Enteric bacteria from the earthworm (Metaphire posthuma) promote plant growth and remediate toxic trace elements

Phosphate-solubilizing bacteria improve the antioxidant enzyme activity of Potamogeton crispus L. and enhance the remediation effect on Cd-contaminated sediment

Phosphorus-solubilizing bacteria (PSB) assisted phytoremediation of cadmium (Cd) pollution is an effective method, but the mechanism of PSB-enhanced in-situ remediation of Cd contaminated sediment by submerged plants is still rare. In this study, PSB (Leclercia adecarboxylata L1-5) was inoculated in the rhizosphere of Potamogeton crispus L. (P. crispus) to explore the effect of PSB on phytoremediation. The results showed that the inoculation of PSB effectively improved the Cd extraction by P. crispus under different Cd pollution and the Cd content in the aboveground and underground parts of P. crispus all increased. The μ-XRF images showed that most of the Cd was enriched in the roots of P. crispus. PSB especially showed positive effects on root development and chlorophyll synthesis. The root length of P. crispus increased by 51.7 %, 80.5 % and 74.2 % under different Cd pollution, and the Ca/Cb increased by 38.9 %, 15.2 % and 8.6 %, respectively. Furthermore, PSB enhanced the tolerance of P. crispus to Cd. The contents of soluble protein, MDA and H2O2 in 5 mg·kg-1 and 7 mg·kg-1 Cd content groups were decreased and the activities of antioxidant enzymes were increased after adding PSB. The results showed that the application of PSB was beneficial to the in-situ remediation of submerged plants.

Exploring the Toxicity of Oxytetracycline in Earthworms (Eisenia fetida) Based on the Integrated Biomarker Response Method

Antibiotic contamination has become a global environmental issue of widespread concern, among which oxytetracycline contamination is very severe. In this study, earthworm (Eisenia fetida) was exposed to oxytetracycline to study its impact on the soil environment. The total protein (TP), catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), malondialdehyde (MDA), glutathione S-transferase (GST), and glutathione peroxidase (GPX) oxidative stress indicators in earthworms were measured, and the integrated biomarker response (IBR) approach was used to evaluate the toxic effect of oxytetracycline on earthworms. A Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) and a path analysis model were used to explore the physiological and metabolic processes of earthworms after stress occurs. The results showed that SOD, GPX, and GST play important roles in resisting oxytetracycline stress. In addition, stress injury showed a good dose-effect relationship, and long-term stress from pollutants resulted in the most serious damage to the head tissue of earthworms. These results provide a theoretical basis for understanding the toxic effect of oxytetracycline on soil animals, monitoring the pollution status of oxytetracycline in soil, and conducting ecological security risk assessment.

Plant growth-promoting bacteria isolated from earthworms enhance spinach growth and its phytoremediation potential in metal-contaminated soils

The aim of this study was to evaluate the impact of metal-tolerant plant growth-promoting bacteria (PGPB) isolated from the chloragogenous tissue of Aporrectodea molleri, which represents a unique habitat. Our objectives were to investigate their effects on the growth of Spinacia oleracea under heavy metal stress and assess their potential for enhancing phytoremediation capabilities. The experiment was conducted in an alkaline soil contaminated with 7 mg kg-1 of cadmium, 100 mg kg-1 of nickel, 150 mg kg-1 of copper, 300 mg kg-1 of Zinc, and mg kg-1 of 600 Manganese. The results showed that heavy metal stress considerably diminished root (42.8%) and shoot length (60.1%), biomass (80%), chlorophyll content (41%), soil alkaline (45%), and acid (51%) phosphatases (42%) and urease (42%). However, soil inoculation with bacterial isolates remarkably improved plant growth. Soil bioaugmentation increased spinach growth (up to 74.5% for root length, up to 106.3% for shoot length, and up to 5.5 folds for fresh biomass) while significantly increasing soil enzyme activity and NPK content. Multivariate data analysis indicated that soil inoculation with Bacillus circulans TC7 promoted plant growth while limiting metal bioaccumulation, whereas Pseudomonas sp. TC33 and Bacillus subtilis TC34 increased metal bioaccumulation in spinach tissues while minimizing their toxicity. Our study confirms that earthworms are a reservoir of multi-beneficial bacteria that can effectively improve phytoremediation efficiency and mitigate the toxic effects of heavy metals on plant growth. Further studies are needed to investigate the long-term effects and feasibility of using these isolates as a consortium in field applications.

Biological roles of soil microbial consortium on promoting safe crop production in heavy metal(loid) contaminated soil: A systematic review

Heavy metal(loid) (HM) pollution of agricultural soils is a growing global environmental concern that affects planetary health. Numerous studies have shown that soil microbial consortia can inhibit the accumulation of HMs in crops. However, our current understanding of the effects and mechanisms of inhibition is fragmented. In this review, we summarise extant studies and knowledge to provide a comprehensive view of HM toxicity on crop growth and development at the biological, cellular and the molecular levels. In a meta-analysis, we find that microbial consortia can improve crop resistance and reduce HM uptake, which in turn promotes healthy crop growth, demonstrating that microbial consortia are more effective than single microorganisms. We then review three main mechanisms by which microbial consortia reduce the toxicity of HMs to crops and inhibit HMs accumulation in crops: 1) reducing the bioavailability of HMs in soil (e.g. biosorption, bioaccumulation and biotransformation); 2) improving crop resistance to HMs (e.g. facilitating the absorption of nutrients); and 3) synergistic effects between microorganisms. Finally, we discuss the prospects of microbial consortium applications in simultaneous crop safety production and soil remediation, indicating that they play a key role in sustainable agricultural development, and conclude by identifying research challenges and future directions for the microbial consortium to promote safe crop production.

Native microalgae and Bacillus XZM remediate arsenic-contaminated soil by forming biological soil crusts

Biological soil crusts (BSCs) are a useful tool for immobilization of metal(loid)s in mining areas. Yet, the typical functional microorganisms involved in promoting the fast development of BSCs and their impacts on arsenic(As) contaminated soil remain unverified. In this study, As-contaminated soil was inoculated with indigenous Chlorella thermophila SM01 (C. thermophila SM01), Leptolyngbya sp. XZMQ, isolated from BSCs in high As-contaminated areas and plant growth-promoting (PGP) bacteria (Bacillus XZM) to construct BSCs in different manners. After 45 days of ex-situ culture experiment, Leptolyngbya sp. XZMQ and bacteria could form obvious BSCs. Compared to single-inoculated microalgae, the co-inoculation of Leptolyngbya sp. XZMQ and Bacillus XZM increased soil pH and water content by 10% and 26%, respectively, while decreasing soil EC and density by 19% and 14%, respectively. The soil catalase, alkaline phosphatase, sucrase, and urease activities were also increased by 30.53%, 96.24%, 154.19%, and 272.17%, respectively. The co-inoculation of Leptolyngbya sp. XZMQ and Bacillus XZM drove the formation of BSCs by producing large amounts of extracellular polymeric substances (EPS). The three-dimensional fluorescence spectroscopy (3D-EEM) analysis showed that induced BSCs increased As immobilization by enhancing the contents of tryptophan and tyrosine substances, fulvic acid, and humic acid in EPS. The presence of the -NH2 and -COOH functional groups in tryptophan residues were determined using Fourier Transform Infrared Spectroscopy (FTIR). X-Ray Diffraction (XRD) analysis showed that there were iron (hydrogen) oxides in BSCs, which could form ternary complexes with humic acid and As, thereby increasing the adsorption of As. Therefore, BSCs formed by co-inoculation of Leptolyngbya sp. XZMQ and Bacillus XZM increased the immobilization of As, thereby reducing the content of soluble As in the environment. In summary, our findings innovatively provided a new method for the remediation of As-contaminated soil in mining areas.

Augmentation of plant biomass productivity using epigeic earthworm Perionyx excavatus and Eisenia fetida as soil nutrient facilitators

With the increasing demand for organic food production, the earthworm is used as a soil nutrient facilitator. The present study was conducted to assess the effect of epigeic earthworms Perionyx excavatus and Eisenia. fetida on soil nutrients and the consequent improvement of biomass productivity and yield of Capsicum chinense Jacq and Zea mays L. The experiment was conducted in 5 L and 15 L capacity plastic pots for C. chinense and Z. mays with 150 g and 300 g of half-decomposed cow dung, respectively. It was observed that the weekly harvest rate of ripened chili was 17.59 g, 13.91 g, and 9.24 g in P. excavatus, control, and E. fetida pot showing 26.49% higher in P. excavatus. Also, the total kernel count per corn was significantly different (F(2, 9) = 37.78, p < 0.05), with the highest kernel present in P. excavatus(333.5 ± 13.5), followed by E. fetida(261.5 ± 16.5) and control (235 ± 22). The impact of P. excavatus was more perceptible in C. chinense, indicated by higher leaf biomass (69.16%), root length (30.14%), and fruit harvest (71.03%). However, the effect of E. fetida was noticed more in Z. mays (stem length, 19.24%, stem biomass, 14.39%, root biomass, 20.9%, kernel count, 41.91%, and kernel weight, 95.07%). Enhanced plant productivity was also supported by an increasing soil nutrient turnover in organic carbon (OC) (25.76% and 23.4%), Phosphorus (P) (31.03% and 25.67%), and Potassium (K) (41.67% and 12.26) in P. excavatus and E. fetida worked soil respectively. The findings indicate that earthworms have a notable impact on plant biomass productivity by promoting the mineralization of soil nutrients and imply on possibility of organic cultivation of seasonal vegetables without using synthetic fertilizers.

Turning earthworms into moonworms: Earthworms colonization of lunar regolith as a bioengineering approach supporting future crop growth in space

The earthworms beneficial effects on soils may be promising to improve lunar soil fertility, enabling the use of local substrates for space farming. Herein, we investigated the effects of the lunar regolith simulant (LHS-1) at different concentrations in cow manure mixtures on the survival and fitness of Eisenia fetida. During 14 and 60-day experiments, although E. fetida showed an increased mortality with LHS-1 alone, most of the population survived. More numerous tunnels were observed when exposed to the higher concentrations of LHS-1 (poor in nutrients for earthworms). This may be related to an increased mobility for food search. The cocoons production was not affected by different substrate treatments, except for the highest concentration of LHS-1. No effects of different LHS-1 concentrations on the amount of ingested substrate were recorded. This study shows that E. fetida can potentially colonize lunar regolith representing a future valuable biological tool for supporting crops growth on the Moon.

Vermiremediation applied to PCB and PCDD/F contaminated soils and its implications for percolating water

PCDD/Fs (polychlorinated dibenzo-p-dioxins/dibenzofurans) and PCBs (polychlorinated biphenyls) are ubiquitous persistent pollutants with reduced bioavailability, which bioremediation using soil fauna is still managed to treat. This research set out to: (i) study the suitability of earthworms (Eisenia fetida), alone and associated with plants (Lepidium sativum), for the decontamination of PCDD/F and PCB polluted soils in Brescia-Caffaro (Italy), at total and congener concentration levels; (ii) simulate the action of earthworms in groundwater contamination process and nutrient mobility. Five treatments were set up: (i) uncontaminated soil with E. fetida (NC); (ii) contaminated soil (C); (iii) contaminated soil with E. fetida (CEf); (iv) contaminated soil with L. sativum (CLs); (v) contaminated soil with E. fetida and L. sativum (CEfLs). PCBs and PCDD/Fs in the soil prior to testing were measured. Analysis was repeated in soil treatments and percolating water at the end of the test period (4 months). Dissolved nutrient concentrations were measured in percolated water. PCB and PCDD/F concentrations, initially 259333.33 ± 10867.89 ng/kg and 176 ± 10.69 ngTE/kg, were significantly reduced after 4 months in all treatments. Treatments did not differ in total PCBs concentration (from 160,000 ng/kg to 194,000 ng/kg), but CEfLs congeners concentrations were less environmentally threatening; CEf and CLs resulted in lower PCDD/Fs concentration (79.43 ± 3.34 ngTE/kg and 73.03 ± 4.09 ngTE/kg, respectively). The action of earthworms could enhance contaminants and soluble reactive phosphorous content in percolating water.

Assessment of the eco-toxicological effects in zoxamide polluted soil amended with fertilizers-An indoor evaluation

Zoxamide is a benzamide fungicide applied to control diseases caused by oomycete fungi. Fertilizers are important agricultural supplies to adjust soil properties and increase nutrition. To investigate the impact of zoxamide and seven fertilizers urea, phosphate fertilizer, potash fertilizer, compound fertilizer, organic fertilizer, vermicompost and soya bean cakes on the soil environment, the enantioselective dissipation characteristics of zoxamide, soil enzyme activities, pH and N, P nutrition changes were comprehensively analyzed in our present study. The enantioseparation method was successfully validated to quantify the zoxamide enantiomers in soil by HPLC using Chiral NQ (2)-RH column. Our results demonstrated that the R-(-)- and S-(+)-zoxamide half dissipated in the range of 10.88-17.81 and 8.05-14.41 days, respectively. S-(+)-zoxamide disappeared faster in soil. The vermicompost accelerated the dissipation rate of S-(+)-zoxamide, while urea, phosphate, organic and vermicompost fertilizer increased the dissipation selectivity. Zoxamide and fertilizers other than urea caused soil acidification during 80 days. Zoxamide was beneficial to soil catalase, instead inhibited soil urease, dehydrogenase activities and available phosphorus content. No significant effects on sucrase activity and available nitrogen content were found by zoxamide. Vermicompost and soya bean cakes had lasting and outstanding performance in efficiently improving soil enzyme activity and N, P nutrition. The comprehensive understanding of the ecological impact induced by chiral pesticide enantiomers and fertilizers on soil is vital to ensure the sustainable development and safety of agricultural production.

An invasive weed-associated bacteria confers enhanced heat stress tolerance in wheat

Global temperatures are expected to increase due to climate change, and heat stress is one of the major limiting factors affecting future agriculture. To identify plant-associated microorganisms which can promote heat stress tolerance in wheat, we have screened several bacteria isolated from etiolated seedlings of the invasive noxious weed Parthenium hysterophorus. One isolate designated as Ph-04 was found to confer enhanced heat stress tolerance in wheat. The 16S rRNA gene sequence analysis showed that Ph-04 isolate shared highest sequence identity with Bacillus paramycoides species of the Bacillus cereus group. Ph-04 treated wheat seeds exhibited enhanced germination, longer coleoptile, radicle and seminal root length than control seedlings when grown in the dark at optimum and high temperatures. Similarly, under autotrophic conditions, Ph-04 treated plants also exhibited enhanced heat stress tolerance with a significant increase in membrane integrity and significantly reduced levels of H₂O₂ under heat stress compared to control plants. This observed heat stress tolerance is associated with constitutively higher basal levels of proline, and activity of antioxidant enzymes, catalase (CAT) and ascorbate peroxidase (APX) in Ph-04 treated plants grown under unstressed conditions with further increase under heat stress conditions compared to controls. Plant recovery after heat stress also showed that the Ph-04 treated plants exhibited significantly less damage in terms of survival percentage and exhibited better morphological and physiological characteristics compared to control plants. The study proves that invasive weeds can harbour potentially beneficial microorganisms, which can be transferred to non-native crop (host) plants to improve climate resilience characteristics.

Vermicomposting of cow manure: Effect of time on earthworm biomass and chemical, physical, and biological properties of vermicompost

Vermicomposting is a biological process for efficient cattle manure treatment, but the vermicomposting time determines the quality of the vermicompost. The objective of this study was to evaluate the effect of cattle manure vermicomposting time on earthworm biomass and the changes in physical, chemical, and biological in properties of the vermicompost. The cattle manure was inoculated with Eisenia andrei earthworms and conducted vermicomposting for 0, 15, 30, 45, 60, and 120 days. The analysis of 44 chemical, physical, and biological properties allowed the vermicomposting process to be divided into initial (<45 days) and final (45-120 days) phases. The initial phase was characterized by high microbial activity and the final by high physical-chemical transformation of the vermicompost and an increase in earthworm density. The organic matter aromaticity increased until the 45th day, subsequently decreasing. Although 30 d of vermicompost are sufficient to obtain a high-quality organic fertilizer, 120 d are necessary for producing matrices.

Taxonomic and functional characteristics of aerobic bacteria isolated from the chloragogenous tissue of the earthworm Aporrectodea molleri

Earthworms are considered as a rich microhabitat for the growth and proliferation of diverse soil microorganisms. Hence, earthworms' associated bacteria attracted interest due to their high metabolic profiles and benefits to soil fertility and plant growth. In this study, we aimed to isolate for the first-time aerobic bacteria present in the chloragogenous tissue of the earthworm Apporectodea molleri and test their Plant Growth-Promoting abilities and their resistance to heavy metals (Mn, Zn, Cu, Cd, and Ni). The 16S rRNA gene sequencing revealed the affiliation of the fifteen isolates to six main bacterial genera: Enterobacter, Citrobacter, Aeromonas, Pseudomonas, Bacillus, Terribacillus. These strains displayed different plant growth promoting traits (e.g., indole-3-acetic acid IAA, siderophores, nitrogen fixation, phosphate, and potassium solubilization), in addition, they were able to resist differently to heavy metals. Bacillus strains were most effective as three strains, namely B. subtilis strain TC34; B. circulans strain TC7 and Bacillus sp. strain TC10, were positive to all PGP traits and resisted to all heavy metals. This study illustrates the potential of bacteria from the chloragogenous tissue to exhibit multiple properties, which can be related to the functional feature of this tissue to stock metabolites and neutralize toxic elements.

Insights into the mechanisms underlying the remediation potential of earthworms in contaminated soil: A critical review of research progress and prospects

In recent years, soil pollution is a major global concern drawing worldwide attention. Earthworms can resist high concentrations of soil pollutants and play a vital role in removing them effectively. Vermiremediation, using earthworms to remove contaminants from soil or help to degrade non-recyclable chemicals, is proved to be an alternative, low-cost technology for treating contaminated soil. However, knowledge about the mechanisms and framework of the vermiremediation various organic and inorganic contaminants is still limited. Therefore, we reviewed the research progress of effects of soil contaminants on earthworms and potential of earthworm used for remediation soil contaminated with heavy metals, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), polycyclic aromatic hydrocarbons (PAHs), pesticides, as well as crude oil. Especially, the possible processes, mechanisms, advantages and limitations, and how to boost the efficiency of vermiremediation are well addressed in this review. Finally, future prospects of vermiremediation soil contamination are listed to promote further studies and application of vermiremediation in contaminated soils.