Reducing water use by alternate-furrow irrigation with livestock wastewater reduces antibiotic resistance gene abundance in the rhizosphere but not in the non-rhizosphere

Effects of environmentally relevant concentrations of oxytetracycline and sulfadiazine on the bacterial communities, antibiotic resistance genes, and functional genes are different between maize rhizosphere and bulk soil

Antibiotic contamination in soil has become a major concern worldwide. At present, it is not clear how two co-existed antibiotics with environmentally relevant concentrations would affect soil bacterial community structure, the abundances of antibiotic resistance genes (ARGs) and functional genes, and whether the effects of antibiotics would differ between rhizosphere and bulk soil. We conducted a greenhouse pot experiment to grow maize in a loess soil treated with oxytetracycline (OTC) or sulfadiazine (SDZ) or both at an environmentally relevant concentration (1 mg kg-1) to investigate the effects of OTC and SDZ on the rhizosphere and bulk soil bacterial communities, abundances of ARGs and carbon (C)-, nitrogen (N)-, and phosphorus (P)-cycling functional genes, and on plant growth and plant N and P nutrition. The results show that the effects of environmentally relevant concentrations of OTC and SDZ on bacterial communities and abundances of ARGs and functional genes differ between maize rhizosphere and bulk soil. The effects of two antibiotics resulted in a higher absolute abundances of accA, tet(34), tnpA-04, and sul2 in the rhizosphere soil than in the bulk soil and different bacterial community compositions and biomarkers in the rhizosphere soil and the bulk soil. However, OTC had a stronger inhibitory effect on the abundances of a few functional genes in the bulk soil than SDZ did, and their combination had no synergistic effect on plant growth, ARGs, and functional genes. The role of co-existed OTC and SDZ decreased shoot height and increased root N concentration. The results demonstrate that environmentally relevant concentrations of antibiotics shift soil microbial community structure, increase the abundances of ARGs, and reduce the abundances of functional genes. Furthermore, soil contamination with antibiotics can diminish agricultural production via phytotoxic effects on crops, and combined effects of antibiotics on plant growth and nutrient uptake should be considered.

Impacts of irrigation with treated livestock wastewater on the accumulation characteristic of ARGs in the farmland soil: a case study in Hohhot, China

Irrigation with treated livestock wastewater (TWW) is a promising strategy for reusing resources. However, TWW irrigation might introduce antibiotic resistant genes (ARGs) into the soil, posing environmental risks associated with antibiotic resistance. This study focuses on investigating the influence of irrigation amounts and duration on the fate of ARGs and identifies key factors driving their changes. The results showed that there were 13 ARGs in TWW, while only 5 ARGs were detected in irrigated soil. That is some introduced ARGs from TWW could not persistently exist in the soil. After 1-year irrigation, an increase in irrigation amount from 0.016 t/m2 to 0.048 t/m2 significantly enhanced the abundance of tetC by 29.81%, while ermB and sul2 decreased by 45.37% and 76.47%, respectively (p < 0.01). After 2-year irrigation, the abundance of tetC, ermB, ermF, dfrA1, and total ARGs significantly increased (p < 0.05) when the irrigation amount increased. The abundances of ARGs after 2-year irrigation were found to be 2.5-34.4 times higher than 1 year. Obviously, the irrigation years intensified the positive correlation between ARGs abundance and irrigation amount. TetC and ermF were the dominant genes resulting in the accumulation of ARGs. TWW irrigation increased the content of organic matter and total nitrogen in the soil, which affected microbial community structure. The changes of the potential host were the determining factors driving the ARGs abundance. Our study demonstrated that continuous TWW irrigation for 2 years led to a substantial accumulation of ARGs in soil.

Study on the effect of fluorinated solvent electrolyte on the active material and cycle performance of a commercial 21700-type battery

Different electrolyte schemes were studied on the traditional commercial 21700-type battery. The effect of different fluorinated electrolytes on the cycle performance of the battery was systematically investigated. When methyl (2,2,2-trifluoroetyl) carbonate (FEMC) was introduced, due to the low conductivity of FEMC, the polarization and internal resistance of the battery increased, which leads to the increase of constant voltage charging time, leading to the cracking of the cathode material and reduction of the cycle performance. When ethyl difluoroacetate (DFEA) was introduced, the poor chemical stability caused by its low molecular energy level led to the decomposition of the electrolyte. Thus, affecting the cycle performance of the battery. However, the introduction of fluorinated solvents can form a protective film on the surface of the cathode, which can effectively inhibit the dissolution of metal elements. The fast-charging cycle of commercial batteries is generally set at 10-80% SOC, which can effectively reduce the H2 to H3 phase transformation process, and the temperature rise caused by fast-charging can also reduce the effect of electrolytic conductivity, so that the protective effect of the fluorinated solvent on the cathode material is dominant. Therefore, the fast-charging cycle performance is improved.

Using HRMS fingerprinting to explore micropollutant contamination in soil and vegetables caused by swine wastewater irrigation

Livestock wastewater has been reused for agricultural irrigation to save water and fertilise the soil. However, micropollutants excreted by livestock animals may contaminate the soil and crops through livestock wastewater irrigation. This study employed high-resolution mass spectrometry (HRMS) to facilitate broad-scope suspect screening of soil and vegetables and identify changes in micropollutant fingerprints caused by swine wastewater irrigation. Field trials were performed to simulate the practical cultivation of small leafy vegetables. Soil and pak choi were irrigated with groundwater, a reasonable amount of swine wastewater, and excessive swine wastewater (three times the reasonable amount) and were sampled at three time points. The samples were extracted using organic solvents and analysed with a liquid chromatography-quadrupole-time-of-flight HRMS system. The molecular features were compared to over 3000 micropollutants in commercial libraries. The relative concentrations of suspect micropollutants among the irrigation groups were compared using multivariate and univariate analyses. The marker micropollutants that increased with swine wastewater irrigation were rigorously identified based on the MS/MS spectra. Fifty-three micropollutants were frequently found in the soil (n = 54) and 36 in the pak choi (n = 53). Partial least squares discriminant analysis (PLS-DA) models revealed significant differences in the micropollutant fingerprints in the soil among the three irrigation groups, but not in the pak choi. Eight micropollutants with variable importance in projection scores above 1.0 in the PLS-DA model and significantly higher relative concentrations (p < 0.05) in the soil irrigated with swine wastewater were confirmed as markers. Besides veterinary drugs and their metabolites, cinnamic acid and phenylalanine were the markers relevant to swine feed that were not previously reported. Nevertheless, accumulations of micropollutants in the soil or contamination of the pak choi due to swine wastewater irrigation were not found under the trial conditions.

Horizontal transfer of the multidrug resistance plasmid RP4 inhibits ammonia nitrogen removal dominated by ammonia-oxidizing bacteria

Antibiotic resistance genes (ARGs) have become an important public health concern. Particularly, although several ARGs have been identified in wastewater treatment plants (WWTPs), very few studies have characterized their impacts on reactor performance. Therefore, our study sought to investigate the effect of a representative conjugative transfer plasmid (RP4) encoding multidrug resistance genes on ammonia oxidation. To achieve this, we established sequencing batch reactors (SBRs) and a conjugation model with E. coli donor strains carrying the RP4 plasmid and a typical ammonia-oxidating (AOB) bacterial strain (Nitrosomonas europaea ATCC 25978) as a recipient to investigate the effect of conjugative transfer of plasmid RP4 on AOB. Our findings demonstrated that the RP4 plasmid carried by the donor strains could be transferred to AOB in the SBR and to Nitrosomonas europaea ATCC 25978. In SBR treated with donor strains carrying the RP4 plasmid, ammonia removal efficiency continuously decreased to 71%. Once the RP4 plasmid entered N. europaea ATCC 25978 in the conjugation model, ammonia removal was significantly inhibited and nitrite generation was decreased. Furthermore, the expression of several functional genes related to ammonia oxidation in AOB was suppressed following the transfer of the RP4 plasmid, including amoA, amoC, hao, nirK, and norB. In contrast, the cytL gene encoding cytochrome P460 was upregulated. These results demonstrated the ecological risk of ARGs in WWTPs, and therefore measures must be taken to avoid their transfer.

Cropping system exerts stronger influence on antibiotic resistance gene assemblages in greenhouse soils than reclaimed wastewater irrigation

The effects of reclaimed wastewater (RW) irrigation on the spread of antibiotic resistance genes (ARGs) in soil is modulated by a myriad of biotic and abiotic factors and their relative significance remains vague. We compared microbial communities, assemblages of genes associated with microbial resistance to antibiotics, biocides and metals, and insertion sequences (ISs) in soils following 16 years of irrigation with groundwater (GW), RW or alternately with GW and RW in two greenhouses with different cropping systems, using shotgun metagenome sequencing. The results showed that cropping system exerted greater influence than irrigation on the profile of ISs and resistance genes. This influence was most strongly associated with concentrations of copper, mercury and perfloxacin in the soils. There was no significant difference in soil ARG profiles between continuous RW irrigation and alternating GW and RW irrigation. Proteobacteria, Actinobacteria and Firmicutes and a limited number of ISs were closely associated with the detected ARGs. Most ARGs were found to co-occur with metal and biocide resistance genes through the mechanism of efflux pumps. These findings highlight the significance of understanding and improving crop management in mitigating the dissemination of ARGs in soils irrigated with RW.

Field aging alters biochar's effect on antibiotic resistome in manured soil

Current understanding of biochar's effect on antibiotic resistance genes (ARGs) in soil is limited, and whether the effect could change after long-term field aging remains largely unknown. In this study, we employed high-throughput quantitative PCR to assess the effect of biochar amendment on soil resistome as affected by three years of field aging. Application of fresh biochar significantly elevated the number and abundance of ARGs in the manured soil, but did not show such effect under pakchoi cultivation. The presence of aged biochar caused a marked reduction of ARGs only in the planted manured soil. Results of principal coordinate analysis and structural equation modeling indicate that biochar's effect on soil ARG profile was changed by field aging through altering soil microbial composition. These results highlight the necessity of considering aging effect of biochar during its on-farm application to mitigate soil antibiotic resistance.

Responses of Cirrhinus mrigala to second-generation fluoroquinolone (ciprofloxacin) toxicity: Assessment of antioxidants, tissue morphology, and inorganic ions

Ciprofloxacin drugs are a second-generation fluoroquinolone highly prescribed medication against various bacterial infections in human and aquaculture practices. These drugs are chemically designed to persist in the body long enough to achieve target objectives. Extensive usage has resulted in ciprofloxacin becoming a ubiquitous contaminant in the environment. Unfortunately, the ecotoxicological profiles for ciprofloxacin are scanty. This study was aimed to assess the ecotoxicity of ciprofloxacin at environmentally relevant concentrations (1 μg/L, and 1.5 μg/L) to a cultivable fish Cirrhinus mrigala. Responses of antioxidant enzymes, histological anomalies, and inorganic ion levels were studied. SOD activity in gill, liver, and kidney tissues was elevated in ciprofloxacin-exposed groups when compared with the control group. CAT activity was predominantly decreased in ciprofloxacin treated groups relative to the control group. GST activity in the ciprofloxacin treated groups was increased (except kidney tissues [Treatment I (1 μg/L)], and gill tissues fifteenth day) significantly (p < .05). The LPO level was elevated in the ciprofloxacin treatment groups throughout the study period (except Treatment II (1.5 μg/L) tenth day in kidney tissues). A series of histological anomalies were noticed in the gill, liver, and kidney tissues of the ciprofloxacin treated groups. Ciprofloxacin exposure caused a significant decrease of sodium, potassium, and chloride levels in the plasma of C. mrigala. A parallel among an imbalanced oxidative defense system, tissue structural changes, and alterations of plasma inorganic ions could be considered as a reliable biomarker for antibiotic toxicity study. This study could be a primary platform for further toxicity studies to understand the potential molecular impacts and adverse effects of ciprofloxacin on aquatic organisms.

Subsurface drip irrigation reduces cadmium accumulation of pepper (Capsicum annuum L.) plants in upland soil

Given that Cd pollution in dry land has aroused wide public concern, numerous remediation technologies has been utilized, yet there are limited cost-effective techniques that do not affect the original planting patterns. Fortunately, irrigation management can meet these requirements, while the effects of irrigation practices on Cd uptake by crops in slightly Cd-polluted upland soil remain elusive. Here, we aimed to investigate how the irrigation methods altered the Cd availability in soil, Cd accumulation in plants, microorganism population in soil, root morphology, and enzyme activities in soil and plants. We examined three irrigation treatments - surface drip irrigation (DI), subsurface drip irrigation (SDI), alternate-rows irrigation (ARI), and the control conventional furrow irrigation (CFI). The results showed that SDI remarkably reduced Cd content in roots, shoots and fruits, increased yield, and improved root growth and activity in soil of 20-40 cm compared to other treatments, though the Cd concentration in rhizosphere was not decreased significantly. The microbial population and enzyme activities in rhizosphere and enzyme activities in leaves and roots in SDI and ARI were basically higher than DI and CFI. Therefore, SDI has the prominent potential to reduce Cd uptake by crops in upland soil polluted with low Cd.

Linkage of antibiotic resistance genes, associated bacteria communities and metabolites in the wheat rhizosphere from chlorpyrifos-contaminated soil

Rhizosphere is a crucial site for the proliferation of antibiotic resistance genes (ARGs) in agricultural soil. Pesticide contamination is ubiquitous in soil, such as chlorpyrifos as one of the most commonly used pesticides. However, limited knowledge is reported about ARGs profiles changes and the driving mechanism of ARGs prevalence in rhizosphere soil after adding pesticide. In this study, irrespective of chlorpyrifos presence, the abundances of ARGs (tetM, tetO, tetQ, tetW, tetX, sul1 and sul2) and intI1 in rhizosphere soil of wheat were obviously higher than those in bulk soil. 20.0 mg·kg^-1 chlorpyrifos significantly increased the abundance of total ARGs and intI1 in bulk soil, respectively, at day 50 and 100, but not in rhizosphere soil. Rhizosphere influence on ARGs was far greater than chlorpyrifos. ARGs and intI1 abundances were higher at day 50 than ones at day 100. C/N ratio and NO₃^--N content, which were affected by rhizosphere and cultivation time, significantly explained the increased ARGs. Compared to bulk soil, rhizosphere shifted host bacteria of tetracycline resistance genes (TRGs), intI1 at genus level, and host bacteria of sul1, sul2 at phylum level. Rhizosphere simplified the linkage of ARGs, host bacteria and metabolites. Bacterial communities played important roles in the variation of ARGs and intI1, and the difference in the distribution of potential hosts between bulk and rhizosphere soil was related to metabolites abundance and composition. These results provide valuable information for understanding the linkage of ARGs, associated bacteria communities and metabolites in the wheat rhizosphere soil.

Insights into factors driving the transmission of antibiotic resistance from sludge compost-amended soil to vegetables under cadmium stress

Sludge compost is often used as a fertilizer for crops, although it might be enriched with antibiotic resistance genes (ARGs) and heavy metals that cannot be removed through composting. A robust understanding of the factors affecting the transmission of ARGs to vegetables grown in soils treated with sludge products is lacking. In this study, target ARGs in the bulk and rhizosphere soils and endophytes of shallots under heavy metal stress (i.e., Cd) were assessed, and the factors driving the transmission of ARGs were identified. Cd stress resulted in an increase in the relative abundances of target ARGs in the bulk and rhizosphere soils and endophytes. The driving factors were different in soils and plants under different degrees of Cd stress. The fungal community composition was the main driving factor of ARG variation in both bulk and rhizosphere soils. Moreover, endophytic bacteria played a crucial role in transferring ARGs to plants. Higher Cd stress promoted the transfer of most target ARGs from the below-ground plant parts to the above-ground parts. These findings indicate that application of sludge contaminated with heavy metals, such as Cd, can facilitate the dissemination of ARGs into vegetables, which must be considered while assessing the risks to public health.

Alleviated Antibiotic-Resistant Genes in the Rhizosphere of Agricultural Soils with Low Antibiotic Concentration

The influence of the rhizosphere on the abundance and diversity of antibiotic resistance genes (ARGs) has been recognized but there is a lack of consensus because of broad ranges of plant species and antibiotic concentrations across different habitats and the elusive underlying mechanisms. Here, we profiled antibiotic concentrations and resistomes in the rhizosphere and bulk soils by cultivating 10 types of crops in manure-amended agricultural soils. Rhizosphere effects altered the antibiotic resistome structure, significantly increased the absolute abundance of the antibiotic resistome, and decreased their relative abundance, contrasting previous studies. Such plantation-driven variation in ARGs resulted from the boost of bacterial lineages with negative relationships with ARGs and the constraint of the potential ARG-hosts in the rhizosphere of plants cultivated in soils with low antibiotic concentrations as the selective pressure. This mechanism is not reported previously and deepens our understanding about the rhizosphere effects on ARGs.

Biochar combined with polyvalent phage therapy to mitigate antibiotic resistance pathogenic bacteria vertical transfer risk in an undisturbed soil column system

The vertical migration of antibiotic resistance pathogenic bacteria (ARPB) and antibiotic resistance genes (ARGs) in the surface soil-vadose soil system has become a new threat to ecological safety and public health; there is an imperative need to develop an efficient technique for targeted control and inactivation of ARPB in these systems. In this work, undisturbed soil columns (0 ∼ -5 m) were constructed to investigate the impact of biochar amendment or/and polyvalent bacteriophage (ΦYSZ-KK) therapy on the vertical control and inactivation of tetracycline-resistant Escherichia coli K-12 and chloramphenicol-resistant Klebsiella pneumonia K-6. The simultaneous application of polyvalent phage and biochar impeded the vertical migration of ARPB from the top soil to lower soil layers and stimulated the ARPB dissipation in the soil column. After 60-day incubation, levels of ARPB and ARGs decreased significantly in the soil column by magnitudes of 2-6. Additionally, high throughput sequencing indicated that the simultaneous application of biochar and phage clearly maintained the structure and diversity of the soil microbial communities (p <  0.05). This work therefore demonstrates that the application of a biochar/phage combination is an environmentally friendly, efficacious measure for the control and inactivation of ARPB/ARGs in vertical soil column systems.