A method to study the effects of combined stress of cadmium and microplastics on the acute toxicity of Eisenia fetida.

The compound pollutants formed by microplastics and cadmium present a significant potential threat to the soil-based ecosystem, and it is urgent to carry out relevant ecotoxicological studies. However, the lack of appropriate test methods and scientific mathematical analysis models has restricted the progress of research. Based on an orthogonal test design, a ternary combined stress test was performed to study the effect of microplastics and cadmium on earthworms. This study used the particle size and concentration of microplastics as well as the concentration of cadmium as test factors. Using the improved factor analysis model and the TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) method, a new model was constructed according to the response surface methodology to analyze the acute toxic effects on earthworms under the combined stress of microplastics and cadmium. In addition, the model was tested in a soil-polluted environment. The results show that the model can perfectly integrate the spatiotemporal cross effects of the concentration and time of the applied stress, and the scientific data analysis process ensures the efficient development of ecotoxicological research in the actual compound pollution environment. Moreover, the results of the filter paper test and soil test showed that the equivalent toxicity ratio of cadmium concentration, microplastic concentration, and microplastic particle size to earthworms as 26:35:39 and 23:36:41, respectively. In terms of the interaction effect, a certain positive interaction was observed between the cadmium concentration and that of the microplastics and their particle size, while a negative interaction was observed between the concentration of microplastics and their particle size. This research provides a test basis and model reference for early monitoring of the health of contaminated soils and assessments of ecological safety and security.

Effect of the lignocellulolytic Psychrotroph Lelliottia sp. on bacterial community succession in corn straw compost.

This study aimed to explore the effect of an inoculation, Lelliottia sp., on the corn straw compost's physico-chemical properties, composition, and the succession of bacterial community structure. The compost community composition and succession changed after Lelliottia sp. inoculation. Inoculation increased the bacterial community diversity and abundance in the compost to promote composting. The inoculated group entered the thermophilic stage on the first day, lasting 8 days. Judging the pile maturity based on the carbon:nitrogen ratio and germination index values, the inoculated group reached the maturity standard, which was 6 days faster than the control group. The relationship between environmental factors and bacterial communities was comprehensively analyzed using redundancy analysis. Temperature and carbon:nitrogen ratio were the main environmental factors driving the succession of bacterial communities, to provide basic information on the changes of physicochemical indexes and bacterial community succession in Lelliottia sp. inoculated maize straw composting, providing assistance for practical composting applications of this strain.

Study on the life maintenance mechanism of Eisenia fetida under low-density polyethylene stress: Based on path analysis and canonical correlation analysis.

The widespread use but low recovery rate of agricultural films has led to microplastic accumulation in farmlands, which poses a serious threat to the health of the soil ecosystem. There is an urgent need for early warning and monitoring of soil microplastics pollution, as well as the performance of bioremediation research. In this study, earthworms were used as test organisms to carry out toxicological tests under low-density polyethylene (LDPE) stress. A canonical correlation analysis model (CCA) was established to analyze the relationship between oxidative stress and microbial community. A path analysis model (PA) was also constructed to examine the detoxification mechanism of earthworms under LDPE stress. The results showed that low concentrations (100 and 500 mg/kg) of LDPE did not cause oxidative damage to earthworms but stimulated their physiological metabolism. Meanwhile, 1000 mg/kg LDPE concentrations caused oxidative damage to earthworms and altered their internal microbial community structure. Furthermore, at 1500 mg/kg LDPE concentrations, the oxidative stress to the earthworms is aggravated, and their physiological responses work in conjunction with the microbial community to cope with the adverse condition. Lastly, treatment with 2000 mg/kg LDPE induced the appearance of LDPE tolerant populations in the microbial community in vivo. Taken together, our results provide a theoretical basis for revealing the physiological response of earthworms when challenged in a polluted environment and provide a model for pollution remediation and ecological security monitoring of soil ecosystems.

Evaluation of the toxicity effects of microplastics and cadmium on earthworms.

Microplastics (MPs) and heavy metal pollution have become research hotspots in recent years. This study focused on the comprehensive evaluation of the toxicity effect on Eisenia fetida under combined exposure to MPs and the heavy metal cadmium (Cd). With Cd concentration, MPs concentration and MPs partical size as stress factors, the TOPSIS model was constructed to explore the toxicity levels of the stress factors. A short-term co-exposure test and a long-term co-exposure test were designed by orthogonal combination tests with equivalent toxicity levels. The activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), glutathione peroxidase (GPX), glutathione S transferase (GST), and acetylcholinesterase (AChE) and the contents of protein (TP), glutathione (GSH), and malondialdehyde (MDA) in earthworms were determined. Integrated biological responses version 2 (IBRv2) was used to evaluate the toxicity of MPs and Cd combined exposure on earthworms. The results showed that the toxicity ratio of Cd concentration, MPs concentration and MPs partical size was 46 to 29 to 25. Combined exposure to MPs and Cd enhanced the activities of SOD, POD, CAT, GPX and GST, MDA and GSH contents also increased, while the AChE activities were inhibited. SOD, GPX and GST play important roles in the resistance of earthworms to pollutant stress. During short-term co-exposure, Cd concentration had antagonistic effects with on MPs concentration and MPs partical size, while they showed synergistic effects during long-term co-exposure.

Evolution of the earthworm (Eisenia fetida) microbial community in vitro and in vivo under tetracycline stress.

Bioremediation of contaminated soil has received increasing attention, and the effects of antibiotic residues on the soil ecological environment are a current research hotspot. Earthworms are the first choice of soil organisms to indicate the degree of soil pollution, and their detoxification mechanism after antibiotic stress must be further explored. Taking Eisenia fetida as the research object, an antibiotic (tetracycline) stress test was carried out in sterile artificial soil. The stress concentrations were set at 0, 0.3, 3, 30, 300 and 600 mg/kg. The ECO method was used to cultivate microbes in earthworms and soil. The carbon source utilization intensity algorithm developed by our team was used for data statistics, and a factor analysis model was constructed to explore the succession process of microbes of earthworms in vivo and in vitro under tetracycline stress. The results showed that there were four processes in the evolution of microbes under short-term tetracycline stress: at 1-3 days, the microbes in worms played a leading role; at 4-5 days, the microbes in the worms and the soil microbes jointly resisted TET stress; after 6-8 days of stress, the microbes in worms still played the main role, but their role was weakened; and after 9-10 days, soil microbes played a leading role, and tolerant microbes appeared. Under long-term stress, the microbes of earthworms in vivo and in vitro were obvious different, and there may be no regulatory relationship. And the factor analysis model is suitable for the analyse of the changes in microbial communities in vivo and in vitro under TET stress. The research results provide a reference method and model basis for the bioremediation of antibiotic-contaminated soil and the study of earthworm detoxification mechanisms, and help agricultural development.

Study on the regulatory mechanism of the earthworm microbial community in vitro and in vivo under cadmium stress.

In this paper, cadmium (Cd) stress tests were performed on Eisenia fetida in sterile artificial soil, and its regulatory mechanism between microbial communities in vivo and in vitro after Cd stress was explored. In the test, 0, 50, 100, 125, 250 and 500 mg kg-1 Cd stress concentrations were implemented. After long-term and short-term stress, the microbes in the earthworms and the soil were cultured with ECO plates. The data statistics of carbon source utilization intensity were carried out using the method developed by our team. CCA was scientifically integrated into TOPSIS to establish a new data analysis model to find the regulatory nodes after stress (Ning et al., 2020). Macro gene sequencing technology revealed that the species with the highest absolute abundance in the microbial communities in vivo and in vitro were all unnamed new species. It was confirmed that the HBA gene, NEUROD1 gene and ABCA3 gene were the regulatory genes of the microbial community in the earthworms under Cd stress, while the TC.FEV.OM gene and cheBR gene were the main regulatory genes of the microbial community in the soil. These results provide a scientific and theoretical reference and model basis for the bioremediation of Cd-contaminated soil and the detoxification mechanism of earthworms.

The relationship between the oxidative stress reaction and the microbial community by a combinative method of PA and CCA.

Earthworms, as the first choice for soil monitoring and bio-remediation of cadmium (Cd)-contaminated soil, need to identify its mechanism under Cd stress. In this study, an artificial soil test method was used to determine the oxidative stress reaction indices, amino acid composition, and microbial community changes in earthworms under different stress durations and concentrations. For the first time, the canonical correlation analysis model and path analysis model were innovatively introduced into the data analysis to determine the mechanism that drives earthworm physiological functions after Cd stress. The results showed that in the low-stress concentration treatments (50-125 mg.kg-1 DW), there was a driving relationship between oxidative stress reaction and microbial community in earthworm, and the driving factor was glycyl-L-glutamic acid at 50 mg.kg-1 DW. With the increase of Cd stress intensity, the enzymes of oxidative stress promoted the survival microbes to begin to proliferate, and SOD became the main driving factor under 125 mg.kg-1 DW Cd stress. In the high-stress concentration treatments (250-500 mg.kg-1 DW), the driving effects were weakened or disappeared; while Cd-resistant microbial population appeared. This study provides a theoretical basis for the driving mechanism between oxidative stress effect and microbial community after Cd stress.

Temporal dynamics of earthworm (Eisenia fetida) microbial communities after cadmium stress based on a compound mathematical model.

Soil cadmium (Cd) pollution has received increasing attention from scholars. In the field of Cd pollution remediation, there is an urgent need to study the combined bioremediation technology of earthworms and microbes. In this paper, a short-term stress test and a long-term stress test were conducted. Eisenia fetida were inoculated into artificial soil that was contaminated with Cd. After different Cd stress times, the regulation process between the microbial communities in the earthworms and in the soil was studied. Canonical correlation analysis and the TOPSIS method were combined to establish a mathematical model for data analysis, and the changes in the carbon source utilization intensity by microbes were analysed. The results showed that in the short-term stress tests, the regulation process could be divided into five stages. Specifically, after 1-3 days of stress, the microbial community in the earthworms regulated the soil microbial community, but on the 3rd day, the regulation was weakened. On the 4th day, the soil microbial community was affected not only by the microbes in the earthworms but also by the increasing intensity of Cd stress. After 5 days of stress, the microbial communities in the earthworms and the soil were both greatly affected by Cd poisoning, and the microbes transitioned from stable to declining. At 6-7 days, the microbes in the earthworms gained control over those in the soil once again, and the Cd-tolerant microbes began to appear and proliferate. At 8-10 days, the regulation of the soil microbes by the earthworm microbes weakened, while the Cd-tolerant population in the soil microbial communities gradually evolved at this stage to adapt to the increasing Cd stress. The long-term stress tests showed that the difference between the microbial communities in the soil and in the earthworms increased, and there was almost no regulation between them.

Study on the microbial community in earthworm and soil under cadmium stress based on contour line analysis.

Cadmium (Cd) contamination in soil has become the focus of widespread concern in society today. In this paper, with Eisenia fetida as research subjects, an indoor simulation experiment was conducted. A BIOLOG microplate technique was used to determine the carbon source (single-carbon) utilization of the microbial communities in the contaminated soil and earthworms under Cd stress. Contour line analysis was used for the first time to study the difference of carbon source metabolism in microbial communities. And the effects of Cd stress on the functional diversity of the microbial communities and the detoxification mechanism in earthworms were researched. With two test groups, a short-term test and the long-term test were performed. The former test lasted for 10 days, with the removal of an earthworm every day for analysis; the latter test lasted for 30 days, with the removal of an earthworm every 10 days. The Cd2+ concentration was set at 0, 50, 100, 125, 250, or 500 mg kg-1 dry weight, and 10 earthworms were inoculated in each concentration treatment. The earthworm homogenate and soil extracts were used to determine the carbon source utilization of the microbial communities. The results show that Cd stress changed the functional diversity of the microbial communities in the soil and earthworms. With the extension of stress time and the increase of stress concentration, earthworms will adjust their own physiological functions (including the microbial community structure and stress mechanism in the body) and regulate the microbial community structure in the external environment to obtain the necessary substances for growth. In addition, 2-hydroxybenzoic acid, γ-hydroxybutyric acid, glutamyl-L-glutamic acid, α-butyric acid, threonine, and α-cyclodextrin were important carbon sources for the earthworms to maintain their normal physiological metabolism under Cd stress. This study confirms that changes in microbial communities can be used to reveal the detoxification mechanisms of earthworm under heavy metal stress.

Screening indices for cadmium-contaminated soil using earthworm as bioindicator.

Artificial soil simulation tests were conducted to study the response of oxidative stress in different parts of Eisenia fetida under cadmium Cd) stress. Factor analysis and analytic hierarchy process were used to establish a comprehensive mathematical model to screen key monitoring indices of the Cd-contaminated soil early warning system. This paper sets the short-term group and the long-term group. The former lasted 10 days, and the latter was 30 days. Gradient solution of 0, 50, 100, 125, 250, and 500 mg kg-1 Cd2+ was used in each test group. The earthworm was cut into two parts from its clitellum to determine oxidative stress indices. Results showed that during the short-term stress, TP (total protein) in the head tissues of the earthworm was the key monitoring index for 3-4 and 8-9 days of Cd stress. In addition, the TP in tail tissues was the key index for 2, 4, 6, and 8-10 days of stress. On the first and second days, the key monitoring indices in the tail tissues were both the CAT (catalase), while in the head, they were CAT and TP, respectively. On the 5th, the 7th, and the 9th days, the focus should be on monitoring POD (peroxidase) in the tail tissues, while in the head tissues, they were POD, CAT, and TP, respectively. In the long-term test after 10 days of Cd stress, the key monitoring index in head tissues was GPX (glutathione peroxidase), and in the tail, it was TP. At 20-30 days, the key monitoring indices were TP in the head and MDA (malondialdehyde) in the tail.

Study on the influential biochemical indices of Cd(II) on Eisenia fetida in oxidative stress by principal component analysis in the natural soil.

With the aggravation of heavy metal pollution in soil, the individual heavy metal content monitoring cannot predict the true effects of harmful substances on the ecosystems. Thus, the effective biological evaluation system should be established to assess the pollution risk caused by heavy metal. Earthworms are widely distributed in the soil, and at the bottom of the food chain, the changes of biochemical indices play an important role in the early warning for heavy metal pollution. Principal component analysis (PCA) is a statistical method that derives several independent principal components from the original variable based on retaining the information as much as possible. This paper is aimed at finding out and analyzing the key monitoring factors related to Cd2+ on the earthworm Eisenia fetida in oxidative stress. The Cd2+ stress concentrations were set at 0, 1, 10, 20, 100, 200, 400, and 800 mg kg-1, and the post-clitellum segment of earthworm was chosen to determine TP, POD, SOD, GST, GPX, CAT, MDA, VE, and AChE. The results showed that the main bioindicators associated with oxidative stress reaction were GST, POD, and MDA at the exposure time of 10 days; at 20 days GPX, MDA, and AChE; at 30 days CAT, TP, and GPX; CAT, MDA, and SOD at 40th day. These results indicated that PCA can quickly, effectively, directly, and scientifically select biomarkers of oxidative stress induced by Cd and improve the accuracy and scientificity of earthworm as a biomarker in monitoring and early warning for heavy metal-contaminated soil.

Study on the influential factors of Cd(2+) on the earthworm Eisenia fetida in oxidative stress based on factor analysis approach.

When earthworms are exposed to pollutants, their antioxidant system will have responses immediately. Consequently earthworms are widely used to monitor various pollutants as a sensitive bio-indicator. However, there are a large number of indices associated with the oxidative stress response. Finding out the key monitoring indices in the stress process becomes a practical demand of the pollution monitoring and warning process. Factor analysis approach is a statistical method that uses a few factors to replace many original factors. This paper is aimed at analyzing and sorting factors related to Cd(2+) on the earthworm Eisenia fetida in oxidative stress. We studied two groups, the short-term test and the long-term test. The former test lasted for ten days, removing an earthworm every day for analysis; The latter test lasted for 30 days, taking out an earthworm every ten days. The Cd(2+) concentration was set at 0, 50, 100, 125, 250 and 500 mg kg(-1), post-clitellum segments of earthworms were chosen to determine SOD, POD, GPX, GST, CAT, VE, MDA and AChE. The results showed that in the short-term group, the main bioindicator associated with oxidative stress reaction was CAT at the exposure time of 1-3 days, at 4-5 days MDA, 6-7 days POD, and GST and GPX at 8th day, CAT at 9-10 days. While with the long-term test, the main bioindicator associated with oxidative stress reaction was GPX.