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PubMed1980

Evidence for HCO(3) Transport by the Blue-Green Alga (Cyanobacterium) Coccochloris peniocystis.

The possibility of HCO(3) (-) transport in the blue-green alga (cyanobacterium) Coccochloris peniocystis has been investigated. Coccochloris photosynthesized most rapidly in the pH range 8 to 10, where most of the inorganic C exists as HCO(3) (-). If photosynthesis used only CO(2) from the external solution the rate of photosynthesis would be limited by the rate of HCO(3) (-) dehydration to CO(2). Observed rates of photosynthesis at alkaline pH were as much as 48-fold higher than could be supported by spontaneous dehydration of HCO(3) (-) in the external solution. Assays for extracellular carbonic anhydrase were negative. The evidence strongly suggests that HCO(3) (-) was a direct C source for photosynthesis.Weakly buffered solutions became alkaline during photosynthesis with a one-to-one stoichiometry between OH(-) appearance in the medium and HCO(3) (-) initially added. Alkalization occurred only during photosynthesis and was blocked by 3-(3,4-dichlorophenyl)-1, 1-dimethylurea, diuron. It is suggested that HCO(3) (-) was transported into cells of Coccochloris in exchange for OH(-) produced as a result of HCO(3) (-) fixation in photosynthesis.The inorganic C concentration required to support a rate of photosynthesis of half the maximum rate (K(m)) was 6 micromolar at pH 8.0 or, in terms of available CO(2), a K(m) of 0.16 micromolar. This value is two orders of magnitude lower than reported K(m) values for the d-ribulose-1,5-bisphosphate carboxylase for blue-green algae. It is suggested that the putative HCO(3) (-) transport by Coccochloris serves to raise the CO(2) concentration around the carboxylase to levels high enough for effective fixation.

Journal Article↗

PubMed1994

Biotransformation of finasteride (MK-0906) by Selenastrum capricornutum (green algae).

Finasteride (MK-0906), a drug used for the treatment of benign prostatic hyperplasia, is a highly specific inhibitor of steroid 5 alpha-reductase, an enzyme that converts testosterone (T) to dihydrotestosterone (DHT) in animals and humans. In a study to evaluate the effect of finasteride on the growth of green alga, Selenastrum capricornutum, the parent drug was not detected by HPLC in the posttreatment (14 day) samples, suggesting complete biotransformation. Thermospray LC/MS, followed by NMR analysis, indicated that the major algal metabolite was 11 alpha-hydroxy-finasteride. This metabolite has negligible in vitro bioactivity against human prostatic 5 alpha-reductase; its potency is only 2% that of finasteride. The primary metabolite of finasteride produced by the green alga involved a biotransformation not previously observed in mammalian and human studies. The green alga effectively deactivates the drug, thereby mitigating any potential environmental impact.

5-alpha Reductase Inhibitors↗

PubMed2006

Toxicity assessment of 40 herbicides to the green alga Raphidocelis subcapitata.

The effects of 40 herbicides with nine modes of action on the green alga Raphidocelis subcapitata were studied by 96-h acute toxicity tests. Results showed that the EC50 of the herbicides with respect to the photosynthetic processes of R. subcapitata ranged from 0.0007 to 4.2286 mgL(-1). Photosynthesis was the process of the green alga most sensitive to the tested herbicides. The most toxic herbicides were atrazine, ametryme, simazine, prometryne, cyanazine, isoproturon, chlorotoluron, diuron, methabenzthiazuron, and paraquat. The EC50 of the protoporphyrinogen oxidase inhibitor oxadiargyl, which was the parameter least sensitive to the herbicides tested in this study, was 42.5 mgL(-1). The descending order of the average acute toxicity to R. subcapitata of herbicides with regard to the nine modes of action was as follows: photosynthetic process>cell division>lipid synthesis, acetyl-coenzyme A carboxylase>acetolactate synthase> 5-enolpyruvyl-shikimate-3-phosphate synthase, glutamine synthase, hormone synthesis>protoporphyrinogen oxidase.

Chlorophyta↗

PubMed1983

The nucleotide sequences of 5S rRNAs from a multicellular green alga, Ulva pertusa, and two brown algae, Eisenia bicyclis and Sargassum fulvellum.

The nucleotide sequences of 5S rRNA from a multicellular green alga Ulva pertusa, and multicellular brown algae Eisenia bicyclis and Sargassum fulvellum, have been determined. The 5S rRNA from Ulva is composed of 120 nucleotides, and those from Eisenia and Sargassum have 118 nucleotides. The nucleotide sequence of Ulva 5S rRNA is rather similar to 5S rRNAs from unicellular green algae and higher plants, while those of Eisenia and Sargassum 5S rRNAs are unique.

Animals↗

PubMed1996

Nuclear-encoded rDNA group I introns: origin and phylogenetic relationships of insertion site lineages in the green algae.

Group I introns are widespread in eukaryotic organelles and nuclear-encoded ribosomal DNAs (rDNAs). The green algae are particularly rich in rDNA group I introns. To better understand the origins and phylogenetic relationships of green algal nuclear-encoded small subunit rDNA group I introns, a secondary structure-based alignment was constructed with available intron sequences and 11 new subgroup ICI and three new subgroup IB3 intron sequences determined from members of the Trebouxiophyceae (common phycobiont components of lichen) and the Ulvophyceae. Phylogenetic analyses using a weighted maximum-parsimony method showed that most group I introns form distinct lineages defined by insertion sites within the SSU rDNA. The comparison of topologies defining the phylogenetic relationships of 12 members of the 1512 group I intron insertion site lineage (position relative to the E. coli SSU rDNA coding region) with that of the host cells (i.e., SSU rDNAs) that contain these introns provided insights into the possible origin, stability, loss, and lateral transfer of ICI group I introns. The phylogenetic data were consistent with a viral origin of the 1512 group I intron in the green algae. This intron appears to have originated, minimally, within the SSU rDNA of the common ancestor of the trebouxiophytes and has subsequently been vertically inherited within this algal lineage with loss of the intron in some taxa. The phylogenetic analyses also suggested that the 1512 intron was laterally transferred among later-diverging trebouxiophytes; these algal taxa may have coexisted in a developing lichen thallus, thus facilitating cell-to-cell contact and the lateral transfer. Comparison of available group I intron sequences from the nuclear-encoded SSU rDNA of phycobiont and mycobiont components of lichens demonstrated that these sequences have independent origins and are not the result of lateral transfer from one component to the other.

Base Sequence↗

PubMed2002

Phylogenetic analysis identifies the invertebrate pathogen Helicosporidium sp. as a green alga (Chlorophyta).

Historically, the invertebrate pathogens of the genus Helicosporidium were considered to be either protozoa or fungi, but the taxonomic position of this group has not been considered since 1931. Recently, a Helicosporidium sp., isolated from the blackfly Simulium jonesi Stone & Snoddy (Diptera: Simuliidae), has been amplified in the heterologous host Helicoverpa zea. Genomic DNA has been extracted from gradient-purified cysts. The 185, 28S and 5.8S regions of the Helicosporidium rDNA, as well as partial sequences of the actin and beta-tubulin genes, were amplified by PCR and sequenced. Comparative analysis of these nucleotide sequences was performed using neighbour-joining and maximum-parsimony methods. All inferred phylogenetic trees placed Helicosporidium sp. among the green algae (Chlorophyta), and this association was supported by bootstrap and parsimony jackknife values. Phylogenetic analysis focused on the green algae depicted Helicosporidium sp. as a close relative of Prototheca wickerhamii and Prototheca zopfii (Chlorophyta, Trebouxiophyceae), two achlorophylous, pathogenic green algae. On the basis of this phylogenetic analysis, Helicosporidium sp. is clearly neither a protist nor a fungus, but appears to be the first described algal invertebrate pathogen. These conclusions lead us to propose the transfer of the genus Helicosporidium to Chlorophyta, Trebouxiophyceae.

Actins↗

PubMed2003

Eyespot placement and assembly in the green alga Chlamydomonas.

The eyespot organelle of the green alga Chlamydomonas allows the cell to phototax toward (or away) from light to maximize the light intensity for photosynthesis and minimize photo-damage. At cytokinesis, the eyespot is resorbed at the cleavage furrow and two new eyespots form in the daughter cells 180 degrees from each other. The eyespots are positioned asymmetrically with respect to the microtubule cytoskeleton. Eyespots are assembled from all three chloroplast membranes and carotenoid-filled granules, which form a sandwich structure overlaid by the tightly apposed plasma membrane. This review describes (1) my interest in cellular asymmetry and organelle biology, (2) isolation of mutations that describe four genes governing eyespot placement and assembly, (3) the characterization of the EYE2 gene, which encodes a thioredoxin superfamily member, and (4) the characterization of the MIN1 gene, which is required for the layered organization of granules and membranes in the eyespot. BioEssays 25:410-416, 2003.

Algal Proteins↗

PubMed2002

Toxicity of 40 herbicides to the green alga Chlorella vulgaris.

The effects on the green alga Chlorella vulgaris of 40 herbicides in 19 different chemical structure classes and with 11 dissimilar modes of action were studied through 96-h acute toxicity tests. Experimental results indicated that the average acute toxicity of acetolactate synthase (ALS)-inhibiting herbicides to C. vulgaris was close to those of the acetyl-CoA carboxylase (ACCase)-inhibiting herbicides and the lipid synthesis-inhibiting protoporphyrinogen oxidase (Protox) inhibitor. Their acute toxicities were higher than those of the microtubule process inhibitor, mitotic process inhibitor, the glutamine synthase inhibitors, and 5-enolpyruvyl-shikimate-3-phosphate synthase (EPSP synthase) inhibitors. The acute toxicities of auxin herbicides to C. vulgaris were the lowest among all herbicides tested and that of the photosynthesis-inhibiting herbicides was the highest.

Chlorella↗

PubMed1999

Amino acid sequence, crystallization and structure determination of reduced and oxidized cytochrome c6 from the green alga Scenedesmus obliquus.

Cytochrome c6from the unicellular green alga Scenedesmus obliquus was sequenced, crystallized in its reduced and oxidized state and the three-dimensional structure of the protein in both redox states was determined by X-ray crystallography. Reduced cytochrome c6crystallized as a monomer in the space group P 21212, whereas the oxidized protein crystallized as a dimer in the space group P 3121. The structures were solved by molecular replacement and refined to 1. 9 and 2.0 A, respectively. Comparison of the structures of both redox states revealed only slight differences on the protein surface, whereas a distortion along the axis between the heme iron and its coordinating Met61 residue was observed. No redox-dependent movement of internal water molecules could be detected. The high degree of similarity of the surfaces and charge distributions of both redox states, as well as the dimerization of cytochrome c6as observed in the oxidized crystal, is discussed with respect to its biological relevance and its implications for the reaction mechanisms between cytochrome c6and its redox partners. The dimer of oxidized cytochrome c6may represent a molecular structure occurring in a binary complex with cytochrome b6f. This assembly might be required for the correct orientation of cytochrome c6with respect to its redox partner cytochrome b6f, facilitating the electron transfer within the complex. If the dimerization is not redox-dependent in vivo, the almost identical surfaces of both redox states do not support a long range differentiation between reduced and oxidized cyt c6, i.e. a random collision model for the formation of an electron transfer complex must be assumed.

Amino Acid Sequence↗

PubMed1977

Photosynthetic activity of diimidoester-modified cells, permeaplasts, and cell-free membrane fragments of the blue-green alga Anacystis nidulans.

On treating the blue green alga Anacystis nidulans with dimethylsuberimidate up to 70% of the free NH2 of the photosynthetic membrane is amidinated, and presumably inter- and intramolecular cross-links are established in the membrane proteins. Amidination destroys the ability of A. nidulans to photoreduce HCO3(-) but leaves the photochemical activities of Photosystems II and I nearly intact. With added electron acceptors, photosynthetic O2 evolution can be demonstrated both with permeable cells (permeaplasts) prepared by digestion of the cell wall of dimethylsuberimidate-reacted A. nidulans with lysozyme, as well as with heavy membrane particles (36 000 x g) prepared from dimethylsuberimidate-reacted cells. Permeaplasts prepared from dimethylsuberimidate-reacted cells resist damage in hypoosmotic medium, whereas those prepared from unreacted cells are induced to release C-phycocyanin. On the other hand, the former are inactivated more easily by heat stress than the latter. On this basis, it is concluded that cross-linking with dimethylsuberimidate confers functional instability to photosynthetic membranes.

Cell Membrane↗

PubMed1999

Purification and characterization of hydrogenase from the marine green alga, Chlorococcum littorale.

Hydrogenase from the marine green alga, Chlorococcum littorale, was purified 1485-fold, resulting in a specific activity for hydrogen evolution of 75.7 micromol/min/mg of protein at 25 degrees C, using reduced methyl viologen as an electron donor. The K(m) value for methyl viologen was 0.5 mM. The purity of the enzyme was judged by native PAGE. The molecular weight was estimated to be 55 kDa by SDS-PAGE, and 57 kDa by gel filtration. The optimum temperature and pH value for hydrogen evolution were 50 degrees C and 7.5, respectively. The partially purified hydrogenase catalyzed hydrogen evolution from ferredoxin that had been isolated from the same cells, but not from NADH or NADPH. The K(m) value for ferredoxin was 0.68 microM. The enzyme was extremely oxygen sensitive, losing over 95% of its activity upon exposure to air within minutes, even at 4 degrees C. Two peptide fragments were obtained from the hydrogenase protein digested enzymatically, and their amino acid sequences were determined. No significant homology was found to any other known sequences of hydrogenases.

Amino Acid Sequence↗

PubMed2002

Cloning and characterization of novel extensin-like cDNAs that are expressed during late somatic cell phase in the green alga Volvox carteri.

Asexual individuals of the green alga Volvox carteri consist of two cell types, somatic and reproductive cells. The somatic cells are terminally differentiated post-mitotic cells which undergo gradual senescence leading to cell death in every generation. To understand the gene expression programs associated with senescence of somatic cells, we cloned two cDNAs, LSG1 and LSG2, that are preferentially expressed during this late developmental stage. These two cDNAs were deduced to encode Pro-rich motifs characteristic of extensin proteins that are components of the extracellular matrix. LSG1 also resembled genes encoding plant pathogenesis-related protein 1 (PR-1), while LSG2 showed similarities with genes encoding matrix metalloproteinases, including a gamete lytic enzyme of Chlamydomonas. We also found that S9, one of the late somatic cDNAs previously cloned by Tam and Kirk (Dev. Biol. 145 (1991) 51), was deduced to encode a protein with a composition similar to LSG2. The expression of PR-1 and a matrix-metalloproteinase-encoding gene has been shown to be induced during senescence in higher plants. These results indicate that some of the late somatic genes in V. carteri are related to the senescence-associated genes in higher plants.

Amino Acid Sequence↗

PubMed1997

Identification of a copper-sensitive ascorbate peroxidase in the unicellular green alga Selenastrum capricornutum.

Extracts from the unicellular green alga Selenastrum capricornutum exhibit high superoxide dismutase activity, but only traces of catalase activity. The excess hydrogen peroxide (H2O2) generated by the superoxide dismutase in S. capricornutum may be degraded by a unique peroxidase. This peroxidase has a high specificity for ascorbate as its electron donor. The enzyme has an optimum pH at 8, is insensitive to cyanide and is inhibited by oxine. Addition of low concentrations of copper to algal cultures stimulates the peroxidase activity threefold. This enzymatic system could be used as a sensitive bioindicator for copper in fresh water.

Ascorbate Peroxidases↗

PubMed1971

Subunit structure of the phycobiliproteins of blue-green algae.

The phycobiliproteins of the blue-green algae Synechococcus sp. and Aphanocapsu sp. were characterized with respect to homogeneity, isoelectric point, and subunit composition. Each of the biliproteins consisted of two different noncovalently associated subunits, with molecular weights of about 20,000 and 16,000 for phycocyanin, 17,500 and 15,500 for allophycocyanin, and 22,000 and 20,000 for phycoerythrin. Covalently bound chromophore was associated with each subunit.

Animals↗

PubMed1979

Effect of Growth Temperature on the Lipid and Fatty Acid Composition, and the Dependence on Temperature of Light-induced Redox Reactions of Cytochrome f and of Light Energy Redistribution in the Thermophilic Blue-Green Alga Synechococcus lividus.

The thermophilic blue-green alga Synechococcus lividus was grown at 55 and 38 C. Arrhenius plots of the transient reduction of cytochrome during actinic illumination with light that excited both pigment systems revealed breaks near 43 and 26 C for cells grown at 55 C. In cells grown at 38 C these breaks occurred near 37 and 28 C, respectively. The shift from pigment state 1 to state 2 measured by fluorescence transients also showed characteristic breaks in the Arrhenius plots at 44 C for cells grown at 55 C and at 37 to 38 C and possibly at 25 C for cells grown at 38 C. The break points in the Arrhenius plots for the state shift as well as for the cytochrome f reduction are discussed in relation to phase transitions of thylakoid membrane lipids as studied by the temperature dependence of chlorophyll a fluorescence.The variations of fatty acid composition with growth temperature was also studied. When the growth temperature was lowered from 55 to 38 C, the amount of the saturated fatty acid 18:0 in the negatively charged lipids sulfoquinovosyl diglyceride and phosphatidyl glycerol decreased while the unsaturated fatty acids 18:1 and 16:1 increased. In mono- and digalactosyl diglycerides the saturated fatty acids 18:0 and 16:0 decreased and the unsaturated fatty acid 16:1 increased. In general there was an increase in the more fluid lipids in all of the lipid classes when the cells were grown at the lower temperature.

Journal Article↗

PubMed1983

Iron-sulfur centers and activities of the photosynthetic electron transport chain in iron-deficient cultures of the blue-green alga aphanocapsa.

Cultures of the blue-green alga, Aphanocapsa, were grown under iron-limiting conditions and changes in concentration of redox components of the photosynthetic electron transport chain, particularly iron-sulfur centers, were monitored by spectroscopic methods. A moderate iron depletion (1/10 of the normal concentration) had little effect on photosynthetic electron transport reactions and growth. Nevertheless, the amount of membrane-bound non-heme iron decreased sharply, and ferredoxin was nearly totally replaced by a flavin-containing protein, flavodoxin. Severe iron-deficiency (1/100 of the normal concentration) was accompanied by growth inhibition and decreased rates of photosynthetic electron flow. The Photosystem I reaction center was most affected by iron depletion as evidenced by a decrease in the amounts of iron-sulfur centers A, B, and X. However, formation of other redox proteins, even those that do not contain iron, was also inhibited by severe iron deficiency.

Journal Article↗

PubMed1990

Acclimation of Photosynthetic Light Reactions during Induction of Inorganic Carbon Accumulation in the Green Alga Chlamydomonas reinhardtii.

Cells of the unicellular green algae Chlamydomonas reinhardtii were grown in high dissolved inorganic carbon (DIC) concentrations (supplied with 50 milliliters per liter CO(2)[g]) and transferred to low DIC concentrations (supplied with </= 100 microliters per liter CO(2)[g]). Immediately after transfer from high to low DIC the emission of photosystem II related chlorophyll a fluorescence was substantially quenched. It is hypothesized that the suddenly induced inorganic carbon limitation of photosynthesis resulted in a phosphorylation of LHCII, leading to the subsequent state 1 to state 2 transition. After 2 hours of low-DIC acclimation, 77 K fluorescence measurements revealed an increase in the fluorescence emitted from photosystem I, due to direct excitation, suggesting a change in photosystem II/photosystem I stoichiometry or an increased light harvesting capacity of photosystem I. After 5 to 6 hours of acclimation a considerable increase in spillover from photosystem II to photosystem I was observed. These adjustments of the photosynthetic light reactions reached steady-state after about 12 hours of low DIC treatment. The quencher of fluorescence could be removed by 5 minutes of dark treatment followed by 5 minutes of weak light treatment, of any of four different light qualities. It is hypothesized that this restoration of fluorescence was due to a state 2 to state 1 transition in low-DIC acclimated cells. A decreased ratio of violaxanthin to zeaxanthin was also observed in 12 hour low DIC treated cells, compared with high DIC grown cells. This ratio was not coupled to the level of fluorescence quenching. The role of different processes during the induction of a DIC accumulating mechanism is discussed.

Journal Article↗

PubMed2006

Temperature- and pH-dependent accumulation of heat-shock proteins in the acidophilic green alga Chlamydomonas acidophila.

Chlamydomonas acidophila, a unicellular green alga, is a dominant phytoplankton species in acidic water bodies, facing severe environmental conditions such as low pH and high heavy metal concentrations. We examined the pH-, and temperature-dependent accumulation of heat-shock proteins in this alga to determine whether heat-shock proteins play a role in adaptation to their environment. Our results show increased heat-shock proteins accumulation at suboptimal pHs, which were not connected with any change in intracellular pH. In comparison to the mesophilic Chlamydomonas reinhardtii, the acidophilic species exhibited significantly higher accumulations of heat-shock proteins under control conditions, indicating an environmental adaptation of increased basal levels of heat-shock proteins. The results suggest that heat-shock proteins might play a role in the adaptation of C. acidophila, and possibly other acidophilic algae, to their extreme environment.

Adaptation, Physiological↗