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PubMed2006

Genotype versus phenotype variability in Chlorella and Micractinium (Chlorophyta, Trebouxiophyceae).

The most recent revision of the genus Chlorella, based on biochemical and SSU rDNA analyses, suggested a reduction to a set of four "true" spherical Chlorella species, while a growing number of morphologically different species such as Micractinium (formerly Micractiniaceae) were found to cluster within the clade of "true"Chlorella. In this study, the generic concept in Chlorellaceae to Chlorella and Micractinium was evaluated by means of combined SSU and ITS-2 rDNA sequence analyses and biotests to induce development of bristles on the cell wall. Molecular phylogenetic analyses of Chlorella and Micractinium strains confirmed their separation into two different genera. In addition, non-homoplasious synapomorphies (NHS) and compensatory base changes (CBC) in the secondary structures of SSU and ITS-2 rDNA sequences were found for both genera using this approach. The Micractinium clade can be differentiated into three different genotypes. Using culture medium of the rotifer Brachionus calyciflorus, phenotypic plasticity in Chlorella and Micractinium was studied. Non-bristled Micractinium cells developed bristles during incubation with Brachionus culture medium, whereas Chlorella did not produce bristles. Grazing experiments with Brachionus showed the rotifer preferred to feed on non-bristled cells. The dominance of colonies versus solitary cells in the Micractinium culture was not correlated with the "Brachionus factor". These results suggest that morphological characteristics like formation of bristles represent phenotypic adaptations to the conditions in the ecosystem.

Adaptation, Physiological↗
PubMed2005

Evolution and phylogeography of Halimeda section Halimeda (Bryopsidales, Chlorophyta).

Nuclear ribosomal and plastid DNA sequences of specimens belonging to section Halimeda of the pantropical green seaweed genus Halimeda show that the group under scrutiny contains many more genetically delineable species than those recognized by classical taxonomy. Discordances between phylograms inferred from nuclear and plastid DNA sequences suggest that reticulate evolution has been involved in speciation within the clade. Nonetheless, our data do not allow ruling out certain alternative explanations for the discordances. Several pseudo-cryptic species are restricted to the margins of the generic distribution range. In a clade of H. cuneata sibling species from widely separated subtropical localities in the Indian Ocean, the South African sibling branches off first, leaving the Arabian and West Australian species as closest relatives. We hypothesize that geographic isolation of the siblings may have taken place following Pleistocene or Pliocene periods of climatic cooling during which subtropical species occupied larger distribution ranges. A more basal separation of Atlantic, Indo-Pacific, and Mediterranean species indicates vicariance. The alternative events that could have caused this vicariance are discussed.

Base Composition↗
PubMed1997

Fine chemical structure analysis of oligosaccharides produced by an ulvan-lyase degradation of the water-soluble cell-wall polysaccharides from Ulva sp, (Ulvales, Chlorophyta).

A marine bacterium degrading the water-soluble cell wall polysaccharides from Ulva sp. (ulvan) has been isolated. The good correlation between ulvan degradation monitored by reducing-power, UV absorbance and viscosimetry, indicated that the crude enzymatic extract contains essentially an endo-ulvan lyase activity. This activity was rapidly inhibited by the reaction products which consisted of a series of ulvanobiouronic acid A 3-sulfate [-->4)-beta-D-GlcpA-(1-->4)-alpha-L-Rhap 3-sulfate-(1-->]n with 4-deoxy-L-threo-hex-4-enopyranosiduronic acid at the non-reducing end. Other deviant repeating structures with beta-D-Xylp or alpha-IdopA replacing beta-D-GlcpA in the repeating ulvanobiouronic acid disaccharide and the presence of two consecutive (1-->4) linked beta-D-Glc pA demonstrated the great variability and complexity of ulvan chemical structure.

Carbohydrate Conformation↗
PubMed1998

NMR spectroscopic characterisation of oligosaccharides from two Ulva rigida ulvan samples (Ulvales, Chlorophyta) degraded by a lyase.

The chemical structure and the sequence of repeating units in ulvans of similar compositions from two different Ulva rigida samples collected in the Canary Islands and in Brittany were studied after ulvan-lyase degradation and NMR spectroscopic analysis of the reaction products. Both ulvans were composed of ulvanobiuronic acid 3-sulfate type A [-->4)-beta-D-GlcA-(1-->4)-alpha-L-Rha 3-sulfate-(1-->] (symbolised as A3s) and contained disaccharides composed of [-->4)-beta-D-Xyl-(1-->4)-alpha-L-Rha 3-sulfate-(1-->] and [-->4)-beta-D-Xyl 2-sulfate-(1-->4)-alpha-L-Rha 3-sulfate], respectively referred to as ulvanobiose 3-sulfate (U3s) and ulvanobiose 2',3-disulfate (U2's,3s). In the Canary Islands sample, these U3s and U2's,3s occurred dispersed among A3s sequences and as short blocks of two or three units. In contrast, in the Brittany samples, these units were dispersed among A3s structures and next to A3s units branched at O-2 of alpha-L-Rha 3-sulfate by a terminal beta-D-GlcA and symbolised as A2g,3s. However, more complex structures are likely to occur in the enzyme resistant fraction remaining from this ulvan. An average structure sequence of these two ulvans was proposed. The transposition of the 13C NMR data of the new identified structures to the parent polysaccharides was not possible, probably due to the different sequence distributions affecting the carbons chemical shifts.

Carbohydrate Sequence↗
PubMed2002

Accumulation of arachidonic acid-rich triacylglycerols in the microalga Parietochloris incisa (Trebuxiophyceae, Chlorophyta).

The freshwater green microalga Parietochloris incisa is the richest known plant source of the polyunsaturated fatty acid (PUFA), arachidonic acid (20:4omega6, AA). While many microalgae accumulate triacylglycerols (TAG) in the stationary phase or under certain stress conditions, these TAG are generally made of saturated and monounsaturated fatty acids. In contrast, most cellular AA of P. incisa resides in TAG. Using various inhibitors, we have attempted to find out if the induction of the biosynthesis of AA and the accumulation of TAG are codependent. Salicylhydroxamic acid (SHAM) affected a growth reduction that was accompanied with an increase in the content of TAG from 3.0 to 6.2% of dry weight. The proportion of 18:1 increased sharply in all lipids while that of 18:2 and its down stream products, 18:3omega6, 20:3omega6 and AA, decreased, indicating an inhibition of the Delta12 desaturation of 18:1. Treatment with the herbicide SAN 9785 significantly reduced the proportion of TAG. However, the proportion of AA in TAG, as well as in the polar lipids, increased. These findings indicate that while there is a preference for AA as a building block of TAG, the latter can be produced using other fatty acids, when the production of AA is inhibited. On the other hand, inhibiting TAG construction did not affect the production of AA. In order to elucidate the possible role of AA in TAG we have labeled exponential cultures of P. incisa kept at 25 degrees C with [1-14C]arachidonic acid and cultivated the cultures for another 12 h at 25, 12 or 4 degrees C. At the lower temperatures, labeled AA was transferred from TAG to polar lipids, indicating that TAG of P. incisa may have a role as a depot of AA that can be incorporated into the membranes, enabling the organism to quickly respond to low temperature-induced stress.

Arachidonic Acid↗
PubMed2003

Assessment of ammonia toxicity in tests with the microalga, Nephroselmis pyriformis, Chlorophyta.

Previous studies of an industrial effluent have indicated toxic effects by the ammonium/water system in tests with the unicellular green alga, Nephroselmis pyriformis. This investigation was undertaken to determine the toxicity of ammonia to this alga, and to identify the dominant toxicant in an industrial process effluent. The algal standard test was modified to improve the pH control, i.e. by testing at shorter exposure time and in the presence of a buffering agent, 3 mM HEPES. Ammonia was found to be the predominant toxic form in the dissociating ammonium/water system and the specific toxicity of ammonia (EC50, 24 h exposure) was 2.34 microM (32.8 microg ammonia nitrogen/L). Due to the dissociation, the toxicity is strongly pH dependent. Joint toxicity with additive effects of ammonia and ammonium ions was indicated, but the toxicity of ammonium ions was almost a factor 100 less (EC50, 24 h exposure, 224 microM or 3140 microg ammonium-nitrogen/L). According to the results the EC50 for effect on growth rate of N. pyriformis in seawater of pH 8.0 is 71 microM total ammonium. Hence, this alga appears to be more sensitive to ammonia than other studied marine plankton algae. Ammonia was found to be the dominant toxicant in the industrial effluent, using N. pyriformis as test organism.

Ammonia↗
PubMed2004

Effects of copper on Enteromorpha flexuosa (Chlorophyta) in vitro.

Enteromorpha species are widely used as biomonitors of copper (Cu) contamination in coastal waters, but the effects of Cu at the subcellular level and possible mechanisms of metal resistance are scarcely known. To contribute to the understanding of the Cu accumulation process in macroalgae species, we exposed adult individuals of Enteromorpha flexuosa to 50, 250, and 500 microg Cu/L in seawater for 5 days under controlled conditions. Thereafter, gross photosynthesis rate (GPR) and metal accumulation were measured. Conventional transmission electron microscopy (CTEM) and energy-dispersive X-ray analysis (EDXA) were used to study the metal accumulation process at the cellular level. Treatments with 250 and 500 microg Cu/L were observed to cause an inhibition of the GPR in the algae. Cu accumulation in samples exposed to 500 microgCu/L was 5284+/-561 microg Cu/g (dry wt), whereas in control samples (no Cu addition), accumulation was 9+/-1 microg/g. In cells of plants undergoing the 50 microg Cu/L treatment, the cytoplasm was clearly vacuolated. Thickening of cell walls and increase of relative number of starch granules and of lipid bodies were the main cellular changes observed in plants exposed to 250 and 500 microg Cu/L. EDXA of algae cells after 250 and 500 microg Cu/L exposure detected Cu mainly in vacuole precipitates. Cu was also detected in chloroplasts and in some epiphytic bacteria. It was concluded that E. flexuosa did not avoid penetration of Cu into the cytoplasm and consequently its toxic effects in concentrations of 250 and 500 microg Cu/L. Precipitates containing Cu in vacuoles should be related to a metal immobilization mechanism, minimizing the Cu toxicity for cells. The epiphytic bacteria can act as a biofilter diminishing the availability of free Cu(+2) for algae accumulation.

Biodegradation, Environmental↗
PubMed2001

Hsp70 expression in Enteromorpha intestinalis (Chlorophyta) exposed to environmental stressors.

Numerous studies have indicated that stress proteins have potential as biomarkers of exposure to environmental contaminants. Analysis of stress proteins in animals, especially Hsp70, has dominated this research area despite increasing interest in the use of plants as pollution monitors. In the present study Hsp70 expression in Enteromorpha intestinalis has been investigated under exposure to a variety of stressors, to evaluate the potential use of Hsp70 as a biomarker of contaminant exposure in this seaweed. E. intestinalis was exposed to thermal stress, copper under differing conditions of nutrient availability and the triazine herbicide Irgarol 1051. Measurements were also taken to compare Hsp70 with conventional sublethal endpoints of toxicity such as growth and fluorescence induction parameters such as Fv/Fm. E. intestinalis exhibited a typical heat shock response. Hsp70 expression was increased with copper exposure, but proved to be a relatively insensitive biomarker of copper exposure compared to growth measurements. Nutrient limitation enhanced copper toxicity and significantly impaired growth, Fv/Fm and Hsp70 production. Fv/Fm and growth were strongly affected by Irgarol 1051 exposure, but Hsp70 levels were unaltered following exposure to the herbicide. The implications of using Hsp70 expression in E. intestinalis as a biomarker are discussed.

Chlorophyta↗
PubMed2000

Carotenoid content of chlorophycean microalgae: factors determining lutein accumulation in Muriellopsis sp. (Chlorophyta).

Fifteen strains of chlorophycean microalgae have been investigated with regard to their carotenoid profile. Lutein, beta-carotene and violaxanthin were present in virtually all of the strains, lutein, in general, being the most abundant carotenoid, whereas canthaxanthin and astaxanthin were found in some strains only. Chlorella fusca SAG 211-8b, Chlorococcum citriforme SAG 62.80, Muriellopsis sp., Neospongiococcum gelatinosum SAG B 64.80 and Chlorella zofingiensis CCAP 211/14 exhibited high lutein levels, the latter strain containing in addition substantial amounts of astaxanthin. Muriellopsis sp. was further characterized, since besides a high lutein content (up to 35 mg l(-1) culture), it had the highest growth rate (up to 0.17-0.23 h(-1)) and maximal standing cell density (up to 8 x 10(10) cells l(-1) culture). These levels of lutein are in the range of those reported for astaxanthin in Haematococcus and for beta-carotene in Dunaliella, microalgae of recognized interest for the production of these carotenoids. Lutein content of Muriellopsis sp. increased during the exponential phase of growth, with the highest value being recorded in the early stationary phase. Maximum levels of lutein in Muriellopsis sp. cultures were recorded at 20-40 mM NaNO3, 2-100 mM NaCl, 460 micromol photon m(-2) s(-1), pH 6.5 and 28 degrees C, conditions which were, in general, also optimal for cell growth. Growth-limiting conditions, such as pH values of 6 or 9 and a temperature of 33 degrees C, were found to stimulate carotenogenesis in Muriellopsis sp. This strain represents a potential source of lutein, a commercially interesting carotenoid of application in aquaculture and poultry farming, as well as in the prevention of cancer and diseases related to retinal degeneration.

Cell Division↗
PubMed2004

The respiratory inhibitor antimycin A specifically binds Fe(III) ions and mediates utilization of iron by the halotolerant alga Dunaliella salina (Chlorophyta).

It is demonstrated that Antimycin A (AA), a respiratory inhibitor produced by Streptomyces bacteria, forms lipophylic complexes with Fe(III) ions. Spectroscopic titration indicates that Fe(III) ions interact with 2AA molecules. At growth-limiting Fe concentrations, AA mediates Fe uptake and promotes growth and chlorophyll synthesis better than other Fe chelators in the halotolerant alga Dunaliella salina. It is proposed that AA enhances Fe bioavailability in hypersaline solutions by formation of lipophylic Fe-AA complexes which are taken-up and utilized by the algae. The results suggest that the respiratory inhibitor AA can affect Fe metabolism in microorganisms.

Antimycin A↗
PubMed2001

Phylogenetic analyses of Caulerpa taxifolia (Chlorophyta) and of its associated bacterial microflora provide clues to the origin of the Mediterranean introduction.

The accidental introduction of Caulerpa taxifolia into the Mediterranean is no longer under dispute. What has eluded researchers until now, is definitive evidence for the original, biogeographical source population. Here we present two independent lines of evidence that support an Australian origin for the Mediterranean populations of C. taxifolia. First, we reanalysed algal rDNA-internal transcribed spacer (rDNA-ITS) sequences, combining previously published sequences from different studies with 22 new sequences. The ITS sequence comparison showed that the Australian sample is the sister group of the Mediterranean-aquarium clade. Second, cloned bacterial 16S rDNA gene sequences were analysed from the associated microflora of C. taxifolia collected from Australia, Tahiti, the Philippines and the Mediterranean. Five bacterial lineages were identified, of which three were dominant. Alpha Proteobacteria were the most abundant and were found in all samples. In contrast, members of the beta Proteobacterial line and Cytophaga-Flexibacter-Bacteroides line (CFB) were mainly associated with Mediterranean and Australian samples. Frequency distributions of the five bacterial lineages were significantly different among biogeographical locations. Phylogenetic analyses of the 54 bacterial sequences derived from the four C. taxifolia individuals resulted in a well-resolved tree with high bootstrap support. The topologies of the beta Proteobacteria and CFB mirror the geographical sources of their algal hosts. Bacterial-algal associations provide an identification tool that may have wide application for the detection of marine invasions.

Base Sequence↗
PubMed2002

The contribution of haploids, diploids and clones to fine-scale population structure in the seaweed Cladophoropsis membranacea (Chlorophyta).

Local populations of Cladophoropsis membranacea exist as mats of coalesced thalli composed of free-living haploid and diploid plants including clonally reproduced plants of either phase. None of the phases are morphologically distinguishable. We used eight microsatellite loci to explore clonality and fine-scale patch structure in C. membranacea at six sites on the Canary Islands. Mats were always composites of many individuals; not single, large clones. Haploids outnumbered diploids at all sites (from 2:1 to 10:1). In both haploid and diploid plants, genetic diversity was high and there was no significant difference in allele frequencies. Significant heterozygote deficiencies were found in the diploid plants at five out of six sites and linkage disequilibrium was associated with the haploid phase at all sites. Short dispersal distances of gametes/spores and small effective population sizes associated with clonality probably contribute to inbreeding. Spatial autocorrelation analysis revealed that most clones were found within a radius of approximately 60 cm and rarely further than 5 m. Dominance of the haploid phase may reflect seasonal shifts in the relative frequencies of haploids and diploids, but may alternatively reflect superiority of locally adapted and competitively dominant, haploid clones; a strategy that is theoretically favoured in disturbed environments. Although sexual reproduction may be infrequent in C. membranacea, it is sufficient to maintain both life history phases and supports theoretical modelling studies that show that haploid-diploid life histories are an evolutionarily stable strategy.

Chlorophyta↗
PubMed2003

Chilling-induced photoinhibition in nine isolates of Valonia utricularis (Chlorophyta) from different climate regions.

Chilling induced inhibition of photosynthesis was studied in nine isolates of the marine tropical to warm-temperate green macrophyte Valonia utricularis (Roth) C. Agardh. According to their temperature requirements for growth and survival, the isolates belong to a cold-tolerant Atlantic/Mediterranean group and a cold-sensitive Indo-west Pacific group. After 5 hours exposure to 5 degrees C under moderate light, all isolates experienced similar substantial photoinhibition, which approached steady state levels after a decline in Fv/Fm to about 40% of the initial values. After return to optimal temperature and dim light conditions, Fv/Fm values increased with biphasic kinetics. A fast phase with half-life times of less than 30 minutes (dynamic photoinhibition) was followed by a slow phase lasting a few hours, indicating repair of photodamaged PSII reaction centres (chronic photoinhibition). In the Atlantic/Mediterranean isolates the fast phase accounted for more than 80 % of the recovery response, showing that these isolates were able to cope with the applied low temperature stress by down-regulating their PSII reaction centres. In contrast, the two isolates from the Seychelles were predominantly photodamaged. In a second experiment, three isolates (Corsica, Seychelles, Japan) were exposed to a similar relative amount of cold stress (0, 10, 15 degrees C, respectively). The Japanese isolate and the isolate from the Seychelles showed significantly less inhibition compared to 5 degrees C exposure, but no significant difference was found in the Corsican isolate. However, the degree of low temperature stress had no significant influence on the relative contributions of dynamic and chronic photoinhibition. Only two of the seven investigated isolates had a lower final inhibition level when grown at sub-optimal temperatures than at optimal temperatures. However, all sub-optimally grown Atlantic/Mediterranean isolates exhibited faster recovery kinetics from chilling-induced photoinhibition than optimally grown plants. This is related to a faster recovery from chronic photoinhibition than to a higher relative contribution of dynamic photoinhibition. A specific role of the photoprotective pigments of the xanthophyll cycle, leading to an acclimation response in the Atlantic/Mediterranean isolates may be involved. We conclude that ecotypic differentiation in V. utricularis is mirrored in different degrees of susceptibility to low temperature stress.

Acclimatization↗
PubMed2002

Cloning and prokaryotic expression of a salt-induced cDNA encoding a chloroplastic fructose-1,6-diphosphate aldolase in Dunaliella salina (Chlorophyta).

A salt-induced fructose-1,6-diphosphate (FDP) aldolase cDNA (DsALDP) in Dunaliella salina was cloned by suppression subtractive hybridization (SSH) and rapid amplification of cDNA ends (RACE) techniques. Sequence analysis of DsALDP revealed that the 1520 bp cDNA had an open reading frame (ORF) of 327 amino acid residues. BLAST Search showed that DsALDP shared an amino acid identity (73-66%) with AldP in other plants. Alignment with homologues in other plants indicated that all the conserved substrate-specific binding sites could also be found in DsALDP. Phylogenetic analysis further confirmed the deduced amino acid sequence of the D. salina DsALDP gene belonged to the same subfamily to AldP of other green algae. Southern blot analysis suggested possible presence of the D. salina DsALDP gene as a few copies and Northern blot analysis confirmed salt-induced expression pattern at the transcriptional level. A 62 kDa fusion protein generated by adding a Trx-His.tag at the N-terminal of DsALDP was induced by IPTG in Escherichia coli BL21. An improvement of salt tolerance in E. coli expressing DsALDP fusion protein was observed.

Amino Acid Sequence↗
PubMed1996

Fatty acid composition and chilling resistance in the green alga Caulerpa prolifera (Forrskal) Lamouroux (Chlorophyta, Caulerpales).

Plant resistance to chilling injury depends on the maintenance of membrane functions. An increase in the degree of unsaturation of membrane fatty acids can help maintain membrane function at low temperatures by reducing the temperature at which deleterious membrane phase-transitions occur. The fatty acid composition of membranes of the chlorophycean Caulerpa prolifera was determined in summer and winter in the Mar Menor coastal Lagoon (SE Spain). In January the percentage of polyunsaturated fatty acids was higher than in August. Membrane content of mono- and diunsaturated fatty acids was similar in the two seasons. The unsaturation index of membranes changed from 76.15 +/- 1.80 (mean +/- standard error) in August to 128.05 +/- 0.32 in January. It is suggested that this increase in the degree of unsaturation might be important to allow C. prolifera to decrease its lower threshold of survival temperature and acclimate net photosynthesis and dark respiration rates to winter temperatures in the Mar Menor.

Cell Membrane↗
PubMed2006

Morphology and phylogenetic position of Spongiochrysis hawaiiensis gen. et sp. nov., the first known terrestrial member of the order Cladophorales (Ulvophyceae, Chlorophyta).

Spongiochrysis hawaiiensis gen. et sp. nov. is described from material collected at two sites on O'ahu, Hawaiian Islands. This alga produced golden-yellow crusts on the bark of Casuarina trees and consisted of globular cells with an axial stellate chloroplast. The only form of reproduction was a specialized type of autosporulation in which a budding-like division of the mother cell produced daughter cells of different sizes. Phylogenetic analyses of the 18S rRNA gene showed that Spongiochrysis hawaiiensis is a member of the freshwater clade of the Cladophorales/Siphonocladales lineage in the green algal class Ulvophyceae. On the basis of its unicellular habit and terrestrial habitat, this species is well differentiated from all other members of the same lineage and can be considered as the first known successful step of a member of the order Cladophorales into terrestrial habitats. The implications of the description of this species with regard to both green algal evolution and conservation of little-known tropical habitats are discussed. The holotype specimen of Spongiochrysis hawaiiensis is GALW015489 and isotype specimens have also been deposited in the BISH and BM herbaria.

Chlorophyta↗
PubMed2005

Ecotype diversity in the marine picoeukaryote Ostreococcus (Chlorophyta, Prasinophyceae).

The importance of the cyanobacteria Prochlorococcus and Synechococcus in marine ecosystems in terms of abundance and primary production can be partially explained by ecotypic differentiation. Despite the dominance of eukaryotes within photosynthetic picoplankton in many areas a similar differentiation has never been evidenced for these organisms. Here we report distinct genetic [rDNA 18S and internal transcribed spacer (ITS) sequencing], karyotypic (pulsed-field gel electrophoresis), phenotypic (pigment composition) and physiological (light-limited growth rates) traits in 12 Ostreococcus strains (Prasinophyceae) isolated from various marine environments and depths, which suggest that the concept of ecotype could also be valid for eukaryotes. Internal transcribed spacer phylogeny grouped together four deep strains isolated between 90 m and 120 m depth from different geographical origins. Three deep strains displayed larger chromosomal bands, different chromosome hybridization patterns, and an additional chlorophyll (chl) c-like pigment. Furthermore, growth rates of deep strains show severe photo-inhibition at high light intensities, while surface strains do not grow at the lowest light intensities. These features strongly suggest distinct adaptation to environmental conditions encountered at surface and the bottom of the oceanic euphotic zone, reminiscent of that described in prokaryotes.

Chlorophyll↗