The emergence of clinically relevant β-lactam-resistant bacteria poses a serious threat to human health and presents a major challenge for medical treatment. How opportunistic pathogenic bacteria acquire antibiotic resistance and the prevalence of antibiotic-resistant opportunistic pathogenic bacteria in the environment are still unclear. In this study, we further confirmed that the selective pressure of heavy metals contributes to the increase in ampicillin-resistant opportunistic pathogens in the Xiangjiang River. Four ampicillin-resistant opportunistic pathogenic bacteria (Pseudomonas monteilii, Aeromonas hydrophila, Acinetobacter baumannii, and Staphylococcus epidermidis) were isolated on Luria-Bertani (LB) agar plates and identified by 16S rRNA sequencing. The abundance of these opportunistic pathogenic bacteria significantly increased in the sites downstream of the Xiangjiang River that were heavily influenced by metal mining activities. A microcosm experiment showed that the abundance of β-lactam resistance genes carried by opportunistic pathogenic bacteria in the heavy metal (Cu²⁺ and Zn²⁺) treatment group was 2–10 times higher than that in the control. Moreover, heavy metals (Cu²⁺ and Zn²⁺) significantly increased the horizontal transfer of plasmids in pathogenic bacteria. Of particular interest is that heavy metals facilitated the horizontal transfer of conjugative plasmids, which may lead to the prevalence of multidrug-resistant pathogenic bacteria in the Xiangjiang River.

Studies in the literature concern the toxicity of nanoparticles either in a Petri dish or in agar media-based tests. Therefore, for environmental relevance, individual and binary mixtures of metal oxide nanoparticles (M-NPs) cadmium oxide (CdO-NP) and copper oxide (CuO-NP) were tested in this study for their effect on Vigna radiata in soil with and without the addition of sawdust. Seed germination was 67% in 100 mg CuO-NP in soil without sawdust. Seeds failed to germinate in 100 mg CdO +100 mg CuO-NPs in soil without the addition of sawdust and germination was 83% at the same concentration in soil with sawdust. In sawdust added to soil, when compared with control (soil without M-NPs), the maximum reduction in shoot (82%) and root (80%) length and wet (61%) and dry (54%) weight of plant was recorded in CdO-NP treated soil. Similarly, compared with control (soil without sawdust and M-NPs), the percent reduction in shoot (61%) and root (70%) length and wet (44%) and dry (48%) weight was highest in CdO-NP treated soil not supplemented with sawdust. In a binary mixture test (CdO-NP + CuO-NP), the addition of sawdust promoted the above plant growth parameters compared with individual CdO-NP and CuO-NP tests. Cadmium (511 mg kg⁻¹ for individual and 303 mg kg⁻¹ for binary mixture tests) and Cu (953 mg kg⁻¹ for individual and 2954 mg kg⁻¹ for binary mixture tests) accumulation was higher in plants grown in soil without sawdust. The beneficial effect of sawdust addition was observed in seed germination, plant growth, and metal accumulation. With or without sawdust, the binary mixture of CdO and CuO was antagonistic. These results indicate that sawdust can prevent M-NP-induced toxicity and reduce metal accumulation in plant tissues.

The removal of antibiotics has attracted much attention due to their extremely high adverse impacts on the environment. However, the potential risks of degradation intermediates are seldom reported. In this work, the influence of different factors on the electro-catalytic degradation efficiency of tetracycline hydrochloride (TCH) by the prepared carbon nanotubes/agarose/indium tin oxide (CNTs/AG/ITO) electrode was investigated. Under optimal conditions (10 wt% CNTs dosage, pH = 7), the maximum degradation efficiency for TCH (10 mg L⁻¹) reached up to 96% within 30 min treatment with 4 V potential. Superoxide anions (•O₂⁻) played an important role in the electro-catalytic degradation. Totally 10 degradation intermediates were identified using HPLC-MS/MS, and the degradation pathway was proposed. Toxicities of the parent antibiotic and the identified intermediates were calculated using the ECOSAR (Ecological Structure Activity Relationship) program in EPISuite, and results showed that more toxic intermediates were generated. The maximal chronic toxicity for green algae of the intermediate increased 1439.92 times. Furthermore, antimicrobial activity was further verified by disk agar biocidal tests with Escherichia coli ATCC25922 and higher biotoxicity intermediates compared with parent compounds were confirmed to be formed. Therefore, more attention should be paid on the potential risk of degradation intermediates in the treatment of wastewater containing antibiotics.

The probabilistic ecological risk assessment using terrestrial toxicity data has been mainly based on microfauna or mesofauna. Soil algae, which are food source for microfauna and mesofauna, may be alternatively used for assessing soil toxicity. However, there are no internationally recommended guidelines for soil algal bioassays, and the collection of algae from the test soils has some limitations. In this study, we suggested the paper-disc method as an easy-to-use alternative. This method has been widely used for testing the antibacterial toxicity of various chemicals in agar media by measuring the diameter of the inhibition zone around the disc. We adapted the paper-disc method for screening the toxicity of copper (Cu) and nickel (Ni) to the soil alga Chlorococcum infusionum using various evaluation endpoints, such as growth zone, chlorophyll fluorescence, and photosynthetic activity. Chlorophyll fluorescence and photosynthetic activity decreased with the increasing concentrations of Cu+2 or Ni+2 contaminated soils. Algal growth zone was analyzed visually and showed similar results to those of chlorophyll fluorescence. The direct ethanol extraction method and indirect culture medium extraction method were similarly effective; however, the former was easier to perform, while the latter might facilitate the analysis of additional endpoints in future studies. Overall, the results suggested that the paper-disc method was not only a user-friendly assay for screening soil toxicity, but also effective due to its association with indirect soil quality indicators.

The environment of a large-scale vegetable production area can be exposed to antibiotic residues and antibiotic-resistant bacteria (ARB) via animal manure and irrigation with contaminated water, which can facilitate the dissemination of ARB. However, the occurrence of ARB in plantation areas and their dissemination in this environment remain largely unexplored. In total, 382 samples including those from vegetable (n = 106), soil (n = 87), well water (n = 24), river water (n = 20), river sediments (n = 20), farmer feces (n = 58) and farmer hands (n = 67) were collected in 2019 from a large-scale cultivation area in Shandong, China. Selective agar plates were used to screen for carbapenem-resistant Enterobacteriaceae (CRE) and whole-genome sequencing and Southern blotting were used to characterise isolates and mobile genetic elements carrying carbapenem resistance determinants. A total of nine NDM-5-producing isolates of Escherichia coli, Klebsiella pneumoniae, and Citrobacter spp. were identified from environmental sources and human feces, all of which were multidrug-resistant. Single nucleotide polymorphism analysis suggested clonal transmission of carbapenem-resistant Citrobacter sedlakii within greenhouse soils in the area. Eight of the isolates carried closely related or identical IncX3 plasmids carrying blaNDM₋₅, which were shown to be conjugative via filter mating experiments, indicating the highly transmissible nature of this genetic element. Isolates of E. coli and Citrobacter freundii were detected in the feces of local farm workers and contained similar IncX3 plasmids with blaNDM₋₅ environmental isolates, suggesting a potential risk of CRE transfer from the work environment to the farm workers. Thus, further research is required to investigate the potential health risks associated with environmental exposure to CRE in vegetable cultivation areas.

Since the introduction of standardized nematode toxicity assays by the American Society for Testing and Materials (ASTM) and International Organization for Standardization (ISO), many studies have reported their use. Given that the currently used standardized nematode toxicity assays have certain limitations, in this study, we examined the use of a novel nematode offspring counting assay for evaluating soil ecotoxicity based on a previous soil-agar isolation method used to recover live adult nematodes. In this new assay, adult Caenorhabditis elegans were exposed to soil using a standardized toxicity assay procedure, and the resulting offspring in test soils attracted by a microbial food source in agar plates were counted. This method differs from previously used assays in terms of its endpoint, namely, the number of nematode offspring. The applicability of the bioassay was demonstrated using metal-spiked soils, which revealed metal concentration-dependent responses, and with 36 field soil samples characterized by different physicochemical properties and containing various metals. Principal component analysis revealed that texture fraction (clay, sand, and silt) and electrical conductivity values were the main factors influencing the nematode offspring counting assay, and these findings warrant further investigation. The nematode offspring counting assay is a rapid and simple process that can provide multi-directional toxicity assessment when used in conjunction with other standard methods.

Fate and toxicity of manufactured nanoparticles (NPs) in the living organisms and the environment are highly related to their transformation. In the present study, the effect of phosphate on the phytotoxicity and transformation of CeO2 NPs was investigated in an agar medium using head lettuce plants that are sensitive to Ce³⁺ ions. Plants were treated by CeO2 NPs with or without phosphate for 10 days. Results suggest that the treatments of P deficiency (P(-)) and CeO2 NPs (P(+)&Ce) could separately induce significant inhibition on the growth of lettuce seedlings and cause oxidative stress, but the inhibition was the most serious when the two conditions were combined (P(-)&Ce). In the absence of phosphate, more CeO2 NPs were transformed to Ce(III) in the roots and more Ce³⁺ ions were translocated to the shoots, which induced higher toxicity to head lettuce. Phosphates could alleviate the phytotoxic effect of CeO2 NPs through the precipitation of dissociated Ce³⁺ ions. Considering the wide existence of phosphate in the environment, phosphate-related transformation may be a critical factor in evaluating the toxicity and fate of many other metal-based NPs.

Food quality affects the food consumption rate, flux through the gut, and exposure to contaminants in animals. This study evaluated the effects of food quality on cadmium exposure in the soil collembolan Folsomia candida. Animals were exposed to constant concentrations of cadmium for 38 h via artificial food consisting of an agar medium with various concentrations of sugar (glucose), total nutrients (baker's yeast), or fungal odour (1-octen-3-ol). The expression of the gene encoding a deduced metallothionein-like motif containing protein was used as a biomarker of cadmium exposure. Glucose concentrations of 2% or higher reduced the expression levels of the biomarker. Within the range of 0.1–8% yeast, medium concentrations led to higher biomarker levels. At high concentrations of 1-octen-3-ol (2000 mg/l), feeding and the biomarker response were reduced. These results suggest that even at equivalent cadmium concentrations, food quality affects cadmium exposure by altering food consumption rates.

Contamination of heavy metals is a serious threat, which causes threats to the environment. Our study aimed to determine the role of endophytic bacteria in Cd phytoremediation and heavy metal ATPase gene expression. Cadmium (Cd) resistant endophytic bacteria were isolated from Solanum nigrum on LB agar plates, contaminated with 0–30 mg/L Cd. The phosphate solubilization and indole-3-acetic acid (IAA) production of endophytes were estimated by growing them on Pikovskaya agar medium and GC-MS analysis, respectively. An experiment in a pot was performed to evaluate the effects of bacteria on rice plants contaminated with 5–25 mg/L of Cd. Expression of Cd response genes was quantified through qRT–PCR and Cd translocation from one part to another part of the plant was measured through the ICP. BLAST alignment of 16 S-rDNA gene sequences confirmed the bacterial isolates as Serratia sp. AI001 and Klebsiella sp. Strain AI002. Both strains tolerated Cd up to 25 mg/L and produced 27–30 μg/mL of IAA. Inoculation of AI001 and AI002 improved plant growth dynamics (i.e., plant length, biomass, chlorophyll contents), relieved electrolyte leakage, and improved reduced glutathione significantly (P < 0.05). The inoculation of AI001 and AI002 significantly (P < 0.05) induced the expression of heavy metal ATPase genes ie., “HMA2, HMA3, and HMA4” and Cd translocation compared to uninoculated plants. Both AI001 and AI002 exhibited very prominent plant-growth-promoting and Cd phytoremediation properties. The results revealed that isolates also contributed a lot to the expression of rice plant heavy metal ATPase genes and in the Cd translocation in the plant.

Lead is a dangerous pollutant that accumulates in plant tissues and causes serious damage to plant cell macromolecules. However, plants have evolved numerous tolerance mechanisms, including ectomycorrhizae, to maintain cellular Pb²⁺ at the lowest possible level. When those mechanisms are successful, Pb-exposed plants should exhibit no negative phenotypic changes. However, actual molecular-level plant adjustments at Pb concentrations below the toxicity threshold are largely unknown, similar to the molecular effects of protective ectomycorrhizal root colonization. In this study, we (1) determined the molecular adjustments in plants exposed to Pb but without visible Pb stress symptoms and (2) examined ectomycorrhizal root colonization (the role of fungal biofilters) with respect to molecular-level Pb perception by plant root cells. Biochemical, microscopic, proteomic and metabolomic studies were performed to determine the molecular status of Populus × canescens microcuttings grown in agar medium enriched with 0.75 mM Pb(NO₃)₂. Noninoculated and inoculated with Paxillus involutus poplars were analyzed in two independent comparisons of the corresponding control and Pb treatments. After six weeks of growth, Pb caused no negative phenotypic effects. No Pb-exposed poplar showed impaired growth or decreased leaf pigmentation. Proteomic signals of intensified Pb sequestration in the plant cell wall and vacuoles, cytoskeleton modifications, H⁺-ATPase-14-3-3 interactions, and stabilization of protein turnover in chronically Pb-exposed plants co-occurred with high metabolomic stability. There were no differentially abundant root primary metabolites; only a few differentially abundant root secondary metabolites and no Pb-triggered ROS burst were observed. Our results strongly suggest that proteome adjustments targeting Pb sequestration and ROS scavenging, which are considerably similar but less intensive in ectomycorrhizal poplars than in control poplars due to the P. involutus biofilter (as confirmed in a mineral study), were responsible for the metabolomic and phenotypic stability of poplars exposed to chronic mild Pb stress.