Herbicide prometryn adversely affects the development and reproduction of Tigriopus japonicus by disturbing the ecdysone signal pathway and chitin metabolic pathway

Chitin Synthase Is Required for Cuticle Formation and Molting in the Chinese Mitten Crab Eriocheir sinensis

Chitin synthase is an essential enzyme of the chitin synthesis pathway during molting. In this study, we identified and characterized a chitin synthase (EsCHS) gene in the Chinese mitten crab, Eriocheir sinensis. The spatio-temporal expression and functional role of EsCHS were investigated. The open reading frame of EsCHS was 4725 bp long and encoded 1574 amino acid residues that contained the typical domain structure of the glycosyltransferase family 2. Phylogenetic analysis revealed that EsCHS belongs to the group I chitin synthase family. The expression of EsCHS was found in regenerative limbs, the cuticle and the intestines. During the molting cycle, EsCHS began to increase in the pre-molt stage and reached a significant peak in the post-molt stage. The knockdown of EsCHS resulted in the significant downregulation of chitin biosynthesis pathway genes, including TRE, HK, G6PI, PAGM and UAP. Moreover, the long-term RNAi of EsCHS resulted in thinning procuticles, abnormal molting and high mortality, suggesting that EsCHS is indispensable for the formation of chitin in the cuticle during molting. In conclusion, EsCHS is involved in the chitin biosynthesis pathway and plays an important role in molting in E. sinensis. These findings highlight the potential of incorporating EsCHS into selective breeding programs to optimize molting regulation and improve growth performance in crustacean aquaculture.

Pollution level and ecological risk assessment of triazine herbicides in Laizhou Bay and derivation of seawater quality criteria

Triazine herbicides are widely used in agriculture and have become common pollutants in marine environments. However, the spatiotemporal distribution characteristics and water quality criteria (WQC) of triazine herbicides are still unclear. This study found that triazine herbicides had a high detection rate of 100 % in surface seawater of Laizhou Bay, China, with average concentrations of 217.61, 225.13, 21.97, and 1296.72 ng/L in March, May, August, and October, respectively. Moreover, estuaries were important sources, and especially the Yellow River estuary exhibited the highest concentrations of 16,115.86 ng/L in October. The 10 triazine herbicides were detected in the sediments of Laizhou Bay, with a concentration ranging from 0.14-1.68 μg/kg. Atrazine and prometryn accounted for 33.41 %-59.10 % and 28.93 %-50.06 % of the total triazine herbicides in the seawater, and prometryn had the highest proportion (63.50 %) in the sediments. Correlation analysis revealed that triazine herbicides led to the loss of plankton biodiversity, which further decreased the dissolved oxygen. In addition, this study collected 45 acute toxicity data and 22 chronic toxicity data of atrazine, 16 acute toxicity data of prometryn, and supplemented with toxicity experiments of prometryn on marine organisms. Based on the toxicity database, the WQCs of atrazine and prometryn were derived using species sensitivity distribution. The overall risk probability of atrazine and prometryn were both less than 1.75 % in the Laizhou Bay, indicating an acceptable risk. This study not only clarified the pollution status and ecological risk of triazine herbicides, but also provided scientific basis for their environmental management standards.

Reproductive Capacity, but not Food Consumption, is Reduced by Continuous Exposure to Typical Genotoxic Stressor γ-Rays in the sentinel species Gammarus fossarum

The long-term impacts of radiocontaminants (and the associated risks) for ecosystems are still subject to vast societal and scientific debate while wildlife is chronically exposed to various sources and levels of either environmental or anthropogenic ionizing radiation from the use of nuclear energy. The present study aimed to assess induced phenotypical responses in both male and female gammarids after short-term continuous γ-irradiation, acting as a typical well-characterized genotoxic stressor that can interact directly with living matter. In particular, we started characterizing the effects using standardized measurements for biological effects on few biological functions for this species, especially feeding inhibition tests, molting, and reproductive ability, which have already been proven for chemical substances and are likely to be disturbed by ionizing radiation. The results show no significant differences in terms of the survival of organisms (males and females), of their short-term food consumption which is linked to the general health status (males and females), and of the molting cycle (females). In contrast, exposure significantly affected fecundity (number of embryos produced) at the highest dose rates for irradiated females (51 mGy h-1) and males (5 and 51 mGy h-1). These results showed that, in gammarids, reproduction, which is a critical endpoint for population dynamics, is the most radiosensitive phenotypic endpoint, with significant effects recorded on male reproductive capacity, which is more sensitive than in females. Environ Toxicol Chem 2024;43:2071-2079. © 2024 SETAC.

Long-term exposure to prometryn damages the visual system and changes color preference of female zebrafish (Danio rerio)

Color vision, initiated from the cone photoreceptors, is essential for fish to obtain environmental information. Although the visual impairment of triazine herbicide prometryn has been reported, data on the effect of herbicide such as prometryn on natural color sensitivity of fish is scarce. Here, zebrafish were exposed to prometryn (0, 1, 10, and 100 μg/L) from 2 h post-fertilization to 160 days post-fertilization, to explore the effect and underlying mechanism of prometryn on color perception. The results indicated that 10 and 100 μg/L prometryn shortened the height of red-green cone cells, and down-regulated expression of genes involved in light transduction pathways (arr3a, pde6h) and visual cycle (lrata, rpe65a); meanwhile, 1 μg/L prometryn increased all-trans-retinoic acid levels in zebrafish eyes, and up-regulated the expression of genes involved in retinoid metabolism (rdh10b, aldh1a2, cyp26a1), finally leading to weakened red and green color perception of female zebrafish. This study first clarified how herbicide such as prometryn affected color vision of a freshwater fish after a long-term exposure from both morphological and functional disruption, and its hazard on color vision mediated-ecologically relevant tasks should not be ignored.

Multigenerational effects of glyphosate-based herbicide and emamectin benzoate insecticide on the reproduction and gene expression of the copepod Pseudodiaptomus annandalei (Sewell, 1919)

This study investigates the effects of glyphosate-based herbicide (GLY) and pure emamectin benzoate (EB) insecticide on the brackish copepod Pseudodiaptomus annandalei. The 96h median lethal concentration (96 h LC50) was higher in the GLY exposure (male: 3420.96 ± 394.67 μg/L; female: 3093.46 ± 240.67 μg/L) than in the EB (male: 79.10 ± 7.30 μg/L; female: 6.38 ± 0.72 μg/L). Based on the result of 96h LC50, we further examined the effects of GLY and EB exposures at sub-lethal concentrations on the naupliar production of P. annandalei. Subsequently, a multigenerational experiment was conducted to assess the long-term impact of GLY and EB at concentrations 375 μg/L, and 0.025 μg/L respectively determined by sub-lethal exposure testing. During four consecutive generations, population growth, clutch size, prosome length and width, and sex ratio were measured. The copepods exposed to GLY and EB showed lower population growth but higher clutch size than the control group in most generations. Gene expression analysis indicated that GLY and EB exposures resulted in the downregulation of reproduction-related (vitellogenin) and growth-related (myosin heavy chain) genes, whereas a stress-related gene (heat shock protein 70) was upregulated after multigenerational exposure. The results of the toxicity test after post-multigenerational exposure indicated that the long-term GLY-exposed P. annandalei displayed greater vulnerability towards GLY toxicity compared to newly-exposed individuals. Whereas, the tolerance of EB was significantly higher in the long-term exposed copepod than in newly-exposed individuals. This suggests that P. annandalei might have greater adaptability towards EB toxicity than towards GLY toxicity. This study reports for the first time the impacts of common pesticides on the copepod P. annandalei, which have implications for environmental risk assessment and contributes to a better understanding of copepod physiological responses towards pesticide contaminations.

Can a shift in dominant species of Microcystis alter growth and reproduction of waterfleas?

The bloom-forming species Microcystis wesenbergii and M. aeruginosa occur in many lakes globally, and may exhibit alternating blooms both spatially and temporally. As environmental changes increase, cyanobacteria bloom in more and more lakes and are often dominated by M. wesenbergii. The adverse impact of M. aeruginosa on co-existing organisms including zooplanktonic species has been well-studied, whereas studies of M. wesenbergii are limited. To compare effects of these two species on zooplankton, we explored effects of exudates from different strains of microcystin-producing M. aeruginosa (Ma905 and Ma526) and non-microcystin-producing M. wesenbergii (Mw908 and Mw929), on reproduction by the model zooplankter Daphnia magna in both chronic and acute exposure experiments. Specifically, we tested physiological, biochemical, molecular and transcriptomic characteristics of D. magna exposed to Microcystis exudates. We observed that body length and egg and offspring number of the daphnid increased in all treatments. Among the four strains tested, Ma526 enhanced the size of the first brood, as well as total egg and offspring number. Microcystis exudates stimulated expression of specific genes that induced ecdysone, juvenile hormone, triacylglycerol and vitellogenin biosynthesis, which, in turn, enhanced egg and offspring production of D. magna. Even though all strains of Microcystis affected growth and reproduction, large numbers of downregulated genes involving many essential pathways indicated that the Ma905 strain might contemporaneously induce damage in D. magna. Our study highlights the necessity of including M. wesenbergii into the ecological risk evaluation of cyanobacteria blooms, and emphasizes that consequences to zooplankton may not be clear-cut when assessments are based upon production of microcystins alone.

Multigenerational effects of elevated temperature on host-microbiota interactions in the marine water flea Diaphanosoma celebensis exposed to micro- and nanoplastics

Rising ocean temperatures are driving unprecedented changes in global marine ecosystems. Meanwhile, there is growing concern about microplastic and nanoplastic (MNP) contamination, which can endanger marine organisms. Increasing ocean warming (OW) and plastic pollution inevitably cause marine organisms to interact with MNPs, but relevant studies remain sparse. Here, we investigated the interplay between ocean warming and MNP in the marine water flea Diaphanosoma celebensis. We found that combined exposure to MNPs and OW induced reproductive failure in the F2 generation. In particular, the combined effects of OW and MNPs on the F2 generation were associated with key genes related to reproduction and stress response. Moreover, populations of predatory bacteria were significantly larger under OW and MNP conditions during F2 generations, suggesting a potential link between altered microbiota and host fitness. These results were supported by a host transcriptome and microbiota interaction analysis. This research sheds light on the complex interplay between environmental stressors, their multigenerational effects on marine organisms, and the function of the microbiome.

Prometryn exposure disrupts the intestinal health of Eriocheir sinensis: Physiological responses and underlying mechanism

Most toxicity studies of prometryn in non-target aquatic animals have focused on hepatotoxicity, cardiotoxicity, embryonic developmental and growth toxicity, while studies on the molecular mechanisms of intestinal toxicity of prometryn are still unknown. In the current study, the intestinal tissues of the Chinese mitten crab (Eriocheir sinensis) were used to uncover the underlying molecular mechanisms of stress by 96-h acute in vivo exposure to prometryn. The results showed that prometryn activated the Nrf2-Keap1 pathway and up-regulated the expression of downstream antioxidant genes. Prometryn induced the expression of genes associated with non-specific immunity and autophagy, and induced apoptosis through the MAPK pathway. Interestingly, the significant up-or down-regulation of the above genes mainly occurred at 12 h- 24 h after exposure. Intestinal flora sequencing revealed that prometryn disrupted the intestinal normal barrier function mainly by reducing beneficial bacteria abundance, which further weakened the intestinal resistance to exogenous toxicants and caused an inflammatory response. Correlation analyses found that differential flora at the genus level had potential associations with gut stress-related genes. In conclusion, our study contributes to understanding the molecular mechanisms behind the intestinal stress caused by herbicides on aquatic crustaceans.

A novel electrochemical aptasensor for ultrasensitive detection of herbicide prometryn based on its highly specific aptamer and Ag@Au nanoflowers

Herbicide prometryn has become a common pollutant in aquatic environments and caused adverse impacts on ecosystems. This study developed an ultrasensitive electrochemical aptasensor for prometryn based on its highly affinitive and specific aptamer and Ag@Au nanoflowers (Ag@AuNFs) for signal amplification. Firstly, this study improved the Capture-SELEX strategy to screen aptamers and obtained aptamer P60-1, which had a high affinity (Kd: 23 nM) and could distinguish prometryn from its structural analogues. Moreover, the typical stem-loop structure in aptamer P60-1 was found to be the binding pocket for prometryn. Subsequently, an electrochemical aptasensor for prometryn was established using multiwalled carbon nanotubes and reduced graphene oxide as electrode substrate, Ag@Au NFs as signal amplification element, and aptamer P60-1 as recognition element. The aptasensor had a detection range of 0.16-500 ng/mL and a detection limit of 60 pg/mL, which was much lower than those of existing detection methods. The aptasensor had high stability and good repeatability, and could specifically detecting prometryn. Furthermore, the utility of the aptasensor was validated by measuring prometryn in environmental and biological components. Therefore, this study provides a robust and ultrasensitive aptasensor for accurate detection for prometryn pollution.