Genome-wide identification of the entire 90 glutathione S-transferase (GST) subfamily genes in four rotifer Brachionus species and transcriptional modulation in response to endocrine disrupting chemicals

Changes in transcriptome regulations of a marine rotifer Brachionus plicatilis under methylmercury stress

Mercury (Hg), a heavy metal pollutant worldwide, can be transformed into methylmercury (MeHg) by various aquatic microorganisms in water, thus accumulating along the aquatic food chain and posing a particular challenge to human health. Zooplankton plays a crucial role in aquatic ecosystems and serves as a major component of the food chain. To evaluate the effects of MeHg on the rotifer Brachionus plicatilis and reveal the underlying mechanism of these effects, we exposed B. plicatilis to MeHg by either direct immersion or by feeding with MeHg-poisoned Chlorella pyrenoidesa, respectively, and conducted a transcriptomic analysis. The results showed that B. plicatilis directly exposed to MeHg by immersion showed significant enrichment of the glutathione metabolism pathway for detoxification of MeHg. In addition, the exposure to MeHg by feeding induced a significant enrichment of lysosome and notch signaling pathways of rotifers, supporting the hypothesis that MeHg can induce autophagy dysfunction in cells and disturb the nervous system of rotifers. In two different routes of MeHg exposure, the pathway of cytochrome P450 in rotifers showed significant enrichment for resisting MeHg toxicity. Our results suggest further studies on the potential mechanism and biological responses of MeHg toxicity in other links of the aquatic food chain.

Effect of melatonin and luzindole antagonist on fipronil toxicity, detoxification and antioxidant enzyme system in different tissues of Helicoverpa armigera (Lepidoptera: Noctuidae)

Studies have investigating the detoxification and antioxidant enzymes with melatonin under pesticide stress in many vertebrates, whereas no reports produced in invertebrates. In this study possible role of melatonin and luzindole effect on fipronil toxicity and the detoxification, antioxidant enzymes in H. armigera has been reported. Result showed high toxicity of fipronil treatment (LC50 4.24 ppm), followed by increased LC50 value with melatonin pretreatment (6.44 ppm). Whereas decreased toxicity was observed with melatonin and luzindole combination (3.72 ppm). The detoxification enzymes AChE, esterase and P450 were increased in larval head and whole body with exogenous melatonin level compared to control 1-1.5 μmol/mg of protein. The antioxidant levels of CAT, SOD and GST in whole body and head tissue had been increased by melatonin and fipronil combination 1.1-1.4 unit/mg of protein followed by GPx and GR in larval head (1-1.2 μmol/mg of protein). Mean while the luzindole antagonist inhibits CAT, SOD, GST and GR oxidative enzyme level (1-1.5 fold) in most of the tissue compared to melatonin and fipronil treatment (p < 0.01). Hence this study concludes that the melatonin pretreatment can reduce the fipronil toxicity by enhanced detoxification and antioxidant enzyme system in H. armigera.

Alleviation of Tris(2-chloroethyl) Phosphate Toxicity on the Marine Rotifer Brachionus plicatilis by Polystyrene Microplastics: Features and Molecular Evidence

As emerging pollutants, microplastics (MPs) and organophosphorus esters (OPEs) coexist in the aquatic environment, posing a potential threat to organisms. Although toxicological studies have been conducted individually, the effects of combined exposure are unknown since MPs can interact with OPEs acting as carriers. In this study, we assessed the response of marine rotifer, Brachionus plicatilis, to co-exposure to polystyrene MPs and tris(2-chloroethyl) phosphate (TCEP) at different concentrations, including population growth, oxidative status, and transcriptomics. Results indicated that 0.1 μm and 1 μm MPs were accumulated in the digestive system, and, even at up to 2000 μg/L, they did not exert obvious damage to the stomach morphology, survival, and reproduction of B. plicatilis. The presence of 1 μm MPs reversed the low population growth rate and high oxidative stress induced by TCEP to the normal level. Some genes involved in metabolic detoxification and stress response were upregulated, such as ABC and Hsp. Subsequent validation showed that P-glycoprotein efflux ability was activated by combined exposure, indicating its important role in the reversal of population growth inhibition. Such results challenge the common perception that MPs aggravate the toxicity of coexisting pollutants and elucidate the molecular mechanism of the limited toxic effects induced by MPs and TCEP.

Reproductive toxicity of environmental levels of triphenyltin to the marine rotifer, Brachionus plicatilis

Triphenyltin (TPT) is a representative organotin often used in marine antifouling coatings, herbicides, and pesticides. However, leaching of TPT into water may be toxic to aquatic life. In this study, environmental concentrations of TPT were used to explore reproductive toxicity of TPT to Brachionus plicatilis, a representative marine rotifer. Toxicity was examined at individual, biochemical, and molecular levels and via phenotypic traits. Rotifers exposed to 10 ng/L TPT group showed increased population size, improved reproductive rate, and a higher weekly growth rate. At 100 ng/L TPT group, the greatest degree of oxidative damage was seen. Exposure to 200 ng/L TPT group shorten generation time, delayed reproduction, and obscured the reproductive peak. Expression of the Vasa gene associated with reproduction was increased after exposure to 10 and 200 ng/L TPT group and decreased at 100 ng/L TPT group. High concentrations of TPT reduced rotifer body length and width and slowed swimming speed. Findings provide a better understanding of the adverse effects of changing TPT concentrations on marine rotifer, by the life cycle parameters, oxidative stress defense mechanisms, expression of a gene related to reproduction, and phenotypic traits. This paper firstly analyzed the reproductive toxicity of environmental levels of organotin compounds to zooplankton, which provided new data support for the comprehensive evaluation of its marine ecological toxicity.

Structural and Functional Characterization of Camelus dromedarius Glutathione Transferase M1-1

Glutathione transferases (GSTs; EC. 2.5.1.18) are a large family of multifunctional enzymes that play crucial roles in the metabolism and inactivation of a broad range of xenobiotic compounds. In the present work, we report the kinetic and structural characterization of the isoenzyme GSTM1-1 from Camelus dromedarius (CdGSTM1-1). The CdGSΤM1-1 was expressed in E. coli BL21 (DE3) and was purified by affinity chromatography. Kinetics analysis showed that the enzyme displays a relative narrow substrate specificity and restricted ability to bind xenobiotic compounds. The crystal structures of CdGSΤM1-1 were determined by X-ray crystallography in complex with the substrate (GSH) or the reaction product (S-p-nitrobenzyl-GSH), providing snapshots of the induced-fit catalytic mechanism. The thermodynamic stability of CdGSTM1-1 was investigated using differential scanning fluorimetry (DSF) in the absence and in presence of GSH and S-p-nitrobenzyl-GSH and revealed that the enzyme’s structure is significantly stabilized by its ligands. The results of the present study advance the understanding of camelid GST detoxification mechanisms and their contribution to abiotic stress adaptation in harsh desert conditions.

Differential gene expression profile of male and female copepods in response to cadmium exposure

In this study, the whole transcriptome and sex-specific differential gene expression of the copepod Pseudodiaptomus annandalei exposed to cadmium (Cd) were investigated. P. annandalei were exposed to 40 μg/L Cd from the naupliar stage to male and female adults. High-throughput transcriptome sequencing (RNA-seq) was performed with copepod samples using an Illumina Hiseq™ 2000 platform. TransDecoder analysis found 32,625 putative open reading frame contigs. At p-values of <0.001, a total of 4756 differentially expressed genes (DEGs) (2216 up-regulated and 2540 down-regulated genes) were found in male copepods. Whereas a total of 2879 DEGs (2007 up-regulated and 872 down-regulated genes) were found in female copepods. A few selected cellular stress response genes, involved in xenobiotic metabolism, energy metabolism, growth, and development as a result of Cd exposure in the copepods were discussed. The study showed that most of these processes were changed in a sex-specific manner, accounting for the different sensitivities of male and female copepods. Results suggest and reinforce that sex is an important factor to be considered in ecotoxicogenomics.

Two antidepressants fluoxetine and sertraline cause growth retardation and oxidative stress in the marine rotifer Brachionus koreanus

To understand effects of two widely used antidepressant on the antioxidant defense mechanism in the marine rotifer Brachionus koreanus, we assessed acute toxicity and measured population growth, reactive oxygen species (ROS) levels, glutathione (GSH) levels, and antioxidant enzymatic activities (GST, GR, and SOD) in response to fluoxetine hydrochloride (FLX) and sertraline hydrochloride (SER). The no observed effect concentration-24 h of fluoxetine and sertraline were 1000 μg/L and 450 μg/L, respectively, whereas the median lethal concentration (LC50)-24 h of fluoxetine and sertraline were 1560 μg/L and 507 μg/L, respectively. Both fluoxetine and sertraline caused significant reduction (P < 0.05) in the population growth rate indicating that both antidepressants have a potential adverse effect on life cycle parameters of B. koreanus. The intracellular ROS level and GSH level were significantly modulated (P < 0.05) in response to fluoxetine and sertraline. In addition, antioxidant enzymatic activities have shown significant modulation (P < 0.05) in response to FLX and SER in B. koreanus. Furthermore, transcriptional profiles of antioxidant genes (GSTs, SODs, and GR) have shown modulation in response to FLX compared to SER-exposed B. koreanus. Our results indicate that fluoxetine and sertraline induce oxidative stress, leading to reduction in the population density and modulation of antioxidant defense mechanism in the marine rotifer B. koreanus.

Protective Role of Freshwater and Marine Rotifer Glutathione S-Transferase Sigma and Omega Isoforms Transformed into Heavy Metal-Exposed Escherichia coli

Glutathione S-transferases (GSTs) play an important role in phase II of detoxification to protect cells in response to oxidative stress generated by exogenous toxicants. Despite their important role in defense, studies on invertebrate GSTs have mainly focused on identification and characterization. Here, we isolated omega and sigma classes of GSTs from the freshwater rotifer Brachionus calyciflorus and the marine rotifer Brachionus koreanus and explored their antioxidant function in response to metal-induced oxidative stress. The recombinant Bc- and Bk-GSTs were successfully transformed and expressed in Escherichia coli. Their antioxidant potential was characterized by measuring kinetic properties and enzymatic activity in response to pH, temperature, and chemical inhibitor. In addition, a disk diffusion assay, reactive oxygen species assay, and morphological analysis revealed that GST transformed into E. coli significantly protected cells from oxidative stress induced by H₂O₂ and metals (Hg, Cd, Cu, and Zn). Stronger antioxidant activity was exhibited by GST-S compared to GST-O in both rotifers, suggesting that GST-S plays a prominent function as an antioxidant defense mechanism in Brachionus spp. Overall, our study clearly shows the antioxidant role of Bk- and Bc-GSTs in E. coli and provides a greater understanding of GST class-specific and interspecific detoxification in rotifer Brachionus spp.

Genome-wide analysis of the Tetrahymena thermophila glutathione S-transferase gene superfamily

The ciliate Tetrahymena thermophila has a rapid response to detoxify xenobiotics, which presents opportunity to study the diversification of Glutathione S-Transferase superfamily. In-silico identification of putative GST genes were resulted with 70 GST genes; 49 TtGSTmu, 7 TtGSTomega, 5 TtGSTtheta, 2 TtGSTzeta, 4 TtMAPEG and 3 TtEF1G. TtGST superfamily has short intron carrying or intronless genes. The most expressed mRNAs of TtGST are limited to 4 members at all life stages. TtGST genes are widely distributed to all five micronuclear chromosomes with the highest diversified members from different classes in chromosome 4. The clustering and the orientation of some TtGSTs in the T. thermophila genome give clues about the recent gene duplication. Analysis of GSH affinity-purified GST proteins with Western blot and activity assay showed GST activity carrying purified TtGST populations. In conclusion, the enhanced genome capacity of TtGST superfamily may have evolved through improved GST enzymatic activity.