Effects of eutrophication on the horizontal transfer of antibiotic resistance genes in microalgal-bacterial symbiotic systems.

Overloading of nutrients such as nitrogen causes eutrophication of freshwater bodies. The spread of antibiotic resistance genes (ARGs) poses a threat to ecosystems. However, studies on the enrichment and spread of ARGs from increased nitrogen loading in algal-bacterial symbiotic systems are limited. In this study, the transfer of extracellular kanamycin resistance (KR) genes from large (RP4) small (pEASY-T1) plasmids into the intracellular and extracellular DNA (iDNA, eDNA) of the inter-algal environment of Chlorella pyrenoidosa was investigated, along with the community structure of free-living (FL) and particle-attached (PA) bacteria under different nitrogen source concentrations (0-2.5 g/L KNO3). The results showed that KR gene abundance in the eDNA adsorbed on solid particles (D-eDNA) increased initially and then decreased with increasing nitrogen concentration, while the opposite was true for the rest of the free eDNA (E-eDNA). Medium nitrogen concentrations promoted the transfer of extracellular KR genes into the iDNA attached to algal microorganisms (A-iDNA), eDNA attached to algae (B-eDNA), and the iDNA of free microorganisms (C-iDNA); high nitrogen contributed to the transfer of KR genes into C-iDNA. The highest percentage of KR genes was found in B-eDNA with RP4 plasmid treatment (66.2%) and in C-iDNA with pEASY-T1 plasmid treatment (86.88%). In addition, dissolved oxygen (DO) significantly affected the bacterial PA and FL community compositions. Nephelometric turbidity units (NTU) reflected the abundance of ARGs in algae. Proteobacteria, Cyanobacteria, Bacteroidota, and Actinobacteriota were the main potential hosts of ARGs. These findings provide new insights into the distribution and dispersal of ARGs in the phytoplankton inter-algal environment.

Exploring the influence of sulfadiazine-induced stress on antibiotic removal and transformation pathway using microalgae Chlorella sp.

Sulfadiazine (SDZ) is a kind of anti-degradable antibiotics that is commonly found in wastewater, but its removal mechanism and transformation pathway remain unclear in microalgal systems. This study investigated the effects of initial algae concentration and SDZ-induced stress on microalgal growth metabolism, SDZ removal efficiency, and transformation pathways during Chlorella sp. cultivation. Results showed that SDZ had an inhibitory effect on the growth of microalgae, and increasing the initial algal biomass could alleviate the inhibitory effect of SDZ. When the initial algal biomass of Chlorella sp. was increased to 0.25 g L-1, the SDZ removal rate could reach 53.27%-89.07%. The higher the initial algal biomass, the higher the SOD activity of microalgae, and the better the protective effect on microalgae, which was one of the reasons for the increase in SDZ removal efficiency. Meanwhile, SDZ stress causes changes in photosynthetic pigments, lipids, total sugars and protein content of Chlorella sp. in response to environmental changes. The main degradation mechanisms of SDZ by Chlorella sp. were biodegradation (37.82%) and photodegradation (23%). Most of the degradation products of SDZ were less toxic than the parent compound, and the green algae were highly susceptible to SDZ and its degradation products. The findings from this study offered valuable insights into the tradeoffs between accumulating microalgal biomass and antibiotic toxic risks during wastewater treatment, providing essential direction for the advancement in future research and full-scale application.

Developing a Chromochloris zofingiensis Mutant for Enhanced Production of Lutein under CO2 Aeration.

Microalgae are competitive and commercial sources for health-benefit carotenoids. In this study, a Chromochloris zofingiensis mutant (Cz-pkg), which does not shut off its photosystem and stays green upon glucose treatment, was generated and characterized. Cz-pkg was developed by treating the algal cells with a chemical mutagen as N-methyl-N'-nitro-N-nitrosoguanidine and followed by a color-based colony screening approach. Cz-pkg was found to contain a dysfunctional cGMP-dependent protein kinase (PKG). By cultivated with CO2 aeration under mixotrophy, the mutant accumulated lutein up to 31.93 ± 1.91 mg L-1 with a productivity of 10.57 ± 0.73 mg L-1 day-1, which were about 2.5- and 8.5-fold of its mother strain. Besides, the lutein content of Cz-pkg could reach 7.73 ± 0.52 mg g-1 of dry weight, which is much higher than that of marigold flower, the most common commercial source of lutein. Transcriptomic analysis revealed that in the mutant Cz-pkg, most of the genes involved in the biosynthesis of lutein and chlorophylls were not down-regulated upon glucose addition, suggesting that PKG may regulate the metabolisms of photosynthetic pigments. This study demonstrated that Cz-pkg could serve as a promising strain for both lutein production and glucose sensing study.

Changes to the amino acid profile and proteome of the tropical freshwater microalga Chlorella sp. in response to copper stress.

Contamination of freshwaters is increasing globally, with microalgae considered one of the most sensitive taxa to metal pollution. Here, we used 72 h bioassays to explore the biochemical effects of copper (Cu) on the amino acid (AA) profile and proteome of Chlorella sp. and advance our understanding of the molecular changes that occur in algal cells during exposure to environmentally realistic Cu concentrations. The Cu concentrations required to inhibit algal growth rate by 10% (EC10) and 50% (EC50) were 1.0 (0.7-1.2) µg L-1 and 2.0 (1.9-2.4) µg L-1, respectively. The AA profile of Chlorella sp. showed increases in glycine and decreases in isoleucine, leucine, valine, and arginine, with increasing Cu. Proteomic analysis revealed the modulation of several proteins involved in energy production pathways, including: photosynthesis, carbon fixation, glycolysis, and oxidative phosphorylation, which likely assists in meeting increased energy demands under Cu-stressed conditions. Copper exposure also caused up-regulation of cellular processes and signalling proteins, and the down-regulation of proteins related to ribosomal structure and protein translation. These changes in biomolecular pathways have direct effects on the AA profile and total protein content and provide an explanation for the observed changes in amino acid profile, cell growth and morphology. This study shows the complex mode of action of Cu on Chlorella under environmentally realistic Cu concentrations and highlights several potential biomarkers for future investigations.

Singlet oxygen damages the function of Photosystem II in isolated thylakoids and in the green alga Chlorella sorokiniana.

Singlet oxygen (1O2) is an important damaging agent, which is produced during illumination by the interaction of the triplet excited state pigment molecules with molecular oxygen. In cells of photosynthetic organisms 1O2 is formed primarily in chlorophyll containing complexes, and damages pigments, lipids, proteins and other cellular constituents in their environment. A useful approach to study the physiological role of 1O2 is the utilization of external photosensitizers. In the present study, we employed a multiwell plate-based screening method in combination with chlorophyll fluorescence imaging to characterize the effect of externally produced 1O2 on the photosynthetic activity of isolated thylakoid membranes and intact Chlorella sorokiniana cells. The results show that the external 1O2 produced by the photosensitization reactions of Rose Bengal damages Photosystem II both in isolated thylakoid membranes and in intact cells in a concentration dependent manner indicating that 1O2 plays a significant role in photodamage of Photosystem II.

Toxicity assessment of synthesized titanium dioxide nanoparticles in fresh water algae Chlorella pyrenoidosa and a zebrafish liver cell line.

This study aims to assess the toxicity of the commonly-spread titanium dioxide nanoparticles (TiO2 NPs) by evaluating the exposure impact of the particles on both freshwater algae Chlorella pyrenoidosa and zebrafish liver cell line (ZFL), the two common in vitro models in toxicological studies. To compare the toxic effects of TiO2 NPs with different physiochemical properties, three types of manufactured TiO2 were used: bulk TiO2, Degussa P25 TiO2, and ultrafine TiO2 NPs. Both short and long-term biological responses of green algae, such as the effect on the cell growth rate, pigment autofluorescence, and esterase activity were investigated. The dosage, physical property of TiO2 particles, and their interactions with algal cells affect cellular growth, especially after short-term exposure. The hydrodynamic size plays a critical role in determining the acute toxicity to C. pyrenoidosa in terms of autofluorescence and esterase activity, while all types of TiO2 NPs show toxic effects after exposure for 14 days. However, this observation is not seen when studying the effect of introduced particles in ZFL, for the precipitated Degussa P25 TiO2 showed the highest cellular inhibition. Interestingly, despite the obvious overall toxicity toward C. pyrenoidosa, the photocatalytical properties of TiO2 NPs may contribute to the enhanced photosynthesis in the low concentration range (<40 µg mL-1). Overall, we found that the physical interactions between TiO2 particles and the cells, particles' size and dispersibility play critical role in the cytotoxic effect for both algal and ZFL cells, while the photocatalytical properties of TiO2 particles may produce mixed effects on the cytotoxicity of green algae.

Effects of three antibiotics on growth and antioxidant response of Chlorella pyrenoidosa and Anabaena cylindrica.

Antibiotics are essential for treatments of bacterial infection and play important roles in the fields of aquaculture and animal husbandry. Antibiotics are accumulated in water and soil due to the excessive consumption and incomplete treatment of antibiotic wastewater. The accumulation of antibiotics in ecological systems leads to global environmental risks. The toxic effects of spiramycin (SPI), tigecycline (TGC), and amoxicillin (AMX) on Chlorella pyrenoidesa and Anabaena cylindrica were evaluated based on growth inhibition experiments, and determinations of ROS production and antioxidant enzyme activities (catalase, superoxide dismutase, and malondialdehyde). Half maximal effective concentrations (EC50) of TGC, SPI, and AMX for A. cylindrica were 62.52 µg/L, 38.40 µg/L, and 7.66 mg/L, respectively. Those were 6.20 mg/L, 4.58 mg/L, and > 2 g/L for C. pyrenoidesa, respectively. It was shown that A. cylindrica was much more sensitive to these antibiotics than C. pyrenoidesa. In addition, EC50 values of SPI and TGC were lower than that of AMX. It was indicated that SPI and TGC had higher toxic than AMX to C. pyrenoidesa and A. cylindrica. The current study is helpful to evaluating possible ecological risks of TGC, SPI, and AMX by green microalgae and cyanobacteria.

Effect of cadmium in the microalga Chlorella sorokiniana: A proteomic study.

Cadmium is one of the most common heavy metals in contaminated aquatic environments and one of the most toxic contaminants for phytoplankton. Nevertheless, there are not enough studies focused on the effect of this metal in algae. Through a proteomic approach, this work shows how Cd can alter the growth, cell morphology and metabolism of the microalga Chlorella sorokiniana. Using the sequential window acquisition of all theoretical fragment ion spectra mass spectrometry (SWATH-MS), we concluded that exposure of Chlorella sorokiniana to 250 µM Cd2+ for 40 h caused downregulation of different metabolic pathways, such as photosynthesis, oxidative phosphorylation, glycolysis, TCA cycle and ribosomal proteins biosynthesis. However, photorespiration, antioxidant enzymes, gluconeogenesis, starch catabolism, and biosynthesis of glutamate, cysteine, glycine and serine were upregulated, under the same conditions. Finally, exposure to Cd also led to changes in the metabolism of carotenoids and lipids. In addition, the high tolerance of Chlorella sorokiniana to Cd points to this microalga as a potential microorganism to be used in bioremediation processes.

Characterization of a novel herbicide and antibiotic-resistant Chlorella sp. with an extensive extracellular matrix.

A herbicide and antibiotic-resistant microalgal strain, isolated from a eutrophic site at Giofyros river (Heraklion, Crete, Greece) was extensively characterized. In the presence of relatively high concentrations of common photosynthesis inhibitors (DCMU and atrazine), as well as various antibiotics (spectinomycin, kanamycin, and chloramphenicol), the green microalga was able to increase its biomass in approximately equal levels compared to the control. Despite the high concentrations of the inhibitors, photosynthetic efficiency and chlorophyll a amount per dry cell biomass were comparable to those of control cultures in almost all cases. 18S rDNA analysis showed that this microalga belongs to the Chlorella genus. Optical and electron microscopy studies revealed the presence of an extensive extracellular matrix (EM) that surrounds the cells and plays an important role in colony formation and cell-cell interactions. Fourier transform infrared spectroscopy provided evidence that the EM consists of a polysaccharide. This matrix could be separated from the cells with a simple centrifugation. Depending on growth conditions, the dry cell biomass of this Chlorella strain was found to contain 35-39% proteins and 27-42% carbohydrates. The results of this study have demonstrated that the EM plays a protective role for cell homeostasis maintenance against the various chemical agents. This green microalga is a suitable candidate for further studies regarding sustainable biomass production in waste waters for a series of applications.

Effect of fluorescent dye positioning and concentration on the growth parameters and lipid content of Chlorella sp. in a flat panel photobioreactor.

In this study, two different concentrations of fluorescent dye Rhodamine 6G (R6G) with two different strategies were used in a double layer flat panel photobioreactor (PBR) for investigation of its effect on growth parameters of microalgae Chlorella sp. Results showed that in the first strategy, when the light passed through the dye before reaching the broth, biomass productivity rate (P) and maximum specific growth rate (µmax) relative to control case, were increased up to 60 and 23% respectively. Increasing in these parameters were more, for the low dye concentration. Also, in the second strategy, when the light passed through the microalgae before reaching the dye solution, P and µmax for lower concentration increased about 9 and 15%, respectively. But using high dye concentration growth of the algae was decreased. Furthermore, using R6G caused increase in the lipid and chlorophyll content of the microalgae Chlorella sp.

Predicting chronic algal toxicity from 1- to 48-h pulsed exposures to mine site waters using time-averaged concentrations.

Despite concentrations often fluctuating in aquatic systems that receive contaminant inputs, there has only been a relatively small number of studies investigating the toxicity of intermittent exposures. This is particularly the case for industrial and mine effluents that may contain complex mixtures of contaminants and other stressors. The lack of information is impeding the regulation of such contaminant exposures, whose risk is often assessed by comparison to continuous exposures in whole effluent toxicity (direct toxicity assessment) testing. The current study compared the toxicity from continuous (72-h) and pulsed (1- to 48-h) exposures of two neutralised mine waters (NMWs) to the freshwater algae, Chlorella sp. When the algal toxicity of the different exposures was related to the time-averaged concentration (TAC) of contaminants, it was found that the TAC was a good predictor of toxicity in any given test, with variability in toxicity between tests mainly related to differences in contaminant concentrations from the neutralisation of the acidic mine waters. When the data from tests on two samples were combined on a whole-effluent TAC basis, the EC50 values (95% confidence intervals) for the continuous and pulsed exposures were 0.68% (0.36-1.3) and 0.63% (0.38-1.1) respectively, for NMW sample one, while the corresponding EC50 values for NMW sample two were 1.3% (1.0-1.7) and 1.9% (1.6-2.2), respectively. The toxicity of the second water was strongly influenced by the zinc, and probably copper, concentrations, while the toxicity of the first appeared to be related to additive or synergistic toxicity from Al, Cd, Mn and Pb. The findings are discussed in relation to using a contaminant TAC-approach to revise water quality guideline values derived for continuous exposures for application to pulsed exposures, where higher concentrations may be permissible for short durations.

Interactive effects of roxithromycin and freshwater microalgae, Chlorella pyrenoidosa: Toxicity and removal mechanism.

Roxithromycin (ROX) has received increasing concern due to its large usage, ubiquitous detection in environment and high ecotoxicology risk. This study investigated the acute and chronic effects of ROX on the growth, chlorophyll, antioxidant enzymes, and malonaldehyde (MDA) content of Chlorella pyrenoidosa, as well as the removal mechanism of ROX during microalgae cultivation. The calculated 96 h median effective concentration of ROX on yield (EyC50) and specific growth rate (ErC50) of C. pyrenoidosa was 0.81 and 2.87 mg/L, respectively. After 96 h exposure, 1.0 ~ 2.0 mg/L of ROX significantly inhibited the synthesis of chlorophyll and promoted the activities of SOD and CAT (p < 0.05). The MDA content increased with the ROX concentration increasing from 0.5 ~ 1.0 mg/L, and then decreased to 105.76% of the control exposure to 2.0 mg/L ROX, demonstrating the oxidative damage could be moderated by the upregulation of SOD and CAT activities. During the 21 d chronic exposure, low concentration of ROX (0.1 and 0.25 mg/L) showed no significant effect on the growth and chlorophyll content of algae during the first 14 d, but significantly inhibited the growth of algae and the synthesis of chlorophyll at 21 d (p < 0.05 or p < 0.01). 1.0 mg/L ROX significantly inhibited the growth of microalgae during 3 ~ 21 d and the synthesis of chlorophyll at 7 ~ 21 d. High concentration and long-term exposure of low concentration of ROX caused the SOD and CAT activities and MDA content to increase, demonstrating a higher level of oxidative damage of microalgae. During the first 14 d, abiotic removal of ROX played a more important role, contributing about 12.21% ~ 21.37% of ROX removal. After 14 d, the biodegradation of ROX by C. pyrenoidosa gradually became a more important removal mechanism, contributing about 45.99% ~ 53.30% of ROX removal at 21 d. Bio-adsorption and bioaccumulation both played minor roles in the removal of ROX during algae cultivation.

Using a freshwater green alga Chlorella pyrenoidosa to evaluate the biotoxicity of ionic liquids with different cations and anions.

With the extensive use of ionic liquids (ILs) in various industrial fields, their potential toxicity to aquatic ecosystem has attracted considerable attention. In this work, biotoxicity of ILs with different cations and anions was evaluated by using a freshwater green alga Chlorella pyrenoidosa. Results showed that 1-butyl-3-methylimidazolium chloride ([C4mim]Cl), 1-octyl-3-methylimidazolium chloride ([C8mim]Cl), 1-octyl-3-methylimidazolium nitrate ([C8mim]NO3), 1-octyl-3-methylimidazolium tetrafluoroborate ([C8mim]BF4), and 1-dodecyl-3-methylimidazolium chloride ([C12mim]Cl) had a significant inhibition on the algal growth with EC50 values of 23.48, 4.72, 3.80, 4.44, and 0.10 mg L-1 at the 72 h of exposure, respectively. These data suggested that the toxicity of ILs increased with the increase of side alkyl chain length, while anions had little influences on their toxicity to this alga. Moreover, changes in chlorophyll a content and chlorophyll fluorescence parameters (Fv/Fm and ΦPSII) indicated that the five ILs could damage the photosynthetic system of this alga resulting in the decrease of photosynthetic efficiency. The increased soluble protein content and antioxidase activity could be considered as an active response mechanism of this alga against the exposure of ILs. Content of malondialdehyde (MDA) in this alga increased significantly when it was exposed to ILs, suggesting that reactive oxygen species (ROS) were accumulated in the algal cells, which would cause injury of the algal biofilm and chloroplast. Therefore, results obtained in this work would help to explain the possible underlying toxic mechanisms of ILs to C. pyrenoidosa, and provide a significant theoretical support for assessing the toxicity of ILs to aquatic organisms.

The combined toxicity influence of microplastics and nonylphenol on microalgae Chlorella pyrenoidosa.

Microplastics and nonylphenol (NP) are considered as emerging pollutant and have attracted wide attention, while their combined toxicity on aquatic organisms is barely researched. Therefore, the combined toxicity influence of NP with three types of microplastics containing polyethylene (PE1000, 13 µm and PE, 150 µm), polyamide (PA1000, 13 µm and PA, 150 µm) polystyrene (PS, 150 µm) on microalgae Chlorella pyrenoidosa was analyzed. Both growth inhibition, chlorophyll fluorescence, superoxide dismutase (SOD), malondialdehyde (MDA), and catalase (CAT) were determined. We found that single microplastics and NP both inhibited algal growth, thereby causing oxidative stress. The order of inhibition effect in single microplastics experiment was PE1000 > PA1000 > PE ≈ PS > PA. The combined toxicity experiment results indicated that the presence of microplastics had positive effect in terms of alleviating NP toxicity to C. pyrenoidosa, and the microplastics adsorption capacity to NP was the dominant contributing factor for this effect. According to the independent action model, the combined toxicity was antagonistic. Because the negative effect of smaller size microplastics on algal growth was aggravated with prolonged exposure time, the optimum effect of microplastics alleviated NP toxicity was PA1000 at 48 h, while this effect was substituted by PA at 96 h during combined toxicity. Thus, the toxicity of smaller size microplastics has a nonnegligible influence on combined toxicity. This study confirms that microplastics significantly affected the toxicity of organic pollutants on microalgae. Further research on the combined toxicity of smaller size microplastics with pollutants in chronic toxicity is needed.

The comparison of transcriptomic response of green microalga Chlorella sorokiniana exposure to environmentally relevant concentration of cadmium(II) and 4-n-nonylphenol.

The transcriptomic response of green microalga Chlorella sorokiniana exposure to environmentally relevant concentration of cadmium(II) (Cd) and 4-n-nonylphenol (4-n-NP) was compared in the present study. Cd and 4-n-NP exposure showed a similar pattern of dys-regulated pathways. The photosystem was affected due to suppression of chlorophyll biosynthesis via down-regulation of Mg-protoporphyrin IX chelatase subunit ChlD (CHLD) and divinyl chlorophyllide a 8-vinyl-reductase (DVR) in Cd group and via down-regulation of DVR in 4-n-NP group. Furthermore, the reactive oxygen species (ROS) could be induced through down-regulation of solanesyl diphosphate synthase 1 (SPS1) and homogentisate phytyltransferase (HPT) in Cd group and via down-regulation of HPT in 4-n-NP group. Additionally, Cd and 4-n-NP would both cause the dys-regulation of carbohydrate metabolism and protein synthesis. On the other hand, there are some different responses or detoxification mechanism of C. sorokiniana to 4-n-NP stress compared to Cd exposure. The increased ROS would cause the DNA damage and protein destruction in Cd exposure group. Simultaneously, the RNA transcription was dys-regulated and a series of changes in gene expressions were observed. This included lipid metabolism, protein modification, and DNA repair, which involved in response of C. sorokiniana to Cd stress or detoxification of Cd. For 4-n-NP exposure, no effect on lipid metabolism and DNA repair was observed. The nucleotide metabolism including pyrimidine metabolism and purine metabolism was significantly up-regulated in the 4-n-NP exposure group, but not in the Cd exposure group. In addition, 4-n-NP would induce the ubiquitin-mediated proteolysis and proteasomal degradation to diminish the misfolded protein caused by ROS and down-regulation of heat shocking protein 40. In sum, the Cd and 4-n-NP could cause the same toxicological effects via the common pathways and possess similar detoxification mechanism. They also showed different responses in nucleotide metabolism, lipid metabolism, and DNA repair.

The biological activities of prothioconazole enantiomers and their toxicity assessment on aquatic organisms.

Chiral fungicide prothioconazole has a wide range of antifungal spectrum; however, little research has been conducted to evaluate prothioconazole on an enantiomeric level. Five target pathogens and three common aquatic organisms were tested for the enantioselective bioactivity and toxicity of prothioconazole in this work. The antifungal activity of the enantiomers against wheat phytoalexin, rice blast fungus, exserohilum turcicum, Alternaria triticina, and Fusarium avenaceum was determined, and it was found that (-)-prothioconazole were 85 to 2768 times more active than (+)-prothioconazole toward these target organisms. In order to reflect the risk to aquatic ecosystem, the acute toxicity of the enantiomers to Daphnia magna, Chlorella pyrenoidosa, and Lemna minor L. was assessed. It was observed that the toxicity of (-)-prothioconazole to D. magna was 2.2 times higher than (+)-prothioconazole, but it was lower to C. pyrenoidosa and L. minor L. The toxicities of (+)-enantiomer and (-)-enantiomer to D. magna and C. pyrenoidosa were synergy, indicating that the racemate had higher threat to the organisms. It could be concluded that the effects of prothioconazole on target organisms and the acute toxicity to nontarget species were enantioselective with (-)-enantiomer possessing higher efficiency and lower toxicity. Such enantiomeric differences should be taken into consideration when assessing the performance of prothioconazole.

Ecotoxicological effects and removal of 17ß-estradiol in chlorella algae.

17ß-estradiol (E2) is a steroid estrogen able to affect the reproduction of aquatic organisms even at extremely low concentrations. The behavior of E2 in the presence of chlorella algae was investigated in laboratory experiments. The results showed that the algae's growth was inhibited by 26% after 7 days of culturing in a 2.0 mg L-1 solution of E2. The 96 h EC50 value of 21.46 mg L-1 reflected moderate toxicity. Even low concentrations of E2 were found to affect total chlorophyll and carotenoid levels after 7 and 10 days and to alter stress-generated enzymatic activity in the algae. The efficiency of chlorella's E2 degradation decreased with the increasing of E2 concentration, but 92% of the E2 can be removed from a 0.5 mg L-1 solution over 10 days. The degradation mechanism was speculated. The microalgae suffered relatively less growth inhibition at low E2 concentrations, and their removal effectiveness was then better. The data help to elucidate the interaction between chlorella algae and E2 in an aquatic environment.

Evaluation of the novel nanoparticle material - CdSe quantum dots on Chlorella pyrenoidosa and Scenedesmus obliquus: Concentration-time-dependent responses.

Quantum dots (QDs), as a kind of novel nanomaterial, have the extensive applications in various fields, inevitably leading to increasing risks for the ecological environment. The mobilization of cadmium including metal smelting and subsequent machining for multifarious applications has caused the release of cadmium element into the environment. In this study, we evaluated the potential toxicity of a novel nanoparticle material CdSe QDs, using two green algae Chlorella pyrenoidosa and Scenedesmus obliquus. The impact of CdSe QDs and cadmium ions on algae and the sensitivity of the two algae on target compounds were also considered and compared. Our results showed the algal growth rates and chlorophyll content decreased with increasing exposure concentrations and durations. Moreover, the glutathione levels were decreased while the activities of superoxide dismutase increased, exhibiting their pivotal functions in defeating toxic stress. The increment of malondialdehyde levels revealed that the stresses of CdSe QDs and cadmium ions were contributed to the occurrence of oxidative damage. Our study also indicated that the impact of CdSe QDs was stronger than that of cadmium nitrate and the algal response was also species-specific. In addition, the TEM photographs of the algal ultrastructure showed the presence of surface attachment and uptake of QDs.

Enantioselective mechanism of toxic effects of triticonazole against Chlorella pyrenoidosa.

The rational use and the environmental safety of chiral pesticides have attracted significant research interest. Here, enantioselective toxic effects and the selective toxic mechanism of triticonazole (TRZ) against the aquatic microalgae Chlorella pyrenoidosa were studied. The 96h-EC50 values of rac-, (R)-(-)-, and (S)-(+)-TRZ were 1.939, 0.853, and 22.002 mg/L, respectively. At a concentration of 1 mg/L, the contents of photosynthetic pigments of C. pyrenoidosa exposed to (R)-(-)-TRZ were lower than if exposed to S-(+)-form and racemate. Transmission electron microscopic images showed that the R-(-)-form compromised the integrity of cells and disrupted the chloroplast structure. R-(-)-TRZ stimulated vast reactive oxygen species (ROS) and significantly increased superoxide dismutase (SOD) and catalase (CAT) activities, as well as malondialdehyde (MDA) content. For lipid accumulation experiments, nicotinamide adenine dinucleotide (NADH) and triacylglycerol (TAG) accumulations in algal cells treated with R-(-)-TRZ were 171.50% and 280.76%, respectively, compared with the control group. This far exceeded levels of algal cells treated with S-(+)- and rac-TRZ. Based on these data, R-(-)-TRZ was concluded to selectively affect the photosynthetic system, antioxidant system, and lipid synthesis of algal cells, thus causing enantioselective toxic effects of TRZ against C. pyrenoidosa, which indicating that the use of racemate may cause unpredictable environmental harm. Therefore, to reduce the hidden dangers of chiral pesticides for the ecological environment, the environmental risk of TRZ should be evaluated at the stereoselective level.

Synergistic effect of co-exposure to cadmium (II) and 4-n-nonylphenol on growth inhibition and oxidative stress of Chlorella sorokiniana.

Toxicological effect of freshwater algae co-exposure to Cd and 4-n-nonylphenol (4-n-NP) was seldom reported. In the present study, Chlorella sorokiniana was selected for testing the single and combined effect of Cd and 4-n-NP by detecting the growth inhibition and oxidative stress after exposure for 48 h, 72 h, and 96 h. The combined effects were evaluated by using toxic units (TU) method and concentration addition（CA）model. The synergistic effect of mixture on algal growth inhibition was both observed at 48 h and 72 h, and the additive effect was observed at 96 h. In addition, the significant alterations of superoxide, thiobarbituric acid reactive substances and antioxidant defenses (superoxide dismutase, catalase, glutathione) have been detected. It could be observed that the mixture predominantly lead to synergistic effects in superoxide induction, and the antagonistic effects in the GSH induction. A similar trend between the superoxide induction and growth inhibition were observed, which may indicate that the oxidative effects of Chlorella sorokiniana contributed to the growth inhibition after exposure to Cd and 4-n-NP. These findings may have important implications in the risk assessments of heavy metals and endocrine disruptors in the aquatic environment.