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ATP sulfurylase (ATPS) catalyzes the first step of sulfur assimilation in photosynthetic organisms. An ATPS type A is mostly present in freshwater cyanobacteria, with four conserved cysteine residues. Oceanic cyanobacteria and most eukaryotic algae instead, possess an ATPS-B containing seven to ten cysteines; five of them are conserved, but only one in the same position as ATPS-A. We investigated the role of cysteines on the regulation of the different algal enzymes. We found that the activity of ATPS-B from four different microorganisms was enhanced when reduced and decreased when oxidized. The LC-MS/MS analysis of the ATPS-B from the marine diatom Thalassiosira pseudonana showed that the residue Cys-247 was presumably involved in the redox regulation. The absence of this residue in the ATPS-A of the freshwater cyanobacterium Synechocystis sp. instead, was consistent with its lack of regulation. Some other conserved cysteine residues in the ATPS from T. pseduonana and not in Synechocystis sp.were accessible to redox agents and possibly play a role in the enzyme regulation. Furthermore, the fact that oceanic cyanobacteria have ATPS-B structurally and functionally closer to that from most of eukaryotic algae than to the ATPS-A from other cyanobacteria suggests that life in the sea or freshwater may have driven the evolution of ATPS. [ABSTRACT FROM AUTHOR]

Microalgae have previously been reported to contain β- N -methylamino- l -alanine (BMAA), and the global presence of these primary producers has been associated with the widespread occurrence of BMAA in marine organisms. It has been repeatedly shown that filter-feeding bivalves accumulate phytoplankton species and their toxins. In this study, the concentrations of total soluble BMAA and DAB as a function of growth phase were observed for four non-axenic diatom species ( i.e. Phaeodactylum tricornutum , Chaetoceros sp., Chaetoceros calcitrans and Thalassiosira pseudonana ). These strains had previously been shown to contain BMAA using a highly selective HILIC-MS/MS method. BMAA cell quota appeared to be species-specific, however, highest BMAA concentrations were always obtained during the stationary growth phase, for all four species, suggesting that BMAA is a secondary metabolite. While DAB was detected in a bacterial culture isolated from a culture of P. tricornutum , the presence or absence of a bacterial population did not influence production of BMAA and DAB by P. tricornutum , i.e. no significant difference was noted for BMAA and DAB production between axenic and non-axenic cultures. The presence of DAB in bacteria had previously been shown, and raised the question as to whether DAB observed in many species of microalgae may arise from the non-axenic culture conditions or from the microalgae themselves. [ABSTRACT FROM AUTHOR]

Diatoms are one of the most productive and successful photosynthetic taxa on Earth and possess attributes such as rapid growth rates and production of lipids, making them candidate sources of renewable fuels. Despite their significance, few details of the mechanisms used to regulate growth and carbon metabolism are currently known, hindering metabolic engineering approaches to enhance productivity., To characterize the transcript level component of metabolic regulation, genome-wide changes in transcript abundance were documented in the model diatom Thalassiosira pseudonana on a time-course of silicon starvation. Growth, cell cycle progression, chloroplast replication, fatty acid composition, pigmentation, and photosynthetic parameters were characterized alongside lipid accumulation., Extensive coordination of large suites of genes was observed, highlighting the existence of clusters of coregulated genes as a key feature of global gene regulation in T. pseudonana. The identity of key enzymes for carbon metabolic pathway inputs (photosynthesis) and outputs (growth and storage) reveals these clusters are organized to synchronize these processes., Coordinated transcript level responses to silicon starvation are probably driven by signals linked to cell cycle progression and shifts in photophysiology. A mechanistic understanding of how this is accomplished will aid efforts to engineer metabolism for development of algal-derived biofuels. [ABSTRACT FROM AUTHOR]

Although many studies have reported the aluminum (Al) impacts on freshwater organisms and terrestrial plants in acidic and neutral pH media, little information is available on the effects of Al on organisms in the alkaline seawater. In this study, the Al effects on marine phytoplankton were investigated by growing the axenic diatom Thalassiosira weissflogii in seawater media amended with varied nutrient levels. Under phosphorus (P) limited conditions, Al enrichment resulted in an enhanced diatom growth and higher biomass accumulation, as well as the maintenance of high diatom biomass during the stationary phase. The diatom displayed higher cellular alkaline phosphatase activity (APA) under Al-enriched and P-limited conditions, which was responsible for the increased uptake of dissolved organic phosphorus (DOP). Lower dissolved APA was observed in the Al-enriched culture. In contrast, Al addition did not change the phosphate speciation in seawater or the diatom uptake of dissolved inorganic P (DIP) at low concentration, but instead made the diatoms uncompetitive under high DIP conditions. The results strongly indicated that Al treatment increased the proportion of the diatom cellular APA and their utilization efficiency of DOP, which may partly account for the beneficial effects of Al on the diatom under P-limited conditions. It is thus likely that Al may influence the ocean carbon cycling by promoting the phytoplankton utilization of DOP. [ABSTRACT FROM AUTHOR]

The health beneficial omega-3 long-chain polyunsaturated fatty acids (LC-PUFAs), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) are naturally synthesized by diatoms through consecutive steps of fatty acid elongase and desaturase enzymes. In Thalassiosira pseudonana, these fatty acids constitute about 10-20 % of the total fatty acids, with EPA accumulation being five to ten times higher than DHA. In order to identify the subcellular localization of enzymes in the pathway of LC-PUFA biosynthesis in T. pseudonana and to manipulate the production of EPA and DHA, we generated constructs for overexpressing each of the T. pseudonana long-chain fatty acid elongase genes. Full-length proteins were fused to GFP, and transgenic lines were generated. In addition, overexpressed native proteins with no GFP fusion were tested. The subcellular localization of each elongase protein was determined. We then examined the total amount of lipids and analyzed the fatty acid profile in each of the transgenic lines compared to wild type. Lines with overexpressed elongases showed an increase of up to 1.4-fold in EPA and up to 4.5-fold in DHA, and the type of fatty acid that was increased (EPA vs. DHA) depended on the type of elongase that was overexpressed. This data informs future metabolic engineering approaches to further improve EPA and DHA content in diatoms. [ABSTRACT FROM AUTHOR]

The nano- and micropatterned biosilica cell walls of diatoms are remarkable examples of biological morphogenesis and possess highly interesting material properties. Only recently has it been demonstrated that biosilica-associated organic structures with specific nanopatterns (termed insoluble organic matrices) are general components of diatom biosilica. The model diatom Thalassiosira pseudonana contains three types of insoluble organic matrices: chitin meshworks, organic microrings, and organic microplates, the latter being described in the present study for the first time. To date, little is known about the molecular composition, intracellular assembly, and biological functions of organic matrices. Here we have performed structural and functional analyses of the organic microrings and organic microplates from T. pseudonana. Proteomics analysis yielded seven proteins of unknown function (termed SiMat proteins) together with five known silica biomineralization proteins (four cingulins and one silaffin). The location of SiMat1-GFP in the insoluble organic microrings and the similarity of tyrosine- and lysine-rich functional domains identifies this protein as a new member of the cingulin protein family. Mass spectrometric analysis indicates that most of the lysine residues of cingulins and the other insoluble organic matrix proteins are post-translationally modified by short polyamine groups, which are known to enhance the silica formation activity of proteins. Studies with recombinant cingulins (rCinY2 and rCinW2) demonstrate that acidic conditions (pH 5.5) trigger the assembly of mixed cingulin aggregates that have silica formation activity. Our results suggest an important role for cingulins in the biogenesis of organic microrings and support the hypothesis that this type of insoluble organic matrix functions in biosilica morphogenesis. [ABSTRACT FROM AUTHOR]

Diatoms are widespread in aquatic ecosystems where they may be limited by the supply of inorganic carbon. Their carbon dioxide-concentrating mechanisms ( CCMs) involving transporters and carbonic anhydrases ( CAs) are well known, but the contribution of a biochemical CCM involving C4 metabolism is contentious., The CCM(s) present in the marine-centric diatom, Thalassiosira pseudonana, were studied in cells exposed to high or low concentrations of CO2, using a range of approaches., At low CO2, cells possessed a CCM based on active uptake of CO2 (70% contribution) and bicarbonate, while at high CO2, cells were restricted to CO2. CA was highly and rapidly activated on transfer to low CO2 and played a key role because inhibition of external CA produced uptake kinetics similar to cells grown at high CO2. The activities of phosphoenolpyruvate ( PEP) carboxylase ( PEPC) and the PEP-regenerating enzyme, pyruvate phosphate dikinase ( PPDK), were lower in cells grown at low than at high CO2. The ratios of PEPC and PPDK to ribulose bisphosphate carboxylase were substantially lower than 1, even at low CO2., Our data suggest that the kinetic properties of this species results from a biophysical CCM and not from C4 type metabolism. [ABSTRACT FROM AUTHOR]

In algae, the biosynthesis of docosahexaenoic acid (22:6ω3; DHA) proceeds via the elongation of eicosapentaenoic acid (20:5ω3; EPA) to 22:5ω3, which is required as a substrate for the final Δ4 desaturation. To isolate the elongase specific for this step, we searched expressed sequence tag and genomic databases from the algae Ostreococcus tauri and Thalassiosira pseudonana, from the fish Oncorhynchus mykiss, from the frog Xenopus laevis, and from the sea squirt Ciona intestinalis using as a query the elongase sequence PpPSE1 from the moss Physcomitrella patens. The open reading frames of the identified elongase candidates were expressed in yeast for functional characterization. By this, we identified two types of elongases from O. tauri and T. pseudonana: one specific for the elongation of (Δ6-)C18-PUFAs and one specific for (Δ5-)C20-PUFAs, showing highest activity with EPA. The clones isolated from O. mykiss, X. laevis, and C. intestinalis accepted both C18- and C20-PUFAs. By coexpression of the Δ6- and Δ5-elongases from T. pseudonana and O. tauri, respectively, with the Δ5- and Δ4-desaturases from two other algae we successfully implemented DHA synthesis in stearidonic acid-fed yeast.This may be considered an encouraging first step in future efforts to implement this biosynthetic sequence into transgenic oilseed crops.

Diatoms account for a large proportion of marine primary productivity, they tend to be the predominant species in the phytoplankton communities in the surface ocean with frequent and large light fluctuations. To understand the impacts of increased CO 2 on diatoms' capacity in exploitation of variable solar radiation, we cultured a model diatom Thalassiosira pseudonana with 400 or 1000ppmv CO 2 and exposed it to high photosynthetically active radiation (PAR) alone or PAR plus ultraviolet radiation (UVR) to examine its physiological performances. The results showed that the maximum photochemical efficiency (F v /fm) was significantly reduced by high PAR and PAR + UVR in T. pseudonana , UVR-induced inhibition on PSII activity was exacerbated by high CO 2. PSII activity drops coincide approximately with PsbA content in the cells exposed to high PAR or PAR + UVR, which was pronounced at high CO 2. The removal of PsbD in T. pseudonana cells declined under high CO 2 during UVR exposure, limiting the repair capacity of PSII. In addition, high CO 2 reversed the induction of energy-dependent form of NPQ by UVR to the increase of Y (No) , indicating the severe damage of the photoprotective reactions. Our findings suggest that the adverse impacts of UVR on PSII function of T. pseudonana were aggravated by the elevated CO 2 through modulating its capacity in repair and protection, which thereby would influence its abundance and competitiveness in phytoplankton communities. • High CO 2 exacerbated the UVR-induced inhibition on PSII activity. • UVR stimulated the removal rates of both PsbA and PsbD. • The removal of PsbD declined by high CO 2 under the exposure of UVR. • High CO 2 reversed the UVR-induced Y NPQ to Y No. [ABSTRACT FROM AUTHOR]

Increasing marine microplastics (MPs) pollution potentially threatens the stability of phytoplankton community structures in marine environments. MPs toxicities to microalgae are largely determined by particle size, while the size-dependent mechanisms are still not fully understood. In this study, two sizes (0.1 µm and 1 µm) of polystyrene (PS) MPs were used as experimental targets to systemically compare their different effecting mechanisms on the marine model diatom Thalassiosira pseudonana with respect to oxidative stress and photosynthesis. The results indicated the toxicity of 1 µm sized MPs was higher than 0.1 µm sized MPs regarding to population growth. In condition of similar microalgal population inhibition rates, we found more enhanced cellular oxidative stress and cell death happened in the 1 µm MPs treatments, which could be linked to higher zeta potential of 1 µm MPs and more severe cell surface damage; microalgal surface light shading and cellular pigments decline were more obvious in the 0.1 µm MPs treatment, which could be linked to high aggregation abilities of 0.1 µm MPs. Gene expressions supported the morphological and physiological findings on the transcriptional level. Environmental related MPs concentrations (5 μg L−1) also aroused gene expression changes of T. pseudonana while more changing genes were found under 0.1 µm MPs than 1 µm MPs. These results provide novel insights into the size-dependent mechanisms of MPs toxicity on marine microalgae, as well as their potential influence on the marine environment. [Display omitted] • Size dependent effecting mechanisms of MPs on diatoms were evaluated. • 1 µm sized MPs was more toxic than 0.1 µm on population growth. • 1 µm sized MPs could cause more cell damage and oxidative stress of diatom cells. • 0.1 µm sized MPs affected diatom cells mainly by light shading and pigments decline. [ABSTRACT FROM AUTHOR]

Diatoms are among the most diverse groups of phytoplankton in the ocean. Despite their widely recognized influence on ocean ecosystems and global biogeochemistry, little is known about the impact of this diversity on large-scale processes. Here, we examined the ramifications of between-species diversity by documenting the transcriptional response of three diatoms - Thalassiosira pseudonana, Fragilariopsis cylindrus, and Pseudo-nitzschia multiseries - to the onset of nitrate limitation of growth, a common limiting nutrient in the ocean. The three species shared 5,583 clusters of orthologous genes based on OrthoMCL clustering of publically available diatom genomes. These clusters represent 30-54% of the predicted genes in each diatom genome. Less than 5% of genes within these core clusters displayed the same transcriptional responses across species when growth was limited by nitrate availability. Orthologs, such as those involved in nitrogen uptake and assimilation, as well as carbon metabolism, were differently expressed across the three species. The two pennate diatoms, F. cylindrus and P. multiseries, shared 3,839 clusters without orthologs in the genome of the centric diatom T. pseudonana. A majority of these pennate-clustered genes, as well as the non-orthologous genes in each species, had minimal annotation information, but were often significantly differentially expressed under nitrate limitation, indicating their potential importance in the response to nitrogen availability. Despite these variations in the specific transcriptional response of each diatom, overall transcriptional patterns suggested that all three diatoms displayed a common physiological response to nitrate limitation that consisted of a general reduction in carbon fixation and carbohydrate and fatty acid metabolism and an increase in nitrogen recycling. Characterization of these finely tuned responses will help to better predict which types of diatoms will bloom under which sets of environmenta

The projected ocean acidification (OA) associated with increasing atmospheric CO 2 alters seawater chemistry and hence the bio-toxicity of metal ions. However, it is still unclear how OA might affect the long-term resilience of globally important marine microalgae to anthropogenic metal stress. To explore the effect of increasing p CO 2 on copper metabolism in the diatom Thalassiosira pseudonana (CCMP 1335), we employed an integrated eco-physiological, analytical chemistry, and transcriptomic approach to clarify the effect of increasing p CO 2 on copper metabolism of Thalassiosira pseudonana across different temporal (short-term vs. long-term) and spatial (indoor laboratory experiments vs. outdoor mesocosms experiments) scales. We found that increasing p CO 2 (1,000 and 2,000 μatm) promoted growth and photosynthesis, but decreased copper accumulation and alleviated its bio-toxicity to T. pseudonana . Transcriptomics results indicated that T. pseudonana altered the copper detoxification strategy under OA by decreasing copper uptake and enhancing copper-thiol complexation and copper efflux. Biochemical analysis further showed that the activities of the antioxidant enzymes glutathione peroxidase (GPX), catalase (CAT), and phytochelatin synthetase (PCS) were enhanced to mitigate oxidative damage of copper stress under elevated CO 2 . Our results provide a basis for a better understanding of the bioremediation capacity of marine primary producers, which may have profound effect on the security of seafood quality and marine ecosystem sustainability under further climate change., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Xu, Huang, Fan, Zhang, Wang, Wang, Beardall, Brennan and Ye.)

Three centric diatoms, Thalassiosira pseudonana (diameter ~ 4 μm), Thalassiosira weissflogii (~ 11 μm), and Thalassiosira punctigera (~ 47 μm), were exposed to low and high levels of UV radiation. UV-induced inhibition on photosystem II was correlated with cell size under high light levels, though it was insignificant under low light levels (PAR < 63 W m − 2 ). The highest inhibition (~ 15%) was observed for the smallest species. Several mechanisms may explain the observed relationship between cell size and response to UV. All three species counteracted UV-related photosystem damage via protein synthesis within the chloroplast. Non-photochemical quenching (NPQ) was induced when that process was blocked with an inhibitor in T. pseudonana and T. weissflogii , but not T. punctigera , as neither radiation nor the inhibitor had a significant effect on NPQ in this species. Moreover, UV-induced inhibition for cells treated with lincomycin was highest for T. weissflogii , which was in accordance with the highest UV exposure within the cell. The intracellular UV distribution was not associated with cell size, indicating that the package effect was not the only determinant of cell-size dependent UV sensitivity in phytoplankton. [ABSTRACT FROM AUTHOR]

Emiliania huxleyi, a ubiquitous marine algae, was cultured under replete and Cu-limiting conditions to investigate Cu uptake strategies involving thiols and associated redox reactions; comparisons to a model diatom, Thalassiosira pseudonana, were also drawn. Cu-limitation increased rates of cell surface reduction of Cu(II) to Cu(I) in E. huxleyi but not in T. pseudonana. Furthermore, Cu-limited E. huxleyi cells took up more Cu when cysteine was present compared to when no ligand was added, although a dependence on cysteine concentration was not observed. In contrast, Cu uptake by replete cells was dependent upon the relative abundance of inorganic species [Cu(I)']. We also show that cysteine can increase the bioavailability of Cu to Cu-limited cells, of both species, through the reductive release of Cu(I) from fairly strong Cu(II) ligands such as EDTA. Finally, support for a mechanism involving uptake of a Cys-Cu complex in E. huxleyi is drawn from the observation that Cu-limitation significantly enhances cysteine uptake by transporters that exhibit Michaelis-Menten kinetics. These Cu uptake strategies help explain the presence and distribution of dissolved thiols in surface seawater and have implications for the biogeochemical cycling of Cu in low Cu environments. [ABSTRACT FROM AUTHOR]

Among marine phytoplankton groups, diatoms span the widest range of cell size, with resulting effects upon their nitrogen uptake, photosynthesis and growth responses to light. We grew two strains of marine centric diatoms, the small Thalassiosira pseudonana and the larger T. punctigera in high and low nitrogen media, across a range of growth light levels. Nitrogen and total proteins per cell decreased with increasing growth light in both species when grown under low nitrogen media. Surprisingly, low nitrogen increased the cellular allocation to RUBISCO and the rate of electron transport away from Photosystem II for the smaller diatom under low growth light, and for the larger diatom across the range of growth lights. Low nitrogen decreased the growth rate of the smaller diatom, particularly under higher light, but stimulated the growth rate of the larger diatom. Our results show that the high nitrogen in common growth media favours the growth rate of a small diatom but inhibits growth of a larger species. [ABSTRACT FROM AUTHOR]

Energy transfer dynamics in dimeric photosystem II (PSII) complexes isolated from four diatoms, Chaetoceros gracilis , Cyclotella meneghiniana , Thalassiosira pseudonana , and Phaeodactylum tricornutum , are examined. Time-resolved fluorescence measurements were conducted in the range of 0–80 ns. Delayed fluorescence spectra showed a clear difference between PSII monomer and PSII dimer isolated from the four diatoms. The difference can be interpreted as reflecting suppressed energy transfer between PSII monomers in the PSII dimer for efficient energy trapping at the reaction center. The observation was especially prominent in C. gracilis and T. pseudonana . The pathways seem to be suppressed under a low pH condition in isolated PSII complexes from C. gracilis , and excitation energy may be quenched with fucoxanthin chlorophyll a/c -binding protein (FCP) that was closely associated with PSII in C. gracilis . The energy transfer between PSII monomers in the PSII dimer may play a role in excitation energy regulation in diatoms. [ABSTRACT FROM AUTHOR]

Diatoms are heterokont unicellular algae with a widespread distribution throughout all aquatic habitats. Research on diatoms has advanced significantly over the last decade due to available genetic transformation methods and publicly available genome databases. Yet up to now, proteins involved in the regulation of the cytoskeleton in diatoms are largely unknown. Consequently, this work focuses on actin and actin-related proteins (ARPs) encoded in the diatom genomes of Thalassiosira pseudonana , Thalassiosira oceanica , Phaeodactylum tricornutum , Fragilariopsis cylindrus and Pseudo-nitzschia multiseries . Our comparative genomic study revealed that most diatoms possess only a single conventional actin and a small set of ARPs. Among these are the highly conserved cytoplasmic Arp1 protein and the nuclear Arp4 as well as Arp6. Diatom genomes contain genes coding for two structurally different homologues of Arp4 that might serve specific functions. All diatom species examined here lack ARP2 and ARP3 proteins, suggesting that diatoms are not capable of forming the Arp2/3 complex, which is essential in most eukaryotes for actin filament branching and plus-end dynamics. Interestingly, none of the sequenced representatives of the Bacillariophyta phylum code for profilin. Profilin is an essential actin-binding protein regulating the monomer actin pool and is involved in filament plus-end dynamics. This is the first report of organisms not containing profilin. [ABSTRACT FROM AUTHOR]

Recent progress made on epigenetic studies revealed the conservation of epigenetic features in deep diverse branching species including Stramenopiles, plants and animals. This suggests their fundamental role in shaping species genomes across different evolutionary time scales. Diatoms are a highly successful and diverse group of phytoplankton with a fossil record of about 190 million years ago. They are distantly related from other super-groups of Eukaryotes and have retained some of the epigenetic features found in mammals and plants suggesting their ancient origin. Phaeodactylum tricornutum and Thalassiosira pseudonana , pennate and centric diatoms, respectively, emerged as model species to address questions on the evolution of epigenetic phenomena such as what has been lost, retained or has evolved in contemporary species. In the present work, we will discuss how the study of non-model or emerging model organisms, such as diatoms, helps understand the evolutionary history of epigenetic mechanisms with a particular focus on DNA methylation and histone modifications. [ABSTRACT FROM AUTHOR]

Due to the ongoing effects of climate change, phytoplankton are likely to experience enhanced irradiance, more reduced nitrogen, and increased water acidity in the future ocean. Here, we used Thalassiosira pseudonana as a model organism to examine how phytoplankton adjust energy production and expenditure to cope with these multiple, interrelated environmental factors. Following acclimation to a matrix of irradiance, nitrogen source, and CO2 levels, the diatom's energy production and expenditures were quantified and incorporated into an energetic budget to predict how photosynthesis was affected by growth conditions. Increased light intensity and a shift from [ABSTRACT FROM AUTHOR]

The model diatom Thalassiosira pseudonana is believed to be a single species with a global distribution, but it has not been confirmed previously whether isolates from different environmental and geographic origins are genotypically and phenotypically identical. In the present study, a polyphasic approach was employed to characterize nine clonal isolates, plus an additional replicate of one of the isolates, of the diatom T. pseudonana from culture collections to investigate whether there was any cryptic speciation in the publicly available strains of this species. Morphological analysis using scanning electron microscopy concluded that the strains were indistinguishable. Furthermore, conventional DNA barcoding genes (SSU rDNA, ITS1 and ITS2 rDNA and rbcL), revealed no nucleotide variation among the strains tested. On employing a whole genome fingerprinting technique, Amplified Fragment Length Polymorphism (AFLP), three clusters were revealed, although the level of variation between the clusters was surprisingly low. These findings indicate a low level of diversity among these cultured T. pseudonana strains, despite their wide spatial and temporal distribution and the salinity range of their original habitats. Based on the limited number of available strains, this suggests that T. pseudonana is a highly conserved diatom that nevertheless has an ability to tolerate wide ranges of salinity and populate varied geographic locations. [ABSTRACT FROM PUBLISHER]

This study comprehensively investigated the influences of salinity, exposure concentration and time on the aggregate size, surface charge and dissolution of zinc oxide nanoparticles (ZnO–NPs; 20 nm) in seawater, and examined the interacting effect of salinity and waterborne exposure of ZnO–NPs on the marine diatom Thalassiosira pseudonana for 96 h. We found that aggregate sizes of ZnO–NPs significantly increased with increasing salinity, but generally decreased with increasing exposure concentration. Ion release decreased with increasing salinity, whereas the surface charge of the particles was not affected by salinity. The increased aggregate size and decreased ion release with increasing salinity, and consequently lower concentration of bioavailable zinc ions, resulted in decreased toxicity of ZnO–NPs at higher salinity in general in terms of growth inhibition (IC50) and chlorophyll fluorescence (EC50 – Ф Po and EC50 – Ф 2 ). However, IC50s and EC50s of ZnO–NPs were smaller than those of Zn 2+ (from ZnO–NPs ultrafiltrate and ZnCl 2 ), indicating that dissolved Zn 2+ can only partially explain the toxicity of ZnO–NPs. SEM images showed that ZnO–NPs attached on the diatom frustule surface, suggesting that the interaction between the nanoparticles and the cell surface may acerbate the toxicity of ZnO–NPs. Our results linked the physicochemical characteristics of ZnO–NPs in seawater with their toxicities to the marine diatom and highlighted the importance of salinity as an influential environmental factor governing the aggregation, dissolution and the toxicity of ZnO–NPs. [ABSTRACT FROM AUTHOR]

Biogenic aerosols critically control atmospheric processes. However, although bacteria constitute major portions of living matter in seawater, bacterial aerosolization from oceanic surface layers remains poorly understood. We analysed bacterial diversity in seawater and experimentally generated aerosols from three Kongsfjorden sites, Svalbard. Construction of 16S rRNA gene clone libraries from paired seawater and aerosol samples resulted in 1294 sequences clustering into 149 bacterial and 34 phytoplankton operational taxonomic units ( OTUs). Bacterial communities in aerosols differed greatly from corresponding seawater communities in three out of four experiments. Dominant populations of both seawater and aerosols were Flavobacteriia, Alphaproteobacteria and Gammaproteobacteria. Across the entire dataset, most OTUs from seawater could also be found in aerosols; in each experiment, however, several OTUs were either selectively enriched in aerosols or little aerosolized. Notably, a SAR11 clade OTU was consistently abundant in the seawater, but was recorded in significantly lower proportions in aerosols. A strikingly high proportion of colony-forming bacteria were pigmented in aerosols compared with seawater, suggesting that selection during aerosolization contributes to explaining elevated proportions of pigmented bacteria frequently observed in atmospheric samples. Our findings imply that atmospheric processes could be considerably influenced by spatiotemporal variations in the aerosolization efficiency of different marine bacteria. [ABSTRACT FROM AUTHOR]

Investigation of the production and structural characteristics of the extracellular polysaccharides (ECPS) released by diatoms according to nutrient status is urgently necessary for our understanding of the roles of ECPS in aquatic ecosystem. In this study, the effects of N and P depletion and variable nutrient sources on the production and structural characterization of the soluble ECPS released by the marine diatom Thalassiosira pseudonana in batch culture were examined. The abundance of the soluble ECPS produced under N (NO) depletion was higher than that obtained in the P (PO) depletion and control treatments. NH rather than NO and urea and sodium-glycerophosphate rather than PO were found to induce a higher abundance of soluble ECPS production at the end of the experiment, indicating that the abundance of soluble ECPS is also affected by the nutrient source. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis of the structural characteristics of the soluble ECPS samples showed that the degree of polymerization (d.p.) profiles and the distribution of the polymers with different molecular masses varied in response to nutrient depletion and different nutrient sources. An increase in the proportion of both low- and high-molecular-weight polymers under the N (NO) and P (PO) depletion treatments was found. Based on the different characteristics of high- and low-molecular-weight polymers, our results suggest that the production of soluble ECPS may be one of the strategies that T. pseudonana utilizes to survive under nutrient stress conditions. [ABSTRACT FROM AUTHOR]

Copepods are key links between primary producers and higher pelagics. We investigated, for the first time, under laboratory conditions, some aspects of the reproductive behaviour and feeding preferences of Apocyclops procerus (Copepoda: Cyclopoida) under different conditions of salinity and food supply. This is also its first record for Pernambuco (NE Brazil). The females carry their eggs until their eclosion and present several cycles of egg production without being further fecundated. Egg production and adult life span were not affected by differences in salinity or food supply. Offspring predation was also observed. From the three microalgae species offered to A. procerus individuals, Thalassiosira weissflogii, Chaetoceros muelleri (Ochrophyta) and Isochrysis galbana (Haptophyta), the small round-shaped I. galbana was preferred over the large and spiny diatoms, in spite of its lower nutritional value. The high salinity tolerance and apparently omnivorous feeding habits of A. procerus may enable it to predominate in estuarine waters. [ABSTRACT FROM AUTHOR]

The plastids of ecologically and economically important algae from phyla such as stramenopiles, dinoflagellates and cryptophytes were acquired via a secondary endosymbiosis and are surrounded by three or four membranes. Nuclear-encoded plastid-localized proteins contain N-terminal bipartite targeting peptides with the conserved amino acid sequence motif ' ASAFAP'. Here we identify the plastid proteomes of two diatoms, Thalassiosira pseudonana and Phaeodactylum tricornutum, using a customized prediction tool ( ASAFind) that identifies nuclear-encoded plastid proteins in algae with secondary plastids of the red lineage based on the output of SignalP and the identification of conserved ' ASAFAP' motifs and transit peptides. We tested ASAFind against a large reference dataset of diatom proteins with experimentally confirmed subcellular localization and found that the tool accurately identified plastid-localized proteins with both high sensitivity and high specificity. To identify nucleus-encoded plastid proteins of T. pseudonana and P. tricornutum we generated optimized sets of gene models for both whole genomes, to increase the percentage of full-length proteins compared with previous assembly model sets. ASAFind applied to these optimized sets revealed that about 8% of the proteins encoded in their nuclear genomes were predicted to be plastid localized and therefore represent the putative plastid proteomes of these algae. [ABSTRACT FROM AUTHOR]

Quantification of fatty acids has been crucial to elucidate lipid biosynthesis pathways in plants. To date, fatty acid identification and quantification has relied mainly on gas chromatography ( GC) coupled to flame ionization detection ( FID) or mass spectrometry ( MS), which requires the derivatization of samples and the use of chemical standards for annotation. Here we present an alternative method based on a simple procedure for the hydrolysis of lipids, so that fatty acids can be quantified by liquid chromatography mass spectrometry ( LC- MS) analysis. Proper peak annotation of the fatty acids in the LC- MS-based methods has been achieved by LC- MS measurements of authentic standard compounds and elemental formula annotation supported by 13C isotope-labeled Arabidopsis. As a proof of concept, we have compared the analysis by LC- MS and GC- FID of two previously characterized Arabidopsis thaliana knock-out mutants for FAD6 and FAD7 desaturase genes. These results are discussed in light of lipidomic profiles obtained from the same samples. In addition, we performed untargeted LC- MS analysis to determine the fatty acid content of two diatom species. Our results indicate that both LC- MS and GC- FID analyses are comparable, but that because of higher sensitivity and selectivity the LC- MS-based method allows for a broader coverage and determination of novel fatty acids. [ABSTRACT FROM AUTHOR]

Genes involved with many Fe functions and some Cu functions are annotated in the Thalassiosira pseudonana Hasle et Heimdal genome. Using bioinformatics, we performed a systematic Blastp search to obtain all relevant sequences and to select the most complete gene models for putative components of Cu acquisition and distribution. We identified homologs of high-affinity Cu transporters (CTR), Cu transporting P 1B -type ATPases, Cu chaperones and ZIP transporters. The putative CTRs in T. pseudonana have the conserved CTR Cu-binding motifs and transmembrane domains, and their gene expression was down-regulated by a Cu addition to low Cu acclimated cultures. The sequences of some putative Tp ZIPs were similar to those of well-known Zn and Fe transporters. Cu addition affected the expression of some TpZIP genes, suggesting an interaction between Cu metabolism and that of Zn and/or Fe. For intracellular Cu distribution, we identified putative Cu transporting P 1B -type ATPases, proposed to deliver Cu to the trans-Golgi or the secretory compartment, as well as putative Cu chaperones, proposed to deliver Cu to the mitochondrion. Their gene expression was down-regulated by a Cu addition, indicating that these putative intracellular Cu transporters and chaperones might redistribute Cu, allowing T. pseudonana to meet key metabolic needs under Cu deficiency. [ABSTRACT FROM AUTHOR]