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PubMed2001

Chemical defenses of the sacoglossan mollusk Elysia rufescens and its host Alga bryopsis sp.

Sacoglossans are a group of opisthobranch mollusks that have been the source of numerous secondary metabolites; however, there are few examples where a defensive ecological role for these compounds has been demonstrated experimentally. We investigated the deterrent properties of the sacoglossan Elysia rufescens and its food alga Bryopsis sp. against natural fish predators. Bryopsis sp. produces kahalalide F, a major depsipeptide that is accumulated by the sacoglossan and that shows in vitro cytotoxicity against several cancer cell lines. Our data show that both Bryopsis sp. and Elysia rufescens are chemically protected against fish predators, as indicated by the deterrent properties of their extracts at naturally occurring concentrations. Following bioassay-guided fractionation, we observed that the antipredatory compounds of Bryopsis sp. were present in the butanol and chloroform fractions, both containing the depsipeptide kahalalide F. Antipredatory compounds of Elysia rufescens were exclusively present in the dichloromethane fraction. Further bioassay-guided fractionation led to the isolation of kahalalide F as the only compound responsible for the deterrent properties of the sacoglossan. Our data show that kahalalide F protects both Brvopsis sp. and Elysia rufescens from fish predation. This is the first report of a diet-derived depsipeptide used as a chemical defense in a sacoglossan.

Adaptation, Physiological↗
PubMed2001

Ligation-mediated suppression-PCR as a powerful tool to analyse nuclear gene sequences in the green alga Chlamydomonas reinhardtii.

To improve the analysis of unknown flanking DNA sequences adjacent to known sequences in nuclear genomes of photoautotrophic eukaryotic organisms, we established the technique of ligation-mediated suppression-PCR (LMS-PCR) in the green alga Chlamydomonas reinhardtii for (1) walking from a specific nuclear insertion fragment of random knockout mutants into the unknown flanking DNA sequence to identify and analyse disrupted genomic DNA regions and for (2) walking from highly conserved DNA regions derived from known gene iso-forms into flanking DNA sequences to identify new members of protein families. The feasibility of LMS-PCR for these applications was successfully demonstrated in two different approaches. The first resulted in the identification of a genomic DNA fragment flanking a nuclear insertion vector in a random knockout mutant whose phenotype was characterised by its inability to perform functional LHC state transitions. The second approach targeted the cab gene family. An oligonucleotide of a cabII gene, derived from a highly conserved region, was used to identify potential cab gene regions in the nuclear genome of Chlamydomonas. LMS-PCR combined with 3' rapid amplification of cDNA ends (3' RACE) and a PCR-based screening of a cDNA library resulted in the identification of the new cabII gene lhcb4. Both results clearly indicate that LMS-PCR is a powerful tool for the identification of flanking DNA sequences in the nuclear genome of Chlamydomonas reinhardtii.

Journal Article↗
PubMed2002

A new voltammetric method for the simultaneous monitoring of heavy metals in sea water, sediments, algae and clams: application to the Goro Bay ecosystem.

Arsenic(III), selenium(IV), copper(II), lead(II), cadmium(II), zinc(II) have been determined in sea water, sediments, algae and clams by differential pulse cathodic (DPCSV) and anodic (DPASV) stripping voltammetry. The voltammetric measurements are carried out using a conventional three-electrode cell and the ammonia-ammonium chloride buffer pH 9.2 as supporting electrolyte. The analytical procedure has been verified by the analysis of the standard reference materials (Estuarine Sediment BCR- CRM 277, Ulva Lactuca BCR-CRM 279 and Mussel Tissue BCR-CRM 278). The precision and the accuracy are less than 5%. This procedure is utilized for the monitoring of heavy metals in the Po river mouth area (Italy).

Animals↗
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↗
PubMed2002

Use of serially coupled capillary columns with different polarity of stationary phases for the separation of the natural complex volatile mixture of the marine red alga Corallina elongata.

Separation of a complex of natural volatile compounds using serially coupled capillary columns with different polarity of stationary phases by gas chromatography-mass spectrometry from the medicinal marine red alga Corallina elongata is reported. Nearly 200 hydrocarbons, halogen compounds, fatty acids, and other metabolites were found. Using this gas chromatography procedure we demonstrate the successful separation of different volatile organic compounds.

Adsorption↗
PubMed2003

A thylakoidal processing peptidase from the heterokont alga Heterosigma akashiwo.

Heterokont algae such as diatoms, brown seaweeds and the raphidophyte Heterosigma akashiwo acquired their chloroplasts via a secondary endosymbiosis involving a red algal endosymbiont and a eukaryote host, resulting in chloroplasts surrounded by four membranes rather than two. The precursor of a nuclear-encoded thylakoid lumen protein, PsbO, from Heterosigma has a presequence composed of a typical ER signal peptide followed by putative stromal and thylakoid targeting domains. A processing enzyme associated with Heterosigma thylakoids cleaved the presequence (with or without the ER signal sequence) in a single step, giving a product of the size of the mature protein. Its sensitivity to a penem inhibitor and insensitivity to other protease inhibitors suggest that it is a member of the Type I signal peptidase family. Furthermore the Heterosigma enzyme appeared to have similar substrate specificity to the pea thylakoidal processing peptidase.

Algal Proteins↗
PubMed2003

Light induction of carotenoid biosynthesis genes in the green alga Haematococcus pluvialis: regulation by photosynthetic redox control.

The unicellular green alga Haematococcus pluvialis accumulates large amounts of the red ketocarotenoid astaxanthin when exposed to various stress situations such as salt stress and high light intensities. Here, the light regulation of Haematococcus carotenoid biosynthesis was examined. Isolation and characterization of the lycopene beta cyclase gene involved in carotenoid biosynthesis was carried out using a functional complementation approach. Subsequently, gene expression of lycopene cyclase, phytoene synthase, phytoene desaturase and carotenoid hydroxylase was analysed in green flagellate cells. All four genes revealed higher transcript levels in response to increased illumination. Not only the induction of astaxanthin biosynthesis but also carotenoid gene expression was found to be correlated with the redox state of the photosynthetic electron transport. In accordance with this result, increased transcript levels for carotenoid biosynthesis genes were detected under both blue and red light conditions. The application of different inhibitors of the photosynthetic electron flow indicated that the photosynthetic plastoquinone pool functions as the redox sensor for the up-regulation of carotenoid biosynthesis genes. These results suggested that in Haematococcus not only the specific astaxanthin pathway but also general carotenoid biosynthesis is subject to photosynthetic redox control.

Amino Acid Sequence↗
PubMed2003

Class XIII myosins from the green alga Acetabularia: driving force in organelle transport and tip growth?

The green alga Acetabularia cliftonii (Dasycladales) contains at least two myosin genes, which already have been assigned class XIII of the myosin superfamily (Cope et al., 1996, Structure 4: 969-987). Here we report a complete analysis of their gene structure and their corresponding transcripts Aclmyo1 and Aclmyo2. Despite promising Northern blot data no evidence for alternative splicing could be found. Dissecting the primary structure at complementary deoxyribonucleic acid (cDNA) level we found a myosin typical organization in head, neck and variable tail region. Most striking is the extremely short tail region of Aclmyo1 with only 18 residues and the maximum number of 7 IQ motifs in Aclmyo2. Probing Acetabularia protein extracts with an antibody raised to a synthetic peptide derived from the amino terminal region in Alcmyo1 showed cross-reactivity to a polypeptide with a molecular mass of approximately 100 kD. This corresponds to the predicted molecular weight of Aclmyo1, which is 106 kD as deduced from the amino acid sequence. Additionally, the same cross-reactive protein is capable of binding F-actin as indicated by a co-sedimentation assay. Confocal laser scanning microscopy with raised antibody revealed co-localization with organelles, the budding region of lateral whorls and the cell apex suggesting involvement of putative Acetabularia myosin in organelle transport and tip growth.

3' Untranslated Regions↗
PubMed2003

Growth and photosynthesis limitation of marine red tide alga Skeletonema costatum by low concentrations of Zn2+.

The specific growth rate, cell final yields and extracellar carbonic anhydrase activity of the red tide alga Skeletonema costatum increased with increasing concentrations of Zn2+ from 0 to 12 pM, but decreased when Zn2+ was over 24 pM. However, cells grown under high concentrations of Zn2+ had higher activities of intracellular carbonic anhydrase than those grown under low concentrations of Zn2+. Chlorophyll a-specific light-saturated photosynthetic rate (P(Chla)), dark respiration rate (R(chla)) and apparent photosynthetic efficiency (alpha(chla)) significantly increased with increasing concentrations of Zn2+ from 0 to 3 pM, but decreased when increasing concentrations of Zn2+ from 3 to 66 pM. Photorespiration is the lowest when cells cultured in 3 pM Zn2+. The results suggest physiological activity of Skeletonema costatum is very sensitive to the prevailing concentration of Zn2+.

Carbonic Anhydrases↗
PubMed2003

Cryopreservation of the unicellular marine alga, Nannochloropsis oculata.

In microalgal culture collections, as in many biological resource centres, cryoconservation is the most attractive method for the long-term, secure storage of living material. Nannochloropsis oculata, a marine unicellular alga, is of interest in the field of biotechnology due to its high lipid content. Of various cryoprotectants tested for their toxicity and for their ability to prevent cryoinjury, glycerol (final concentration 1.1 M) was the most efficient. When glycerol-treated cultures were submitted to a strictly regulated cooling rate (-3 degrees C min(-1)), they attained the control culture density within 13 d after thawing.

Cell Culture Techniques↗
PubMedDate not supplied

[Inositol-containing sphingolipid from red algae Gracilaria verrucosa].

An unusual polar lipid was isolated from the red alga Gracilaria verrucosa. Inositol, sphingosine bases, fatty acids, and phosphate were identified by GC and GC-MS analysis among the products of its acid methanolysis. On the basis of the lipid composition, chromatographic behavior, chemical properties, and mass spectra, the inositolphosphoceramide structure was proposed for this lipid. Similar lipids were previously found only in fungi and some protozoa. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2004, vol. 30, no. 2; see also http://www.maik.ru.

Gracilaria↗
PubMed2002

Nitrogen-assimilating enzymes in land plants and algae: phylogenic and physiological perspectives.

An important biochemical feature of autotrophs, land plants and algae, is their incorporation of inorganic nitrogen, nitrate and ammonium, into the carbon skeleton. Nitrate and ammonium are converted into glutamine and glutamate to produce organic nitrogen compounds, for example proteins and nucleic acids. Ammonium is not only a preferred nitrogen source but also a key metabolite, situated at the junction between carbon metabolism and nitrogen assimilation, because nitrogen compounds can choose an alternative pathway according to the stages of their growth and environmental conditions. The enzymes involved in the reactions are nitrate reductase (EC 1.6.6.1-2), nitrite reductase (EC 1.7.7.1), glutamine synthetase (EC 6.3.1.2), glutamate synthase (EC 1.4.1.13-14, 1.4.7.1), glutamate dehydrogenase (EC 1.4.1.2-4), aspartate aminotransferase (EC 2.6.1.1), asparagine synthase (EC 6.3.5.4), and phosphoenolpyruvate carboxylase (EC 4.1.1.31). Many of these enzymes exist in multiple forms in different subcellular compartments within different organs and tissues, and play sometimes overlapping and sometimes distinctive roles. Here, we summarize the biochemical characteristics and the physiological roles of these enzymes. We also analyse the molecular evolution of glutamine synthetase, glutamate synthase and glutamate dehydrogenase, and discuss the evolutionary relationships of these three enzymes.

Journal Article↗
PubMed2003

Microbodies of the alga Chara.

Chara fragilis possesses microbodies with a remarkably large size of up to 2 micro m in diameter. Many of the organelles contain huge nucleoids of amorphous material or paracrystalline inclusions. After isolation of the organelles by gradient centrifugation the specific density of the microbodies was determined to be 1.25 g cm-3. Catalase, glycolate oxidase and hydroxypyruvate reductase as well as enzymes of the fatty acid beta-oxidation pathway were demonstrated to be constituents of the microbodies in Chara indicating that they are similar to those in green leaves. The data obtained are in agreement with the view that the Charophyceae and especially the algae in the subgroup of Charales are very closely related to the land plants.

Journal Article↗
PubMed1988

Creatine accelerates the circadian clock in a unicellular alga.

The circadian clock is considered to be a universal feature of eucaryotic organisms, controlling the occurrence and rates of many different aspects of life, ranging from single enzymatic reactions and metabolism to complex behaviours such as activity and rest. Although the nature of the underlying cellular/biochemical oscillator is still unknown, many substances are known to influence either phase or period of circadian rhythms in different organisms. These include D2O, electrolytes and ion channel inhibitors, small organic molecules such as alcohols and aldehydes, inhibitors of protein synthesis and amino-acid analogues. Certain transmitter and neurochemical drugs also influence the circadian clock in higher animals. We report here that the period of free-running circadian rhythms in the unicellular marine alga Gonyaulax polyedra is shortened by extracts from mammalian cells. The effect is dose-dependent, accelerating the circadian clock by as much as 4 hours per day. The substance responsible for this effect has been isolated from bovine muscle and identified as creatine. Authentic creatine has identical biological effects at micromolar concentrations and is known in animal systems for its involvement in cellular energy metabolism. A period shortening substance with similar chemical properties is also present in extracts of Gonyaulax itself.

Animals↗
PubMed2004

Phenotypic consequences of 1,000 generations of selection at elevated CO2 in a green alga.

Estimates of the effect of increasing atmospheric CO2 concentrations on future global plant production rely on the physiological response of individual plants or plant communities when exposed to high CO2 (refs 1-6). Plant populations may adapt to the changing atmosphere, however, such that the evolved plant communities of the next century are likely to be genetically different from contemporary communities. The properties of these future communities are unknown, introducing a bias of unknown sign and magnitude into projections of global carbon pool dynamics. Here we report a long-term selection experiment to investigate the phenotypic consequences of selection for growth at elevated CO2 concentrations. After about 1,000 generations, selection lines of the unicellular green alga Chlamydomonas failed to evolve specific adaptation to a CO2 concentration of 1,050 parts per million. Some lines, however, evolved a syndrome involving high rates of photosynthesis and respiration, combined with higher chlorophyll content and reduced cell size. These lines also grew poorly at ambient concentrations of CO2. We tentatively attribute this outcome to the accumulation of conditionally neutral mutations in genes affecting the carbon concentration mechanism.

Animals↗
PubMed2005

Algae acquire vitamin B12 through a symbiotic relationship with bacteria.

Vitamin B12 (cobalamin) was identified nearly 80 years ago as the anti-pernicious anaemia factor in liver, and its importance in human health and disease has resulted in much work on its uptake, cellular transport and utilization. Plants do not contain cobalamin because they have no cobalamin-dependent enzymes. Deficiencies are therefore common in strict vegetarians, and in the elderly, who are susceptible to an autoimmune disorder that prevents its efficient uptake. In contrast, many algae are rich in vitamin B12, with some species, such as Porphyra yezoensis (Nori), containing as much cobalamin as liver. Despite this, the role of the cofactor in algal metabolism remains unknown, as does the source of the vitamin for these organisms. A survey of 326 algal species revealed that 171 species require exogenous vitamin B12 for growth, implying that more than half of the algal kingdom are cobalamin auxotrophs. Here we show that the role of vitamin B12 in algal metabolism is primarily as a cofactor for vitamin B12-dependent methionine synthase, and that cobalamin auxotrophy has arisen numerous times throughout evolution, probably owing to the loss of the vitamin B12-independent form of the enzyme. The source of cobalamin seems to be bacteria, indicating an important and unsuspected symbiosis.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed2002

The oxylipin chemistry of attraction and defense in brown algae and diatoms.

This review covers the research on brown algal pheromones from the first structural characterisation of an active principle in 1971 to the recent detailed insight into their biosynthesis. Development of analytical methods and bioassays that lead to the identification of a structural variety of different fatty acid-derived pheromones are reported. Special emphasis is focused on the inactivation of initially released pheromones through pericyclic reactions. The impact of pheromone-research on the defensive chemistry of brown algae and diatoms is discussed. 121 references are cited.

Catalysis↗