Toxicological Responses of Chlorella vulgaris to Dichloromethane and Dichloroethane

Ecotoxicity studies reveal that organic cations in dicamba-derived ionic liquids can pose a greater environmental risk than the herbicide itself

The following research provides novel and relevant insights into potential environmental consequences of combination of various organic cations with commercial systemic herbicide (dicamba), in accordance with a 'herbicidal ionic liquids' (HILs) strategy. Toxicity assays of five dicamba-based HILs comprising different hydrophobic and hydrophilic cations, namely choline [CHOL][DIC], ethyl betainate [BETC2][DIC], decyl betainate [BETC10][DIC], hexadecyl betainate [BETC16][DIC] and didecyldimethylammonium [DDA][DIC]), have been tested towards bacteria (Pseudomonas putida, Escherichia coli, Bacillus subtilis), algae (Chlorella vulgaris), fresh and marine water crustaceans (Daphnia magna, Artemia franciscana). The structure of respective substituents in the cation emerged as a decisive determinant of toxicity in the case of tested species. In consequence, small ions of natural origin ([CHOL] and [BETC2]) demonstrated toxicity numerous orders of magnitude lower compared to fully synthetic [DDA]. These results emphasize the role of cations' hydrophobicity, as well as origin, in the observed acute toxic effect. Time-dependent toxicity assays also indicated that betaine-type cations comprising an ester bond can rapidly transform into less harmful substances, which can generally result in a reduction in toxicity by even several orders of magnitude. Nonetheless, these findings challenge the concept of ionic liquids with herbicidal activity and give apparent parallels to adjuvant-dependent toxicity issues recently noted in typical herbicidal formulations.

Transcriptome analysis of changes in M. aeruginosa growth and microcystin production under low concentrations of ethinyl estradiol

Ethinyl estradiol (EE2) is a synthetic environmental estrogen with considerable estrogenic activity. It has been found to consequently pose a significant threat to the aquatic ecosystem. Harmful algal blooms are a major aquatic ecological issue. However, the relationship between EE2 and cyanobacterial bloom is mainly unknown. In this study, the physiological and molecular responses of Microcystis aeruginosa to EE2 exposure were investigated. A low level of EE2 (0.02 μg/L) significantly enhanced the growth of algal cells (P < 0.05), whereas higher concentrations of EE2 (0.2-200 μg/L) inhibited it. EE2 at doses ranging from 0.02 to 200 μg/L promoted the production of microcystins (MCs), with genes mcyABD playing a key role in the regulation of MC synthesis. The alterations of chlorophyll-a, carotenoid, and phycocyanin contents caused by EE2 showed the same trend as cell growth. At the molecular level, 200 μg/L EE2 significantly down-regulated genes in photosynthetic pigment synthesis, light harvesting, electron transfer, NADPH, and ATP generation. High concentrations of EE2 caused oxidative damage to algal cells on the 4th d. After 12d exposure, although there was no significant change in superoxide dismutase (SOD) content and no damage observed in membrane lipids, genes related to SOD and glutathione were changed. In addition, due to the down-regulation of pckA, PK, gltA, nrtA, pstS, etc., carbon fixation, glycolysis, TCA cycle, nitrogen and phosphorus metabolism were hindered by EE2 (200 μg/L). Gene fabG in fatty acid biosynthesis was significantly up-regulated, promoting energy storage in cells. These findings provide important clues to elucidate the effects and mechanisms of cyanobacterial blooms triggered by EE2 and help to effectively prevent and control cyanobacterial blooms.

Weighted gene Co-expression network analysis (WGCNA) reveals a set of hub genes related to chlorophyll metabolism process in chlorella (Chlorella vulgaris) response androstenedione

Androstenedione (ADSD) was the main androgen detected in wastewaters. Chlorella was the most widely used plant in biological wastewater treatment process. In order to understand the toxicological response of chlorella to ADSD contamination, we used the weighted gene co-expression network analysis (WGCNA) method to systematically analyze the gene regulatory networks of chlorella after ADSD treatments. Total of 25 modules was identified from gene co-expression networks, and the turquoise module were selected for GO and KEGG enrichment analysis. Results showed that most hub genes were associated with chloroplast organizations or photosystems processes. Among them, the expressions profiles of hcar, nol, pao and sgr genes were highly correlated to the content fluctuations of chlorophylls after different ADSD treatments. All these results demonstrated that chlorophylls play a key role in preventing cell damage of chlorella caused by ADSD contamination. Besides, we proposed a possible chlorophyll metabolism pathway in chlorella response to ADSD contamination.

Impact of P-Chloroaniline on Oxidative Stress and Biomacromolecules Damage in the Clam Ruditapes philippinarums: A Simulate Toxicity Test of Spill Incident

As a hazardous chemical, p-chloroaniline (PCA) shows intensive adsorption and accumulation after entering the aquatic ecosystem, which can be enriched in organisms and cause damage. With the objective of achieving an integrated and mechanistic view of the toxic effects of PCA in the marine sentinel organism Ruditapes philippinarum, Manila clams were exposed to different concentration of PCA (0.5, 2 and 5 mg/L) for 15 days. Focusing on the gills, first targeting the toxic and digestive gland, the metabolic detoxification organ, we detected dose- and time-related changes inantioxidase activities and biomacromolecular damages in treated clams. Glutathione S-transferase (GST) activity and glutathione (GSH) contents were significantly induced, and superoxide dismutase (SOD) activity increased at the beginning of exposure and then decreased. The malondialdehyde (MDA) and protein methylation (PC) contents which represent lipid peroxidation and carbonylation of proteins, increased first with exposure time and then decreased in the digestive gland. DNA strand break levels were consistently higher than those in the control group. The digestive gland showed more sensitivity to the stress of PCA than the gills. GST and MDA in the gill and GST, GSH, SOD, DNA strand break level in the digestive gland showed significant correlation with PCA exposure, which indicated that these parameters can be used as sensitive biomarkers to indicate toxic effects from chloraniline leakage.

Toxicity of BPNSs against Chlorella vulgaris: Oxidative damage, physical damage and self-protection mechanism

Black phosphorus nanosheets (BPNSs) has extensive application prospect in the fields of optoelectronics and biomedicine, due to its unique physicochemical properties. Therefore, a systematic toxic study is necessary to assess its environmental safety. Herein, BPNSs was prepared by liquid exfoliation procedure, the primary producer Chlorella vulgaris (C. vulgaris) was used as a test subject. After the exposure for 120 h at 15, 45 and 75 mg/L BPNSs, the cell viabilities were 45.05%, 18.86% and 4.60% for each treatment group, respectively. The extent of lipid peroxidation and peroxidative damage in C. vulgaris was confirmed by measuring reactive oxygen species (ROS) levels, superoxide dismutase (SOD) and catalase (CAT) activities, followed by determination of malondialdehyde (MDA) content. Morphological analysis results (i.e., SEM and TEM) showed that BPNSs adhered to the cell surface and enter the cell to severely damage cell structure. Furthermore, BPNSs were shown to accelerate apoptosis in C. vulgaris by flow cytometry analysis. Finally, GC-MS was used to explore the metabolic regulatory mechanism of C. vulgaris in response to BPNSs stress. The results of this study can provide theoretical support for subsequent studies on the potential enrichment risk of BPNSs in the water environmental food chain.

Toxic effect of p-chloroaniline and butyl acrylateon Nannochloropsis oculata based on water samples from two sea areas

To compare the influence of water samples collected from various areas on toxic effect of HNS, we examined the toxic effect of two commonly found HNS: p-chloroaniline and butyl acrylate, on Nannochloropsis oculata cultured in seawater collected from Laizhou bay and Jiaozhou bay (China). The results showed that both p-chloroaniline and butyl acrylate had significant toxic effect on N. oculata cultured in both water samples. P-chloroaniline inhibited its net oxygenation rate and oxygen consumption rate. Butyl acrylate inhibited the net oxygenation rate whereas significantly stimulated oxygen consumption rate. Performance of N. oculata changed between two water samples under same level of p-chloroaniline and butyl acrylate. The net oxygenation rate of N. oculata cultured in the seawater from the Jiaozhou bay increased by 11.60 %, the oxygen consumption rate increased by 26.91 %, algae cell growth decreased by 16.83 %, compared to those from Laizhou bay. The Fv/Fm of N. oculata cultured in Jiaozhou bay was more significantly inhibited at 0.5 and 2.0 mg L^-1 p-chloroaniline, while it was significantly inhibited at 5. 0 mg L^-1 of butyl acrylate, compared to those from Laizhou bay. Moreover, the toxic effect of both HNS on net oxygenation rate and oxygen consumption rate were significantly attenuated as the concentration increased. The growth inhibition of microalgae cultured in two seawater samples was more evident at 0.5 and 5.0 mg L^-1 p-chloroaniline than at 2.0 mg L^-1 p-chloroaniline,and the growth inhibition of microalgae cultured in two seawater samples was more evident at 2.0 and 5.0 mg L^-1 butyl acrylate than at 0.5 mg L^-1 butyl acrylate. These results indicated that toxic effect of p-chloroaniline and butyl acrylate on the growth of N. oculata was influenced by the pollutants in the two water samples. Consequently, a corresponding research on water sample is required in advance to increase accuracy of future ecological risk assessment of HNS.

Effects of zinc and mercury on ROS-mediated oxidative stress-induced physiological impairments and antioxidant responses in the microalga Chlorella vulgaris

The rapid growth of industrialization and urbanization results in deterioration of freshwater systems around the world, rescinding the ecological balance. Among many factors that lead to adverse effects in aquatic ecology, metals are frequently discharged into aquatic ecosystems from natural and anthropogenic sources. Metals are highly persistent and toxic substances in trace amounts and can potentially induce severe oxidative stress in aquatic organisms. In this study, adverse effects of the two metal elements zinc (maximum concentration of 167.25 mg/L) and mercury (104.2 mg/L) were examined using Chlorella vulgaris under acute and chronic exposure period (48 h and 7 days, respectively). The metal-induced adverse effects have been analyzed through photosynthetic pigment content, total protein content, reactive oxygen species (ROS) generation, antioxidant enzymatic activities, namely catalase and superoxide dismutase (SOD) along with morphological changes in C. vulgaris. Photosynthetic pigments were gradually reduced (~32-100% reduction) in a dose-dependent manner. Protein content was initially increased during acute (~8-12%) and chronic (~57-80%) exposure and decreased (~44-56%) at higher concentration of the two metals (80%). Under the two metal exposures, 5- to 7-fold increase in ROS generation indicated the induction of oxidative stress and subsequent modulations in antioxidant activities. SOD activity was varied with an initial increase (58-129%) followed by a gradual reduction (~3.7-79%), while ~1- to 12-fold difference in CAT activity was observed in all experimental condition (~83 to 1605%). A significant difference was observed in combined toxic exposure (Zn+Hg), while comparing the toxic endpoint data of individual metal exposure (Zn and Hg alone). Through this work, lethal effects caused by single and combined toxicity of zinc and mercury were assessed, representing the significance of appropriate monitoring system to trim down the release of metal contaminants into the aquatic ecosystems.

Effect of metals of treated electroplating industrial effluents on antioxidant defense system in the microalga Chlorella vulgaris

The microalga Chlorella vulgaris is one of the prominent and most widely distributed green microalgae found in aquatic environments, often used in toxicity tests due to its sensitivity to various pollutants. To examine the toxicity of metals found in the effluent discharges from an electroplating industry, physicochemical parameters in the microalga C. vulgaris were measured. pH, turbidity, total dissolved solids, color, and the concentrations of metals such as chromium (1.97 mg/L), mercury (104.2 mg/L), and zinc (167.25 mg/L) were found exceeding the permissible limits. Several endpoints such as total protein content, reactive oxygen species (ROS) production, photosynthetic pigment contents, and antioxidant enzymatic activities, including those of superoxide dismutase (SOD) and catalase (CAT), were measured in C. vulgaris in response to treated electroplating industrial effluent (TEPIE). In addition, concentration-dependent morphological changes were also observed in response to TEPIE. Under both acute and chronic TEPIE exposure, increase in the ROS level was observed indicating increased production of ROS in C. vulgaris cells. The total protein and chlorophyll contents were found to be gradually decreasing in an effluent concentration-dependent manner. Moreover, lower concentrations of effluent stimulated the antioxidant enzyme systems. A concentration-dependent increase was observed in both SOD and CAT enzymatic activities. The results indicated toxic impairments by the effluent on the function of C. vulgaris in response to both acute and chronic exposure, indicating an urgent need of proper treatment processes/modification of the existing one of TEPIE, with continuous monitoring of the discharge of the pollutants into the aquatic ecosystems using biological assays.

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.

Effect of Organic Solvents on Microalgae Growth, Metabolism and Industrial Bioproduct Extraction: A Review

In this review, the effect of organic solvents on microalgae cultures from molecular to industrial scale is presented. Traditional organic solvents and solvents of new generation-ionic liquids (ILs), are considered. Alterations in microalgal cell metabolism and synthesis of target products (pigments, proteins, lipids), as a result of exposure to organic solvents, are summarized. Applications of organic solvents as a carbon source for microalgal growth and production of target molecules are discussed. Possible implementation of various industrial effluents containing organic solvents into microalgal cultivation media, is evaluated. The effect of organic solvents on extraction of target compounds from microalgae is also considered. Techniques for lipid and carotenoid extraction from viable microalgal biomass (milking methods) and dead microalgal biomass (classical methods) are depicted. Moreover, the economic survey of lipid and carotenoid extraction from microalgae biomass, by means of different techniques and solvents, is conducted.

The effect of cadmium on the growth and antioxidant response for freshwater algae Chlorella vulgaris

The objective of the present work was to evaluate the effect of exogenously applied cadmium on the physiological response of green algae Chlorella vulgaris. The study investigated the long-term effect (18 days) of cadmium on the levels of algae biomass, assimilation pigment composition, soluble protein, oxidative status (production of hydrogen peroxide and superoxide anion), antioxidant enzymes (such as superoxide dismutase, peroxidase, catalase and glutathione reductase enzyme) in C. vulgaris. The results showed that growth, the amount of chlorophyll a (Chl a), chlorophyll b (Chl b) and carotenoids gradually decreased with increasing cadmium over 18 days exposure. Cadmium at concentration of 7 mg L(-1) inhibited algal growth expressed as the number of cells. Our research found that C. vulgaris has a high tolerance to cadmium. Contents of chlorophylls (Chl a and Chl b) and carotenoids (Car) of C. vulgaris was significantly decline with rising concentration of cadmium (p < 0.05). The decrease of 54.04 and 93.37 % in Chl a, 60.65 and 74.32 % in Chl b, 50.00 and 71.88 % in total carotenoids was noticed following the treatment with 3 and 7 mg L(-1) cadmium doses compared with control treatment, respectively. Cadmium treatments caused a significant change in the physiological competence (calculated as chlorophyll a/b) which increased with increasing Cd(II) doses up to 1 mg L(-1) but decreased at 3 mg L(-1). While accumulation of soluble protein was enhanced by presence of cadmium, the treatment with cadmium at 3 and 7 mg L(-1) increased the concentration of soluble proteins by 88, 95.8 % in C. vulgaris, respectively. Moreover, low doses of cadmium stimulated enzymatic (superoxide dismutase, catalase and glutathione reductase) in C. vulgaris, The content of peroxidase increased with the increasing cadmium concentration, and had slightly decreased at the concentration of 7 mg L(-1), but was still higher than control group, which showed that cadmium stress at high concentration mainly peroxidase works in C. vulgaris. And therefore, suppressed reactive oxygen species (hydrogen peroxide and superoxide) accumulated. The present study also showed that cadmium increased oxidative stress and induced antioxidant defense systems against reactive oxygen species. The observation in here analyzed C. vulgaris after exposure to cadmium indicate that hydrogen peroxide, superoxide and peroxidase in the alga with exposure to Cd(II) seemed to be parameters as biomarkers for metal-induced oxidative stress.

Transcriptomic profiles reveal the genome-wide responses of the harmful dinoflagellate Cochlodinium polykrikoides when exposed to the algicide copper sulfate

Background

Harmful algal blooms (HABs) caused by the dinoflagellate Cochlodinium polykrikoides lead to severe environmental impacts in oceans worldwide followed by huge economic losses. Algicide agent copper sulfate (CuSO₄) is regard as an economical and effective agent for HABs mitigation; its biochemical and physiological effects were revealed in C. polykrikoides. However, molecular mechanisms of CuSO₄ effect on the C. polykrikoides, even other HAB species, have not been investigated. The present study investigated the transcriptional response of C. polykrikoides against CuSO₄ treatments, with the aim of providing certain molecular mechanism of CuSO₄ effect on the C. polykrikoides blooms.

Results

RNA-seq generated 173 million reads, which were further assembled to 191,212 contigs. 43.3 %, 33.9 %, and 15.6 % of contigs were annotated with NCBI NR, GO, and KEGG database, respectively. Transcriptomic analysis revealed 20.6 % differential expressed contigs, which grouped into 8 clusters according to K-means clustering analysis, responding to CuSO₄; 848 contigs were up-regulated and 746 contigs were down-regulated more than 2-fold changes from 12 h to 48 h exposure. KEGG pathway analysis of eukaryotic homologous genes revealed the differentially expressed genes (DEGs) were involved in diverse pathway; amongst, the genes involved in the translation, spliceosome, and/or signal transduction genes were highly regulated. Most of photosystem related genes were down-regulated and most of mitochondria related genes were up-regulated. In addition, the genes involved in the copper ion binding or transporting and antioxidant systems were identified. Measurement of chlorophyll fluorescence showed that photosynthesis was significantly inhibited by CuSO₄ exposure.

Conclusions

This study reported the first transcriptome of the C. polykrikoides. The widely differential expressed photosystem genes suggested photosynthetic machinery were severely affected, and may further contribute to the cell death. Furthermore, gene translation and transcription processes may be disrupted, inhibiting cell growth and proliferation, and possibly accelerating cell death. However, antioxidant systems resistant to CuSO₄ caused stress; mitochondrion may compensate for photosynthesis efficiency decreasing caused energy deficiency. In addition, various signal transduction pathways may be involved in the CuSO₄ induced regulation network in the C. polykrikoides. These data provide the potential transcriptomic mechanism to explain the algicide CuSO₄ effect on the harmful dinoflagellate C. polykrikoides.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2341-3) contains supplementary material, which is available to authorized users.