Improvement of the soil nitrogen content and maize growth by earthworms and arbuscular mycorrhizal fungi in soils polluted by oxytetracycline

Are earthworms the victim, facilitator or antidote of antibiotics and antibiotic resistance at the soil-animal-human interface? A One-Health perspective

The transfer of antibiotics and antibiotic resistance (AR) to the soil systems poses ecological hazards to various organisms, including earthworms. Understanding the complex interactions between earthworms, antibiotics, and AR in the soil system requires a comprehensive assessment. Hence, the present review investigates the behaviour, fate, impacts, and mechanisms involved in the interaction of earthworms with antibiotics and AR. The antibiotics and AR detected in earthworms and their associated media, such as vermicompost, are presented, but several other antibiotics and AR widely detected in soils remain understudied. As receptors and bioassay organisms, earthworms are adversely affected by antibiotics and AR causing (1) acute and chronic toxicity, and (2) emergence of AR in previously susceptible earthworm gut microbiota, respectively. The paper also highlights that, apart from this toxicity, earthworms can also mitigate against antibiotics, antibiotic-resistant bacteria and antibiotic-resistance genes by reducing bacterial diversity and abundance. The behaviour and fate processes, including biodegradation pathways, biomarkers of antibiotics and AR in earthworms, are discussed. In addition, the factors controlling the behaviour and fate of antibiotics and AR and their interactions with earthworms are discussed. Overall, earthworms mitigate antibiotics and AR via various proximal and distal mechanisms, while dual but contradictory functions (i.e., mitigatory and facilitatory) were reported for AR. We recommend that future research based on the One-World-One-Health approach should address the following gaps: (1) under-studied antibiotics and AR, (2) degradation mechanisms and pathways of antibiotics, (3) effects of environmentally relevant mixtures of antibiotics, (4) bio-augmentation in earthworm-based bioremediation of antibiotics, (5) long-term fate of antibiotics and their metabolites, (6) bio-transfers of antibiotics and AR by earthworms, (7) development of earthworm biomarkers for antibiotics and AR, (8) application of earthworm-based bioremediation of antibiotics and AR, (9) cascading ecological impacts of antibiotics and AR on earthworms, and (10) pilot-scale field applications of earthworm-based bioremediation systems.

Metabolomics and microbiomics revealed the combined effects of different-sized polystyrene microplastics and imidacloprid on earthworm intestinal health and function

The coexistence of pesticides and plastic film residues in agricultural soils poses a significant threat to soil organisms due to their potential long-term contamination and combined toxic effects. Specifically, earthworms are at risk of simultaneously ingesting residual pesticides and microplastics, yet the impact of this combined exposure on their intestinal health and function remains poorly understood. In this study, earthworm (Eisenia fetida) were single and combined exposed to three particle sizes (10 μm, 500 μm, and 2 mm) of polyethylene microplastics (PE MPs) and imidacloprid (IMI) for 28 days, respectively. Our findings underscore that compared to single exposures, the combined exposure inflicted more profound injuries on intestinal tissues and elicited a heightened activation of intestinal digestive enzymes. Furthermore, the combined exposure significantly perturbed the relative abundance of several pivotal metabolic-associated gut microbiota, fostering an enrichment of pathogenic species. Metabolomics analysis showed combined exposure increased differential metabolites, disrupting amino acid, fatty acid, and carbohydrate metabolism in earthworm intestines, potentially hindering nutrient absorption and causing toxic metabolite accumulation. An integrated omics analysis implies that combined exposures have the potential to disrupt the relative abundance of crucial gut microbiota in earthworms, thereby altering their intestinal metabolism and subsequently impacting intestinal health and functionality. Overall, the results reveal that combined exposure of IMI and PE MPs exacerbate the negative effects on earthworm gut health, and this study holds significant implications for the holistic understanding of the combined toxic effects of microplastics and pesticide on soil ecosystems.

Sustainable Remediation of Soil and Water Utilizing Arbuscular Mycorrhizal Fungi: A Review

Phytoremediation is recognized as an environmentally friendly technique. However, the low biomass production, high time consumption, and exposure to combined toxic stress from contaminated media weaken the potential of phytoremediation. As a class of plant-beneficial microorganisms, arbuscular mycorrhizal fungi (AMF) can promote plant nutrient uptake, improve plant habitats, and regulate abiotic stresses, and the utilization of AMF to enhance phytoremediation is considered to be an effective way to enhance the remediation efficiency. In this paper, we searched 520 papers published during the period 2000-2023 on the topic of AMF-assisted phytoremediation from the Web of Science core collection database. We analyzed the author co-authorship, country, and keyword co-occurrence clustering by VOSviewer. We summarized the advances in research and proposed prospective studies on AMF-assisted phytoremediation. The bibliometric analyses showed that heavy metal, soil, stress tolerance, and growth promotion were the research hotspots. AMF-plant symbiosis has been used in water and soil in different scenarios for the remediation of heavy metal pollution and organic pollution, among others. The potential mechanisms of pollutant removal in which AMF are directly involved through hyphal exudate binding and stabilization, accumulation in their structures, and nutrient exchange with the host plant are highlighted. In addition, the tolerance strategies of AMF through influencing the subcellular distribution of contaminants as well as chemical form shifts, activation of plant defenses, and induction of differential gene expression in plants are presented. We proposed that future research should screen anaerobic-tolerant AMF strains, examine bacterial interactions with AMF, and utilize AMF for combined pollutant removal to accelerate practical applications.

Vermiremediation of heavy metals (HMs)-contaminated agricultural land: synergistic changes in soil enzyme activities and earthworm's growth parameters

In this investigation the heavy metals (Cu, Zn, Mn, Cr and Ni) remediation potential of Eisenia fetida was studied in the crude oil polluted soil. The potential of E. fetida was evaluated based on the decrease in concentrations of Cu, Zn, Mn, Cr and Ni, and improvement in the soil enzyme activities at the end of 90 days of experimental trials. Moreover, soil health quality, inter-relationship between the enzyme activities and the growth parameters of E. fetida and synergistic relation among the enzyme activities were also evaluated through G-Mean and T-QSI indices, chord plot analysis and principal component analysis (PCA) to confirm the performance of E. fetida during vermiremediation. The results revealed that the soil treated with E. fetida showed a reduction in the concentration of Cu, Zn, Mn, Cr and Ni by 17.4% 19.45%, 9.44%, 23.8% and 9.6% respectively by end of the experimental trials. The cellulase, amylase, polyphenol oxidase, peroxidase, urease, dehydrogenase and catalase activities in the E. fetida-treated soil were enhanced by 89.83%, 99.17%, 142%, 109.9%, 92.9%, 694.3% and 274.5% respectively. The results of SEM-EDS revealed enhancement in the O, K, Na, Mg and P content by 62.36%, 96.2%, 97.9%, 93.7% and 98.2% respectively by the end of the experimental trial. The G-Mean and T-QSI indices also confirmed the improvement in soil enzyme activities thereby indicating the positive influence of E. fetida on soil decontamination process. The chord plot indicated the interrelationship between the earthworm's growth parameters and enzyme activities of the soil as indicated by the high linkage between the nodes. Finally, the PCA confirmed the negative effect of the heavy metals on the soil enzyme activities and synergistic interrelationship between the enzyme activities during the vermiremediation process. Thus, this study demonstrated the changes in the soil enzyme activities and their interconnected influences during vermiremediation of crude oil sourced heavy metals from polluted soil.

The single and combined effects of sulfamethazine and cadmium on soil nitrification and ammonia-oxidizing microorganisms

The coexistence of antibiotics and heavy metals in soil has attracted increasing attention due to their negative effects on microorganisms. However, how antibiotics and heavy metals affect functional microorganisms related to nitrogen cycle remains unclear. The goals of this work were to explore the individual and combined effects of sulfamethazine (SMT) and cadmium (Cd), selected as target pollutants in soil, on potential nitrification rates (PNR) and ammonia oxidizers (ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB)) structure and diversity by 56-day cultivation experiment. Results showed that PNR in Cd- or SMT-treated soil decreased at the beginning of the experiment and then increased over time. PNR was significantly correlated with AOA and AOB-amoA relative abundance (P < 0.01). SMT addition (10 and 100 mg kg^-1) significantly improved AOA activity by 13.93% and 17.93%, respectively, and had no effect on AOB at day 1. Conversely, Cd at 10 mg kg^-1 significantly inhibited AOA and AOB by 34.34% and 37.39%, respectively. Moreover, the relative abundance of AOA and AOB in combined SMT and Cd addition clearly higher relative to single Cd at 1 day. The single and combined Cd and SMT increased and reduced the community richness of AOA and AOB, respectively, but reduced the diversity of both after 56 days. Cd and SMT treatments significantly changed the relative abundance of AOA phylum levels and AOB genus levels in the soil. It was mainly manifested in reducing the relative abundance of AOA Thaumarchaeota, and increasing the relative abundance of AOB Nitrosospira. Besides, AOB Nitrosospira was more tolerant to the compound addition of both than single application.

Arbuscular mycorrhizal fungi reduce potassium, cadmium and ammonium losses but increases nitrate loss under high intensity leaching events

BACKGROUND

Nutrients and heavy metals can be lost from soils via leaching, and arbuscular mycorrhizal fungi (AMF) can influence these events. Soil column experiments were carried out to examine whether leaching intensity and AMF can alter nutrient and Cd uptake in white clover plants and the extent of their losses through leaching.

RESULTS

The presence of AMF significantly increased shoot and total biomass, as well as increased N, P, Cu and Zn uptake independent of water amount applied; while root P and Cu uptakes were promoted by AMF at any water amount treatments. Higher water amounts led to reductions in total N, K and Zn uptake for AMF-colonized plants in comparison to moderate water amount treatments. In the absence of AMF, white clover at low water amount treatment exhibited maximal root Cd uptake. At high water amount treatments, the presence of AMF significantly decreased leachate volumes and the amount of leached NH₄⁺, K and Cd while AMF significantly increased the amounts of leached NO₃^-.

CONCLUSIONS

Overall we found that AMF-colonized white clover plants reduced NH₄⁺, K and Cd loss from soils but increased the risk of NO₃^- loss under high intensity leaching conditions.

Changes in rhizobacterial community mediating atrazine dissipation by arbuscular mycorrhiza

Although it was well known that arbuscular mycorrhizal fungus (AMF) inoculation significantly increased atrazine dissipation in the soil, the effect of AMF on bacterial community, especially potential atrazine-degrading bacteria mediating atrazine dissipation has been overlooked. In the present study, there were four different treatments: Funnelliformis mosseae inoculation with or without atrazine; and non-AMF inoculation with or without atrazine. F. mosseae significantly increased atrazine dissipation rate from 28.7% to 53.3%. Then 16S rRNA gene sequencing results indicated that bacteria community differed significantly by F. mosseae inoculation and atrazine addition. The Shannon index decreased significantly with AMF and atrazine at phylum and family level, and significant inhibition of atrazine on evenness was also observed. LEFSe analysis revealed that Terrimonas and Arthrobacter were significantly associated with F. mosseae, as well as unidentified_Nitrospiraceae associated with atrazine addition. There are several bacterial taxa associated with both F. mosseae inoculation and atrazine addition. Totally, twelve atrazine-degrading bacterial genera (>0.10%) were identified. When atrazine was added, the abundance of Arthrobacter, Burkholderia, Mycobacterium and Streptomyces increased in F. mosseae inoculation treatment, but Nocardioides, Pseudomonas, Bradyrhizobium, Rhizobium, Rhodobacter, Methylobacterium, Bosea and Shinella decreased. In the presence of atrazine, activities of dehydrogenase, urease, acid and alkaline phosphatase in F. mosseae inoculation treatment were significantly higher than those in non-inoculation. However, there was no significant relationship between bacterial community and any soil enzyme activity in four treatments. Our findings reveal the potential relationship between soil bacterial community and AMF inoculation during atrazine dissipation.

The effects of tetracycline concentrations on tetracycline resistance genes and their bacterial hosts in the gut passages of earthworms (Eisenia fetida) feeding on domestic sludge

Vermi-composting is considered to be a feasible method for reducing tetracycline resistance genes (TRGs) in the sludge. Nevertheless, the way different gut passages of earthworm might affect the fates of TRGs and whether this process is affected by tetracycline (TC) concentrations need to be further investigated. In this study, we examined the effects of TC concentrations on changes in TRGs and bacterial communities in gut passages of earthworm were determined by using quantitative PCR and Illumina high-throughput sequencing. TRGs and intI1 were mainly reduced in the hindgut under the TC concentrations ranging from 0 to 25 mg/kg, while they were enriched under higher TC stress exposure. Consequently, we suggest the TC limitation of 25 mg/kg in the domestic sludge (DS) for vermi-composting. Although the predominant genera were TC sensitive under TC stress, many bacterial hosts harboring multiple TRGs (especially those in the hindgut) should be paid further attention to. In the foregut, five genera with abundant tetracycline-resistant bacteria (TRB) were specialized taxa. Among these genera, Unclassified_Solirubrobacterales and Pirellulaceae were probably related to the digestion processes. Other unclassified taxa related to the TRGs were probably derived from the DS. Five genera with abundant TRB were shared in the gut passages, and three specialized genera in the hindgut. These genera could spread TRGs and intI1 to the environment. These results suggest that vermi-composting is a feasible approach for TRG control in the DS containing TC concentration that does not exceed 25 mg/kg. Fates of TRGs and intI1 widely differ in the gut passages, showing inevitable connections with bacterial communities.

An arbuscular mycorrhizal fungus ameliorates plant growth and hormones after moderate root damage due to simulated coal mining subsidence: a microcosm study

Arbuscular mycorrhizal fungi (AMF) are obligate plant root symbionts delivering a range of benefits to the host plant such as improved nutrient acquisition and resistance to pathogens and abiotic stress. However, whether they can enhance the function of plant root systems damaged due to subsidence caused by excessive coal mining has not been well explored. In the present study, we investigated the effects of AMF using Funneliformis mosseae (FM) as the test fungus on maize (Zea mays L.) growth and hormone levels under different levels of root damage stress by simulating mining subsidence. The results show that plants treated with FM had more shoots, roots, mycorrhizal colonization and higher hyphal density than those without FM under the same simulated mining-induced subsidence conditions. In addition, plants treated with FM also possessed higher N, P, K, Ca, and Mg contents in the shoots and the roots and higher indole-3-acetic acid, gibberellin (GA), and cytokinin (CTK) contents in the roots, indicating that the mycorrhizal association promoted plant biomass and nutrient uptake. FM treatment was no longer beneficial when root damage due to mining-induced subsidence affected more than half of the roots. Soil SOC, AK, and TG were identified as key factors affecting GA, CTK, IAA, and ABA, and AMF can alter plant hormones directly via the hyphae and indirectly by altering soil physicochemical properties under root damage stress. Overall, our results provide baseline data for assessing the biological reclamation effects of AMF on coal mining-induced subsidence.

Effects of different fertilizers on residues of oxytetracycline and microbial activity in soil

Oxytetracycline (OTC), a type of tetracycline, was used widely as feeding additive to promote animal growth in breeding industry in the world. Its residue has been found in soils. Based on potted maize experiments, the influences of OTC on soil enzyme activity, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and soil fertility were investigated during the growth stages of maize receiving different fertilizers (spent mushroom substrate, worm manure, and biochar, among others, with single applications and combined applications with their cooperating microbial inoculants). The results showed that OTC negatively affected the soil enzyme activity, MBC, MBN, and cation exchange capacity (CEC). Enzyme activity, MBC, and MBN were more sensitive to OTC than soil fertility. The significant negative correlations were found between OTC concentrations and catalase, MBC, and CEC (p < 0.05). This indicated that the effects of OTC on soil can be alleviated by different fertilizers, and the effects of T6 (microbial inoculants), T7 (microbial inoculants + worm manure), T8 (microbial inoculants + SMS), and T9 (microbial inoculants + biochar) were the best among those of all treatments. During the mature stage of maize, the content of OTC in the soil of T7 was the lowest compared with other treatments. The results provide a good basis for the development of methods to remediate OTC-contaminated soils.

Insight Into the Variation of Bacterial Structure in Atrazine-Contaminated Soil Regulating by Potential Phytoremediator: Pennisetum americanum (L.) K. Schum

Although plants of the genus Pennisetum can accelerate the removal of atrazine from its rhizosphere, the roles played by this plant in adjusting the soil environment and soil microorganism properties that might contribute to pollutant removal are incompletely understood. We selected Pennisetum americanum (L.) K. Schum (P. americanum) as the test plant and investigated the interaction between P. americanum and atrazine-contaminated soil, focusing on the adjustment of the soil biochemical properties as well as bacterial functional and community diversity in the rhizosphere using Biolog EcoPlates and high-throughput sequencing of the 16S rRNA gene. The results demonstrate that the rhizosphere soil of P. americanum exhibited higher catalase activity, urease activity and water soluble organic carbon (WSOC) content, as well as a suitable pH for microorganisms after a 28-day incubation. The bacterial functional diversity indices (Shannon and McIntosh) for rhizosphere soil were 3.17 ± 0.04 and 6.43 ± 0.86 respectively, while these indices for non-rhizosphere soil were 2.95 ± 0.06 and 3.98 ± 0.27. Thus, bacteria in the P. americanum rhizosphere exhibited better carbon substrate utilization than non-rhizosphere bacteria. Though atrazine decreased the richness of the soil bacterial community, rhizosphere soil had higher bacterial community traits. For example, the Shannon diversity indices for rhizosphere and non-rhizosphere soil were 5.821 and 5.670 respectively. Meanwhile, some bacteria, such as those of the genera Paenibacillus, Rhizobium, Sphingobium, and Mycoplana, which facilitate soil nutrient cycling or organic pollutants degradation, were only found in rhizosphere soil after a 28-day remediation. Moreover, redundancy analysis suggests that the soil biochemical properties that were adjusted by the test plant exhibited correlations with the bacterial community composition and functional diversity. These results suggest that the soil environment and bacterial properties could be adjusted by P. americanum during phytoremediation of atrazine-contaminated soil.