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Perfluoroalkyl substances (PFAS) are widely dispersed persistent organic pollutants (POPs) throughout marine ecosystems. Due to ban of traditional long-chain PFAS, the emerging short-chain ones showed increased environmental detection as substitutes. As the foundation of aquatic food webs, microalgae play a pivotal role in the stability of marine environments. However, the toxicity of those short-chain PFAS was lack of investigation. Therefore, we chose 4C PFAS perfluorobutanoic acid (PFBA) and the marine model diatom Thalassiosira pseudonana as research targets, comprehensively studied the toxicity of PFBA to T. pseudonana in terms of the population growth, photosynthetic physiology and oxidative stress. Our results characterized the inhibited growth, inhibited photosynthetic parameters, increased reactive oxygen species (ROS) levels and activated antioxidant system under PFBA exposure. Further transcriptome analysis revealed the underlying molecular mechanisms: photosynthetic genes were slightly down-regulated and the expression of oxidative stress-related genes was enhanced; significant up-regulation of genes related to the DNA excision repair and replication-coupled DNA repair pathways; the expression of carbon metabolisms-related genes was increased, including the Calvin cycle, glycolysis, pentose phosphate pathway, tricarboxylic acid (TCA) cycle and fatty acid biosynthesis, that could provide sufficient energy for the recovery processes of microalgal cells. This study elucidated the underlying toxic mechanisms of PFBA on phytoplankton, and provided novel insights for assessing the environmental risks of PFAS. • PFBA exhibited toxic effects on T. pseudonana in terms of population growth and physiological-biochemical parameters. • Oxidative stress was induced in T. pseudonana under PFBA exposure. • Various DNA repair pathways were activated in response to PFBA stress. • Enhanced carbon metabolisms provided sufficient energy for T. pseudonana to restore physiological activities. [ABSTRACT FROM AUTHOR]

As emerging pollutants in the aquatic environments, micro- and nano-plastics (MNPs) aroused widespread environmental concerns for their potential threats to the ecological health. Previous research has proved that microalgae growth could recover from the MNPs toxicities, in which the extracellular polymeric substances (EPS) might play the key role. In order to comprehensively investigate the recovery process of microalgae from MNPs stress and the effecting mechanisms of EPS therein, this study conducted a series of experiments by employing two sizes (0.1 and 1 μm) of polystyrene (PS) MNPs and the marine model diatom Thalassiosira pseudonana during 14 days. The results indicated: the pigments accumulations and photosynthetic recovery of T. pseudonana under MPs exposure showed in the early stage (4–5 days), while the elevation of reactive oxygen species (ROS) and EPS contents lasted longer time period (7–8 days). EPS was aggregated with MNPs particles and microalgal cells, corresponding to the increased settlement rates. More increase of soluble (SL)-EPS contents was found than bound (B)-EPS under MNPs exposure, in which the increase of the protein proportion and humic acid-like substances in SL-EPS was found, thus facilitating aggregates formation. ROS was the signaling molecule mediating the overproduction of EPS. The transcriptional results further proved the enhanced EPS biosynthesis on the molecular level. Therefore, this study elucidated the recovery pattern of microalgae from MNPs stress and linked "ROS-EPS production changes-aggregation formation" together during the growth recovery process, with important scientific and environmental significance. [Display omitted] • Microalgae recovered time orderly under MNPs stress. • Increased EPS contents and changes of EPS compositions were stimulated by MNPs. • Aggregations of MNPs particles and microalgal cells were caused by EPS. • ROS was the signaling molecule for mediating EPS overproduction. [ABSTRACT FROM AUTHOR]

Triphenyltin (TPT) often coexists with tributyltin (TBT) and Cu in coastal waters worldwide. The combined toxic effect of TPT and TBT has always been assumed to be additive without any scientific proof, and the combined effect of Cu and TPT on marine organisms has not been vigorously studied. This study, therefore, investigated the acute toxicity of binary mixture of TPT/Cu and TPT/TBT to five selected marine species including Thalassiosira pseudonana , Skeletonema costatum , Tigriopus japonicus , Brachionus koreanus and Oryzias melastigma . The interaction between TPT and TBT or Cu was modeled antagonistic based on concentration addition (CA) model, while it was synergistic according to response addition (RA) model. Both model well predicted the toxicity of binary mixtures to the five organisms. As for the environmental risk assessment, CA overestimated the toxicity in most cases and thus is a more conservative model than RA model for assessing the toxicity of these chemical mixtures. [ABSTRACT FROM AUTHOR]

A 96-h exposure experiment was conducted to elucidate the toxicity responses of the marine diatom Thalassiosira pseudonana upon exposure to different temperatures and copper (Cu) concentrations. Three Cu treatments (seawater control; 200 μg/L Cu, EC 50 for the yield at 25 °C; and 1000 μg/L Cu, EC 50 for growth inhibition at 25 °C) were conducted against four temperatures (10 °C, 15 °C, 25 °C and 30 °C). Growth rate and photosynthetic responses showed a significant interacting thermal-chemical effect with strong synergistic responses observed at 30 °C treatments. Expression of heat shock protein ( hsp ) was positively modulated by increasing temperatures. Hsp 90 , hsp90–2 and sit1 (related to silica shell formation) were highly expressed at 30 °C under 1000 μg/L Cu, while the genes encoding light harvesting proteins ( 3HfcpA and 3HfcpB ) and silaffin precursor sil3 were significantly up-regulated at 15 °C under 200 μg/L Cu. Our results indicated an increase Cu toxicity to T. pseudonana under high temperature and Cu dose. [ABSTRACT FROM AUTHOR]

Occurrence of algal blooms in coastal waters is predicted to be more prevalent in future. To minimize their occurrence, manipulating the grazing pressure by suspension feeders is a potential management strategy, but its effectiveness may depend on their feeding preference. Therefore, we assessed the clearance rate of a widespread serpulid polychaete Hydroides elegans in larval and adult stages on various coastal phytoplankton. Additionally, the growth and development of H. elegans after consuming these phytoplankton were determined to reflect its sustainability to counter algal blooms. Results showed that H. elegans can consume and utilize different phytoplankton, except diatom Thalassiosira pseudonana , for growth and development in both life stages. Given the fast-colonizing ability which allows easy manipulation of abundance, H. elegans is considered practically and biologically ideal for tackling algal blooms. Other suspension feeders with different feeding niches could be used in combination to maximize the versatility of the top-down control. [ABSTRACT FROM AUTHOR]

Mangroves are productive ecosystems that are highly threatened by anthropogenic activities. We investigated the environmental quality of the Serinhaém river estuary located in a legally protected area. Through chemical analysis of sediments and tissues of Cardisoma guanhumi , in addition to bioassays with elutriate involving Nitokra sp. and Thalassiosira pseudonana , we determined the contamination status and risk factors related to trace metals in the estuary. For the sediment, the concentrations of Cr and Ni were above the limit established by CONAMA n° 454/2012 in the "City" site, and Cr above the TEL in all sampling sites. Ecotoxicological tests showed high toxicity in samples from "City" and "Tributary". The elements Cr, Mn, Ni and Zn were also higher in crabs from these sites. Cr levels exceeded the Brazilian limit for food consumption. The bioaccumulation factor was not significant. However, the overall analysis proved that this estuary is increasingly impacted by anthropogenic pressure. • The estuary is located in a protected area that was hit by the biggest oil spill accident in the history of Brazil. • The Cr contents were above the TEL for all sample points, indicating a moderate contamination in the sediment. • The bioassay with elutriate showed high toxicity with growth inhibition of Thalassiosira pseudonana. • There was less Nitokra sp spawning after exposure to elutriate from the point close to the urban area. • The Cr content in tissues of Cardisoma guanhumi is above that established for human consumption by Brazilian legislation. [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 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]

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]

Post-translational modifications of histones affect many biological processes by influencing higher order chromatin structure that affects gene and genome regulation. It is therefore important to develop methods for extracting histones while maintaining their native post-translational modifications. While histone extraction protocols have been developed in multicellular and single celled organisms such as yeast and Arabidopsis, they are inefficient in diatoms that have a silica cell wall that is likely to hinder histone extraction. We report in this work a rapid and reliable method for extraction of large amounts of high quality histones from the two model diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana. The protocol is an important enabling step permitting downstream applications such as western blotting and mass spectrometry. [ABSTRACT FROM AUTHOR]

Post-translationalmodifications of histones affectmany biological processes by influencing higher order chromatin structure that affects gene and genome regulation. It is therefore important to develop methods for extracting histoneswhilemaintaining their native post-translationalmodifications. While histone extraction protocols have been developed inmulticellular and single celled organisms such as yeast and Arabidopsis, they are inefficient in diatoms that have a silica cell wall that is likely to hinder histone extraction. We report in this work a rapid and reliable method for extraction of large amounts of high quality histones from the two model diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana. The protocol is an important enabling step permitting downstream applications such as western blotting and mass spectrometry. [ABSTRACT FROM AUTHOR]

Abstract: Post-translational modifications of histones affect many biological processes by influencing higher order chromatin structure that affects gene and genome regulation. It is therefore important to develop methods for extracting histones while maintaining their native post-translational modifications. While histone extraction protocols have been developed in multicellular and single celled organisms such as yeast and Arabidopsis, they are inefficient in diatoms that have a silica cell wall that is likely to hinder histone extraction. We report in this work a rapid and reliable method for extraction of large amounts of high quality histones from the two model diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana. The protocol is an important enabling step permitting downstream applications such as western blotting and mass spectrometry. [Copyright &y& Elsevier]

Herbivory of microzooplankton is an emerging key factor of diatom mortality in the ocean. As part of the microbial loop, protozoan grazers also feed on bacteria that accelerate the degradation of diatom detritus. The potentially pivotal effect of microzooplankton grazing on Si(OH)4 recycling was investigated with cultures of single-celled diatoms, Thalassiosira pseudonana and Chaetoceros gracilis, and heterotrophic protozoans, the dinoflagellate Oxyrrhis marina and the ciliate Strombidium sp. Both grazers ingested diatoms and the bacteria in the non-axenic cultures. C. gracilis, whose frustule is “armed” with setae, was less suitable as a prey than T. pseudonana. Ingestion rates of T. pseudonana were comparable for O. marina and Strombidium, but the dinoflagellate produced two orders of magnitude more detrital bSiO2 than the ciliate, due to the higher abundance reached by O. marina. Total net release of Si(OH)4 was lower in the grazing treatments compared to the control possibly due to the reduced bacterial growth by microzooplankton bacterivory, and to the transient protection of detrital bSiO2 in discarded feeding vacuoles. Over the first 24h, microzooplankton grazing even led to enhanced uptake of Si(OH)4 by diatoms, confirming the potential of grazing to influence the silicification of diatom frustules. Subsequently however, the Si dynamics in bottles with grazers turned rapidly from net uptake to net Si(OH)4 release. Protozoan grazers hence tie Si(OH)4 recycling into the microbial loop by producing detrital bSiO2. [Copyright &y& Elsevier]

Microalgae can synthesize their own active substances by absorbing nitrogen, phosphorus in wastewater to provide the nourishing bait for the aquatic organisms, when purifying the aquaculture wastewater. This research Thalassiosira pseudonana (Tp) and Isochrysis galbana (Ig) were selected to treat fishery wastewater and then evaluation of their active components. The results showed that the highest biomass productivity of Tp and Ig was 0.11 g·L−1·day−1 and 0.14 g·L−1·day−1, respectively, at the optimal initial inoculum biomass of 0.4 g·L−1. Furthermore, the two strains were co-cultured in different initial inoculum volume ratios, and the highest biomass was at the volume ratio of 1:1. With the most suitable inoculum biomass and volume ratio, the removal rates of NH 4 +-N, TN and TP were 80.65%, 85.29% and 92.75%, respectively. Moreover, the cells after wastewater treatment showed high contents of carbohydrate, protein, and lipid, which were 36.62%, 8.72% and 23.11%, respectively. This study showed that co-culturing Thalassiosira pseudonana with Isochrysis galbana to treat fishery wastewater is feasible, and algae cells have high nutritional value, which may provide a feasible technology for ecological protection and resource utilization of aquaculture. • It's feasible to treat fishery wastewater with co-cultured bait algae. • Optimal initial density and inoculum ratios can improve the efficiency of wastewater treatment. • High nutrition of algae cells after treatment may provide a basis for reuse of wastewater. [ABSTRACT FROM AUTHOR]

Alexandrium pacificum is a toxin-producing dinoflagellate with allelopathic effects. The elucidation of allelopathic mechanism of A. pacificum is of great significance for understanding A. pacificum blooms. To this end, using the model diatom Thalassiosira pseudonana as a target species, we observed changes in physiological, biochemical and gene transcription of T. pseudonana upon being co-cultured with A. pacificum. We found reciprocal effects between A. pacificum and T. pseudonana , and corroborated A. pacificum 's allelopathy on T. pseudonana by observing inhibitory effects of filtrate from A. pacificum culture on the growth of T. pseudonana. We also found that co-culturing with A. pacificum , the expression of T. pseudonana genes related to photosynthesis, oxidative phosphorylation, antioxidant system, nutrient absorption and energy metabolism were drastically influenced. Coupled with the alterations in Fv/Fm (the variable/maximum fluorescence ratio), activity of superoxide dismutase, contents of malondialdehyde, neutral lipid and total protein in T. pseudonana co-cultured with A. pacificum , we propose that A. pacificum allelopathy could reduce the efficiency of photosynthesis and energy metabolism of T. pseudonana and caused the oxidative stress, while the nutrient absorption was also affected by allelopathic effects. The resultant data potentially uncovered the allelopathic molecular mechanism of A. pacificum to model alga T. pseudonana. The changes in nutrient uptake and even energy metabolism in T. pseudonana , as an adaptation to environmental conditions, may prevent it from stress-related injuries. Our finding might advance the understanding of allelopathic mechanism of A. pacificum. • We found reciprocal effects between T. pseudonana (a diatom) and A. pacificum (a dinoflagellate). • A. pacificum dramatically orchestrated expression of some key genes in T. pseudonana. • A. acificum inhibited multiple physiological pathways in T. pseudonana. • Our finding may provide insights into A. pacificum allelopathy. [ABSTRACT FROM AUTHOR]

Karenia mikimotoi is an important toxin-producing dinoflagellate, frequently forming blooms along the coast of China. It has been shown that K. mikimotoi has allelopathic effects on other organisms, which benefited it over other microalgal species in competition. However, the underlying allelopathy mechanisms remain largely unclear. Thalassiosira pseudonana , a worldwide-distributed planktonic diatom, is extensively used as a model in diatom physiology studies. Here, we investigated the responses of T. pseudonana to K. mikimotoi allelopathy when they were co-cultured under laboratory condition. We found that there were reciprocal inhibitory effects between K. mikimotoi and T. pseudonana , and the cell-free filtrate of K. mikimotoi also deeply suppressed the growth of T. pseudonana , corroborating that K. mikimotoi allelopathy mainly accounted for the inhibition of K. mikimotoi against T. pseudonana. After exposed to K. mikimotoi allelopathy, the photosynthetic efficiency, contents of neutral lipid and malondialdehyde (MDA), as well as superoxide dismutase (SOD) activity in T. pseudonana were significantly changed. Meanwhile, the expression of genes involved in photosynthesis, oxidative phosphorylation, detoxifying system and nutrients uptake including PsbO , chlorophyll synthase (ChlG), risp1 , ferredoxin-NADP+ reductase (PetH), ABCB1 , nitrate transporters 1 (NRT1), phosphate transporter (PHT), alkaline phosphatase (ALP) and ascorbate peroxidase (APX) in T. pseudonana dramatically altered. These results suggested that K. mikimotoi could highly affect the efficiency of photosynthesis and energy metabolism of T. pseudonana , and also inhibit the nutrients uptake and assimilation. Our findings might provide insight information for the K. mikimotoi allelopathy. • There were reciprocal inhibitory effects between K. mikimotoi and T. pseudonana. • T. pseudonana cells suffered from oxidative stress when exposed to K. mikimotoi • K. mikimotoi could affect photosynthesis, energy metabolism, and nutrients assimilation in T. pseudonana. • Our findings might provide insight information for the K. mikimotoi allelopathy. [ABSTRACT FROM AUTHOR]

Polybrominated diphenyl ethers (PBDEs) are a series of highly persistent organic pollutants (POPs) ubiquitously distributed in marine environments. As key primary producers, microalgae are the start of PBDEs bioaccumulations and vulnerable to their toxicities. In order to deeply investigate the toxic mechanism of PBDEs on microalgal cells, the occurrence of programmed cell death (PCD) in a model diatom Thalassiosira pseudonana and its possible mediating mechanism were studied. The results indicated: cell death of T. pseudonana happened under the stress of BDE-47, which was proved to be PCD based on the correlations with three biochemical markers (DNA fragmentation, phosphatidylserine externalization and caspase activity) and three molecular markers [Metacaspase 2 gene (TpMC2), Death-associated protein gene (DAP3) and Death-specific protein 1 gene (TpDSP1)]; Furthermore, the changes of cellular ROS levels were correlated with the PCD markers and the dead cell rates, and the cell membrane and the chloroplast were identified as the major ROS production sites. Therefore, we concluded that PCD might be an important toxic mechanism of PBDEs on microalgal cells, and that chloroplast- and cell membrane-produced ROS was an important signaling molecule to mediate the PCD activation process. Our research firstly indicated microalgal PCD could be induced by PBDEs, and increased our knowledge of the toxic mechanisms by which POPs affect microalgal cells. Image 105 • Cell death of T. pseudonana happened under the stress of BDE-47. • The cell death was proven to be PCD by multiple biochemical and molecular evidence. • ROS played an important role in mediating the activation of PCD in T. pseudonana. • Cell membrane and chloroplast were the major ROS production sites. • PCD was an important toxic mechanism of PBDEs on microalgae. BDE-47 stress induced PCD in T. pseudonana ; chloroplast- and cell membrane-produced ROS played an important role in the activation of PCD. [ABSTRACT FROM AUTHOR]

Diatoms are dominant phytoplankton accounting for up to 20% of annual global primary production. Diatoms are also one of the first model organisms amongst secondary endosymbionts, which have a highly chimeric genome structure accommodating genes from multiple endosymbiosis partners in their evolutionary history. Despite their ecological importance and evolutionary uniqueness, molecular-level studies have lagged behind other model organisms, hindered by difficulties in controlling their ploidy and homologous recombination system. Recently, genome editing tools, such as clustered regularly interspaced short palindromic repeat (CRISPR)-Cas9 and transcription activator-like effector nucleases (TALEN), have been established in some diatoms. However, the improvement of CRISPR/Cas9 precision technology in diatoms is still underway, and the experimental complexity of TALEN limits their application in diatom molecular genetics. Cas9 nickase, a mutated version of Cas9 with a paired-single guide RNAs (sgRNAs), was recently developed to introduce a precise double cut of target DNA, suppressing the off-target effects of native Cas9 nuclease. In this study, we developed the Cas9 nickase (D10A) system for genome editing of the marine diatom Thalassiosira pseudonana. Using this system, we successfully introduced mutations into a gene encoding a putative θ-type carbonic anhydrase, a recently discovered class of carbonic anhydrase widespread in Stramenopiles. The results showed that this system introduced precise and relatively short biallelic indels to the diatom genome with minimal off-target effects. • Developed a dual sgRNA vector which works with CRISPR/Cas9 nickase in a diatom. • Demonstrated high efficiency of CRISPR/Cas9 nickase in T. pseudonana. • Showed that the system introduces precise small indels with small off target effects. [ABSTRACT FROM AUTHOR]