [14C]leucine incorporation into protein is detectable after 10 min.

Anthraquinones↗
PubMed1993

Intermolecular nitrogen transfer in the enzymic conversion of glutamate to delta-aminolevulinic acid by extracts of Chlorella vulgaris.

delta-Aminolevulinic acid (ALA), the universal biosynthetic precursor of tetrapyrrole pigments, is synthesized from glutamate in plants, algae, and many bacteria via a three-step process that begins with activation by ligation of glutamate to tRNA(Glu), followed by reduction to glutamate-1-semialdehyde (GSA) and conversion of GSA to ALA. The GSA aminotransferase step requires no substrate other than GSA. A previous study examined whether the aminotransferase reaction proceeds via intramolecular or intermolecular N transfer and concluded that the reaction catalyzed by Chlamydomonas extracts occurs via intermolecular N transfer (Y.-H.L. Mau and W.-Y. Wang [1988] Plant Physiol 86: 793-797). However, in that study the possibility was not excluded that the result was a consequence of N exchange among product ALA molecules during the incubation, rather than intermolecular N transfer during the conversion of GSA to ALA. Therefore, this question was reexamined in another species and with additional controls. A gel-filtered extract of Chlorella vulgaris cells was incubated with ATP, Mg2+, NADPH, tRNA, and a mixture of L-glutamate molecules, one-half of which were labeled with 15N and the other half with 13C at C-1. The ALA product was purified, derivatized, and analyzed by gas chromatography-mass spectrometry. A significant fraction of the ALA molecules was heavy by two mass units, indicating incorporation of both 15N and 13C. These results show that the N and C atoms of each ALA molecule were derived from different glutamate molecules. Control experiments indicated that the results could not be attributed to exchange of N atoms between glutamate or ALA molecules during the incubation. These results confirm the earlier conclusion that GSA is converted to ALA via intermolecular N transfer and extend the results to another species. The labeling results, combined with the results of kinetic and inhibitor studies, support a model for the GSA aminotransferase reaction in which a single molecule of GSA is converted to ALA via an enzyme-bound 4,5-diaminovaleric acid intermediate.

Amination↗
PubMed1989

Synthesis and degradation of nitrate reductase during the cell cycle of Chlorella sorokiniana.

Studies on the diurnal variations of nitrate reductase (NR) activity during the life cycle of synchronized Chlorella sorokiniana cells grown with a 7:5 light-dark cycle showed that the NADH:NR activity, as well as the NR partial activities NADH:cytochrome c reductase and reduced methyl viologen:NR, closely paralleled the appearance and disappearance of NR protein as shown by sodium dodecyl sulfate gel electrophoresis and immunoblots. Results of pulse-labeling experiments with [35S]methionine further confirmed that diurnal variations of the enzyme activities can be entirely accounted for by the concomitant synthesis and degradation of the NR protein.

Cell Cycle↗
PubMed2006

Temperature dependence of nitrate reductase in the psychrophilic unicellular alga Koliella antarctica and the mesophilic alga Chlorella sorokiniana.

Temperature responses of nitrate reductase (NR) were studied in the psychrophilic unicellular alga, Koliella antarctica, and in the mesophilic species, Chlorella sorokiniana. Enzymes from both species were purified to near homogeneity by Blue Sepharose (Pharmacia, Uppsala, Sweden) affinity chromatography and high-resolution anion-exchange chromatography (MonoQ; Pharmacia; Uppsala, Sweden). Both enzymes have a subunit molecular mass of 100 kDa, and K. antarctica NR has a native molecular mass of 367 kDa. NR from K. antarctica used both NADPH and NADH, whereas NR from C. sorokiniana used NADH only. Both NRs used reduced methyl viologen (MVH) or benzyl viologen (BVH). In crude extracts, maximal NADH and MVH-dependent activities of cryophilic NR were found at 15 and 35 degrees C, respectively, and retained 77 and 62% of maximal activity, respectively, at 10 degrees C. Maximal NADH and MVH-dependent activities of mesophilic NR, however, were found at 25 and 45 degrees C, respectively, with only 33 and 23% of maximal activities being retained at 10 degrees C. In presence of 2 microM flavin adenine dinucleotide (FAD), activities of cryophilic NADH:NR and mesophilic NADH:NR were stable up to 25 and 35 degrees C, respectively. Arrhenius plots constructed with cryophilic and mesophilic MVH:NR rate constants, in both presence or absence of FAD, showed break points at 15 and 25 degrees C, respectively. Essentially, similar results were obtained for purified enzymes and for activities measured in crude extracts. Factors by which the rate increases by raising temperature 10 degrees C (Q10) and apparent activation energy (E(a)) values for NADH and MVH activities measured in enzyme preparations without added FAD differed slightly from those measured with FAD. Overall thermal features of the NADH and MVH activities of the cryophilic NR, including optimal temperatures, heat inactivation (with/without added FAD) and break-point temperature in Arrhenius plots, are all shifted by about 10 degrees C towards lower temperatures than those of the mesophilic enzyme. Transfer of electrons from NADH to nitrate occurs via all three redox centres within NR molecule, whereas transfer from MVH requires Mo-pterin prosthetic group only; therefore, our results strongly suggest that structural modification(s) for cold adaptation affect thermodynamic properties of each of the functional domains within NR holoenzyme in equal measure.

Chlorella↗
PubMed1977

Characterization and partial purification of an inducible protein related to hexose proton cotransport of Chlorella vulgaris.

1. Cells of Chlorella vulgaris induced for hexose transport contain a membrane-bound protein component that is missing in non-induced cells. This was shown by double labelling experiments with [14C]phenylalanine and [3H]phenylalanine applying the method of Kolber and Stein [Nature (Lond) 209 (1966) 691]. The specific protein is completely absent from soluble fractions. 2. An enrichment of the double-labelled peak was observed in membrane fractions enriched in plasmalemma. The best purification was obtained when cell walls were purified; the residual membranes attached to the walls contained the transport protein with a 12-times-higher specific activity than the crude extract. 3. The transport protein had the characteristics of an intrinsic membrane protein. Its molecular weight was found to be 30 000 on sodium dodecylsulphate gels. The protein did not show sugar binding activity, however. 4. Induced cells lose their state of induction with a half life of about 4 h; 7 h after induction the double-labelled transport protein is no longer detectable.

Biological Transport, Active↗
PubMed2006

Composition of the sheath produced by the green alga Chlorella sorokiniana.

AIMS: To investigate the chemical characterization of the mucilage sheath produced by Chlorella sorokiniana. METHODS AND RESULTS: Algal mucilage sheath was hydrolysed with NaOH, containing EDTA. The purity of the hydrolysed sheath was determined by an ATP assay. The composition of polysaccharide in the sheath was investigated by high-performance anion-exchange chromatography with pulsed amperometric detection. Sucrose, galacturonic acid, xylitol, inositol, ribose, mannose, arabinose, galactose, rhamnose and fructose were detected in the sheath as sugar components. Magnesium was detected in the sheath as a divalent cation using inductively coupled argon plasma. The sheath matrix also contained protein. CONCLUSIONS: It appears that the sheath is composed of sugars and metals. Mucilage sheath contains many kinds of saccharides that are produced as photosynthetic metabolites and divalent cations that are contained in the culture medium. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report on chemical characterization of the sheath matrix produced by C. sorokiniana.

Algal Proteins↗
PubMed1993

Production of gamma-linolenic acid from the marine green alga Chlorella sp. NKG 042401.

gamma-Linolenic acid (GLA) production using a high GLA producing marine green alga, Chlorella sp. NKG 042401, was studied. GLA was presented in the galactolipid fraction (37.9%/total fatty acids). The effects of growth conditions on GLA production were studied. Optimum salinity for GLA production was 5 g l-1, at which salinity the highest cell concentration was achieved, resulting in a 1.6-fold increase in GLA productivity. Total fatty acid, however, was not drastically affected by change of salinity. Nitrogen starvation decreased the ratio of unsaturated fatty acids, and consequently GLA ratio in total fatty acid decreased. The urea adduct method was used to concentrate GLA from crude extract. As a result, after 5 sequential concentration procedures, GLA was concentrated 5-fold with a yield of 49%.

Chlorella↗
PubMed1999

Expression of eukaryotic plasma membrane transporter HUP1 from Chlorella kessleri in Escherichia coli.

To study the effect of sterols on the activity of the eukaryotic plasma membrane transporter, the hexose-proton symporter HUP1 from the unicellular alga Chlorella kessleri was expressed in Escherichia coli, a prokaryotic microorganism containing virtually no sterols. Under certain conditions, the recombinant protein was partially active in this prokaryotic organism. The heterologously produced HUP1p was purified from membrane fractions of E. coli and reconstituted in an in vitro system. The presence of ergosterol during solubilization, purification and reconstitution resulted in an increased activity of the reconstituted protein. Its activity, however, was 5-6 times lower as compared to the activity of HUP1p produced in Saccharomyces cerevisiae membranes and solubilized, purified, and reconstituted under the same conditions as above.

Biological Transport↗
PubMed1964

SIALIC ACID-CONTAINING GLYCOPEPTIDE FROM CHLORELLA.

A C(14)-labeled polyanion was isolated from Chlorella pyrenoidosa. It contained amino acids, sialic acid, and other carbohydrates, but no uronic acids, phosphate, or sulfate. It was stable to mild alkali, but released sialic acid upon mild acid treatment.

Amino Acids↗
PubMed1997

Hyaluronan synthase of chlorella virus PBCV-1.

Sequence analysis of the 330-kilobase genome of the virus PBCV-1 that infects a chlorella-like green algae revealed an open reading frame, A98R, with similarity to several hyaluronan synthases. Hyaluronan is an essential polysaccharide found in higher animals as well as in a few pathogenic bacteria. Expression of the A98R gene product in Escherichia coli indicated that the recombinant protein is an authentic hyaluronan synthase. A98R is expressed early in PBCV-1 infection and hyaluronan is produced in infected algae. These results demonstrate that a virus can encode an enzyme capable of synthesizing a carbohydrate polymer and that hyaluronan exists outside of animals and their pathogens.

Amino Acid Sequence↗
PubMed2000

A potassium channel protein encoded by chlorella virus PBCV-1.

The large chlorella virus PBCV-1, which contains double-stranded DNA (dsDNA), encodes a 94-codon open reading frame (ORF) that contains a motif resembling the signature sequence of the pore domain of potassium channel proteins. Phylogenetic analyses of the encoded protein, Kcv, indicate a previously unidentified type of potassium channel. The messenger RNA encoded by the ORF leads to functional expression of a potassium-selective conductance in Xenopus laevis oocytes. The channel blockers amantadine and barium, but not cesium, inhibit this conductance, in addition to virus plaque formation. Thus, PBCV-1 encodes the first known viral protein that functions as a potassium-selective channel and is essential in the virus life cycle.

Amantadine↗
PubMed2000

Increased growth of the microalga Chlorella vulgaris when coimmobilized and cocultured in alginate beads with the plant-growth-promoting bacterium Azospirillum brasilense.

Coimmobilization of the freshwater microalga Chlorella vulgaris and the plant-growth-promoting bacterium Azospirillum brasilense in small alginate beads resulted in a significantly increased growth of the microalga. Dry and fresh weight, total number of cells, size of the microalgal clusters (colonies) within the bead, number of microalgal cells per cluster, and the levels of microalgal pigments significantly increased. Light microscopy revealed that both microorganisms colonized the same cavities inside the beads, though the microalgae tended to concentrate in the more aerated periphery while the bacteria colonized the entire bead. The effect of indole-3-acetic acid addition to microalgal culture prior to immobilization of microorganisms in alginate beads partially imitated the effect of A. brasilense. We propose that coimmobilization of microalgae and plant-growth-promoting bacteria is an effective means of increasing microalgal populations within confined environments.

Alginates↗
PubMed2002

Biotransformation and bioconcentration of steroid estrogens by Chlorella vulgaris.

The biotransformation and bioconcentration of natural and synthetic steroid estrogens by Chlorella vulgaris were investigated by using batch-shaking experiments with incubation for 48 h in the light or dark. Estradiol and estrone were interconvertible in both light and dark conditions; however, this biotransformation showed a preference for estrone. In the light, 50% estradiol was further metabolized to an unknown product. Apart from biotransformation, estrone, as well as hydroxyestrone, estriol, and ethinylestradiol, was relatively stable in the algal culture, whereas estradiol valerate was hydrolyzed to estradiol and then to estrone within 3 h of incubation. All of the tested estrogens exhibited a degree of partitioning to C. vulgaris; however, the concentrations of estriol, hydroxyestrone, ethinylestradiol, and estradiol valerate were always below the quantification limits. For estradiol and estrone, the partitioning of these estrogens in the algal extracts to the filtrates was <6% of the total amount present. The average concentration factor for estrone was ca. 27; however, the concentration factor for estradiol was not reported since no equilibrium was reached between the aqueous solution and that within the cells due to continuing biotransformation.

Chlorella↗
PubMed1962

Light-limited growth of Chlorella in continuous cultures.

An analytical model of a continuously fed, completely mixed Chlorella culture in which light is the factor limiting growth is presented. The conclusions from the theory are that in a culture of this type the population density is directly proportional to the retention time and the production rate is independent of retention time. Experimental data are presented to verify the theoretical conclusions.

Chlorella↗
PubMed1962

Carbon dioxide-limited growth of Chlorella in continuous cultures.

The original mathematical model of microbial growth in the Chemostat is modified to describe continuous cultures in which the limiting nutrient is supplied at a rate independent of the dilution rate. The application of this model to continuous Chlorella cultures in which CO(2) is the factor limiting growth is discussed. The conclusions from the model are: (i) at a constant rate of CO(2) supply, the equilibrium population density is directly proportional to the retention time; and (ii) the production rate is directly proportional to the rate of CO(2) supply. Experimental data are presented to verify the theoretical conclusions.

Carbon Dioxide↗