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At least 397 records · Page 22Linked to original sources
PubMed1998

Characterization of novel extrachromosomal DNA from giant-celled marine green algae.

Cloned HinfI fragments of the plasmid-like 2.2-kb DNA from the green alga Ernodesmis verticillata (Kützing) Borgesen hybridized solely to single or double bands within the 2.2-kb DNA in genomic Southern blots. Heterologous probes for nuclear and chloroplast genes hybridized only to high-molecular-weight (HMW) DNA. Thus, the low-molecular-weight (LMW) DNA is extrachromosomal and lacks extensive homology to nuclear or chloroplast genes. There was cross-hybridization to LMW DNA from other Caribbean isolates of E. verticillata, but not to that from a Pacific isolate. Under reduced stringency, cross-hybridization to LMW DNA from the related green alga Boergesenia forbesii (Harvey) Feldmann was also observed, suggesting that the LMW DNA may have a common origin and/or function in these algae. Six out of sixteen unique clones hybridized to discrete bands in northern blots, indicating that the LMW DNA may be actively transcribed in vivo. Four of the putatively transcribed clones have regions with significant deduced amino-acid sequence identity to psa and psb gene products, implying that the plasmid-like molecules might have originated from chloroplast DNA. Sequencing data also indicated a high G/C content, as well as the presence of frequent tandem and direct repeats in many of the cloned fragments. Sequencing and restriction analyses suggest that most of the cloned fragments are portions of different DNA molecules, providing evidence that the 2.2-kb extrachromosomal DNA in Ernodesmis is novel in that it represents a fairly heterogeneous population of molecules.

Amino Acid Sequence↗
PubMed2004

Exploitation of marine algae: biogenic compounds for potential antifouling applications.

Marine algae are one of the largest producers of biomass in the marine environment. They produce a wide variety of chemically active metabolites in their surroundings, potentially as an aid to protect themselves against other settling organisms. These active metabolites, also known as biogenic compounds, produced by several species of marine macro- and micro-algae, have antibacterial, antialgal, antimacrofouling and antifungal properties, which are effective in the prevention of biofouling, and have other likely uses, e.g. in therapeutics. The isolated substances with potent antifouling activity belong to groups of fatty acids, lipopeptides, amides, alkaloids, terpenoids, lactones, pyrroles and steroids. These biogenic compounds have the potential to be produced commercially using metabolic engineering techniques. Therefore, isolation of biogenic compounds and determination of their structure could provide leads for future development of, for example, environmentally friendly antifouling paints. This paper mainly discusses the successes of such research, and the future applications in the context of understanding the systems biology of micro-algae and cyanobacteria.

Animals↗
PubMed2007

The effects of ultraviolet radiation on photosynthetic performance, growth and sunscreen compounds in aeroterrestrial biofilm algae isolated from building facades.

The effects of artificial ultraviolet radiation [UVR; 8 W m(-2) ultraviolet-A (UVA), 0.4 W m(-2) ultraviolet-B (UVB)] on photosynthetic performance, growth and the capability to synthesise mycosporine-like amino acids (MAAs) was investigated in the aeroterrestrial green algae Stichococcus sp. and Chlorella luteoviridis forming biofilms on building facades, and compared with the responses of two green algae, from soil (Myrmecia incisa) and brackish water (Desmodesmus subspicatus). All species exhibited decreasing quantum efficiency (Fv/Fm) after 1-3 days exposure to UVR. After 8-12 days treatment, however, all aeroterrestrial isolates exhibited full recovery under UVA and UVA/B. In contrast, D. subspicatus showed only 80% recovery after treatment with UVB. While Stichococcus sp. and C. luteoviridis exhibited a broad tolerance in growth under all radiation conditions tested, M. incisa showed a significant decrease in growth rate after exposure to UVA and UVA/B. Similarly D. subspicatus grew with a reduced rate under UVA, but UVA/B led to full inhibition. Using HPLC, an UV-absorbing MAA (324 nm-MAA) was identified in Stichococcus sp. and C. luteoviridis. While M. incisa contained a specific 322 nm-MAA, D. subspicatus lacked any trace of such compounds. UV-exposure experiments indicated that all MAA-containing species are capable of synthesizing and accumulating these compounds, thus supporting their function as an UV-sunscreen. All data well explain the conspicuous ecological success of aeroterrestrial green algae in biofilms on facades. Biosynthesis and accumulation of MAAs under UVR seem to result in a reduced UV-sensitivity of growth and photosynthesis, which consequently may enhance survival in the environmentally harsh habitat.

Amino Acids↗
PubMed1999

Purification and characterisation of a novel starch synthase selective for uridine 5'-diphosphate glucose from the red alga Gracilaria tenuistipitata.

Red algae (Rhodophyceae) are photosynthetic eukaryotes that accumulate starch granules in the cytosol. Starch synthase activity in crude extracts of Gracilaria tenuistipitata Chang et Xia was almost 9-fold higher with UDP[U-14C]glucose than with ADP[U-14C]glucose. The activity with UDP[U-14C]glucose was sensitive to proteolytic and oxidative inhibition during extraction whilst the activity with ADP[U-14C]glucose appeared unaffected. This indicates the presence of separate starch synthases with different substrate specificities in G. tenuistipitata. The UDPglucose: starch synthase was purified and characterised. The enzyme appears to be a homotetramer with a native M(r) of 580 kDa and displays kinetic properties similar to other alpha-glucan synthases such as stimulation by citrate, product (UDP) inhibition and broad primer specificity. We propose that this enzyme is involved in cytosolic starch synthesis in red algae and thus is the first starch synthase described that utilises UDPglucose in vivo. The biochemical implications of the different compartmentalisation of starch synthesis in red algae and green algae/plants are also discussed.

Kinetics↗
PubMed2005

Cellular and subcellular localization of kainic acid in the marine red alga Digenea simplex.

Polyclonal antibodies specific for the excitatory amino acid, kainic acid (KA), were raised in rabbits. The antibody recognized KA but did not cross-react with other structurally related amino acids, including glutamate. We used this anti-KA antibody to localize KA immunohistochemically in the KA-producing red alga Digenea simplex. KA immunoreactivity was most dense in the fine cylindrical thallus, which covers the middle to upper part of the alga. The cortical cells, but not the inner layers of the main axis, and cells of the rhizoid were also stained with this antibody. The presence of KA in cells that cover the surface of the alga might reflect its role in chemical defense. At the subcellular level, KA immunoreactivity was most intense in the nucleus, pit plugs, and the electron-dense areas denoted as "granule bodies", which were found only in the pericentral cells of the thallus.

Immunohistochemistry↗
PubMed2006

Community effects following the deletion of a habitat-forming alga from rocky marine shores.

Habitat-forming species increase spatial complexity and alter local environmental conditions, often facilitating a diversified assemblage of plants and animals. Removal of dominant species, therefore, can potentially lead to pronounced changes in diversity and community structure through a series of negative and positive interactions involving several components of the community. Here we test community responses to the deletion of the dominant, canopy-forming alga Hormosira banksii from the mid-intertidal zone of wave-protected rocky shores in southern New Zealand. This species was removed in winter (July) from three 3x3-m areas at each of two platforms (Kaikoura and Moeraki) on the east coast of the South Island. Initially, 59 taxa occurred in stands, but there were only four algal species with greater than 5% cover and three mobile invertebrate species with more than five individuals per 0.25 m(2). By 6 months after Hormosira removal, most fucoid and coralline algae had burned off, and there were blooms of ephemeral algae in the removal plots, but almost no change within controls. After 2 years, diversity declined by 44% relative to controls at Kaikoura and 36% at Moeraki, and the amount of bare space had increased by tenfold at Kaikoura and twofold at Moeraki. Few sessile or mobile invertebrates were present. Recruitment of Hormosira occurred after 14 months in the removal plots. At this time, a "press" disturbance was initiated into one half of each removal plot to test the effects of continued removal of Hormosira on diversity. Similar "end-points" of the control and "press" removal plots were not reached after 2 years, and even after Hormosira recruitment into the original "pulse" experiment there was little recovery of the community. In this mid-intertidal system with considerable thermal stress, and perhaps in others with few perennial species, diversity and community structure can critically depend on positive associations with a single dominant species.

Animals↗
PubMed2006

Can overwintering versus diapausing strategy in Daphnia determine match-mismatch events in zooplankton-algae interactions?

Mismatches between predator and prey due to climate change have now been documented for a number of systems. Ultimately, a mismatch may have far-reaching consequences for ecosystem functioning as decoupling of trophic relationships results in trophic cascades. Here, we examine the potential for climate change induced mismatches between zooplankton and algae during spring succession, with a focus on Daphnia and its algal food. Whereas the development of an overwintering population of daphnids may parallel shifts in phytoplankton phenology due to climate warming, changes in the photoperiod-temperature interaction may cause the emerging population of daphnids to hatch too late and mismatch their phytoplankton prey. A decoupling of the trophic relationship between the keystone herbivore Daphnia and its algal prey can result in the absence of a spring clear water phase. We extended an existing minimal model of seasonal dynamics of Daphnia and algae and varied the way the Daphnia population is started in spring, i.e., from free swimming individuals or from hatching resting eggs. Our model results show that temperature affects the timing of peak abundance in Daphnia and algae, and subsequently the timing of the clear water phase. When a population is started from a small inoculum of hatching resting eggs, extreme climate warming (+6 degrees C) results in a decoupling of trophic relationships and the clear water phase fails to occur. In the other scenarios, the trophic relationships between Daphnia and its algal food source remain intact. Analysis of 36 temperate lakes showed that shallow lakes have a higher potential for climate induced match-mismatches, as the probability of active overwintering daphnids decreases with lake depth. Future research should point out whether lake depth is a direct causal factor in determining the presence of active overwintering daphnids or merely indicative for underlying causal factors such as fish predation and macrophyte cover.

Animals↗
PubMed2003

Impact of hypoosmotic challenges on spongy architecture of the cytoplasm of the giant marine alga Valonia utricularis.

The ultrastructure of the several micrometers thick cytoplasmic layer of the giant marine alga Valonia utricularis displays characteristics which are apparently linked with the capability of this alga to regulate turgor pressure. Transmission and scanning electron microscopy of cells prefixed in different ways, including a protocol that allows prefixation of the alga in a turgescent state, revealed a highly dendritic network of cytoplasmic strands connecting and enveloping the chloroplasts and the nuclei. Innumerable vacuolar entities are embedded in the network, giving the cytoplasm a spongy appearance. Vacuolar perfusion of turgor-pressure-clamped cells with prefixation solution containing tannic acid presented evidence that these vacuolar entities together with the huge central vacuole form a large unstirred continuum. In contrast to the tonoplast, the plasmalemma followed smoothly the lining of the cell wall, even at the numerous cell wall ingrowths. Sucrose, but not polyethylene glycol 6000, induced chloroplast clustering. Acute hypoosmotic treatment (established by reduction of external NaCl or by replacement of part of the external NaCl by equivalent osmotic concentrations of sucrose or polyethylene glycol 6000) resulted in a local relocation of the chloroplasts and cytoplasm towards the central vacuole. This effect did not occur when the relatively low reflection coefficients of these two osmolytes were taken into account. The increase in spacing between the spongy cytoplasm and the plasmalemma by chloroplast relocation (viewed by confocal laser scanning microscopy) was associated with a speckled appearance of the affected surface area under the light microscope. As indicated by electron microscopy, hypoosmotically induced chloroplast relocation resulted from disproportionate swelling of the vacuolar entities located close to the plasmalemma. The cytoskeleton in the cytoplasm and the mucopolysaccharide network in the central vacuole apparently resisted swelling of these compartments. This finding has the important consequence that relevant hydrostatic pressure gradients can be built up throughout the entire multifolded vacuolar space. This gradient could represent the trigger for turgor pressure regulation which is manifested electrically first in the tonoplast.

Chlorophyta↗
PubMed2005

Modulations of the thylakoid system in snow xanthophycean alga cultured in the dark for two months: comparison between microspectrofluorimetric responses and morphological aspects.

The response of the plastid was studied, with a special emphasis on thylakoid structure and function, in a snow filamentous xanthophycean alga (Xanthonema sp.) incubated in darkness for two months. Microspectrofluorimetric analyses were performed on single living cells to study the variations in the assembly of the chlorophyll-protein complexes of photosystem II, in comparison with cells grown in light. In parallel, changes in micro- and submicroscopic plastid morphology and in photosynthetic pigment content were monitored. Throughout the experiment, the lamellar architecture of thylakoids in the alga was relatively well preserved, whereas photosystem II underwent disassembly and degradation triggered by prolonged darkness. Conversely, the light-harvesting complex of photosystem II proved to be relatively stable for long periods in darkness. Moreover, a role of the peripheral antennae in determining thylakoid arrangement in xanthophycean algae is implied. Although the responses observed in Xanthonema sp. can be considered in terms of acclimation to darkness, the progressive destabilisation of the light-harvesting complex of photosystem II testifies to incipient ageing of the cells after 35 days.

Eukaryota↗
PubMed2006

Isolation and culture of a marine bacterium degrading the sulfated fucans from marine brown algae.

Fucoidans are matrix polysaccharides from marine brown algae, consisting of an alpha-L-fucose backbone substituted by sulfate-ester groups and masked with ramifications containing other monosaccharide residues. In spite of their interest as biologically active compounds in a number of homologous and heterologous systems, no convenient sources with fucanase activity are available yet for the degradation of the fucalean algae. We here report on the isolation, characterization, and culture conditions of a bacterial strain capable of degrading various brown algal fucoidans. This bacterium, a member of the family Flavobacteriaceae, was shown to secrete fucoidan endo-hydrolase activity. An extracellular enzyme preparation was used to degrade the fucoidan from the brown alga Pelvetia canaliculata. End products included a tetrasaccharide and a hexasaccharide made of the repetition of disaccharidic units consisting of alpha-1-->3-L-fucopyranose-2-sulfate-alpha-1-->4-L-fucopyranose-2,3-disulfate, with the 3-linked residues at the nonreducing end.

Biodegradation, Environmental↗
PubMed2006

Characterization of chlorophyll-protein complexes isolated from two marine green algae, Bryopsis maxima and Ulva pertusa, growing in the intertidal zone.

Three Chl-protein complexes were isolated from thylakoid membranes of Bryopsis maxima and Ulva pertusa, marine green algae that inhabit the intertidal zone of the Pacific Ocean off the eastern coast of Japan by dodecyl-beta-D-maltoside polyacrylamide gel electrophoresis. The slowest-moving fractions showed low Chl a/b and Chl/P-700 ratios, indicating that this fraction corresponds to complexes in PS I, which is large in both algae. The intermediate and fastest-moving fractions showed the traits of PS II complexes, with some associated Chl a/b-protein complexes and LHC II, respectively. The spectral properties of the separated Chl-proteins were also determined. The absorption spectra showed a shallow shoulder at 540 nm derived from siphonaxanthin in Bryopsis maxima, but not in Ulva pertusa. The 77 K emission spectra showed a single peak in Bryopsis maxima and two peaks in Ulva pertusa. Besides the excitation spectra indicated that the excitation energy transfer to the PS I complexes differed quite a lot higher plants. This suggested that the mechanisms of energy transfer in both of these algae differ from those of higher plants. Considering the light environment of this coastal area, the large size of the antennae of PS I complexes implies that the antennae are arranged so as to balance light absorption between the two photosystems. In addition, we discuss the relationships among the photosystem stoichiometry, the energy transfer, and the distribution between the two photosystems.

Chlorophyta↗
PubMed1978

Excitation energy transfer between pigment system II units in blue-green algae.

Efficiency in excitation energy transfer from closed to open reaction center II in blue-green and red algae was estimated by the method developed by Joliot and Joliot (C.R. Acad. Sci. (1964) 258, 4622--4625) after slight modification; the number of open reaction centers II was counted from the mean O2 yield of repetitive short flashes. The efficiency in energy transfer in Chlorella pyrenoidosa was the same in our measurement as that reported by Joliot and Joliot (0.55 +/- 0.02). However, the values obtained with four blue-green algae and one red alga were very small, in a range of 0.00--0.07. The low efficiency was always obtained independently of the size of the apparent photosynthetic unit which was varied by growth conditions. Results indicated that pigment system II forms a unit in which only one reaction center II is operative.

Cyanobacteria↗
PubMed1980

Oscillations of the NAD(P)H pool size and of the redox state of a cytochrome b during dark respiration of the blue-green alga, Anacystis nidulans.

Oscillations of the oxygen uptake rate of the blue-green alga (cyanobacterium) Anacystis nidulans were induced by light pulses. The pool size of NAD(P)H and the redox state of a cytochrome b showed oscillations of similar shape and frequency. Phase diagrams revealed that these three oscillations were presumably linked. The cytochrome b should be a part of the respiratory chain of this blue-green alga. The oscillations were inducible only in a limited physiological state of the alga.

Cyanobacteria↗
PubMed1984

The binding of selenium to the lipids of two unicellular marine algae.

Axenic cultures of the green algae Dunaliella primolecta and red algae Porphyridium cruentum were grown in the presence of sublethal quantities of selenite. All purified lipids from both algae were found to contain bound selenium, except for saturated hydrocarbons. Of the lipids which contain selenium, carotenoid pigments contain the greatest concentrations. Lipid-associated selenium is not metabolically incorporated. The selenium is probably non-covalently bound to the lipids.

Chlorophyta↗
PubMed1990

Conjugation of benzo[a]pyrene metabolites by freshwater green alga Selenastrum capricornutum.

Benzo[a]pyrene (BaP) undergoes metabolic transformation in mammals via oxidative, hydrolytic, and conjugative processes; however, little is known concerning BaP conjugation in freshwater algae. It has been shown in this laboratory that BaP is metabolized by Selenastrum capricornutum via a dioxygenase pathway. This study describes the conjugation of BaP metabolites by a green alga, Selenastrum capricornutum. Cultures were exposed to 1160 micrograms/l [14C]BaP for 4 days at 23 degrees C under gold fluorescent lights on a diurnal cycle of 16 h light, 8 h dark. Of the total metabolites in the algal culture, 89% were present in media. BaP and non-conjugated metabolites were separated from conjugated metabolites by chromatography on neutral alumina columns using solvents of increasing polarity. Seventy-one percent of the BaP metabolites were conjugates of which 12.2%, 12.0% and 12.4% were sulfate ester and alpha- and beta-glucose conjugates, respectively. Conjugates that coeluted with sulfate esters were hydrolyzed with arylsulfatase, alpha- or beta-glucosidase; high performance liquid chromatography (HPLC) analysis indicated that the major product of each enzymatic hydrolysis was the 4,5-dihydrodiol (87.2, 69 and 53%, respectively). Eighty-six percent of the conjugates were acid labile following incubation for 2 h in 4 N HCl at 37 degrees C. To our knowledge this is the first demonstration of the metabolism of a polynuclear aromatic hydrocarbon by a freshwater green alga through a dioxygenase pathway and subsequent conjugation and excretion.

Acid Phosphatase↗
PubMed1994

Post-coital contraceptive activity of crude extracts of Sri Lankan marine red algae.

This study investigates the potential of marine red algae as a source for post-coital contraceptive agents using three varieties: Gracilaria corticata, Gelidiella acerosa and Jania sp. Methanol: methylene chloride (1:1) extracts of these red algae were made and were orally administered (500 or 1000 mg/kg/day) to female rats from day 1 to day 7 of pregnancy. The higher dose of Gracilaria corticata and both doses of Gelidiella acerosa extracts produced significant post-coital contraceptive activities without any marked side effects. Furthermore, the post-coital contraceptive activity of the latter extract was dose-dependent. On the other hand, extract made from Jania sp. had no significant post-coital contraceptive action. The post-coital contraceptive activity of Gracilaria corticata was due to enhanced pre-implantation loss and of Gelidiella acerosa was due to elevated post-implantation loss. These findings indicate that marine red algae is a useful source to be harvested for potential post-coital contraceptive drugs.

Animals↗
PubMed1994

Trace metal accumulation by algae in Sepetiba Bay, Brazil.

Trace metal concentrations (Zn, Cd, Pb, Cr and Cu) were determined in some benthic algae from Sepetiba Bay, Brazil. This region has been modified by the increase of industrial activities during the last 30 years. Among species sampled the brown algae Padina gymnospora contained the greatest amount of Zn. The Bioconcentration Factor for Zn in P. gymnospora was found to be 10(4) under laboratory conditions. The absorption of (65)Zn depended on exposure time and increased with Zn concentrations in the medium. An insignificant amount of Zn desorbed from algae suggested a very high affinity with cellular binding sites. Zinc uptake by P. gymnospora is discussed by considering field and laboratory conditions.

Journal Article↗
PubMed1980

Ultrastructural aspects of basal body associated fibrous structures in green algae: a critical review.

Ultrastructural aspects of fibrous structures associated with basal bodies of green algae are critically discussed. It is apparent that variation among these structures is much greater than in microtubular flagellar root systems and it is therefore suggested that fibrous structures may be more useful than microtubular roots in elucidating phylogenetic relationships within the Chlorophyceae sensu Stewart and Mattox and the Prasinophyceae sensu Christensen. Two main types of fibrous structures are distinguished: (1) Connecting fibres (these connect different basal bodies); (2) Fibrous roots (these originate at basal bodies and terminate somewhere else in the cell). Fibrous roots are of two types: (a) microtubular-root associated striated fibres (striation pattern 25-35 nm; system I-fibres); (b) striated fibres composed of a bundle of filaments (filament diameter: 5-10 nm; striation pattern greater than 80 nm; system II fibres). Numbers, disposition and substructure of connecting fibres and fibrious roots are variable in different genera of green algae. In the experimental secretion new observations on fibrous roots in the ulvalean genus Enteromorpha as well as preliminary information on fibrous structures in Carteria obtusa and Bryopsis lyngbyei are included. Functional and evolutionary aspects of fibrous structures associated with the flagellar apparatus of green algae are discussed.

Chlorophyta↗