Exploring microbial community structure and biological function in manured soil during ten repeated treatments with chlortetracycline and ciprofloxacin

Ecotoxicity of five veterinary antibiotics on indicator organisms and water and soil communities

This study explores the environmental effects of five common veterinary antibiotics widely detected in the environment, (chlortetracycline,CTC; oxytetracycline,OTC; florfenicol,FF; neomycin, NMC; and sulfadiazine, SDZ) on four bioindicators: Daphnia magna, Vibrio fischeri, Eisenia fetida, and Allium cepa, representing aquatic and soil environments. Additionally, microbial communities characterized through 16 S rRNA gene sequencing from a river and natural soil were exposed to the antibiotics to assess changes in population growth and metabolic profiles using Biolog EcoPlates™. Tetracyclines are harmful to Vibrio fisheri (LC50 ranges of 15-25 µg/mL), and the other three antibiotics seem to only affect D. magna, especially, SDZ. None of the antibiotics produced mortality in E. fetida at concentrations below 1000 mg/kg. NMC and CTC had the highest phytotoxicities in A. cepa (LC50 = 97-174 µg/mL, respectively). Antibiotics significantly reduced bacterial metabolism at 0.1-10 µg/mL. From the highest to the lowest toxicity on aquatic communities: OTC > FF > SDZ ≈ CTC > NMC and on edaphic communities: CTC ≈ OTC > FF > SDZ > NMC. In river communities, OTC and FF caused substantial decreases in bacterial metabolism at low concentrations (0.1 µg/mL), impacting carbohydrates, amino acids (OTC), and polymers (FF). At 10 µg/mL and above, OTC, CTC, and FF significantly decreased metabolizing all tested metabolites. In soil communities, a more pronounced decrease in metabolizing ability, detectable at 0.1 µg/mL, particularly affected amines/amides and carboxylic and ketonic acids (p < 0.05). These new ecotoxicity findings underscore that the concentrations of these antibiotics in the environment can significantly impact both aquatic and terrestrial ecosystems.

Root-associated bacteria strengthen their community stability against disturbance of antibiotics on structure and functions

Antibiotics affect bacterial community structure and functions in soil. However, the response and adaptation of root-associated bacterial communities to antibiotic stress remains poorly understood. Here, rhizobox experiments were conducted with maize (Zea mays L.) upon exposure to antibiotics ciprofloxacin or tetracycline. High-throughput sequencing analysis of bacterial community and quantitative PCR analysis of nitrogen cycling genes show that ciprofloxacin and tetracycline significantly shift bacterial community structure in bulk soil, whereas plant host may mitigate the disturbances of antibiotics on bacterial communities in root-associated niches (i.e., rhizosphere and rhizoplane) through the community stabilization. Deterministic assembly, microbial interaction, and keystone species (e.g., Rhizobium and Massilia) of root-associated bacterial communities benefit the community stability compared with those in bulk soil. Meanwhile, the rhizosphere increases antibiotic dissipation, potentially reducing the impacts of antibiotics on root-associated bacterial communities. Furthermore, rhizospheric effects deriving from root exudates alleviate the impacts of antibiotics on the nitrogen cycle (i.e., nitrification, organic nitrogen conversion and denitrification) as confirmed by functional gene quantification, which is largely attributed to the bacterial community stability in rhizosphere. The present study enhances the understanding on the response and adaptation of root-associated bacterial community to antibiotic pollution.

Effects of repeated afidopyropen treatment on the structure and function of the soil microbial community

Chemical insecticides are the most effective pest control agents. Afidopyropen is a novel insecticide used against sap-sucking insects, such as aphids. However, the effects of repeated afidopyropen application on the structure and function of soil microorganisms remain unknown. In this study, the changes in the enzyme activities, community structure and function, and relative abundance of antibiotic resistance ontology (ARO) of soil microorganisms were investigated during three repeated afidopyropen applications under laboratory conditions at the maximum recommended dosage (M1) and 10 times the M1 (M10). The neutral phosphatase (NPA) and catalase (CAT) activities in the soil were significantly suppressed after afidopyropen treatment. The Simpson diversity index (1/D) and Shannon-Wiener diversity index (H) also decreased in both the M1 and M10 afidopyropen-treated soils, indicating a remarkable decrease in soil microorganism diversity. The average well color development (AWCD) first increased and subsequently recovered to normal levels after the third application of the insecticide, suggesting that afidopyropen application could increase the metabolic activity of soil microorganisms. Metagenomic analysis showed that repeated afidopyropen application in both the M1 and M10 treatment groups altered the community structure of soil microorganisms, albeit in different ways. Furthermore, repeated afidopyropen application significantly increased the relative ARO abundance, especially in the M10 treatment, with the most dominant AROs being adeF, baeS, and IND-6. These findings reveal the effects of excessive afidopyropen application on soil microorganisms and lay an important foundation for the comprehensive evaluation of the impact of this insecticide on the environment.

Key taxa and mobilome-mediated responses co-reshape the soil antibiotic resistome under dazomet fumigation stress

Agrochemicals are emergingly being implicated in the widespread dissemination of antibiotic resistance genes (ARGs) in agroecosystems. However, minimal research exists on the disturbance of fumigant on soil ARGs. Focusing on a typical fumigant dazomet in a simulated soil microcosm, we characterized the dazomet-triggered timely response and longstanding dynamic of ARGs at one-fold and two-fold field recommended doses using metagenome and quantitative PCR. Dazomet treatments reduced 13.17%-69.98% of absolute abundance of 16S rRNA gene and targeted ARGs, but, awfully, boosted diversity and relative abundance of ARGs up to 1.33-1.60 and 1.62-1.90 folds, respectively. Approximately 77.28% of changes in relative abundance of ARGs could be explained by bacterial community and mobile genetic elements (MGEs). Mechanistically, primary hosts of ARGs shifted from Proteobacteria (control) to Firmicutes and Actinobacteria (treatments) accompanied with corresponding changes in their abundance by combining community analysis, host tracking analysis and antibiotic resistant bacteria assay. Meanwhile, dazomet exposure significantly increased the incidence of MGEs and stimulated the conjugation of antibiotic-resistant plasmid. In addition, absolute abundance of targeted ARGs gradually recovered in the post-fumigation stage. Collectively, our results elucidate the dazomet-triggered emergence and spread of soil ARGs and highlight the importance of navigating toward rational use of fumigant in agricultural fields.

Repeated exposure to fungicide tebuconazole alters the degradation characteristics, soil microbial community and functional profiles

Tebuconazole is a broad-spectrum triazole fungicide that has been extensively applied in agriculture, but its toxicity on soil ecology remains unknown after repeated introduction to soil. This study investigated the degradation of tebuconazole and the changes in soil microbial community composition and functional diversity as well as network complexity in soil repeatedly treated with tebuconazole. Tebuconazole degraded slowly as the degradation half-life initially increased and then decreased during the four repeated treatments. High concentration of tebuconazole treatment significantly delayed the degradation of tebuconazole. The soil microbial functional diversity in tebuconazole-treated soils showed an inhibition-recovery-stimulation trend with increasing treatment frequency, which was related to the increased degradation rates of tebuconazole. Tebuconazole significantly decreased soil microbial biomass and bacterial community diversity, and this decreasing trend became more pronounced with increasing treatment frequency and concentration. Moreover, tebuconazole significantly decreased soil bacterial community network complexity, particularly at high concentration of tebuconazole treatment. Notably, four bacterial genera, Methylobacterium, Burkholderia, Hyphomicrobium, and Dermacoccus, were identified as the potential tebuconazole-degrading bacteria, with the relative abundances in the tebuconazole treatment significantly increasing by 42.1-34687.1% compared to the control. High concentration of tebuconazole treatment delayed increases in the relative abundances of Methylobacterium but promoted those of Burkholderia, Hyphomicrobium and Dermacoccus. Additionally, repeated tebuconazole treatments improved only four metabolic pathways, cell motility, membrane transport, environmental information processing, and xenobiotics biodegradation and metabolism, which were associated with the degradation of tebuconazole. The above results indicated that repeated tebuconazole treatments resulted in the significant accumulation of residues and long-term negative effects on soil ecology, and also emphasized the potential roles of dominant indigenous microbial bacteria in the degradation of tebuconazole.

Bioponic system for nitrogen and phosphorus recovery from chicken manure: Evaluation of manure loading and microbial communities

Bioponics integrates the biological treatment of nutrient-rich waste streams with hydroponics. However, there are several challenges of bioponics, especially nutrient availability and qualities, which affect plant yield. In this study, chicken manure based-nutrient film technique bioponics was examined at manure loadings of 200, 300, and 400 g dry wt. per bioponic system (total of 18 plants). Bioponics effectively released nitrogen and phosphorus (total ammonia nitrogen of 5.8-8.0 mgN/L, nitrate of 7.0-11.2 mgN/L, and phosphate of 48.7-74.2 mgP/L) for efficient growth of lettuce (Lactuca sativa; total yield of 1208-2030 g wet wt. per 18 plants). Nitrogen and phosphorus use efficiencies were 35.1-41.8% and 6.8-8.0%, respectively, and were comparable to aquaponics. Next-generation sequencing was used to examine the microbial communities in digested chicken manure and plant roots in bioponics. Results showed that several microbial genera were associated with organic degradation (e.g., Nocardiopsis spp., Cellvibrio spp.), nitrification (Nitrospira spp.), phosphorus solubilization, and plant growth promotion (e.g., WD2101_soil_group, and Bacillus spp.). Nocardiopsis spp., Romboutsia spp. and Saccharomonospora spp. were found at high abundances and a high degree of co-occurrences among the microbiota, suggesting that the microbial organic decomposition to nitrogen and phosphorus release could be the key factors to achieve better nutrient recovery in bioponics.

Recent advances in the application of magnetic Fe3O4 nanomaterials for the removal of emerging contaminants

Emerging contaminants (ECs) are widely distributed and potentially hazardous to human health and the ecological system. However, traditional wastewater treatment techniques are not sufficient to remove ECs. Magnetic nanomaterials are made of ferromagnetic or superparamagnetic magnetic elements such as iron and nickel, which can be easily separated from the aqueous solution, making them ideal adsorbents for contaminants in water. This review focused on the synthesis approaches of magnetic Fe₃O₄ nanoparticles (MFNs), as well as surface modification in order to improve their stability and functional diversity. Also, a detailed summary on the state-of-art application of magnetic nanomaterials on the removal of ECs was addressed. Additionally, challenges and future prospective of applying magnetic nanomaterials into real-world cases were discussed, in which the green and simple synthesis and evaluation of the toxic effects of MFNs are still of great challenge. This work summarizes the recent progress of using magnetic nanomaterials as promising and powerful tools in the treatment of ECs-contaminated water, benefiting researchers interested in nanomaterials and environmental studies.

Dissipation of chlorothalonil in the presence of chlortetracycline and ciprofloxacin and their combined effects on soil enzyme activity

The long-term application of substantial amounts of fungicides and antibiotic-polluted organic manure (OM) in greenhouse has caused the co-existence of fungicides and antibiotics in soils. However, little is known about the effects of antibiotics on the persistence of fungicides in soils or their combined effects on soil enzyme activity. In this study, fungicide chlorothalonil (CTL) alone and in combination with antibiotic chlortetracycline (CTC) or ciprofloxacin (CIP) were repeatedly added to OM-amended soil to investigate the changes in the residual characteristics of CTL and in soil dehydrogenase and urease activity. The results showed that CTL rapidly dissipated in soils with the corresponding half-lives of 0.9-3.2, which initially increased, then decreased and finally stabilized with an increased treatment frequency. The dissipation of CTL was inhibited by CTC and CIP during the first several treatments. The soil dehydrogenase and urease activity in CTL-treated soils was inhibited during the first six treatments and then recovered afterwards. Compared with the OM-amended soil+CTL treatment, the OM-amended soil+CTL+CTC and OM-amended soil+CTL+CIP treatments had stronger inhibitory effects on soil enzyme activity during the first six repeated treatments but exhibited slight stimulating effects afterwards. Therefore, the results obtained in this study suggested that the long-term co-existence of CTL, CTC, and CIP altered the dissipation characteristics of CTL in soil and affected the soil enzyme activity levels. The prudent application of large and frequent of fungicides and OM-containing antibiotic residues in greenhouses should therefore be carefully considered in order to reduce the long-term combined pollution in soils.

The bacterial microbiota in florfenicol contaminated soils: The antibiotic resistome and the nitrogen cycle

Soil antibiotic resistome and the nitrogen cycle are affected by florfenicol addition to manured soils but their interactions have not been fully described. In the present study, antibiotic resistance genes (ARGs) and nitrogen cycle genes possessed by soil bacteria were characterized using real-time fluorescence quantification PCR (qPCR) and metagenomic sequencing in a short-term (30 d) soil model experiment. Florfenicol significantly changed in the abundance of genes conferring resistance to aminoglycosides, β-lactams, tetracyclines and macrolides. And the abundance of Sphingomonadaceae, the protein metabolic and nitrogen metabolic functions, as well as NO reductase, nitrate reductase, nitrite reductase and N₂O reductase can also be affected by florfenicol. In this way, ARG types of genes conferring resistance to aminoglycosides, β-lactamases, tetracyclines, colistin, fosfomycin, phenicols and trimethoprim were closely associated with multiple nitrogen cycle genes. Actinobacteria, Chlorobi, Firmicutes, Gemmatimonadetes, Nitrospirae, Proteobacteria and Verrucomicrobia played an important role in spreading of ARGs. Moreover, soil physicochemical properties were important factors affecting the distribution of soil flora. This study provides a theoretical basis for further exploration of the transmission regularity and interference mechanism of ARGs in soil bacteria responsible for nitrogen cycle.

Azoxystrobin dissipation and its effect on soil microbial community structure and function in the presence of chlorothalonil, chlortetracycline and ciprofloxacin

The residual characteristics and the adsorption-desorption behaviors of azoxystrobin (AZO) as well as the soil ecological effects in the individual repeated treatments of AZO and its combination with chlorothalonil (CTL), chlortetracycline (CTC) and ciprofloxacin (CIP) were systematically studied in organic manure (OM)-amended soil under laboratory conditions. The presence of CTL, CTC, and CIP, both individually and combined, decreased the sorption affinity of AZO with the Freundlich adsorption and desorption coefficient decreasing by 0.3-24.2%, and CTC and CIP exhibited greater adverse effects than CTL. AZO dissipated slowly and the residues significantly accumulated during ten repeated treatments. The dissipation of AZO was inhibited to different degrees in the combined treatments. Biolog analysis revealed that the soil microbial functional diversity in the OM-soil + AZO and OM-soil + AZO + CTL treatments was higher than that in the OM-soil treatment during the former three repeated treatments, but which was inhibited during the latter seven repeated treatments. The soil microbial functional diversity in the OM-soil + AZO + CTC, OM-soil + AZO + CIP and OM-soil + AZO + CTL + CTC + CIP treatments was inhibited during the ten repeated treatments compared with OM-soil treatment. Metagenomic results showed that all repeated treatments significantly increased the relative abundance of Actinobacteria, but significantly decreased that of Proteobacteria and Firmicutes during the ten repeated treatments. Furthermore, the relative abundance of soil dominant bacterial genera Rhodococcus, Mycobacterium and Arthrobacter in all the repeated treatments significantly increased by 1.5-1283.9% compared with the OM-soil treatment. It is concluded that coexistence of CTL, CTC and CIP, both individually and combined, with AZO can inhibit the dissipation of AZO, reduce the adsorption affinity of AZO on soil, and alter the soil microbial community structure and functional diversity.

The influence of oxytetracycline on the degradation and enantioselectivity of the chiral pesticide beta-cypermethrin in soil

Pesticide residues most likely coexist with antibiotics due to the application of animal-based fertilizers in agriculture. In this study, the degradation and enantioselectivity of beta-cypermethrin in soil and chicken manure-amended soil were investigated. The effects of oxytetracycline on the soil microbial community were also estimated. The results showed that the half-life of beta-cypermethrin in the soil was 16.9 days and that the (+)-enantiomer was degraded preferentially in both pairs of enantiomers. The metabolites cis/trans-DCCA(3-(2',2'-dichlorovinyl)-2,2-dimethylcyclopropane carboxylic acid) and 3-PBA (3-Phenoxybenzoic acid) were detected. The trans-DCCA concentrations ranged from 0.094 to 0.120 mg/kg, which were higher than the concentrations of cis-DCCA (0.091-0.120 mg/kg) and 3-PBA (0.022-0.061 mg/kg). In the presence of oxytetracycline, beta-cypermethrin degradation was inhibited slightly, while the enantioselectivity was not affected. Oxytetracycline increased the enrichment and persistence of the metabolites. Addition of chicken manure decreased the cis-DCCA residue levels in the soil and alleviated the effect of oxytetracycline; however, chicken manure increased the accumulation and persistence of 3-PBA. In addition, oxytetracycline perturbed the structure of the soil microbial community. The abundance of Proteobacteria increased, while the abundances of Firmicutes and Actinobacteria decreased. These changes might affect the biodegradation of beta-cypermethrin and its metabolites. Combined pollution with antibiotics should be considered for its potential impact on pesticide residues.