Differential transcription of heat shock protein 90 (HSP90) in the dinoflagellate Prorocentrum minimum by copper and endocrine-disrupting chemicals

An overview of transcription in dinoflagellates

Dinoflagellates are a vital diverse family of unicellular algae widespread in various aquatic environments. Typically large genomes and permanently condensed chromosomes without histones make these organisms unique among eukaryotes in terms of chromatin structure and gene expression. Genomic and transcriptomic sequencing projects have provided new insight into the genetic foundation of dinoflagellate behaviors. Genes in tandem arrays, trans-splicing of mRNAs and lower levels of transcriptional regulation compared to other eukaryotes all contribute to the differences seen. Here we present a general overview of transcription in dinoflagellates based on previously described work.

3-Indoleacrylic acid from canola straw as a promising antialgal agent - Inhibition effect and mechanism on bloom-forming Prorocentrum donghaiense

Harmful algal blooms (HABs) have induced severe damage worldwide. A novel high-efficient antialgal natural chemical, 3-indoleacrylic acid (3-IDC) with a 5-day half-maximal inhibitory concentration (IC_{50, 5d}), was discovered from canola straw, and its algal inhibition mechanism was investigated. Adverse effects were observed on the growth of P. donghaiense with 3-IDC addition, following an increase in reactive oxygen species (ROS) production. 3-IDC also hindered the photosynthetic mechanism of P. donghaiense cells. Transcriptional results showed 3-IDC inhibiting the functions of all the nutrient assimilating genes, down-regulated ribulose-1,5-bisphosphate carboxylase/oxygenase II, and cytochrome f genes. The expression of heat shock protein (HSP) 70 and 90 and rhodopsin genes were also suppressed. The binding affinity of investigated receptors was observed. The conformational changes induced by the spatial microstructural alteration through 3-IDC may further contribute to the perturbation of those enzyme catalytic activities. The present results provide new insights on controlling HABs using 3-IDC.

Expression Patterns of the Heat Shock Protein 90 (Hsp90) Gene Suggest Its Possible Involvement in Maintaining the Dormancy of Dinoflagellate Resting Cysts

Heat shock protein 90 (Hsp90) is a highly conserved molecular chaperone functioning in cellular structural folding and conformational integrity maintenance and thus plays vital roles in a variety of biological processes. However, many aspects of these functions and processes remain to be fully elucidated, particularly for non-model organisms. Dinoflagellates are a group of eukaryotes that are exceedingly important in primary production and are responsible for the most harmful algal blooms (HABs) in aquatic ecosystems. The success of dinoflagellates in dominating the plankton community is undoubtedly pertinent to their remarkable adaptive strategies, characteristic of resting cyst production and broad tolerance to stresses of temperature and others. Therefore, this study was conducted to examine the putative roles of Hsp90 in the acclimation to temperature stress and life stage alterations of dinoflagellates. Firstly, we isolated the full-length cDNA of an Hsp90 gene (StHsp90) via RACE from the cosmopolitan HAB species Scrippsiella trochoidea and tracked its transcriptions in response to varied scenarios via real-time qPCR. The results indicated that StHsp90 displayed significant mRNA augment patterns, escalating during 180-min treatments, when the cells were exposed to elevated and lowered temperatures. Secondly, we observed prominently elevated StHsp90 transcriptions in the cysts that were stored at the cold and dark conditions compared to those in newly formed resting cysts and vegetative cells. Finally, and perhaps most importantly, we identified 29 entries of Hsp90-encoding genes with complete coding regions from a dinoflagellate-specific environmental cDNA library generated from marine sediment assemblages. The observed active transcription of these genes in sediment-buried resting cysts was fully supported by the qPCR results for the cold-stored resting cysts of S. trochoidea. Hsp90s expressions in both laboratory-raised and field-collected cysts collectively highlighted the possible involvement and engagement of Hsp90 chaperones in the resting stage persistence of dinoflagellates.

Chloroacetanilides inhibit photosynthesis and disrupt the thylakoid membranes of the dinoflagellate Prorocentrum minimum as revealed with metazachlor treatment

The chloroacetanilides are among the most commonly used herbicides worldwide, which contaminate aquatic environments and affect aquatic phototrophs. Their sub-lethal toxicity has been evaluated using freshwater algae; however, the modes of cellular toxicity and levels of toxicity to marine organisms are not fully understood. In the present study, we assessed the cellular and molecular effects of chloroacetanilides on marine phototrophs using the dinoflagellate Prorocentrum minimum and the herbicide metazachlor (MZC). The MZC treatment led to a considerable reduction in cell number and pigment, and the EC₅₀ of MZC was calculated to be 0.647 mg/L. The photosynthetic parameters, Fv/Fm and chlorophyll fluorescence significantly decreased with MZC exposure time in a dose-dependent manner. In addition, MZC significantly induced photosynthesis genes, including PmpsbA, PmpsaA, and PmatpB, and the antioxidant PmGST, but not PmKatG. These findings were well matched to reactive oxygen species (ROS) production in MZC-treated cells. Interestingly, we observed inflated vacuoles, undivided chloroplasts, and breakdown of thylakoid membranes in MZC-treated cells. These results support the hypothesis that MZC severely damages chloroplasts, resulting in dysfunction of the dinoflagellate photosynthesis and possibly marine phototrophs in the environment.

Molecular cloning of heat shock protein 70 and HOP from the freshwater green algae Closterium ehrenbergii and their responses to stress

Heat shock proteins (HSPs) and HSP70-HSP90 organizing proteins (HOPs) are related, and they function together to maintain cellular homeostasis and respond to stress. In the present study, we reported the first molecular characteristics of HSP70 (designated as CeHSP70) and HOP (designated as CeHOP) genes from the freshwater green algae Closterium ehrenbergii and examined the changes in their expression profiles under heat stress and toxic chemicals treatment. CeHSP70 presented the conserved motif patterns and EEVD domain specific to cytosolic HSP70; CeHOP contained a typical domain of TPR repeats. Real-time PCR analysis showed that thermal stress considerably up-regulated both CeHOP and CeHSP70. In addition, the genes were significantly induced by CuCl2, CuSO4, and NiSO4, but not by K2Cr2O7, herbicide, and endocrine disrupting chemicals. These results suggest that CeHOP and CeHSP70 function together and play a role in responses to specific stressors and indicate their possible use as sensitive specific biomarkers in risk assessments.

Molecular cloning and oxidative-stress responses of a novel manganese superoxide dismutase (MnSOD) gene in the dinoflagellate Prorocentrum minimum

Dinoflagellate algae are microeukaryotes that have distinct genomes and gene regulation systems, making them an interesting model for studying protist evolution and genomics. In the present study, we discovered a novel manganese superoxide dismutase (PmMnSOD) gene from the marine dinoflagellate Prorocentrum minimum, examined its molecular characteristics, and evaluated its transcriptional responses to the oxidative stress-inducing contaminants, CuSO₄ and NaOCl. Its cDNA was 1238 bp and contained a dinoflagellate spliced leader sequence, a 906 bp open reading frame (301 amino acids), and a poly (A) tail. The gene was coded on the nuclear genome with one 174 bp intron; signal peptide analysis showed that it might be localized to the mitochondria. Real-time PCR analysis revealed an increase in gene expression of MnSOD and SOD activity when P. minimum cells were separately exposed to CuSO₄ and NaOCl. In addition, both contaminants considerably decreased chlorophyll autofluorescence, and increased intracellular reactive oxygen species. These results suggest that dinoflagellate MnSOD may be involved in protecting cells against oxidative damage.

6.0 K microarray reveals differential transcriptomic responses in the dinoflagellate Prorocentrum minimum exposed to polychlorinated biphenyl (PCB)

Endocrine disrupting chemicals (EDCs) have toxic effects on algae; however, their molecular genomic responses have not been sufficiently elucidated. Here, we evaluated genome-scaled responses of the dinoflagellate alga Prorocentrum minimum exposed to an EDC, polychlorinated biphenyl (PCB), using a 6.0 K microarray. Based on two-fold change cut-off, we identified that 609 genes (∼10.2%) responded to the PCB treatment. KEGG pathway analysis showed that differentially expressed genes (DEGs) were related to ribosomes, biosynthesis of amino acids, spliceosomes, and cellular processes. Many DEGs were involved in cell cycle progression, apoptosis, signal transduction, ion binding, and cellular transportation. In contrast, only a few genes related to photosynthesis and oxidative stress were expressed in response to PCB exposure. This was supported by that fact that there were no obvious changes in the photosynthetic efficiency and reactive oxygen species (ROS) production. These results suggest that PCB might not cause chloroplast and oxidative damage, but could lead to cell cycle arrest and apoptosis. In addition, various signal transduction and transport pathways might be disrupted in the cells, which could further contribute to cell death. These results expand the genomic understanding of the effects of EDCs on this dinoflagellate protist.

Salinity stress results in differential Hsp70 expression in the Exaiptasia pallida and Symbiodinium symbiosis

Abiotic factors affect cnidarian-algal symbiosis and, if severe enough, can result in bleaching. Increased temperature and light are well characterized causes of bleaching, but other factors like salinity can also stress the holobiont. In cnidarian-dinoflagellate systems, the expression of host genes, including heat shock protein 70 (Hsp70), changes due to thermal and light stress. In this experiment, we characterized to what extent salinity stress affects Hsp70 expression in the holobiont by simultaneously measuring host and symbiont Hsp70 expression in response to up to 8 h of hypo- and hypersaline conditions in the sea anemone Exaiptasia pallida and its intracellular symbiont Symbiodinium minutum. We show that E. pallida Hsp70 expression increases (6-11-fold) at high salinities whereas Symbiodinium Hsp70 expression shows little change (1.4-2.6-fold). These data suggest that cnidarian Hsp70 response is similar across multiple abiotic stressors further validating the Hsp70 gene as a biomarker for abiotic stress.

A Novel Cyclophilin B Gene in the Red Tide Dinoflagellate Cochlodinium polykrikoides: Molecular Characterizations and Transcriptional Responses to Environmental Stresses

The marine dinoflagellate Cochlodinium polykrikoides is one of the most common ichthyotoxic species that causes harmful algal blooms (HABs), which leads to ecological damage and huge economic loss in aquaculture industries. Cyclophilins (CYPs) belong to the immunophilin superfamily, and they may play a role in the survival mechanisms of the dinoflagellate in stress environments. In the present study, we identified a novel cyclophilin gene from C. polykrikoides and examined physiological and gene transcriptional responses to biocides copper sulphate (CuSO₄) and sodium hypochlorite (NaOCl). The full length of CpCYP was 903 bp, ranging from the dinoflagellate splice leader (DinoSL) sequence to the polyA tail, comprising a 639 bp ORF, a 117 bp 5′-UTR, and a 147 bp 3′-UTR. Motif and phylogenetic comparisons showed that CpCYP was affiliated to group B of CYP. In biocide stressors, cell counts, chlorophyll a, and photosynthetic efficiency (Fv/Fm) of C. polykrikoides were considerably decreased in both exposure time- and dose-dependent manners. In addition, CpCYP gene expression was significantly induced after 24 h exposure to the biocide-treated stress conditions. These results indicate an effect of the biocides on the cell physiology and expression profile of CpCYP, suggesting that the gene may play a role in environmental stress responses.

Physiological and biochemical responses of the freshwater green algae Closterium ehrenbergii to the common disinfectant chlorine

Chlorine (Cl2) is widely used as a disinfectant in water treatment plants and for cleaning swimming pools; it is finally discharged into aquatic environments, possibly causing damage to the non-target organisms in the receiving water bodies. Present study evaluated the effects of the biocide Cl2 to the green alga Closterium ehrenbergii (C. ehrenbergii). Growth rate, chlorophyll a levels, carotenoids, chlorophyll autofluorescence, and antioxidant enzymes were monitored up to 72-h after Cl2 exposure. C. ehrenbergii showed dose-dependent decrease in growth rate and cell division after exposure to Cl2. By using cell counts, the median effective concentration (EC50)-72-h was calculated to be 0.071mgL(-1). Cl2 significantly decreased the pigment levels and chlorophyll autofluorescence intensity, indicating that the photosystem was damaged in C. ehrenbergii. In addition, it increased the production of reactive oxygen species (ROS) in the cells. This stressor significantly increased the activities of antioxidant enzymes, including superoxide dismutase (SOD), catalase, and glutathione, and affected the physiology of the cells. These results indicate that Cl2 induces oxidative stress in the cellular metabolic process and leads to physiological and biochemical damages in the green algae. Cl2 discharged in industrial effluents and from water treatment plants may cause harmful effects to the C. ehrenbergii a common freshwater microalgae and other non-target organisms.

Genome-wide analysis of transcription and photosynthesis inhibition in the harmful dinoflagellate Prorocentrum minimum in response to the biocide copper sulfate

Copper is an essential trace metal for organisms; however, excess copper may damage cellular processes. Their efficiency and physiological effects of biocides have been well documented; however, molecular transcriptome responses to biocides are insufficiently studied. In the present study, a 6.0K oligonucleotide chip was developed to investigate the molecular responses of the harmful dinoflagellate Prorocentrum minimum to copper sulfate (CuSO₄) treatment. The results revealed that 515 genes (approximately 8.6%) responded to CuSO₄, defined as being within a 2-fold change. Further, KEGG pathway analysis showed that differentially expressed genes (DEGs) were involved in ribosomal function, RNA transport, carbon metabolism, biosynthesis of amino acids, photosystem maintenance, and other cellular processes. Among the DEGs, 49 genes were related to chloroplasts and mitochondria. Furthermore, the genes involved in the RAS signaling pathway, MAPK signaling pathway, and transport pathways were identified. An additional experiment showed that the photosynthesis efficiency decreased considerably, and reactive oxygen species (ROS) production increased in P. minimum after CuSO₄ exposure. These results suggest that CuSO₄ caused cellular oxidative stress in P. minimum, affecting the ribosome and mitochondria, and severely damaged the photosystem. These effects may potentially lead to cell death, although the dinoflagellate has developed a complex signal transduction process to combat copper toxicity.

Physiological and Molecular Response of Prorocentrum minimum to Tannic Acid: An Experimental Study to Evaluate the Feasibility of Using Tannic Acid in Controling the Red Tide in a Eutrophic Coastal Water

Bioassay and gene expression experiments were conducted in order to evaluate the growth and physiology of Prorocentrum minimum isolated from a eutrophic coastal water in response to tannic acid. In the bioassay experiments, variations in abundance, chlorophyll (chl) a concentration, maximum fluorescence (in vivo Fm), and photosynthetic efficiency (Fv/Fm) were measured over the course of a seven-day incubation. Moreover, stress-related gene expression in both the control and an experimental (2.5 ppm TA treatment) group was observed for 24 h and 48 h. The molecular markers used in this study were the heat shock proteins (Hsp70 and Hsp90) and cyclophilin (CYP). The findings show that P. minimum can thrive and grow at low concentrations (<2.5 ppm) of tannic acid, and, above this concentration, cells begin to slow down development. In addition, TA concentration of 10 ppm halted photosynthetic activity. At the molecular level, treatment with tannic acid increased the expression of Hsp70, Hsp90, and CYP, and heat shock proteins are more upregulated than the cyclophilin gene. Exposure to tannic acid increased the expression of stress factors over time (48 h) by 10- to 27-fold the expression level of the control group. These results suggest that tannic acid can be used to control harmful algal blooms such as those containing P. minimum in eutrophic coastal waters.

A novel cyclophilin gene from the dinoflagellate Prorocentrum minimum and its possible role in the environmental stress response

Cyclophilins (CYPs) are a family of proteins that bind to cyclosporine and are thought to be involved in the stress response. In dinoflagellate algae, CYPs may function as a survival strategy in cells exposed to environmental stressors. Here, we identified a novel cyclophilin gene (referred to as PmCYP, comprising a 516-bp open reading frame, encoding a 171-aa protein with a molecular mass of 17.5kDa) from the dinoflagellate Prorocentrum minimum, and evaluated the role of dinoflagellate CYP in cells exposed to environmental pollutants copper and polychlorinated biphenyl. In addition, we assessed the cytoprotective role of nitric oxide in relation to the expression of PmCYP. These stressors strongly affected the physiology of the cells, as judged by cell counting, reactive oxygen species (ROS) imaging, and photosynthetic parameters (Fv/Fm and PIABS). PmCYP expression was significantly (P<0.05) induced upon exposure of the cells to all the test pollutants used in this study. These clearly indicate that PmCYP plays a vital role in the oxidative stress response in dinoflagellate survival, although the gene was initially known only for its housekeeping function.

Evaluation and selection of reference genes for ecotoxicogenomic study of the green alga Closterium ehrenbergii using quantitative real-time PCR

The green alga Closterium ehrenbergii occurs in fresh water environments and has been suggested as a model for ecotoxicological assessment. Quantitative real-time PCR (qRT-PCR), with its high sensitivity and specificity, is a preferred method for reliable quantification of gene expression levels. qRT-PCR requires reference genes to normalize the transcription level of the target gene, and selection of appropriate references is crucial. Here, we evaluated nine housekeeping genes, that is, 18S rRNA, ACT, TUA, TUB, eIF, H4, UBQ, rps4, and GAPDH, using 34 RNA samples of C. ehrenbergii cultured in various environments (e.g. exposure to heat shock, UV, metals, and non-metallic chemicals). Each housekeeping gene tested displayed different ranges of C T values for each experimental condition. The gene stability was determined using the descriptive statistic software geNorm, which showed that ACT, H4, and TUA were the most suitable reference genes for all the conditions tested. In addition, at least three genes were required for proper normalization. With these references, we assessed the expression level of the heat shock protein 70 (HSP70) gene in C. ehrenbergii cells exposed to thermal and toxic contaminant stress and found that it was significantly up-regulated by these stressors. This study provides potential reference genes for gene expression studies on C. ehrenbergii with qRT-PCR.

Heat Shock Protein 70 and 90 Genes in the Harmful Dinoflagellate Cochlodinium polykrikoides: Genomic Structures and Transcriptional Responses to Environmental Stresses

The marine dinoflagellate Cochlodinium polykrikoides is responsible for harmful algal blooms in aquatic environments and has spread into the world's oceans. As a microeukaryote, it seems to have distinct genomic characteristics, like gene structure and regulation. In the present study, we characterized heat shock protein (HSP) 70/90 of C. polykrikoides and evaluated their transcriptional responses to environmental stresses. Both HSPs contained the conserved motif patterns, showing the highest homology with those of other dinoflagellates. Genomic analysis showed that the CpHSP70 had no intron but was encoded by tandem arrangement manner with separation of intergenic spacers. However, CpHSP90 had one intron in the coding genomic regions, and no intergenic region was found. Phylogenetic analyses of separate HSPs showed that CpHSP70 was closely related with the dinoflagellate Crypthecodinium cohnii and CpHSP90 with other Gymnodiniales in dinoflagellates. Gene expression analyses showed that both HSP genes were upregulated by the treatments of separate algicides CuSO₄ and NaOCl; however, they displayed downregulation pattern with PCB treatment. The transcription of CpHSP90 and CpHSP70 showed similar expression patterns under the same toxicant treatment, suggesting that both genes might have cooperative functions for the toxicant induced gene regulation in the dinoflagellate.

Transcriptional responses, metabolic activity and mouthpart deformities in natural populations of Chironomus riparius larvae exposed to environmental pollutants

Biomarkers are an important tool in laboratory assays that link exposure or effect of specific toxicants to key molecular and cellular events, but they have not been widely used in invertebrate populations exposed to complex mixtures of environmental contaminants in their natural habitats. The present study focused on a battery of biomarkers and their comparative analysis in natural populations of the benthic larvae of Chironomus riparius (Diptera), sampled in three differentially polluted rivers (the Con, Sar, and Louro in Galicia, Spain). In our study, some parameters were identified, such as hsp70 gene activity, GST enzymatic activity, total glycogen content and mouthpart deformities, which showed significant differences among populations from the three rivers that differed in the levels and types of sedimentary contaminants analyzed (metals, organic-chlorine pesticides, alkylphenols, pharmaceutical, and personal care products). In contrast to these sensitive biomarkers, other parameters showed no significant differences (hsc70 gene, EcR gene, P450 gene, RNA:DNA ratio, total protein content), and were stable even when comparing field and nonexposed laboratory populations. The hsp70 gene seems to be particularly sensitive to conditions of pollutant exposure, while its constitutive counterpart hsc70 showed invariable expression, suggesting that the hsc70/hsp70 ratio may be a potential indicator of polluted environments. Although further studies are required to understand the correlation between molecular responses and the ecological effects of pollutants on natural populations, the results provide new data about the biological responses to multiple-stressor environments. This field study adds new molecular endpoints, including gene expression, as suitable tools that, complementing other ecotoxicological parameters, may help to improve the methodologies of freshwater monitoring under the increasing burden of xenobiotics.

Different transcriptional responses of heat shock protein 20 in the marine diatom Ditylum brightwellii exposed to metals and endocrine-disrupting chemicals

Diatoms are sensitive indicators of water quality, and hence used for environmental hazard assessments; however, their toxicogenomic studies have been insufficiently attempted. In the present study, we determined the cDNA sequence of heat shock protein 20 (Hsp20) gene from the diatom Ditylum brightwellii, and examined the transcriptional responses of the gene after exposing it to environmental stressors such as thermal shock, metals, and endocrine-disrupting chemicals (EDCs). The open reading frame (ORF) of DbHsp20 was 531 bp long, encoding 177 amino acid residues (19.49 kDa) with a conserved C-terminal and α-crystallin domain. The genomic region of DbHsp20 did not contain introns. Phylogeny of eukaryotic Hsp20s showed D. brightwellii was closely related to other diatoms. With regard to the gene expressional profile, real-time PCR results showed that the gene was significantly upregulated (P < 0.001) under thermal stress, with the highest change of 3.2-fold. Metals' (copper and nickel) treatments showed that it was induced after a certain point of treated concentration. On the contrary, EDCs did not display noticeable change on the expression of DbHsp20. These results suggest that the diatom Hsp20 basically responds to thermal stress, but may differentially respond to toxic substances such as metals and organic compounds such as EDCs.

Transcription and Maturation of mRNA in Dinoflagellates

Dinoflagellates are of great importance to the marine ecosystem, yet scant details of how gene expression is regulated at the transcriptional level are available. Transcription is of interest in the context of the chromatin structure in the dinoflagellates as it shows many differences from more typical eukaryotic cells. Here we canvas recent transcriptome profiles to identify the molecular building blocks available for the construction of the transcriptional machinery and contrast these with those used by other systems. Dinoflagellates display a clear paucity of specific transcription factors, although surprisingly, the rest of the basic transcriptional machinery is not markedly different from what is found in the close relatives to the dinoflagellates.

Characterization of a novel catalase-peroxidase (KATG) gene from the dinoflagellate Prorocentrum minimum

Dinoflagellates are a group of eukaryotic microalgae that have many unusual cytological and genomic characteristics. Here, we report the detection of a novel catalase-peroxidase (KatG) gene from the dinoflagellate Prorocentrum minimum, and its transcript levels under copper sulfate (CuSO4 ) treatment. cDNA analysis yielded a 1,293 bp complete open reading frame (ORF) encoding a 431-amino acid (aa) polypeptide (46.6 kDa). The conserved dinoflagellate splice leader (DinoSL) indicates that this gene is nucleus encoded, and a signal sequence at the N-terminus of the deduced protein indicates that the KatG protein may pass across the endoplasmic reticulum or cytoplasmic membrane, but its precise subcellular location is not known. Unlike the typical KatG proteins, P. minimum KatG (PmKatG) only has one conserved domain (N-domain). Gene expression of PmKatG dramatically increased with increasing concentrations of CuSO4 , suggesting that it functions in the defense mechanisms associated with oxidative stress.

Different transcriptional responses of heat shock protein 70/90 in the marine diatom Ditylum brightwellii exposed to metal compounds and endocrine-disrupting chemicals

Environmental hazard assessments using diatoms have been well documented; however, their molecular toxicology has not been sufficiently studied. In this study, we characterized heat shock protein (HSP) 70/90 of the diatom Ditylum brightwellii (Db) and evaluated their transcriptional profiles in response to various environmental stresses (e.g., thermal shocks and metal and non-metal pollutants). Putative DbHSP70 (658aa, 71.7 kDa) and DbHSP90 (707aa, 80.2 kDa) proteins had conserved HSP family motifs but different C-terminus motifs, that is, "EEVD" in DbHSP70 and "MEEVD" in DbHSP90. Phylogenetic analyses of both proteins showed that D. brightwellii was well clustered with other diatoms. Real-time PCR analysis showed that thermal stress considerably upregulated DbHSP70 and DbHSP90. As for chemical pollutants, DbHSP70 greatly responded to CuSO4 and NiSO4 exposure, but not CuCl2 or NiCl2. However, DbHSP90 was significantly upregulated by all the metal compounds tested (CuSO4, NiSO4, CuCl2, and NiCl2). Strikingly, the expression of both genes was not induced by the organic pollutants tested, such as endocrine-disrupting chemicals. These data suggest that DbHSP70 and DbHSP90 are differentially involved in the defense response against various environmental stressors. Moreover, metal toxicity may be specifically affected by the conjugated anion in the metal compounds (e.g., SO4(2-) and Cl(-)).

Physiological and biochemical responses of the marine dinoflagellate Prorocentrum minimum exposed to the oxidizing biocide chlorine

Toxic effects of the commonly used biocide chlorine (Cl2) on the marine dinoflagellate Prorocentrum minimum were assessed using growth-, pigment- and enzyme activity-based endpoints. Cell count, chlorophyll a levels, carotenoids, and chlorophyll autofluorescence were monitored up to 72h after exposure to Cl2, and these parameters showed a dose- and time-dependent decrease. The 72-h median effective concentration (EC50) based on growth rate was 1.177mgL(-1). Cl2 dose above 0.5mgL(-1) were toxic to P. minimum after 6-h exposure to Cl2; the effect increased with increase in exposure time as revealed by a significant reduction in growth rate and decreased chlorophyll fluorescence. Moreover, the activities of antioxidant enzymes, including superoxide dismutase and catalase, were altered proportionally with increasing Cl2 dose. The results of this study show that Cl2 concentrations as observed in power-plant discharges and in drinking-water systems cause physiological and biochemical damage to the microalgae.