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PubMed2001

Phylogenetic relationships among algae based on complete large-subunit rRNA sequences.

The complete or nearly complete large-subunit rRNA (LSU rRNA) sequences were determined for representatives of several algal groups such as the chlorarachniophytes, cryptomonads, haptophytes, bacillariophytes, dictyochophytes and pelagophytes. Our aim was to study the phylogenetic position and relationships of the different groups of algae, and in particular to study the relationships among the different classes of heterokont algae. In LSU rRNA phylogenies, the chlorarachniophytes, cryptomonads and haptophytes seem to form independent evolutionary lineages, for which a specific relationship with any of the other eukaryotic taxa cannot be demonstrated. This is in accordance with phylogenies inferred on the basis of the small-subunit rRNA (SSU rRNA). Regarding the heterokont algae, which form a well-supported monophyletic lineage on the basis of LSU rRNA, resolution between the different classes could be improved by combining the SSU and LSU rRNA data. Based on a concatenated alignment of both molecules, the phaeophytes and the xanthophytes are sister taxa, as well as the pelagophytes and the dictyochophytes, and the chrysophytes and the eustigmatophytes. All these sister group relationships are highly supported by bootstrap analysis and by different methods of tree construction.

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↗
PubMed2002

Stable chloroplast transformation of the unicellular red alga Porphyridium species.

Red algae are extremely attractive for biotechnology because they synthesize accessory photosynthetic pigments (phycobilins and carotenoids), unsaturated fatty acids, and unique cell wall sulfated polysaccharides. We report a high-efficiency chloroplast transformation system for the unicellular red microalga Porphyridium sp. This is the first genetic transformation system for Rhodophytes and is based on use of a mutant form of the gene encoding acetohydroxyacid synthase [AHAS(W492S)] as a dominant selectable marker. AHAS is the target enzyme of the herbicide sulfometuron methyl, which effectively inhibits growth of bacteria, fungi, plants, and algae. Biolistic transformation of synchronized Porphyridium sp. cells with the mutant AHAS(W492S) gene that confers herbicide resistance gave a high frequency of sulfomethuron methyl-resistant colonies. The mutant AHAS gene integrated into the chloroplast genome by homologous recombination. This system paves the way for expression of foreign genes in red algae and has important biotechnological implications.

Acetolactate Synthase↗
PubMed1997

Photoregulation of Chloroplast Gene Transcription in the Chromophytic Alga Heterosigma carterae.

Light acts as a complex regulator of cellular development and gene expression in photoautotrophs. Although light signals are highly effective in controlling cellular division and chloroplast biogenesis in the toxic marine alga Heterosigma carterae, their influence on gene expression has not been well characterized. To address this need cultures of H. carterae synchronized by an alternating light-dark regime were sampled through 12 h of light and 12 h of dark to characterize cell division, chloroplast complement, and chloroplast RNA abundance. These studies have identified a unimodal pattern of chloroplast transcriptional activity for a suite of cellular and photosynthetic genes. To determine the alga's response to a change in photoperiod, 12-h light/12-h dark-synchronized cultures were transferred to constant light and then periodically sampled. Although cellular and chloroplast division cycles remained synchronized in constant conditions for 24 h, the transcriptional apparatus responded by increasing ctRNA abundance within 45 min of the change in photoperiod. However, the ability of the alga to mount this rapid transcriptional response was limited to the first 2 h of the putative dark period. Thus, the chloroplast transcriptional apparatus of H. carterae may initiate a rapid, temporally gated response to a change in photoperiod that is independent of ongoing light-entrained cellular and chloroplast division cycles.

Journal Article↗
PubMed1966

Dark and photometabolism of sugars by a blue green alga: Tolypothrix tenuis.

The carbohydrate metabolism of the autotrophically grown blue-green alga, Tolypothrix tenuis, was studied. The alga respires glucose, fructose, galactose, and ribose. About 60% of the glucose consumed is converted by starved cells into a glucose polysaccharide. Glucose uptake and O(2) consumption are not inhibited by 0.01 m arsenite or by 0.005 m iodoacetamide. The distribution of (14)C in the polysaccharide glucose was established after feeding of glucose-1-(14)C, -2-(14)C, -6-(14)C, ribose-1-(14)C, and fructose-6-(14)C. Randomization of isotope between the 2 halves of the glucose from polysaccharide is limited when the experiments are carried out in the dark. After an extended incubation glucose-2-(14)C yields a glucose molecule with isotope labeled approximately equal in C-1, C-2 and C-3. When the labeled glucoses were fed at a light intensity of compensation point, and in the presence of carbon dioxide, a greater degree of randomization of isotope occurred. The enhanced randomization of isotope is thought to result from an additional supply of triose phosphates as a result of photosynthesis which creates an environment favorable to the reversal of the glycolytic reactions.To account for the labeling patterns and the resistance of respiration to the inhibitors, it is proposed that the oxidative pentose phosphate cycle is the major pathway of carbohydrate breakdown in this alga.

Carbohydrate Metabolism↗
PubMed1967

Changes in Chlorophyll a/b Ratio and Products of CO(2) Fixation by Algae Grown in Blue or Red Light.

Chlamydomonas and Chlorella were grown for 10 days in white light. 955 muw/cm(2) blue light (400-500 mmu) or 685 muw/cm(2) red light (above 600 mmu). Rates of growth in blue or red light were initially slow, but increased over a period of 5 days until normal growth rates were reestablished. During this adaptation period in blue light, total chlorophyll per volume of algae increased 20% while the chlorophyll a/b ratio decreased. In red light no change was observed in the total amount of chlorophyll or in the chlorophyll a/b ratio. After adaptation to growth in blue light and upon exposure to (14)CO(2) with either blue or white light for 3 to 10 minutes, 30 to 36% of the total soluble fixed (14)C accumulated in glycolate-(14)C which was the major product. However, with 1 minute experiments, it was shown that phosphate esters of the photosynthetic carbon cycle were labeled before the glycolate. Glycolate accumulation by algae grown in blue light occurred even at low light intensity. After growth of the algae in red light, (14)C accumulated in malate, aspartate, glutamate and alanine, whereas glycolate contained less than 3% of the soluble (14)C fraction.

Journal Article↗
PubMed1969

Action Spectra for Photosystems I and II in Formaldehyde Fixed Algae.

Action spectra were obtained for photosystems I and II in chemically fixed algal cells and for photosystem I in unfixed lysozyme treated cells. Untreated algal cells yielded neither of the 2 light reactions with the reaction mixtures used. The action spectra for photosystem I in the blue-green alga Anacystis nidulans and red alga Porphyridium cruentum follow the absorption spectrum of chlorophyll a with a small peak in the region of the accessory pigments. In the green alga Chlorella pyrenoidosa the photosystem I action spectrum follows the absorption spectrum of chlorophyll a. Photosystem II action spectra in A. nidulans and P. cruentum follow the absorption spectra of the accessory pigments while that in C. pyrenoidosa is shifted slightly toward the blue spectral region. These results provide additional evidence that formaldehyde fixed cells are valid models for studying the light reactions of photosynthesis.

Journal Article↗
PubMed1972

The Gas Exchange of Hydrogen-adapted Algae as Followed by Mass Spectrometry.

A mass spectrometer inlet and an oxygen electrode in the same vessel allowed the continuous recording of the gases exchanged (H(2), CO(2), O(2)) by hydrogenase-containing anaerobically adapted Scenedesmus obliquus strain D(3) (Gaffron) and Chlorella fusca Shihira et Krauss (= pyrenoidosa) 211-15. A light intensity which produces more photosynthetic oxygen than the cells can re-reduce to water leads to de-adaptation and the substitution of normal photosynthesis for photoreduction. The sequence of these metabolic events was recorded in a matter of a few minutes. Upon exposure of these adapted algae to light, an evolution of hydrogen lasting up to 60 seconds preceded any other light-dependent gas exchange. In the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea, this initial hydrogen production was inhibited approximately 50%, pointing to a contribution of electrons by photosystem II. At very low hydrogen tensions (0.1 microliter per milliliter), a balance between light-induced production and absorption of hydrogen was observed in normal, unpoisoned algae. Addition of either glucose or inhibitors of phosphorylation increased the release of hydrogen in the light very considerably. When the light was turned off the algae consumed the remaining amount of hydrogen, only to release it again upon illumination. This reversible hydrogen exchange persisted even when any concomitant carbon dioxide exchange had been abolished.

Journal Article↗
PubMed1973

Formation of carbon monoxide and bile pigment in red and blue-green algae.

Five blue-green and one red algal species produced carbon monoxide during photosynthetic growth. The blue-green algae synthesized CO and phycocyanobilin in equimolar quantities at identical rates. The red alga, Porphyridium cruentum, incorporated Delta-aminolevulinic acid-5-(14)C into phycoerythrobilin and CO. The ratio of the specific radioactivity of phycoerythrobilin to that of CO, and the kinetics and stoichiometry of phycocyanobilin and CO formation suggest that linear tetrapyrroles in plants are derived by the porphyrin pathway via the intermediate formation of heme. The similarity between bile pigment production in algae and in mammalian systems is discussed.

Journal Article↗
PubMed1975

Oxygen Isotope Fractionation during Photosynthesis in a Blue-Green and a Green Alga.

Oxygen isotope fractionation ((18)O/(16)O) at the natural abundance level has been measured during photosynthesis of a blue-green and a green alga. When sufficient attention is paid to removal of contaminating air O(2) before and during the experiments, then the photosynthetic O(2) evolved, as compared to the water O(2), had an average difference of -0.36% for a blue-green alga and -0.80% for a green alga. These experiments suggest that there is no reason to invoke an inverse isotope effect in photosynthesis as part of the explanation for the (18)O enrichment in atmospheric O(2) relative to O(2) in oceanic waters. In addition, in an indirect way, the experiments also support the argument that the bulk of O(2) evolved during photosynthesis comes from water. A 10% contribution of O(2) arising from CO(2) would have been detectable in the present work.

Journal Article↗
PubMed1979

Measurement of carbon dioxide compensation points of freshwater algae.

A technique is described for the measurement of total dissolved inorganic carbon by acid release as CO(2) followed by its conversion to methane and detection by flame ionization in a modified gas chromatograph. This method was used to determine the dissolved inorganic carbon concentration reached at compensation point when algae were allowed to photosynthesize in a closed system in a buffer at known pH, and the CO(2) compensation point was calculated from this concentration. The CO(2) compensation points of 16 freshwater algae were measured at acid and alkaline pH in air-saturated medium: at acid pH the CO(2) compensation points ranged from 4.8 to 41.5 microliters per liter while at alkaline pH they ranged from 0.2 to 7.2 microliters per liter. Removal of O(2) from the medium caused a slight lowering of compensation point at acid pH but had little effect at alkaline pH. These low, O(2)-insensitive compensation points are characteristic of C(4) plants. It is suggested that these low CO(2) compensation points are maintained by an active bicarbonate uptake by algae especially at alkaline pH.

Journal Article↗
PubMed1983

Relation between the Light-Harvesting Chlorophyll a-Protein Complex LHCPa and Photosystem I in the Alga Chlamydobotrys stellata.

The light-harvesting chlorophyll protein system of the alga Chlamydobotrys stellata consists of an as yet uncharacterized algal chlorophyll a-protein, called LHCPa, and a common photosystem II-related chlorophyll a/b-protein, called LHCPb (Brandt, Kaiser-Jarry, Wiessner 1982 Biochim Biophys Acta 679: 404-409). For further characterization, this LHCPa was isolated from the organism by polyacrylamide isoelectrofocusing and reelectrophoresis. It contains only chlorophyll a and has only one apoprotein (32,000 daltons). When separated from autotrophically grown cells, its absorption peak is at 674 nm and its isoelectric point at 5.3. Photoheterotrophic cultivation of the algae shifts the absorption maximum of LHCPa to 679 nm and its isoelectric point to 4.8. This LHCPa is a component of photosystem I particles. In relation to the total chlorophyll a content, the amount of LHCPa is low in autotrophic algae, but increases under photoheterotrophic growth conditions, where the organisms do not have the ability to assimilate CO(2) photosynthetically.

Journal Article↗
PubMed1983

A New Mechanism for Adaptation to Changes in Light Intensity and Quality in the Red Alga Porphyra perforata: III. Fluorescence Transients in the Presence of 3-(3,4-Dichlorophenyl)-1,1-dimethylurea.

In the red alga Porphyra perforata, the level of chlorophyll fluorescence in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) decreased during illumination of the thallus. The results showed that: (a) this decay was related to the photooxidative activity of photosystem I; (b) Q, the primary electron acceptor of photosystem II, became oxidized during the decay of the fluorescence; (c) reagents which inhibit the back reaction of photosystem II inhibited the decay.From these results, it is suggested that, when conditions in the chloroplasts of this red alga become too oxidative, excess light energy can be converted to heat as a result of an accelerated back reaction of photosystem II. This may be one of the mechanisms by which this alga can cope with the high salt and high light conditions that can occur in its natural habitat.

Journal Article↗
PubMed1987

Photosystem I-Mediated Regulation of Water Splitting in the Red Alga, Porphyra sanjuanensis.

The marine red alga, Porphyra sanjuanensis is found mainly in the high intertidal zone and at low tide subject to frequent and extreme water stress, often accompanied by high temperatures and light intensities. Such exposures can lead to severe desiccation which is accompanied by the progressive loss of photosynthetic activity. Even following the loss of more than 90% of the thallus water content the alga recovers rapidly when returned to seawater. This stress-induced, reversible inactivation of photosynthesis is believed to be a protective adaptation which prevents photodamage to the exposed alga. Effects of light, inhibitors of water splitting, and electron donors to PSI on variable fluorescence and water splitting suggest that activity of the oxygen evolving complex is regulated by the PSI-driven reduction of a component of intersystem electron transport.

Journal Article↗
PubMed1989

Analysis of Chromophytic and Rhodophytic Ribulose-1,5-Bisphosphate Carboxylase Indicates Extensive Structural and Functional Similarities among Evolutionarily Diverse Algae.

Ribulose-1,5-bisphosphate carboxylase (Rubisco) from the algae Olisthodiscus luteus (chromophyte) and Griffithsia pacifica (rhodophyte) are remarkably similar to each other. However, both enzymes differ significantly in the structure and function when compared to Rubisco from green algae and land plants. Analysis of purified Rubisco from O. luteus and G. pacifica indicates that the size of the holoenzyme and stoichiometry of the 55 and 15 kilodalton subunit polypeptides are approximately 550 kilodaltons and eight:eight for both algae. Antigenic determinants are highly conserved between the O. luteus and G. pacifica enzymes and differ from those of the spinach subunit polypeptides. Sequence similarity between the two algal large subunits has been further confirmed by one-dimensional peptide mapping. Substrate ribulose bisphosphate has no effect on the rate of CO(2)/Mg(2+) activation of O. luteus and G. pacifica enzymes which contrasts to the extensive inhibition of spinach Rubisco activation at similar concentrations of this compound. In addition, the Michaelis constant for CO(2) and the inhibition constant for 6-phosphogluconate are similar for the O. luteus and G. pacifica catalyzed carboxylation reaction. Both values are intermediate to those observed for the tight binding spinach enzyme and weak binding prokaryotic (Rhodospirillum rubrum) enzyme. The biochemical similarities documented between O. luteus and G. pacifica may be due to a common evolutionary origin on the chromophytic and rhodophytic chloroplast but could also result from the fact that both subunit polypeptides are chloroplast DNA encoded in these algal taxa.

Journal Article↗
PubMed1990

Codon usage in higher plants, green algae, and cyanobacteria.

Codon usage is the selective and nonrandom use of synonymous codons by an organism to encode the amino acids in the genes for its proteins. During the last few years, a large number of plant genes have been cloned and sequenced, which now permits a meaningful comparison of codon usage in higher plants, algae, and cyanobacteria. For the nuclear and organellar genes of these organisms, a small set of preferred codons are used for encoding proteins. Codon usage is different for each genome type with the variation mainly occurring in choices between codons ending in cytidine (C) or guanosine (G) versus those ending in adenosine (A) or uridine (U). For organellar genomes, chloroplastic and mitochrondrial proteins are encoded mainly with codons ending in A or U. In most cyanobacteria and the nuclei of green algae, proteins are encoded preferentially with codons ending in C or G. Although only a few nuclear genes of higher plants have been sequenced, a clear distinction between Magnoliopsida (dicot) and Liliopsida (monocot) codon usage is evident. Dicot genes use a set of 44 preferred codons with a slight preference for codons ending in A or U. Monocot codon usage is more restricted with an average of 38 codons preferred, which are predominantly those ending in C or G. But two classes of genes can be recognized in monocots. One set of monocot genes uses codons similar to those in dicots, while the other genes are highly biased toward codons ending in C or G with a pattern similar to nuclear genes of green algae. Codon usage is discussed in relation to evolution of plants and prospects for intergenic transfer of particular genes.

Journal Article↗
PubMed1990

Phycobilisome Heterogeneity in the Red Alga Porphyra umbilicalis.

Phycobilisomes were isolated from Rhodophyceae brought from the field (Porphyra umbilicalis) or grown in culture under laboratory conditions (Antithamnion glanduliferum). In P. umbilicalis two kinds of well-coupled (ellipsoidal and hemidiscoidal) phycobilisomes were detected, in contrast to A. glanduliferum cultured algae in which only one kind of well-coupled, ellipsoidaltype phycobilisome appeared. The new phycobilisome-type particle detected in P. umbilicalis is characterized by an impoverishment in R-phycoerythrin and by sedimentation at lower density. The comparison between both phycobilisomes of P. umbilicalis allows determination of the presence of one colorless linker polypeptide (30 kilodaltons) associated with R-phycocyanin and allophycocyanin and two (40 and 38 kilodaltons) associated to R-phycoerythrin. The percentage of linker polypeptides associated with this pigment is low in the new phycobilisome-like particle detected. This suggests that part of the R-phycoerythrin is less strongly bound to the phycobilisome than the other pigments. This feature could probably explain the existence of two kinds of phycobilisomes as intermediary steps of phycobilisome organization in algae exposed to rapid changes in environmental factors. In contrast, algae growing in culture and adapted to specific conditions do not present intermediary organization steps. Polypeptide composition and identification are given for this phycobilisome-like particle.

Journal Article↗
PubMed1990

Anaerobic Metabolism in the N-Limited Green Alga Selenastrum minutum: I. Regulation of Carbon Metabolism and Succinate as a Fermentation Product.

The onset of anaerobiosis in darkened, N-limited cells of the green alga Selenastrum minutum (Naeg.) Collins elicited the following metabolic responses. There was a rapid decrease in energy charge from 0.85 to a stable lower value of 0.6 accompanied by rapid increases in pyruvate/phosphoenolpyruvate and fructose-1,6-bisphosphate/fructose-6-phosphate ratios indicating activation of pyruvate kinase and 6-phosphofructokinase, respectively. There was also a large increase in fructose-2,6-bisphosphate, which, since this alga lacks pyrophosphate dependent 6-phosphofructokinase, can be inferred to inhibit gluconeogenic fructose-1,6-bisphosphatase activity. These changes resulted in an approximately twofold increase in the rate of starch breakdown indicating a Pasteur effect. The Pasteur effect was accompanied by accumulation of d-lactate, ethanol and succinate as fermentation end-products, but not malate. Accumulation of succinate was facilitated by reductive carbon metabolism by a partial TCA cycle (GC Vanlerberghe, AK Horsey, HG Weger, DH Turpin [1989] Plant Physiol 91: 1551-1557). An initial stoichiometric decline in aspartate and increases in succinate and alanine suggests that aspartate catabolism provides an initial source of carbon for reduction to succinate under anoxic conditions. These observations allow us to develop a model for the regulation of anaerobic carbon metabolism and a model for short-term and long-term strategies for succinate accumulation in a green alga.

Journal Article↗