Biosorption of mercury from aqueous solution by Ulva lactuca biomass

The mercury biosorption onto non-living protonated biomass of Ulva lactuca, as an alternative method for mercury removal from aqueous solutions, was investigated. Batch equilibrium tests showed that at pH 3.5, 5.5 and 7 the maxima of mercury uptake values, according to Langmuir adsorption isotherm, were 27.24, 84.74 and 149.25 mg/g, respectively. The ability of Ulva lactuca biomass to adsorb mercury in fixed-bed column, was investigated as well. The influence of column bed height, flow rate and effluent initial concentration of metal was studied. The adsorbed metal ions were easily desorbed from the algal biomass with 0.3 N H₂SO₄ solution. After acid desorption and regeneration with distilled water, the biomass could be reused for other biosorption assays with similar performances.     

DNA content of Ulva compressa (Ulvales, Chlorophyta) nuclei determined with laser scanning cytometry

The green macroalgal genus Ulva (incl. Entemmorpha) contains economically valuable species, is of relevance for coastal management (green tides), and certain taxa serve as experimental organisms for fundamental research in green algae. The nuclear genome size of Ulva (Entemmorpha) compressa Linnaeus was measured in propidium iodide stained nuclei using laser scanning cytometry. Nuclei of fixed gametes yielded reproducible values, whereas nuclei extracted from multicellular gametophytes were unsuitable. With nuclei of Arabidopsis thaliana (L.) Heynh and Saccharomyces cerevisiae Hansen as references, the haploid nuclear genome size of U. compressa was calculated as 135 ± 7 Mbp. This is the smallest genome so far known from any species of Ulva.     

MACROALGAL CANDIDATES FOR GENOMICS1

Genomes from over 130 organisms have been either sequenced completely or are currently under investigation. These studies include a wide array of Bacteria, a smaller number of Archaea, model‐system eukaryotes, parasitic protists, and even several microalgae. However, no major effort is underway to acquire a complete nuclear genome sequence from a single macroalga or seaweed despite their crucial contribution to the biodiversity and energy economy of oceans and estuaries. Here we examine various macroalgae as potential candidates for a genome project. A set of criteria is presented, followed by a brief discussion of how well different candidates from the principal macroalgae groups, green, brown, and red algae, meet these criteria. Based on our analyses, we conclude that the red seaweed, Porphyra yezoensis Ueda, should be the leading candidate for a macroalgal genomics initiative. We realize, of course, that others in the phycological community might have a different opinion and that a broad consensus among algal researchers is required to make seaweed genomics a reality; thus the primary intention of this review is to initiate and encourage further discussion as to where the phycological community should focus its genomic efforts.     

CONTRASTING EFFECTS OF METHIONINE SULFOXIMINE ON UPTAKE AND ASSIMILATION OF AMMONIUM IN ULVA INTESTINALIS (CHLOROPHYCEAE)1

Ammonium is assimilated in algae by the glutamine synthetase (GS)–glutamine:2‐oxoglutarate aminotransferase pathway. In addition to the assimilation of external ammonium taken up across the cell membrane, an alga may have to reassimilate ammonium derived from endogenous sources (i.e. nitrate reduction, photorespiration, and amino acid degradation). Methionine sulfoximine (MSX), an irreversible inhibitor of GS, completely inhibited GS activity in Ulva intestinalis L. after 12 h. However, assimilation of externally derived ammonium was completely inhibited after only 1–2 h in the presence of MSX and was followed by production of endogenous ammonium. However, endogenous ammonium production in U. intestinalis represented only a mean of 4% of total assimilation attributable to GS. The internally controlled rate of ammonium uptake (V_i) was almost completely inhibited in the presence of MSX, suggesting that V_i is a measure of the maximum rate of ammonium assimilation. After complete inhibition of ammonium assimilation in the presence of MSX, the initial or surge (V_s) rate of ammonium uptake in the presence of 400 μM ammonium chloride decreased by only 17%. However, the amount that the rate of ammonium uptake decreased by was very similar to the uninhibited rate of ammonium assimilation. In addition, the decrease in the rate of ammonium uptake in darkness (in the absence of MSX) in the presence of 400 μM ammonium chloride matched the decrease in the rate of ammonium assimilation. However, in the presence of 10 μM ammonium chloride, MSX completely inhibited ammonium assimilation but had no effect on the rate of uptake.     

THALLUS DIFFERENTIATION OF PHOTOSYNTHESIS,GROWTH, REPRODUCTION,AND UV‐B SENSITIVITY IN THE GREEN ALGA ULVA PERTUSA (CHLOROPHYCEAE)1

The chlorophyte Ulva is perceived as a simple and uniform algal form, with little functional differentiation within a thallus. We compared morphology, pigmentation, photosynthesis, growth, reproduction, and UV‐B sensitivity between different thallus regions of Ulva pertusa Kjellman. Thallus thickness and cell size were significantly greater, whereas cell number was less in the basal region than in other regions. Photosynthetic pigment contents were lowest in the basal region and increased toward the marginal region. Photosynthetic capacity and photosynthetic efficiency normalized to fresh weight, area, volume, and cell number showed a progressive increase from the basal to marginal parts; however, on a chl basis those values were equal regardless of thallus part. Values of light saturation point were not statistically different between regions. Growth rates increased from marginal to basal and to middle parts of the thallus, whereas sporulation was highest in marginal (100%) followed by middle (30%) and basal parts (0%). Daily observation over 9 days showed that 56% of the basal cells divided once and did not produce spores, whereas every marginal cell went through its first division and 89% of the primary daughter cells also divided, resulting in 100% sporulation. A 7‐day treatment with PAR and PAR + UV‐A caused a significant decrease in the effective quantum yield of all thallus regions, followed by a recovery toward the initial values, whereas PAR + UV‐A + UV‐B irradiation led to greater photoinhibition and less recovery. Marked differences in the UV‐B sensitivity were observed, with marginal parts being more sensitive and basal parts most resistant.     

温度和盐度对浒苔生长和光合生理特性的影响

为研究海水盐度和温度对大型海藻光合生理影响的复合效应,选取浒苔（Ulva prolifera）为实验材料,探讨不同温度（22℃和15℃）和不同盐度（25和10）对浒苔的相对生长速率、色素含量、叶绿素荧光参数、超氧化物歧化酶（SOD）活性、可溶性蛋白含量等影响。结果表明:在低温条件下,盐度对浒苔生长的影响不显著,而在正常温度条件下,盐度降低显著降低了浒苔的生长;在低盐条件下,尽管差异不显著,温度降低呈现出促进浒苔生长的趋势,但在正常盐度条件下,低温降低了浒苔的生长。相对于温度变化,盐度变化对浒苔潜在的光合效率（F_v/F_m）影响不明显,但低温低盐处理下浒苔具有较高的效光化学效率（F_v’/F_m’）、光能利用效率（α）、非光化学淬灭（NPQ）、SOD酶活性及可溶性蛋白含量。     

Charged hydrophilic polymer brushes and their relevance for understanding marine biofouling

The resistance of charged polymers to biofouling was investigated by subjecting cationic (PDMAEMA), anionic (PSPMA), neutral (PHEMA-co-PEG₁₀MA), and zwitterionic (PSBMA) brushes to assays testing protein adsorption; attachment of the marine bacterium Cobetia marina; settlement and adhesion strength of zoospores of the green alga Ulva linza; settlement of barnacle (Balanus amphitrite and B. improvisus) cypris larvae; and field immersion tests. Several results go beyond the expected dependence on direct electrostatic attraction; PSPMA showed good resistance towards attachment of C. marina, low settlement and adhesion of U. linza zoospores, and significantly lower biofouling than on PHEMA-co-PEG₁₀MA or PSBMA after a field test for one week. PDMAEMA showed potential as a contact-active anti-algal coating due to its capacity to damage attached spores. However, after field testing for eight weeks, there were no significant differences in biofouling coverage among the surfaces. While charged polymers are unsuitable as antifouling coatings in the natural environment, they provide valuable insights into fouling processes, and are relevant for studies due to charging of nominally neutral surfaces.     

SUMMER DECLINE OF ULVA LACTUCA (CHLOROPHYTA) IN A EUTROPHIC EMBAYMENT: INTERACTIVE EFFECTS OF TEMPERATURE AND NITROGEN AVAILABILITY?1

Throughout the summer, abundance of Ulva lactuca L. declined while biomass of Cladophora vagabunda (L.) van den Hoek and Gracilaria tikvahiae McLachlan increased in a New England embayment undergoing eu-trophication (Waquoit Bay, Massachusetts). We investigated the physiological basis for the summer dieback, focusing on temporal variations in photosynthetic performance and tissue nitrogen (N). We also compared photosynthetic and N uptake capabilities of U. lactuca with other abundant species in this eutrophic system. Photosynthetic egiciency and capacity of U. lactuca declined markedly at 25°C, compared with a spring (15°C) peak in photosynthetic performance; P_max was 4.6 ± 0.3 and 1.8 ± 0.6 μmol O₂.m^?2.s^?1 during spring and summer, respectively. Notably, summer p_max of other abundant species of the embayment was 1.5–3 × higher than that measured for U. lactuca. Ulva lactuca showed a signifciant photosynthetic response to dissolved inorganic carbon enrichment during summer, when water-column-dissolved CO₂ levels were 20% of spring values. Although ammonium uptake rates of U. lactuca were extremely high at both subsaturating (15μM) and saturating (75 μM) N concentrations, as predicted by the functional-form hypothesis, tissue N fell to 1% by late summer. We suggest that a carbon imbalance, initiated by rising water temperatures and declining water-column N; thermal stress; and biological factors (competition, grazing) all contribute to the recurrent summer decline of U. lactuca in this shallow, eutrophic embayment. Thus, while the morphology of U. lactuca might be considered a successful strategy for disturbed, or “stressed” (sensu Littler and Littler 1980), habitats, its inability to persist and flourish in this environment emphasizes the complexity of factors at work in natural systems.     

Membrane potential measurements of marine macroalgae: Porphyra purpurea and Ulva lactuca

Abstract. Accumulation of the lipophilic cation tri-phenylmethylphosphonium (TPMP⁺) has been used to estimate the plasmalemma potential (Φm) of Porphyra purpurea (Rhodophyta, Bangiales) and Ulva lactuca (Chlorophyta, Ulvales). Values of Φm obtained using the Nernst equation were −61 mV and −54 mV respectively; these values compare well with those obtained using glass microelectrodes. A trend of hyperpolarization of Φm in P. purpurea was observed with decreasing external salinity. This hyperpolarization was shown to be primarily due to changes in external K⁺ concentration. Varying external Na⁺ concentration was found to have little effect on Φm. The present data suggest that the membrane potential of P. purpurea is not wholly due to a K⁺ diffusion potential, but may have an electrogenic component.     

Carbonate ions appear to neither inhibit nor stimulate use of bicarbonate ions in photosynthesis by Ulva lactuca

Rates of photosynthesis by the marine macroalga Ulva lactuca were measured in a factorial experiment at five concentrations of HCO₃^? and CO₃^2- between 0·20 and 1·26 mol m^?3, but very low concentrations of CO₂. The results demonstrated that HCO₃^? was available for use, but an analysis of variance showed that CO₃^2- had neither an inhibiting nor a stimulating effect on rates of photosynthesis over this concentration range. Over the experiment, pH varied from 8·46 to 10·06 and this also had no significant effect on rates of photosynthesis. The lack of a stimulatory effect of high concentrations of CO₃^2- on the rate of photosynthesis at low concentrations of HCO₃^? was taken as circumstantial evidence for direct uptake of HCO₃^? rather than proton extrusion and external production of CO₂. In the rockpools in which U. lactuca grows, pH values up to 10·35 have been recorded, and for much of the time, CO₃^2- was the major form of inorganic carbon available. The apparent lack of an ability to use CO₃^2- under these conditions suggests that direct use of CO₃^2- as a source of inorganic carbon for photosynthesis is unlikely to be widespread.