Growth and stress responses of the earthworm Eisenia fetida to Escherichia coli O157:H7 in an artificial soil

Detecting microplastics in organic-rich materials and their potential risks to earthworms in agroecosystems

Microplastics (MPs) are a major emerging contaminant in agroecosystems, due to their significant resistance to degradation in terrestrial environments. Although previous investigations have reported the harmful effects of MPs contamination on soil biological properties, still little is known about the characteristics and fate of MPs in biosolid-amended soils and their risks to soil biota, particularly earthworms. We determined microplastics' concentration, size distribution, and chemical composition in 3 sewage sludge biosolids and 6 biosolid-amended agricultural soils. In addition, we assessed the potential short-term risks of MPs to earthworms' (Amynthas Gracilis and Eisenia Fetida) survival rate and fitness in an environmentally relevant exposure study (28 days). Biosolid-amended soils (1000-3100 MPs kg^-1 dry mass) showed ≈30 times lower MPs content than investigated biosolids (55400-73800 MPs kg^-1 dry mass), with microplastic fragment to fibre ratios between 0.2 and 0.6 and 0.3-0.4 in soils and biosolids, respectively. Total MPs dry mass was also ≈19 times lower in assessed soils (12-26 mg kg^-1) than biosolids (328-440 mg kg^-1). On average 77% and 80% of plastic fragments had a lower dimension than 500 µm, while 50% and 67% of plastic fibres had a length of less than 1000 µm in soil and biosolid samples, respectively. Polyethylene (23.6%) was the major source of microplastic contamination in biosolid-amended soils, while polyethylene terephthalate (41.6%) showed the highest concentration in biosolid samples. Spiked polyethylene MPs did not show any significant effect on earthworms' survival rate (93-99%). However, biosolid application significantly (P < 0.05) decreased survival rate of Eisenia Fetida (81%) but showed no significant effect on Amynthas Gracilis (93%). Biosolid amendment significantly (P < 0.05) decreased earthworms' growth rate, with higher impact on Eisenia Fetida than Amynthas Gracilis, while there were no significant differences between control and microplastic spiked treatments. The overall decrease in MPs concentration of earthworm casts, compared with initial MPs concentrations in soil, indicated that the investigated species did not bioaccumulate MPs during the exposure experiment.

Exposure to cypermethrin pesticide disturbs the microbiome and disseminates antibiotic resistance genes in soil and the gut of Enchytraeus crypticus

Worldwide, pyrethroids, such as cypermethrin, are the second most applied group of insecticides, however, their effects on the soil microbiome and non-target soil fauna remain largely unknown. Herein, we assessed the change of bacterial communities and antibiotic resistance genes (ARGs) of soil and in the gut of the model soil species Enchytraeus crypticus using a combination of 16S rRNA gene amplicon sequencing, and high-throughput qPCR of ARGs. Results indicate that cypermethrin exposure enriches potential pathogens (e.g. Bacillus anthracis) in the soil and gut microbiome of E. crypticus, heavily disrupting the latter's microbiome structure, and even disrupts activities of the E. crypticus immune system. The co-occurrence of potential pathogens (e.g. Acinetobacter baumannii), ARGs, and mobile genetic elements (MGEs) revealed the increased risk of pathogenicity as well as antibiotic resistance in potential pathogens. Moreover, structural equation modeling demonstrated that the dissemination of ARGs was not only promoted by MGEs, but also by the ratio of the core to non-core bacterial abundance. Collectively, these results provide an in-depth view of the previously unappreciated environmental risk of cypermethrin on the dissemination of ARGs in the soil and non-target soil fauna.

Toxic effects of benzovindiflupyr, a new SDHI-type fungicide on earthworms (Eisenia fetida)

Benzovindiflupyr has received increasing attention as a new novel succinate dehydrogenase inhibitor (SDHI)-type fungicide. Nonetheless, its traces remaining in soil potentially trigger an ecotoxicological threat to soil organisms including earthworms. This paper evaluates the eco-toxicity of different benzovindiflupyr doses (0.1, 1, 5, and 10 mg kg-1) on earthworms (Eisenia fetida) after long-term exposure. Consequently, benzovindiflupyr at higher doses significantly inhibited the activities of respiratory chain complex II and succinate dehydrogenase (SDH) in E. fetida. Besides, the reactive oxygen species (ROS) and lipid peroxidation (LPO) were significantly induced in earthworms when treated with this fungicide. After benzovindiflupyr exposure, activities of antioxidant enzymes including catalase, peroxidase, and superoxide dismutase were activated. However, glutathione S-transferase activity in E. fetida was initially induced then inhibited in earthworms after treatment. Furthermore, benzovindiflupyr exposure induced the protein carbonylation (PCO) level in cells indicating oxidative damage to the cellular protein. Due to the destruction of the normal function in the coelomocytes, the phagocytic activity was initially activated, then inhibited when earthworms were treated at 5 and 10 mg kg-1 concentrations. Additionally, DNA damage was induced (larger olive tail moment (OTM) values) with the increase of benzovindiflupyr doses and exposure time. The weight was significantly decreased after benzovindiflupyr exposure on days 21 and 28. Benzovindiflupyr at higher doses significantly decreased the reproduction (number of cocoons and juveniles) of E. fetida. These findings reveal that benzovindiflupyr potentially induces a potential toxicological risk to earthworms when applied in the mentioned above dosages.

Effects of a novel fungicide benzovindiflupyr in Eisenia fetida: Evaluation through different levels of biological organization

Although benzovindiflupyr (BZF), which is a novel succinate dehydrogenase inhibitor fungicide, has considerable application potential worldwide, its extensive use is toxic to non-targeted soil organisms. Therefore, this study aimed to evaluate the acute and subchronic toxicity of BZF to earthworms (Eisenia fetida). The acute toxicity of BZF to adult and larval earthworms was measured, as indicated by the following LC₅₀ values obtained after 14 days of exposure: 416 mg/kg for adult earthworms and 341 mg/kg for juveniles. Subchronic toxicity tests were conducted using only adult earthworms. The earthworms' weight gain was slower on days 14 and 28 after commencing the BZF T100 treatment (50 mg/kg of soil). Following 14 days of BZF exposure, enzymes and gene expressions associated with the mitochondrial respiratory chain and energy metabolism were activated to some extent, and the reactive oxygen species level and malondialdehyde content also increased. Antioxidant and detoxifying enzymes and metallothionein gene, Heat shock protein 70 gene associated with resistance to oxidative damage were also activated to varying degrees. Increased BZF concentrations corresponded to increased genotoxicity. Integrated biological response (IBR) values were calculated at the biochemical and molecular levels to show increased toxicity with increased BZF concentration. Although a series of biomarkers changes occurred after initiating BZF treatment, these changes were all likely to have been resisted by the earthworms' own antioxidant defense system and only showed phenotypic (weight-related) changes with treatments of 50 mg/kg. In conclusion, reasonable levels of BZF application may have little impact on earthworms. Our findings provide insights on the toxic effects of BZF on earthworms and may prove useful for risk assessments relating to BZF's impacts on soil ecosystems.

Amynthas corticis genome reveals molecular mechanisms behind global distribution

Earthworms (Annelida: Crassiclitellata) are widely distributed around the world due to their ancient origination as well as adaptation and invasion after introduction into new habitats over the past few centuries. Herein, we report a 1.2 Gb complete genome assembly of the earthworm Amynthas corticis based on a strategy combining third-generation long-read sequencing and Hi-C mapping. A total of 29,256 protein-coding genes are annotated in this genome. Analysis of resequencing data indicates that this earthworm is a triploid species. Furthermore, gene family evolution analysis shows that comprehensive expansion of gene families in the Amynthas corticis genome has produced more defensive functions compared with other species in Annelida. Quantitative proteomic iTRAQ analysis shows that expression of 147 proteins changed in the body of Amynthas corticis and 16 S rDNA sequencing shows that abundance of 28 microorganisms changed in the gut of Amynthas corticis when the earthworm was incubated with pathogenic Escherichia coli O157:H7. Our genome assembly provides abundant and valuable resources for the earthworm research community, serving as a first step toward uncovering the mysteries of this species, and may provide molecular level indicators of its powerful defensive functions, adaptation to complex environments and invasion ability.

Ecotoxicological effects of microplastics and cadmium on the earthworm Eisenia foetida

As microplastics (MPs) have become ubiquitous in both aquatic and terrestrial environments, there has been a growing concern about these new anthropogenic stressors. However, comparatively little is known about the negative effects of MPs, co-contamination of MPs and heavy metals on terrestrial organisms. The objective of this study was performed to understand the adverse effects of exposure to MPs and co-exposure to MPs and cadmium (Cd) on the earthworm Eisenia foetida (E. foetida). Results showed that exposure to MPs only or to a combination of MPs + Cd decreased growth rate and increased the mortality (>300 mg kg^-1) after exposure for 42 d, with MPs + Cd (>3000 mg kg^-1) posing higher negative influence on the growth of E. foetida. Exposure to MPs might induce oxidative damage in E. foetida, and the presence of Cd accelerates the adverse effects of MPs. Furthermore, the MPs particles can be retained within E. foetida, with values of 4.3-67.2 particles·g^-1 earthworm, and can increase the accumulation of Cd in earthworm from 9.7%-161.3%. Collectively, the results of this study demonstrate that combined exposure to MPs and Cd poses higher negative effects on E. foetida, and that MPs have the potential to increase the bioaccessibility of heavy metal ions in the soil environment.

The response of nitrogen cycling and bacterial communities to E. coli invasion in aquatic environments with submerged vegetation

The effects of exogenous Escherichia coli on nitrogen cycling (N-cycling) in freshwater remains unclear. Thus, seven ecosystems, six with submerged plants-Potamogeton crispus (PC) and Myriophyllum aquaticum (MA)-and one with no plants were set up. Habitats were assessed before and after E. coli addition (10⁷ colony-forming units/mL). E. coli colonization of freshwater ecosystems had significant effects on bacterial community structure in plant surface biofilms and surface sediments (ANOVA, P < 0.05). It reduced the relative abundance of nitrosification bacteria (-70.94 ± 26.17%) and nitrifiers (-47.86 ± 23.68%) in biofilms which lead to significant reduction of ammoxidation in water (P < 0.05). The N-cycling intensity from PC systems was affected more strongly by E. coli than were MA systems. Furthermore, the coupling coefficient of exogenous E. coli to indigenous N-cycling bacteria in sediments (6.061, average connectivity degree) was significantly weaker than that in biofilms (9.852). Additionally, at the genus level, E. coli were most-closely associated with N-cycling bacteria such as Prosthecobacter, Hydrogenophaga, and Bacillus in sediments and biofilms according to co-occurrence bacterial network (Spearman). E. coli directly changed their abundance, so that the variability of species composition of N-cycling bacterial taxa was triggered, as well. Overall, exogenous E. coli repressed ammoxidation, but promoted ammonification and denitrification. Our results provided new insights into how pathogens influence the nitrogen cycle in freshwater ecosystems.

Biochemical responses and DNA damage induced by herbicide QYR301 in earthworm (Eisenia fetida)

QYR301, a novel herbicidal inhibitor of 4-hydroxyphenylpyruvate dioxygenase (HPPD), has great potential for resistant weed control in paddy fields, but massive use of pesticides may result in toxicity to soil non-target organisms. Thus, this study was designed to assess subchronic toxicity of different doses of QYR301 in artificial soil (0, 0.1, 1.0, 2.5, and 5.0 mg kg^-1) to earthworms (Eisenia fetida) on days 7, 14, 21, and 28 after exposure, using biomarkers of reactive oxygen species (ROS) and malondialdehyde (MDA) contents, activities of catalase (CAT), superoxide dismutase (SOD), peroxidase (POD) and glutathione-S-transferase (GST), and DNA damage. The ROS content significantly increased for all treatments on 7 and 14 days then decreased, and recovered to control level for 0.1 and 1.0 mg kg^-1 treatment on day 28. Concerning enzymes activities, QYR301 increased POD, SOD, and GST activities, but inhibited CAT activity. Except for POD activity, SOD, CAT, and GST activities of 0.1 mg kg^-1 group recovered to control level on day 28. Also, the MDA content of 0.1 mg kg^-1 group reached control level on day 28. However, DNA damage was observed for all treatments throughout the experiment and it increased with increasing doses and time except for 5.0 mg kg^-1 treatment on day 28. These results suggested that QYR301 induced excessive ROS production leading to oxidative stress in earthworms, which caused lipid membrane peroxidation and DNA damage ultimately. The findings could provide a theoretical foundation for assessing ecological damage of QYR301 to soils and a guide for future QYR301 applications.

Toxicity of thifluzamide in earthworm (Eisenia fetida)

An increase in the area treated with the fungicide thifluzamide has triggered concerns for soil ecosystem service providers such as earthworms. Here, we assessed effects of thifluzamide on earthworm (Eisenia fetida) biomarker indicators of stress responses and reproduction following exposure to 0, 0.1, 1.0, and 10.0 mg of thifluzamide kg^-1 soil for 7, 14, 21, and 28 d (biomarker indicators) and 30 d (reproduction). Growth and reproduction were inhibited by exposure to thifluzamide at 10.0 mg/kg, and the activities of succinate dehydrogenase (SDH) and respiratory chain complex II were inhibited by exposure to 1.0 and 10.0 mg/kg thifluzamide for the majority of the 28-d experiment. Reactive oxygen species (ROS) increased across all thifluzamide treatments, and the activities of superoxide dismutase (SOD) and glutathione-S-transferase (GST) tended to be inhibited by thifluzamide. Upon exposure to thifluzamide, the activities of catalase (CAT) and guaiacol peroxidase (POD) initially increased and then decreased. Increased levels of malondialdehyde (MDA) were detected only at seven days after exposure, and genotoxicity increased as the thifluzamide concentration increased. The results suggest that thifluzamide presents a potential risk to earthworms at the concentration of 10.0 mg/kg, and its use should be moderated to reduce damage to soil ecosystem function.

Growth, DNA damage and biochemical toxicity of cyantraniliprole in earthworms (Eisenia fetida)

Cyantraniliprole is a second-generation diamide insecticide that exhibited excellent biological efficacy against a variety of pests. To assess the toxic impact of cyantraniliprole on earthworms, the levels of reactive oxygen species (ROS) and malondialdehyde (MDA), activities of superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST), as well as DNA damage were measured after exposed to five cyantraniliprole concentrations ranging from 0 to 10.00 mg/kg for 7, 14, 21 and 28 days. In most treatment groups, the ROS levels increased significantly before exposure time of 14 days and then returned to normal levels. However, the SOD and CAT activities showed different response with activities were first significantly decreased and subsequently increased. The peroxidase (POD) activity showed no significant differences between treatment and control groups at first and then significantly increased. However, the opposite pattern characterized the GST activity. Also, maybe being dose-dependent before 14 days. The MDA concentration was used as a measure of lipid peroxidation (LPO). During experiment period, the MDA concentrations significantly increased when treated by this pesticide. The olive tail moment (OTM) was used as a measure of DNA damage. At higher concentrations of cyantraniliprole and longer exposure times, the OTM gradually increased, and DNA damage in the earthworms gradually increased. The weight of the high-dose (i.e., 5 mg/kg, 10 mg/kg) earthworms showed a significant trend of decrease phenomenon. Overall, the results suggest that sub-chronic exposure to cyantraniliprole causes DNA damage and LPO, weight loss and growth inhibition, leading to antioxidant defence responses in earthworms.

Transcriptomic analysis of oligochaete immune responses to myxosporeans infection: Branchiura sowerbyi infected with Myxobolus cultus

The Myxozoa are endoparasites characterized by a two-host life cycle that typically involves invertebrates and vertebrates as definitive and intermediate hosts, respectively. However, little is known about invertebrate-myxosporean interactions, particularly about patterns of host immune defense. We used RNA-sequencing to identify genes that are possibly involved in the immune responses of the oligochaete Branchiura sowerbyi naturally infected with Myxobolus cultus. De novo assembly of the B. sowerbyi transcriptome yielded 119,031 unigenes, with an average length of 896 bp and an N50 length of 1754 bp. Comparative transcriptome analysis revealed 4059 differentially expressed genes (DEGs) between M. cultus-infected and uninfected B. sowerbyi groups, including 3802 upregulated genes and 257 downregulated genes. Among the B. sowerbyi immune factors implicated in the responses to M. cultus infection, DEGs related to lectins, ubiquitin-mediated proteolysis, phagocytosis, oxidative-antioxidative responses, proteases, and protease inhibitors were upregulated. The expression of some immune-related molecules such as calmodulin, heat shock proteins, antimicrobial peptides, lysenin, and serum amyoid A protein were also significantly upregulated. The expression patterns of 14 immune-related DEGs identified by RNA-seq were validated by quantitative real-time polymerase chain reaction. This study is the first attempt to characterize the B. sowerbyi transcriptome and identify immune-related molecules possibly associated with M. cultus infection. It is also the first report of invertebrate host-myxosporean interactions at the transcriptomic level. Our results will facilitate the elucidation of adaptive evolution mechanisms of myxosporean parasites in the definitive host and the genetic basis for differences in resistance of invertebrate hosts of different genotypes to a myxosporean species.

The involvement of McpB chemoreceptor from Pseudomonas aeruginosa PAO1 in virulence

Pseudomonas aeruginosa is an opportunistic human pathogen causing infections in a variety of plant and animal hosts. The gene mcpB, part of the chemosensory gene cluster II, encodes a soluble chemoreceptor whose function remains unknown. Previous studies show that the cheB2 gene, also located in the chemosensory cluster II, is involved in a specific response during infection and it is required for full pathogenicity of P. aeruginosa. To determine whether the McpB (or Aer2) chemoreceptor is involved in virulence processes, we generated a mcpB mutant and tested its phenotype using a virulence-measuring system. This system was developed by our group and is based on different bioassays using organisms living at different soil trophic levels, including microbial, nematode, arthropod, annelid, and plant model systems. The deletion of mcpB resulted in an attenuation of bacterial virulence in different infection models, and wild-type virulence was restored following genetic complementation of the mutant strain. Our study indicates that the McpB chemoreceptor is linked to virulence processes and may constitute the basis for the development of alternative strategies against this pathogen.

Assessment of acute toxicity and biochemical responses to chlorpyrifos, cypermethrin and their combination exposed earthworm, Eudrilus eugeniae

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In the present study, co-exposed administered pesticides induced a higher level of toxicity to Eudrilus eugeniae.

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Statistically significant changes were observed after 48 h exposure of CPF, cypermethrin and combination of the two, reflects the synergistic cumulative impact on the AChE and oxidative stress parameters in dose- dependent manner.

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Significant changes were observed in different body segments (Pre-Clitellar, Clitellar and Post-Clitellar) of earthworm in tissue specific pattern.

Recurrent application of chemical pesticides in the agricultural fields have adverse impact on flora and fauna of soil ecosystem. Earthworms immensely contribute in increasing the fertility of soil. They may act as a bioindicator for the ecotoxicological analysis of pesticide induced soil pollution. Earthworms, Eudrilus eugeniae were exposed to different concentrations of pesticides chlorpyrifos (OP), cypermethrin (a pyrethroid) and their combination for 48 h by paper contact toxicity method. The LC₅₀ for commercial grade of chlorpyrifos, cypermethrin and combined pesticides were determined as 0.165, 0.066 and 0.020 μg/cm², respectively. To assess the sub-lethal effect of these pesticides, E. eugeniae were exposed to 5% and 10% of LC₅₀ of the pesticides for 48 h. Variation in morpho-behavioural changes such as coiling, clitellar swelling, mucus release, bleeding and body fragmentation in earthworms were observed after exposure of both pesticides and their combination. Various biochemical estimations such as specific activity of acetylcholinesterase (AChE), superoxide dismutase (SOD), catalase (CAT), glutathione -S-transferase (GST); levels of lipid peroxidation (LPO) and reduced glutathione (GSH) were carried out in different body segments. Significant changes in these stress markers were observed at low and high sub-acute concentration of pesticides exposed earthworm, Eudrilus eugeniae. Such changes indicate potential health risk to E. eugeniae if exposed to the high concentrations of these pesticides accumulated in soil.

Effects of cucumber mosaic virus-infected chilli plants on non-vector Bemisia tabaci (Hemiptera: Aleyrodidae)

Plant virus infections are known to alter host plant attractiveness and suitability for insect herbivores. This study was conducted to determine how cucumber mosaic virus (CMV)-infected chilli plants affect the fitness and settling preferences of nonvector whitefly, Bemisia tabaci adults under dual-choice conditions with volatile organic compounds analyzed using solid phase microextraction coupled with gas chromatography-mass spectrometry (GC-MS). Results showed that the presence of CMV in chilli plants substantially affects the settling preferences of the B. tabaci, which preferred to settle on noninfected plants. Duration of the egg stage and the longevity and fecundity of adult B. tabaci on CMV-infected chilli plants were not markedly different from those on noninfected chilli plants. In contrast, the developmental time from egg to adult was significantly reduced in CMV-infected chilli plants compared to the noninfected plants. The results also showed that CMV-infected chilli plants released significantly more linalool and phenylacetaldehyde than noninfected plants. Overall, it was suggested that the behavioral response of B. tabaci might be modified by CMV-infected plants, which alter the release of specific headspace volatiles. Based on these results, the modification of plant volatile profiles may help in enhancing the effectiveness of biological control and the protection of crop plants against B. tabaci.

iTRAQ-based quantitative proteomic analysis of the earthworm Eisenia fetida response to Escherichia coli O157:H7

Soil environment contaminated by Escherichia coli O157:H7 which come from the waste of infected animals. Earthworms can live in the pathogens-polluted soil by their innate immunity. How the proteins of earthworms E. fetida will response to E. coli O157:H7-contaminated-soil still unclear? To identify the defense proteins under E. coli O157:H7 stress, we performed a proteomic analysis of earthworm under E. coli O157:H7 exposure through an iTRAQ technology. In total, we found 283 non-redundant proteins, including fibrinolytic protease 1, lombricine kinase, lysozyme, gelsolin, coelomic cytolytic factor-1, antimicrobial peptide lumbricin-l, lysenin, and et al. The proteins participate in metabolic processes, transcription, defense response to bacterium, translation, response to stress, and transport. The study will contribute to understand why earthworm can live in the pathogens-polluted environment.

Bioaccumulation of CeO2 Nanoparticles by Earthworms in Biochar-Amended Soil: A Synchrotron Microspectroscopy Study

The interactions of nanoparticles (NPs) with biochar and soil components may substantially influence NP availability and toxicity to biota. In the present study, earthworms ( Eisenia fetida) were exposed for 28 days to a residential or agricultural soil amended with 0-2000 mg of CeO₂ NP/kg and with biochar (produced by the pyrolysis of pecan shells at 350 and 600 °C) at various application rates [0-5% (w/w)]. After 28 days, earthworms were depurated and analyzed for Ce content, moisture content, and lipid peroxidation. The results showed minimal toxicity to the worms; however, biochar (350 or 600 °C) was the dominant factor, accounting for 94 and 84% of the variance for the moisture content and lipid peroxidation, respectively, in the exposed earthworms. For both soils with 1000 mg of CeO₂/kg at 600 °C, biochar significantly decreased the accumulation of Ce in the worm tissues. Amendment with 350 °C biochar had mixed responses on Ce uptake. Analysis by micro X-ray fluorescence (μ-XRF) and micro X-ray absorption near edge structure (μ-XANES) was used to evaluate Ce localization, speciation, and persistence in CeO₂- and biochar-exposed earthworms after depuration for 12, 48, and 72 h. Earthworms from the 500 mg of CeO₂/kg and 0% biochar treatments eliminated most Ce after a 48 h depuration period. However, in the same treatment and with 5% BC-600 (biochar pyrolysis temperature of 600 °C), ingested biochar fragments (∼50 μm) with Ce adsorbed to the surfaces were retained in the gut after 72 h. Additionally, Ce remained in earthworms from the 2000 mg of CeO₂/kg and 5% biochar treatments after depuration for 48 h. Analysis by μ-XANES showed that, within the earthworm tissues, Ce remained predominantly as Ce⁴⁺O₂, with only few regions (2-3 μm²) where it was found in the reduced form (Ce³⁺). The present findings highlight that soil and biochar properties have a significant influence in the internalization of CeO₂ NPs in earthworms; such interactions need to be considered when estimating NP fate and effects in the environment.

Accumulation and sublethal effects of triclosan and its transformation product methyl-triclosan in the earthworm Eisenia andrei exposed to environmental concentrations in an artificial soil

Municipal biosolids are increasingly used as a low-cost fertilizer in agricultural soil. Biosolids are contaminated by low concentrations (nanograms per gram dry wt range) of a large variety of organic contaminants, such as triclosan. The effect of exposure to low concentrations of organic contaminants on soil biota remains largely undocumented. We evaluated the sublethal effects of triclosan on the earthworm Eisenia andrei using an artificial soil amended with a nominal concentration of triclosan of 50 ng g^-1 dry weight soil. Using a 56-d reproduction test, we monitored the effect of triclosan exposure on adult earthworm survival, growth, and reproduction. The bioaccumulation of triclosan in earthworm tissue (adults and juveniles) and degradation of triclosan were monitored. The genotoxicity of triclosan was evaluated using a comet assay (DNA damage) on adult earthworm coelomocytes. Exposure to a low concentration of triclosan had no significant effects on adult earthworm survival and DNA damage but significantly stimulated growth (p < 0.05) by 2-fold compared with controls. It also significantly affected E. andrei reproduction parameters (p < 0.05), as evidenced by an increase in the number of cocoons and juveniles and a decrease in the mean dry weight of juveniles. The bioaccumulation of triclosan in earthworms was moderate (bioaccumulation factor ∼2). In biosolid-borne trials, the bioaccumulation of methyl-triclosan in earthworm tissues was higher than that of the parent compound triclosan. We conclude that exposure to low concentrations of triclosan in artificial soil can significantly affect the growth and reproductive performance of earthworms (i.e., E. andrei). More research is required with natural soils to assess triclosan bioavailability for earthworms. Environ Toxicol Chem 2018;37:1940-1948. © 2018 SETAC.

Environmental pollutants, pathogens and immune system in earthworms

Earthworms also known as farmer's friends are natural tillers of soil. They belong to Phylum Annelida and class Oligochaeta. Acid soils with organic matter and surface humus maintain the largest fauna of worms and earthworms. Due to their habitat in soil, they are constantly exposed to microbes and pollution generated by anthropogenic sources. Studies have revealed that damage of the immune system of earthworms can lead to alterations of both morphological and cellular characteristics of worms, activation of signalling pathways and can strongly influence their survival. Therefore, the understanding of the robust immune system in earthworms has become very important from the point of view of understanding its role in combating pathogens and pollutants and its role in indicating the soil pollution. In this article, we have outlined the (i) components of the immune system and (ii) their function of immunological responses on exposure to pollutants and pathogens. This study finds importance from the point of view of ecotoxicology and monitoring of earthworm health and exploring the scope of earthworm immune system components as biomarkers of pollutants and environmental toxicity. The future scope of this review remains in understanding the earthworm immunobiology and indicating strong biomarkers for pollution.

Nematodes, exotic earthworms and nitrogen addition: interactions between global change factors lead to cancellation effects

Photos from the experiment described in Shao et al. (): (a) the endogeic (i.e. earthworms that typically live in the soil, burrowing horizontally to acquire nutrients) earthworm Pontoscolex corethrurus that was added to the plots; (b) P. corethrurus in a quiescence state in response to drought; (c) set-up of the control plots (i.e. no earthworms, ambient nitrogen) used in this experiment. [Colour figure can be viewed at wileyonlinelibrary.com] In Focus: Shao, Y., Zhang, W., Eisenhauer, N., Liu, T., Xiong, Y., Liang, C. & Fu, S. (2017) Nitrogen deposition cancels out exotic earthworm effects on plant-feeding nematode communities. Journal of Animal Ecology, 86, 708-717. In this issue of Journal of Animal Ecology, Shao et al. () explored how N addition and exotic earthworms interacted to impact on the plant-feeding nematode community. They demonstrate that exotic earthworm presence alone increased the abundance of less harmful plant-feeding nematodes and decreased the abundance of the more harmful plant-feeding nematodes. However, in plots receiving both exotic earthworms and N addition, such earthworm effects on the nematode community were negated. These findings pull focus on the need to simultaneously consider multiple global change factors (e.g. exotic species invasions and N deposition) when making predictions about how such factors might affect above- and below-ground interactions and thereby alter ecosystem function.

Oxidative stress of imidaclothiz on earthworm Eisenia fetida

Imidaclothiz, a kind of neonicotinoid insecticides, is developed as a commercial pesticide in China and used for the control of sucking and biting insects, including aphids, whiteflies, beetles and some Lepidoptera species as well. In recent years, more and more attention has been focused on the adverse effects of neonicotinoid insecticides on non-target organisms. In this study, inhibition effects of imidaclothiz and recovery capacity of molecular biomarkers (GST, CE, CAT, SOD and POD activity, and DNA damage) in earthworms were detected for the first time. Earthworms were exposed to imidaclothiz (0.3 and 1.0mgkg^-1) for 28days, and then transferred to the clean artificial soil for 28days. Regarding enzyme activities, GST, CE, CAT and POD were inhibited following exposure to imidaclothiz at one or more sample times, while SOD was not affected. After transferring to the clean artificial soil, POD continued to be significantly inhibited till sample time 35days at 0.3mg/kg^-1. For GST, CE, CAT and SOD, activities of them were significantly increased compared to those of the control during the recovery period. The olive tail moments (OTM) in comet assay, as an indication of DNA damage, were significantly increased compared to the control after treatment and then decreased during the recovery period. These results suggested that imidaclothiz induced oxidative damage on earthworms which caused damage to vital macromolecules including DNA. However, the recovery changes of all tested biomarkers following the transfer to clean soil suggested the tested earthworm recovery from imidaclothiz exposure.

Biochemical responses and DNA damage in earthworms (Eisenia fetida) induced by ionic liquid [omim]PF6

Ionic liquids that are not that "green" to many organisms have recently been identified. This study examined the subchronic toxicity of the ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate ([omim]PF6) to earthworms (Eisenia fetida). Earthworms were exposed for a 28-day period (sampled on days 7, 14, 21, and 28) at concentrations of 0, 5, 10, 20, and 40 mg/kg. The levels of reactive oxygen species (ROS), antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (POD)), detoxifying enzyme (glutathione S-transferase (GST)), lipid peroxidation, and DNA damage were measured. ROS significantly accumulated in all the treatment groups; the maximum ROS content was 51.9% higher than the control at 40 mg/kg [omim]PF6 on day 28. Increased SOD activities attenuated over the time of exposure, while the CAT activities of the treatment groups were similar to the controls, except on day 14. Furthermore, the activities of POD and GST were stimulated. Lipid peroxidation in earthworms was not apparent at 5 and 10 mg/kg [omim]PF6 but was quite obvious at 40 mg/kg [omim]PF6. In addition, DNA damage was dose- and time-dependent. In conclusion, [omim]PF6 caused oxidative stress and genotoxicity in earthworms.

Inhibition and recovery of biomarkers of earthworm Eisenia fetida after exposure to thiacloprid

Thiacloprid, a neonicotinoid insecticide, has been used widely in agriculture worldwide. In recent years, the adverse effects of neonicotinoid insecticides on non-target organisms have attracted more and more attention. In the present study, effects of thiacloprid on molecular biomarkers (GST, CarE, CAT, SOD, POD, and DNA damage) of earthworm Eisenia fetida were investigated using the artificial OECD soil for the first time. Earthworms were exposed to thiacloprid (1 and 3 mg/kg) for 7, 14, and 28 days and then transferred to the clean OECD soil for 35, 42, and 56 days. Results showed that activities of GST, CarE, CAT, SOD, and POD are inhibited following the exposure to thiacloprid at one or more sample times and then increased during the recovery course compared with the control. Significant DNA damage to E. fetida was also observed by olive tail moments in comet assay. These results suggested that thiacloprid could have harmful effect on earthworms, and these studied biomarkers might be used in the assessment of the risk of thiacloprid to the soil ecosystem environment.

Integrated assessment of oxidative stress and DNA damage in earthworms (Eisenia fetida) exposed to azoxystrobin

Azoxystrobin has been widely used in recent years. The present study investigated the oxidative stress and DNA damage effects of azoxystrobin on earthworms (Eisenia fetida). Earthworms were exposed to different azoxystrobin concentrations in an artificial soil (0, 0.1, 1, and 10mg/kg) and sampled on days 7, 14, 21, and 28. Superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (POD), glutathione-S-transferase (GST), reactive oxygen species (ROS), and malondialdehyde (MDA) content were measured by an ultraviolet spectrophotometer to determine the antioxidant responses and lipid peroxidation. Single cell gel electrophoresis (SCGE) was used to detect DNA damage in the coelomocytes. Compared with these in the controls, earthworms exposed to azoxystrobin had excess ROS accumulation and greater SOD, POD, and GST activity while the opposite trend occurred for CAT activity. MDA content increased after 14-day exposure, and DNA damage was enhanced with an increase in the concentration of azoxystrobin. In conclusion, azoxystrobin caused oxidative stress leading to lipid peroxidation and DNA damage in earthworms.

Reinforcing effects of non-pathogenic bacteria and predation risk: from physiology to life history

The important ecological role of predation risk in shaping populations, communities and ecosystems is becoming increasingly clear. In this context, synergistic effects between predation risk and other natural stressors on prey organisms are gaining attention. Although non-pathogenic bacteria can be widespread in aquatic ecosystems, their role in mediating effects of predation risk has been ignored. We here address the hypothesis that non-pathogenic bacteria may reinforce the negative effects of predation risk in larvae of the damselfly Coenagrion puella. We found synergistic effects for all three life history variables studied: mortality increased, growth reductions were magnified and bacterial load was higher when both non-lethal stressors were combined. The combined exposure to the bacterium and predation risk considerably impaired the two key antipredator mechanisms of the damselfly larvae: they no longer reduced their food intake under predation risk and showed a synergistic reduction in escape swimming speed. The reinforcing negative effects on the fitness-related traits could be explained by the observed synergistic effects on food intake, swimming muscle mass, immune function and oxidative damage. These are likely widespread consequences of energetic constraints and increased metabolic rates associated with the fight-or-flight response. We therefore hypothesize that the here documented synergistic interactions with non-pathogenic bacteria may be widespread. Our results highlight the ignored ecological role of non-pathogenic bacteria in reinforcing the negative effects of predation risk on prey organisms.

Gene expression of TLR homologues identified by genome-wide screening of the earthworm Dendrobaena veneta

TLRs represent one of the most important components of innate immunity. Currently, these receptors have been extensively studied in vertebrates and insects, but our knowledge for annelids is very limited. Therefore, the aim of our study was to identify earthworm TLR homologs by genome-wide screening, and to determine the expression of candidate genes as a response to Gram-positive and Gram-negative bacteria. Using a combination of deep pyrosequencing and quantitative PCR we found six candidate genes, for which all were expressed in Dentrobaena veneta. Two of the candidates showed significant response to bacterial exposure. In conclusion, TLRs seem to have a role in earthworm immunology.

Oxidative stress and lipid peroxidation in the earthworm Eisenia fetida induced by low doses of fomesafen

Formesafen is a diphenyl ether herbicide that has adverse effects on non-target animals. However, knowledge about the effect of fomesafen on the antioxidant defense system in earthworms is vague. Thus, it is essential to investigate the effects of fomesafen on the antioxidant defense system in earthworms as a precautionary method. In the present study, earthworms (Eisenia fetida) were exposed to artificial soil treated with a range of concentrations of fomesafen (0, 10, 100, and 500 μg kg(-1)) and were collected on the 3rd, 7th, 14th, 21st, and 28th days of exposure. Subsequently, the antioxidant enzyme activities (superoxide dismutase (SOD); catalase (CAT); and guaiacol peroxidase (POD)), reactive oxygen species (ROS) level, and malondialdehyde (MDA) content due to fomesafen treatment were examined in earthworms. Compared with the control, the SOD activity increased on the third and seventh days but decreased on the 14th day due to treatment with 100 and 500 μg kg(-1) of fomesafen. The activities of CAT and POD increased significantly on the third, seventh, and 14th days of exposure. In addition, the ROS level was significantly enhanced throughout the entire experimental period and showed a statistically dose-dependent relationship on the seventh and 14th days. The MDA content markedly increased on the seventh day of exposure; however, obvious changes were not detected at other exposure period. Low doses of fomesafen (≤ 500 μg kg(-1)) may result in oxidative damage and lipid peroxidation in E. fetida by inducing the generation of ROS at short exposure periods (14 days). However, the adverse effects of fomesafen gradually disappear as the cooperation of antioxidant enzymes and exposure time are prolonged. This result may be helpful for further studies on the toxicological mechanisms of fomesafen to earthworms.

Vermicomposting of source-separated human faeces by Eisenia fetida: effect of stocking density on feed consumption rate, growth characteristics and vermicompost production

The main objective of the present study was to determine the optimum stocking density for feed consumption rate, biomass growth and reproduction of earthworm Eisenia fetida as well as determining and characterising vermicompost quantity and product, respectively, during vermicomposting of source-separated human faeces. For this, a number of experiments spanning up to 3 months were conducted using soil and vermicompost as support materials. Stocking density in the range of 0.25-5.00 kg/m(2) was employed in different tests. The results showed that 0.40-0.45 kg-feed/kg-worm/day was the maximum feed consumption rate by E. fetida in human faeces. The optimum stocking densities were 3.00 kg/m(2) for bioconversion of human faeces to vermicompost, and 0.50 kg/m(2) for earthworm biomass growth and reproduction.

Differential expression of genes in the earthworm Eisenia fetida following exposure to Escherichia coli O157:H7

In this study, suppression subtractive hybridization was used to construct forward and reverse cDNA libraries to identify genes involved in the response of Eisenia fetida after exposure to Escherichia coli O157:H7. We cloned 1428 cDNAs or expressed sequence tags (ESTs), of which 738 were confirmed to be differentially expressed on dot blotting analysis. A total of 394 good-quality ESTs (GenBank dbEST accession numbers HO001170-HO001563) were obtained from the raw clone sequences after cleaning. The genes were associated with metabolism (10%), transport (10%), translation (5%), immunity (2%), and the cytoskeleton (1%). Thirteen candidates were selected to assess expression levels in earthworms exposed to artificially contaminated soil by real-time PCR. The translated amino acid sequences of clones were similar to fibrinolytic protease 1, extracellular globin-3, myosin essential light chain, lumbrokinase, lysozyme, ferritin, ATP synthase F0 subunit 6, and hsp 70. Characterization of differential gene expression in the earthworm E. fetida on exposure to E. coli O157:H7 expands our understanding of the molecular mechanisms of interactions at the earthworm-pathogen interface.