Cell wall composition affects Cd2+ accumulation and intracellular thiol peptides in marine red algae

Calcium polypeptide mitigates Cd toxicity in rice via reducing oxidative stress and regulating pectin modification

KEY MESSAGE

Calcium polypeptide plays a key role during cadmium stress responses in rice, which is involved in increasing peroxidase activity, modulating pectin methylesterase activity, and regulating cell wall by reducing malondialdehyde content. Cadmium (Cd) contamination threatens agriculture and human health globally, emphasizing the need for sustainable methods to reduce cadmium toxicity in crops. Calcium polypeptide (CaP) is a highly water-soluble small molecular peptide acknowledged for its potential as an organic fertilizer in promoting plant growth. However, it is still unknown whether CaP has effects on mitigating Cd toxicity. Here, we investigated the effect of CaP application on the ability to tolerate toxic Cd in rice. We evaluated the impact of CaP on rice seedlings under varying Cd stress conditions and investigated the effect mechanism of CaP mitigating Cd toxicity by Fourier transform infrared spectroscopy (FTIR), fluorescent probe dye, immunofluorescent labeling, and biochemical analysis. We found a notable alleviation of Cd toxicity by reduced malondialdehyde content and increased peroxidase activity. In addition, our findings reveal that CaP induces structural alterations in the root cell wall by modulating pectin methylesterase activity. Altogether, our results confirm that CaP not only promoted biomass accumulation but also reduced Cd concentration in rice. This study contributes valuable insights to sustainable strategies for addressing Cd contamination in agricultural ecosystems.

Do we know the cellular location of heavy metals in seaweed? An up-to-date review of the techniques

Seaweeds are dominant organisms in coastal environments. However, in the context of global change, the integrity of these organisms is threatened by metal pollution. It is therefore important to understand how seaweeds are affected by metal concentrations in the water. Measuring the concentrations of metals in seaweed provides information about the effects of metal pollution on the seaweeds themselves and their ecosystems. Nonetheless, correct interpretation of this type of analysis requires knowledge of the cellular location of the pollutants, as the effects will differ depending on whether the metals are present in particles adhered to the surface, attached to external polysaccharides or dissolved in the cytoplasm. Thus, the objectives of this study were to compile the available information on the subcellular distribution of metals in seaweeds and to conduct a critical review of the information. We found that the existing studies provide contrasting, sometimes contradictory, results. Thus, metals have been detected entirely intracellularly and also mainly outside of the cells. In all of the studies reviewed, which used different techniques (mainly extracellular elution, X-ray microanalysis and centrifugation), methodological and/or conceptual problems were identified that raise questions about the effectiveness of each approach. To obtain reliable information about the distribution of metals in algal cells, further studies must be conducted that take into consideration the differences between elements and algal species and the limits of the methods used to measure the elements.

Macroalgae metal-biomonitoring in Antarctica: Addressing the consequences of human presence in the white continent

Marine ecosystems in the Arctic and Antarctica were once thought pristine and away from important human influence. Today, it is known that global processes as atmospheric transport, local activities related with scientific research bases, military and touristic maritime traffic, among others, are a potential source of pollutants. Macroalgae have been recognized as reliable metal-biomonitoring organisms due to their accumulation capacity and physiological responses. Metal accumulation (Al, Cd, Cu, Fe, Pb, Zn, Se, and Hg) and photosynthetic parameters (associated with in vivo chlorophyll a fluorescence) were assessed in 77 samples from 13 different macroalgal species (Phaeophyta; Chlorophyta; Rhodophyta) from areas with high human influence, nearby research and sometimes military bases and a control area, King George Island, Antarctic Peninsula. Most metals in macroalgae followed a pattern influenced by rather algal lineage than site, with green seaweeds displaying trends of higher levels of metals as Al, Cu, Cr and Fe. Photosynthesis was also not affected by site, showing healthy organisms, especially in brown macroalgae, likely due to their great dimensions and morphological complexity. Finally, data did not demonstrate a relationship between metal accumulation and photosynthetic performance, evidencing low anthropogenic-derived impacts associated with metal excess in the area. Green macroalgae, especially Monostroma hariotti, are highlighted as reliable for further metal biomonitoring assessments. In the most ambitious to date seaweed biomonitoring effort conducted towards the Austral pole, this study improved by 91% the overall knowledge on metal accumulation in macroalgae from Antarctica, being the first report in species as Sarcopeltis antarctica and Plocamium cartilagineum. These findings may suggest that human short- and long-range metal influence on Antarctic coastal ecosystems still remains under control.

Selective incorporation of rare earth elements by seaweeds from Cape Mondego, western Portuguese coast

This study examined the mechanism of incorporation of the rare earth elements (REEs), La, Ce, Nd, Eu, Gd, Tb, Yb, into green (Codium tomentosum, Ulva rigida), red (Gracilaria gracilis, Osmundea pinnatifida, Porphyra sp), and brown seaweeds (Saccorhiza polyschides, Undaria pinnatifida) collected from a single site near the coastline of the Cape Mondego, western Portugal. The concentrations of REEs, Mg, Ca, Al, Fe, Zn, and Cu in the biomasses were determined by inductively-coupled plasma mass spectrometry (ICP-MS). The species showed differences in their incorporation and fractionation of REEs from the same environment: the sum of REEs was higher in U. rigida, C. tomentosum, G. gracilis, and O. pinnatifida (0.7-1.7 μg g^-1) than in Porphyra sp., S. polyschides, and U. pinnatifida (0.1-0.2 μg g^-1). Ratios of Ce/Yb ranged from 13 (in S. polyschides) to 103 (in U. rigida), indicating different proportions of light and heavy REEs among species. Good correlations were found between Al and Fe (R² = 0.98), and between these elements and La, Ce, Nd, Gd (R² = 0.88-0.97) and Yb (R² = 0.66-0.71) for all species except C. tomentosum and G. gracilis. Profiles of REE values normalised to average upper-continental crust composition indicated positive anomalies of Eu and Tb that reinforced the singularity of these elements in the REE group. Correlations between the REEs and Al or Fe suggest that detrital terrigenous particles, adhered to seaweed walls, may be an important mechanism for the incorporation of REEs by seaweeds. Different patterns for C. tomentosum and G. gracilis may also be indicative of the higher influence of cell wall composition on REE incorporation.

Mitigation effects of CO2-driven ocean acidification on Cd toxicity to the marine diatom Skeletonema costatum

Ocean acidification (OA) is a global problem to marine ecosystems. Cadmium (Cd) is a typical metal pollutant, which is non-essential but extremely toxic to marine organisms. The combined effects of marine pollution and climate-driven ocean changes should be considered for the effective marine ecosystem management of coastal areas. Previous reports have separately investigated the influences of OA and Cd pollution on marine organisms. However, little is known of the potential combined effects of OA and Cd pollution on marine diatoms. We investigated the sole and combined influences of OA (1500 ppm CO₂) and Cd exposure (0.4 and 1.2 mg/L) on the coastal diatom Skeletonema costatum. Our results clearly showed that OA significantly alleviated the toxicity of Cd to S. costatum growth and mitigated the oxidant stress, although the intercellular Cd accumulation still increased. OA partially rescued S. costatum from the inhibition of photosynthesis and pyruvate metabolism caused by Cd exposure. It also upregulated genes involved in gluconeogenesis, glycolysis, the citrate cycle (TCA), Ribonucleic acid (RNA) metabolism, and especially the biosynthesis of non-protein thiol compounds. These changes might contribute to algal growth and Cd resistance. Overall, this study demonstrates that OA can alleviate Cd toxicity to S. costatum and explores the potential underlying mechanisms at both the cellular and molecular levels. These results will ultimately help us understand the impacts of combined stresses of climate change and metal pollution on marine organisms and expand the knowledge of the ecological risks of OA.

Macroalgae as spatial and temporal bioindicators of coastal metal pollution following remediation and diversion of acid mine drainage

Acid mine drainage (AMD) is a significant contributor of metal pollution leading to ecosystem damage. Bioindicator organisms such as intertidal brown macroalgae have an important role in quantifying the risks of metal bioaccumulation in coastal locations exposed to AMD contamination. Measurement of As, Cd, Cu, Fe, Pb, and Zn accumulation was performed in Fucus serratus, Fucus vesiculosus and Ascophyllum nodosum sampled from two marine locations near to an abandoned Cu mine in Anglesey, Wales, UK. Transect samples were taken from a coastal location (Amlwch) that has seen a substantial increase in AMD contamination over 15 years, in comparison to a nearby estuarine location (Dulas Estuary leading to Dulas Bay) with a historic legacy of pollution. These were compared with samples from the same sites taken 30 years earlier. Some of the Dulas macroalgae samples had Cd, Cu and Zn concentrations that were above background but in general indicated a non-polluted estuary in comparison to substantial pollution over previous decades. In contrast, Fucus samples collected from directly below an AMD outflow at Amlwch showed extremely elevated metal bioaccumulation (>250 mg Fe g^-1, >6 mg Cu g^-1, >2 mg Zn g^-1, >190 μg As g^-1) and evidence of macroalgae toxicity, indicating severe pollution at this site. However, the pollution dispersed within 200 m of the outflow source. This study has demonstrated the efficiency of three brown macroalgae species as indicators for metal bioavailability at high spatial resolution and over time.

Algal cell response to laboratory-induced cadmium stress: a multimethod approach

We examined the response of algal cells to laboratory-induced cadmium stress in terms of physiological activity, autonomous features (motility and fluorescence), adhesion dynamics, nanomechanical properties, and protein expression by employing a multimethod approach. We develop a methodology based on the generalized mathematical model to predict free cadmium concentrations in culture. We used algal cells of Dunaliella tertiolecta, which are widespread in marine and freshwater systems, as a model organism. Cell adaptation to cadmium stress is manifested through cell shape deterioration, slower motility, and an increase of physiological activity. No significant change in growth dynamics showed how cells adapt to stress by increasing active surface area against toxic cadmium in the culture. It was accompanied by an increase in green fluorescence (most likely associated with cadmium vesicular transport and/or beta-carotene production), while no change was observed in the red endogenous fluorescence (associated with chlorophyll). To maintain the same rate of chlorophyll emission, the cell adaptation response was manifested through increased expression of the identified chlorophyll-binding protein(s) that are important for photosynthesis. Since production of these proteins represents cell defence mechanisms, they may also signal the presence of toxic metal in seawater. Protein expression affects the cell surface properties and, therefore, the dynamics of the adhesion process. Cells behave stiffer under stress with cadmium, and thus, the initial attachment and deformation are slower. Physicochemical and structural characterizations of algal cell surfaces are of key importance to interpret, rationalize, and predict the behaviour and fate of the cell under stress in vivo.

Tolerance of Pseudochlorella pringsheimii to Cd and Pb stress: Role of antioxidants and biochemical contents in metal detoxification

The tolerance and antioxidant response of the green alga P. pringsheimii to cadmium (Cd) and lead (Pb) was investigated. The algal biomass was constant at the relatively lower metal concentrations of Cd and Pb (5, 12 µM, and 2.5-200 µM, respectively), whereas higher concentrations severely inhibited the algal biomass yield. The pigment content of P. pringsheimii decreased due to the investigated metals, especially with Cd concentrations. However, the Pb concentrations of 2.5-200 µM enhanced the pigment content. The carotenoids content was highly repressed by the Cd concentrations. Nevertheless, Pb concentrations highly stimulated the carotenoids content, with the exception of 400 and 500 µM Pb. The biochemical contents of P. pringsheimii including phenolic, total soluble protein and carbohydrate contents responded variably to the investigated metals. The concentrations of Cd were found to be harmful to total soluble protein and carbohydrates, but not the phenolic contents. However, all biochemical contents were stimulated under relatively lower Pb concentrations. Markedly for Pb, the radical scavenging, reducing power, and chelating activities improved under the metals exposure excluding higher concentrations. The activities of the antioxidant enzymes (SOD, CAT, and POD) were highly stimulated with all treatments (except for CAT activities at the highest Cd and Pb concentrations, 300 and 500 µM, respectively). Remarkably, Cd treatments have higher antioxidant enzyme activities compared to that of Pb treatments. The antioxidants augmentation of P. pringsheimii under the metal stress may be exploited for future application in several fields.

Removal and recovery of Critical Rare Elements from contaminated waters by living Gracilaria gracilis

The experiments performed in this work proved the ability of Gracilaria gracilis to concentrate and recover Critical Rare Elements (CRE) from contaminated waters. The importance of recycling these elements is related to their very limited sources in Nature and progressive use in technologies. Moreover, their mining exploitation has negative environmental impact, and recent studies point them as new emerging pollutants. To the best of our knowledge, this is the first report on the application of living macroalgae for the removal and recovery of CRE. G. gracilis (2.5gL^-1, fresh weight) was exposed to mono- and multi-element saline solutions of 500μgL^-1 of Y, Ce, Nd, Eu and La. Removal was up to 70% in 48h, with bioaccumulation following Elovich kinetic model. In multi-element solutions, selectivity was not observed although removal of lanthanides improved comparatively to single-element solutions. No mortality or adverse effect on growth was registered. The subsequent macroalgae digestion allowed collecting virtually 100% of all elements in a 300-fold more concentrated solution. The overall results suggest the application of living macroalgae as a simple and effective alternative technology for removing and recovering CRE from wastewaters, contributing to an improvement of water quality and CRE recycling.

Cadmium effect on physiological responses of the tolerant Chlorophyta specie Picocystis sp. isolated from Tunisian wastewaters

This study aims to investigate the effects of different concentrations of cadmium (Cd) (0-800 μM) on the growth, the photosynthetic performance, and the biochemical parameters of the Chlorophyta Picocystis sp. during 3 and 9 days. Results showed that this exposure did not inhibit the Picocystis growth during the first 3 days of treatment. Growth inhibition did not exceed 53%, which was recorded at high Cd concentrations (800 μM) after nine exposure days. Moreover, no inhibitory effect on the Picocystis sp. photosynthesis has been recorded during the three exposure days regardless the Cd concentrations. Lipid peroxidation was significantly increased at high Cd concentrations (500 and 800 μM) by 40 and 80%, respectively. Furthermore, the highest Cd concentration enhanced the thiol protein content, indicating no consequent protein oxidation. The exposure of Picocystis to Cd stimulated the antioxidant activities of catalase and ascorbate peroxidase. These results showed that Picocystis sp. has an impressive tolerance to Cd stress.

Quantitative Relationship between Cadmium Uptake and the Kinetics of Phytochelatin Induction by Cadmium in a Marine Diatom

Heavy metals activate the synthesis of phytochelatins (PCs), while the induced PCs might affect metal uptake via chelating intracellular free metals. However, the relationship of PCs to metal uptake is poorly understood. In this study, we examined the kinetics of cadmium (Cd) accumulation and the synthesis of PCs in a marine diatom, Thalassiosira weissflogii, under different irradiance levels. Irradiance alone could not change the concentrations of PCs in the Cd-free treatments, while higher irradiance accelerated the induction of intracellular PCs at the same [Cd²⁺] level. PC-SH (2 × PC₂ + 3 × PC₃ + 4 × PC₄) was bound with Cd at a stoichiometric ratio of 2 to 49 in our short-term uptake experiments, indicating that PC induction is sufficient to serve as the first line of defense against Cd stress. A positive linear correlation between the induction rate of PCs and the Cd uptake rate was observed, while the ratio of the PC content to intracellular Cd varied greatly when the irradiance was increased several fold. Because metal uptake has been successfully used in predicting acute metal toxicity, our findings are helpful for understanding the role of PCs in metal detoxification and developing PCs as biomarkers for metal sensitivity.

Mechanisms of metal tolerance in marine macroalgae, with emphasis on copper tolerance in Chlorophyta and Rhodophyta

Green and red macroalgae are closely related organisms, and with terrestrial plants, and constitute the base of marine food webs in coastal ecosystems. Green and red seaweeds, as all living organisms, require essential metals, such as copper, iron, zinc, which can act as co-factors for several proteins and enzymes; however, these metals in excess can induce stress and impair cell viability. Most important negative effects of metal excess are related to the induction of an oxidative stress condition, characterized by the over-accumulation of Reactive Oxygen Species (ROS). In this respect, copper, abundant in wastewaters disposed to coastal environments from domestic and industrial activities, has been one of the most studied metals. Different investigations have provided evidence that green and red macroalgae display several defenses against copper excess to prevent, or at least reduce, stress and damage, among which are cellular exclusion mechanisms, synthesis of metal-chelating compounds, and the activation of the antioxidant system. Most important defense mechanisms identified in green and red seaweed involve: metal-binding to cell wall and epibionts; syntheses of metallothioneins and phytochelatins that accumulate in the cytoplasm; and the increase in the activity of antioxidant enzymes such as superoxide dismutase, ascorbate peroxidase, glutathione peroxidase and catalase, and greater production of antioxidant metabolites as glutathione and ascorbate in organelles and the cytoplasm. In this review, we go through historical records, latest advances, and pending tasks aiming to expand our current knowledge on defense mechanisms to copper excess in green and red macroalgae, with emphasis on biochemical and molecular aspects.

The effect of different concentrations of copper and lead on the morphology and physiology of Hypnea musciformis cultivated in vitro: a comparative analysis

Copper and lead, as remnants of industrial activities and urban effluents, have heavily contaminated many aquatic environments. Therefore, this study aimed to determine their effects on the physiological, biochemical, and cell organization responses of Hypnea musciformis under laboratory conditions during a 7-day experimental period. To accomplish this, segments of H. musciformis were exposed to photosynthetic active radiation at 80 μmol photons m(-2) s(-1), Cu (0.05 and 0.1 mg kg(-1)), and Pb (3.5 and 7 mg kg(-1)). Various intracellular abnormalities resulted from exposure to Cu and Pb, including a decrease in phycobiliproteins. Moreover, carotenoid and flavonoid contents, as well as phenolic compounds, were decreased, an apparent reflection of chemical antioxidant defense against reactive oxygen species. Treatment with Cu and Pb also caused an increase in the number of floridean starch grains, probably as a defense against nutrient deprivation. Compared to plants treated with lead, those treated with copper showed higher metabolic and ultrastructural alterations. These results suggest that H. musciformis more readily internalizes copper through transcellular absorption. Finally, as a result of ultrastructural damage and metabolic changes observed in plants exposed to different concentrations of Cu and Pb, a significant reduction in growth rates was observed. Nevertheless, the results indicated different susceptibility of H. musciformis to different concentrations of Cu and Pb.

Cadmium removal by Euglena gracilis is enhanced under anaerobic growth conditions

The facultative protist Euglena gracilis, a heavy metal hyper-accumulator, was grown under photo-heterotrophic and extreme conditions (acidic pH, anaerobiosis and with Cd(2+)) and biochemically characterized. High biomass (8.5×10(6)cellsmL(-1)) was reached after 10 days of culture. Under anaerobiosis, photosynthetic activity built up a microaerophilic environment of 0.7% O₂, which was sufficient to allow mitochondrial respiratory activity: glutamate and malate were fully consumed, whereas 25-33% of the added glucose was consumed. In anaerobic cells, photosynthesis but not respiration was activated by Cd(2+) which induced higher oxidative stress. Malondialdehyde (MDA) levels were 20 times lower in control cells under anaerobiosis than in aerobiosis, although Cd(2+) induced a higher MDA production. Cd(2+) stress induced increased contents of chelating thiols (cysteine, glutathione and phytochelatins) and polyphosphate. Biosorption (90%) and intracellular accumulation (30%) were the mechanisms by which anaerobic cells removed Cd(2+) from medium, which was 36% higher versus aerobic cells. The present study indicated that E. gracilis has the ability to remove Cd(2+) under anaerobic conditions, which might be advantageous for metal removal in sediments from polluted water bodies or bioreactors, where the O₂ concentration is particularly low.

Subcellular Sequestration and Impact of Heavy Metals on the Ultrastructure and Physiology of the Multicellular Freshwater Alga Desmidium swartzii

Due to modern life with increasing traffic, industrial production and agricultural practices, high amounts of heavy metals enter ecosystems and pollute soil and water. As a result, metals can be accumulated in plants and particularly in algae inhabiting peat bogs of low pH and high air humidity. In the present study, we investigated the impact and intracellular targets of aluminum, copper, cadmium, chromium VI and zinc on the filamentous green alga Desmidium swartzii, which is an important biomass producer in acid peat bogs. By means of transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) it is shown that all metals examined are taken up into Desmidium readily, where they are sequestered in cell walls and/or intracellular compartments. They cause effects on cell ultrastructure to different degrees and additionally disturb photosynthetic activity and biomass production. Our study shows a clear correlation between toxicity of a metal and the ability of the algae to compartmentalize it intracellularly. Cadmium and chromium, which are not compartmentalized, exert the most toxic effects. In addition, this study shows that the filamentous alga Desmidium reacts more sensitively to aluminum and zinc when compared to its unicellular relative Micrasterias, indicating a severe threat to the ecosystem.

Response differences between Ectocarpus siliculosus populations to copper stress involve cellular exclusion and induction of the phytochelatin biosynthetic pathway

Some populations of brown seaweed species inhabit metal-polluted environments and can develop tolerance to metal stress, but the mechanisms by which this is accomplished are still to be elucidated. To address this, the responses of two strains of the model brown alga Ectocarpus siliculosus isolated from sites with different histories of metal contamination exposed to total copper (CuT) concentrations ranging between 0 and 2.4 μM for 10 days were investigated. The synthesis of the metal-chelator phytochelatin (PCs) and relative levels of transcripts encoding the enzymes γ-glutamylcysteine synthetase (γ-GCS), glutathione synthase (GS) and phytochelatin synthase (PCS) that participate in the PC biosynthetic pathway were measured, along with the effects on growth, and adsorption and uptake of Cu. Growth of strain LIA, from a pristine site in Scotland, was inhibited to a greater extent, and at lower concentrations, than that of Es524, isolated from a Cu-contaminated site in Chile. Concentrations of intra-cellular Cu were higher and the exchangeable fraction was lower in LIA than Es524, especially at the highest exposure levels. Total glutathione concentrations increased in both strains with Cu exposure, whereas total PCs levels were higher in Es524 than LIA; PC2 and PC3 were detected in Es524 but PC2 only was found in LIA. The greater production and levels of polymerisation of PCs in Es524 can be explained by the up-regulation of genes encoding for key enzymes involved in the synthesis of PCs. In Es524 there was an increase in the transcripts of γ-GCS, GS and PCS, particularly under high Cu exposure, whereas in LIA4 transcripts of γ-GCS1 increased only slightly, γ-GCS2 and GS decreased and PCS did not change. The consequences of higher intra-cellular concentrations of Cu, lower production of PCs, and lower expression of enzymes involved in GSH-PCs synthesis may be contributing to an induced oxidative stress condition in LIA, which explains, at least in part, the observed sensitivity of LIA to Cu. Therefore, responses to Cu exposure in E. siliculosus relate to the contamination histories of the locations from where the strains were isolated and differences in Cu exclusion and PCs production are in part responsible for the development of intra-specific resistance.

Cadmium uptake in Elodea canadensis leaves and its interference with extra- and intra-cellular pH

This study investigated cadmium (Cd) uptake in Elodea canadensis shoots under different photosynthetic conditions, and its effects on internal (cytosolic) and external pH. The plants were grown under photosynthetic (light) or non-photosynthetic (dark or in the presence of a photosynthetic inhibitor) conditions in the presence or absence of CdCl2 (0.5 μm) in a medium with a starting pH of 5.0. The pH-sensitive dye BCECF-AM was used to monitor cytosolic pH changes in the leaves. Cadmium uptake in protoplasts and leaves was detected with a Cd-specific fluorescent dye, Leadmium Green AM, and with atomic absorption spectrophotometry. During cultivation for 3 days without Cd, shoots of E. canadensis increased the pH of the surrounding water, irrespective of the photosynthetic conditions. This medium alkalisation was higher in the presence of CdCl2 . Moreover, the presence of Cd also increased the cation exchange capacity of the shoots. The total Cd uptake by E. canadensis shoots was independent of photosynthetic conditions. Protoplasts from plants exposed to 0.5 μm CdCl2 for 3 days did not exhibit significant change in cytosolic [Cd(2+)] or pH. However, exposure to CdCl2 for 7 days resulted in increased cytosolic [Cd(2+) ] as well as pH. The results suggest that E. canadensis subjected to a low CdCl2 concentration initially sequesters Cd into the apoplasm, but under prolonged exposure, Cd is transported into the cytosol and subsequently alters cytosolic pH. In contrast, addition of 10-50 μm CdCl2 directly to protoplasts resulted in immediate uptake of Cd into the cytosol.

Green tide deactivation with layered-structure cuboids of Ag/CaTiO3 under UV light

In this work, an alternative to deactivate noxious green tide Tetraselmis suecica in the short-term is proposed by employing Perovskite-like cube-shaped, crystalline CaTiO3 semiconductors functionalized with atomic silver nanoparticles. CaTiO3 was prepared by a microwave-assisted hydrothermal method and then Ag(0)NPs (1 wt% of CaTiO3), were added by the photoreduction method. The XRD results show that crystalline CaTiO3 has an orthorhombic unit cell with a Perovskite-like structure. Images obtained by FESEM and HRTEM microscopies show well-faceted CaTiO3 rectangular prismatic morphology functionalizated with silver nanoparticles ≈ 13.5 nm. XPS and EDS-FESEM has confirmed the composition of CaTiO3 and silver occurring mainly as reduced metal. The UV inactivation of noxious T. suecica with Ag/CaTiO3 nanocomposites formed on bare materials results in complete deactivation of the algae in 12 min. The direct contact between harmful algae and Ag/CaTiO3 nanocomposite is necessary to deactivate the algae and inhibits algae viability.

Generation of a phage-display library of single-domain camelid VH H antibodies directed against Chlamydomonas reinhardtii antigens, and characterization of VH Hs binding cell-surface antigens

Single-domain antibodies (sdAbs) are powerful tools for the detection, quantification, purification and subcellular localization of proteins of interest in biological research. We have generated camelid (Lama pacos) heavy chain-only variable VH domain (VH H) libraries against antigens in total cell lysates from Chlamydomonas reinhardtii. The sdAbs in the sera from immunized animals and VH H antibody domains isolated from the library show specificity to C. reinhardtii and lack of reactivity to antigens from four other algae: Chlorella variabilis, Coccomyxa subellipsoidea, Nannochloropsis oceanica and Thalassiosira pseudonana. Antibodies were produced against a diverse representation of antigens as evidenced by sera ELISA and protein-blot analyses. A phage-display library consisting of the VH H region contained at least 10(6) individual transformants, and thus should represent a wide range of C. reinhardtii antigens. The utility of the phage library was demonstrated by using live C. reinhardtii cells to pan for VH H clones with specific recognition of cell-surface epitopes. The lead candidate VH H clones (designated B11 and H10) bound to C. reinhardtii with EC50 values ≤ 0.5 nm. Treatment of cells with VH H B11 fused to the mCherry or green fluorescent proteins allowed brilliant and specific staining of the C. reinhardtii cell wall and analysis of cell-wall genesis during cell division. Such high-complexity VH H antibody libraries for algae will be valuable tools for algal researchers and biotechnologists.

A comprehensive study of metal distribution in three main classes of seaweed

This paper provides one of the most comprehensive studies of metal distributions in three main macroalgae species. In this novel study, levels of total, intracellular and surface bound Pb, Zn, As, Cd, Co, Cr, Cu, Mn and Ni associated with Polysiphonia lanosa (L) Tandy, Ascophyllum nodosum (L) Le Jolis, Fucus vesiculosus (L) and Ulva sp. were determined. Additionally, water and sediment metal levels were analysed to gain an insight into the relative uptake efficiencies of different macroalgal species. Samples were collected from a clean site in Fethard-on-Sea, Wexford, Ireland (52°11'53.68'N, 6°49'34.64'W), in May 2008. Results demonstrated that total, intracellular and surface bound metal levels varied according to metal and seaweed species, with the highest proportion of metals found to be intracellular. Inhibition of Mn uptake by Zn was indicated for P. lanosa. Furthermore, P. lanosa had enhanced bioaccumulation ability, with the highest Concentration Factor reported of any seaweed to date.

Inter-population comparisons of copper resistance and accumulation in the red seaweed, Gracilariopsis longissima

Copper (Cu) resistance and accumulation of five populations of the red seaweed Gracilariopsis longissima collected from sites in south west England (Fal Estuary, Helford Estuary and Chesil Fleet) that differ in their degree of Cu contamination was assessed under controlled laboratory conditions, on two separate occasions (April and October). The effects of a range of Cu concentrations (0-250 μg l(-1)) on relative growth rates was the same for all populations with reductions observable at concentrations as low as 12 μg l(-1) and cessation of growth at 250 μg l(-1). There was no significant difference in the calculated EC(50) values for the April and October samples, with means of 31.1 and 25.8 μg l(-1), respectively. Over the range of concentrations used in this study, copper content increased linearly and the pattern of accumulation was the same for all populations at both time periods. From the linear regressions of the pooled data a concentration factor of 2.25 × 10(3) was calculated. These results imply that G. longissima has an innate tolerance to Cu and that populations have not evolved copper-tolerant ecotypes. In laboratory studies, accumulated Cu was released when transferred to 'clean' seawater with approximately 80% being lost after 8 days, with no significant difference between populations in their response. The results from a 30 days in situ transplantation experiment using two populations from the Fal Estuary provided further evidence for dynamic changes in Cu content in response to changes in Cu bioavailability. The findings in this study are discussed in the context of implications for seaweed biomonitoring.

Metal uptake by microalgae: underlying mechanisms and practical applications

Metal contamination of a few aquatic, atmospheric, and soil ecosystems has increased ever since the industrial revolution, owing to discharge of such elements via the effluents of some industrial facilities. Their presence to excessive levels in the environment will eventually lead to serious health problems in higher animals owing to accumulation throughout the food web. Current physicochemical methods available for recovery of metal pollutants (e.g., chemical precipitation, oxidation/reduction, or physical ion exchange) are either expensive or inefficient when they are present at very low concentrations. Consequently, removal of toxic metals by microorganisms has emerged as a potentially more economical alternative. Microalgae (in terms of both living and nonliving biomass) are an example of microorganisms suitable to recover metals and able to attain noteworthy percent removals. Their relatively high metal-binding capacities arise from the intrinsic composition of their cell walls, which contain negatively charged functional groups. Consequently, microalgal cells are particularly efficient in uptake of those contaminants when at low levels. Self-defense mechanisms developed by microalgal cells to survive in metal-containing media and environmental factors that affect their removal (e.g., pH, temperature, and biomass concentration) are reviewed here in a comprehensive way and further discussed in attempts to rationalize this form of remediation vis-a-vis with conventional nonbiological alternatives.

Algae as promising organisms for environment and health

Algae, like other plants, produce a variety of remarkable compounds collectively referred to as secondary metabolites. They are synthesized by these organisms at the end of the growth phase and/or due to metabolic alterations induced by environmental stress conditions. Carotenoids, phenolic compounds, phycobiliprotein pigments, polysaccharides and unsaturated fatty acids are same of the algal natural products, which were reported to have variable biological activities, including antioxidant activity, anticancer activity, antimicroabial activity against bacteria-virus-algae-fungi, organic fertilizer and bioremediation potentials.

Disarrangement of actin filaments and Ca²⁺ gradient by CdCl₂ alters cell wall construction in Arabidopsis thaliana root hairs by inhibiting vesicular trafficking

Cadmium (Cd), one of the most toxic heavy metals, inhibits many cellular and physiological processes in plants. Here, the involvement of cytoplasmic Ca²⁺ gradient and actin filaments (AFs) in vesicular trafficking, cell wall deposition and tip growth was investigated during root (hair) development of Arabidopsis thaliana in response to CdCl₂ treatment. Seed germination and root elongation were prevented in a dose- and time-dependent manner by CdCl₂ treatment. Fluorescence labelling and non-invasive detection showed that CdCl₂ inhibited extracellular Ca²⁺ influx, promoted intracellular Ca²⁺ efflux, and disturbed the cytoplasmic tip-focused Ca²⁺ gradient. In vivo labelling revealed that CdCl₂ modified actin organization, which subsequently contributed to vesicle trafficking. Transmission electron microscopy revealed that CdCl₂ induced cytoplasmic vacuolization and was detrimental to organelles such as mitochondria and endoplasmic reticulum (ER). Finally, immunofluorescent labelling and Fourier transform infrared (FTIR) analysis indicated that configuration/distribution of cell wall components such as pectins and cellulose was significantly altered in response to CdCl₂. Our results indicate that CdCl₂ induces disruption of Ca²⁺ gradient and AFs affects the distribution of cell wall components in root hairs by disturbing vesicular trafficking in A. thaliana.

Thiol peptides induction in the seagrass Thalassia testudinum (Banks ex König) in response to cadmium exposure

Trace metal accumulation and thiol compounds synthesis as induced by cadmium exposure was studied in the seagrass Thalassia testudinum. Shoots were exposed for 24, 48, 96 and 144 h to several CdCl(2) concentrations (0, 30, 50 and 70 microM). Levels of cadmium, cysteine, glutathione (GSH), gamma-glutamylcysteine (gamma-EC), and phytochelatin-like peptides were determined in green blades, live sheaths and root/rhizomes tissues. Metal accumulation was dependent on Cd concentration and type of tissue, with green blades showing the highest content followed by live sheaths and root/rhizomes. All tissues experienced an increase in thiol-containing compounds as a response to cadmium exposure. Live sheaths showed the highest levels of cysteine, GSH and gamma-EC. This is the first report of induction of thiol peptides, presumably phytochelatins, by a trace metal in a sea grass species.