Microplastics alter cadmium accumulation in different soil-plant systems: Revealing the crucial roles of soil bacteria and metabolism.

Cadmium (Cd) and microplastics (MPs) gradually increased to be prevalent contaminants in soil, it is important to understand their combined effects on different soil-plant systems. We studied how different doses of polylactic acid (PLA) and polyethylene (PE) affected Cd accumulation, pakchoi growth, soil chemical and microbial properties, and metabolomics in two soil types. We found that high-dose MPs decreased Cd accumulation in plants in red soil, while all MPs decreased Cd bioaccumulation in fluvo-aquic soil. This difference was primarily attributed to the increase in dissolved organic carbon (DOC) and pH in red soil by high-dose MPs, which inhibited Cd uptake by plant roots. In contrast, MPs reduced soil nitrate nitrogen and available phosphorus, and weakened Cd mobilization in fluvo-aquic soil. In addition, high-dose PLA proved detrimental to plant health, manifesting in shortened shoot and root lengths. Co-exposure of Cd and MPs induced the shifts in bacterial populations and metabolites, with specific taxa and metabolites closely linked to Cd accumulation. Overall, co-exposure of Cd and MPs regulated plant growth and Cd accumulation by driving changes in soil bacterial community and metabolic pathways caused by soil chemical properties. Our findings could provide insights into the Cd migration in different soil-plant systems under MPs exposure. ENVIRONMENTAL IMPLICATION: Microplastics (MPs) and cadmium (Cd) are common pollutants in farmland soil. Co-exposure of MPs and Cd can alter Cd accumulation in plants, and pose a potential threat to human health through the food chain. Here, we investigated the effects of different types and doses of MPs on Cd accumulation, plant growth, soil microorganisms, and metabolic pathways in different soil-plant systems. Our results can contribute to our understanding of the migration and transport of Cd by MPs in different soil-plant systems and provide a reference for the control of combined pollution in the future research.

Antibiotics and antibiotic resistance gene dynamics in the composting of antibiotic fermentation waste - A review.

Fate of antibiotics and antibiotic resistance genes (ARGs) during composting of antibiotic fermentation waste (AFW) is a major concern. This review article focuses on recent literature published on this subject. The key findings are that antibiotics can be removed effectively during AFW composting, with higher temperatures, appropriate bulking agents, and suitable pretreatments improving their degradation. ARGs dynamics during composting are related to bacteria and mobile genetic elements (MGEs). Higher temperatures, suitable bulking agents and an appropriate C/N ratio (30:1) lead to more efficient removal of ARGs/MGEs by shaping the bacterial composition. Keeping materials dry (moisture less than 30%) and maintaining pH stable around 7.5 after composting could inhibit the rebound of ARGs. Overall, safer utilization of AFW can be realized by optimizing composting conditions. However, further removal of antibiotics and ARGs at low levels, degradation mechanism of antibiotics, and spread mechanism of ARGs during AFW composting require further investigation.

Evaluation of composting parameters, technologies and maturity indexes for aerobic manure composting: A meta-analysis.

Aerobic composting is an efficient method to recover nutrients from animal manure. However, there is considerable variability in the management and maturity criteria used across studies, and a systematic meta-analysis focused on compost maturity is currently lacking. This study investigated the optimal range of startup parameters and practical criteria for manure composting maturity, as well as the effectiveness of in situ technologies in enhancing composting maturity. Most maturity indexes were associated with composting GI, making it an ideal tool for evaluating the maturity of manure composts. GI increased with declined final C/N and (Final C/N)/(Initial C/N) (P < 0.01), and therefore a maturity assessment standard for animal manure composting was proposed: a mature compost has a C/N ratio ≤23 and a GI ≥70, while a highly mature compost has a GI ≥90 and preferably (Final C/N)/(Initial C/N) ≤0.8. Meta-analysis demonstrated that C/N ratio regulation, microbial inoculation and adding biochar and magnesium-phosphate salts are effective strategies for improving compost maturity. Specifically, a greater reduction in the C/N ratio during the composting process is beneficial for improving the maturity of compost product. The optimal startup parameters for composting have been determined, recommending an initial C/N ratio of 20-30 and an initial pH of 6.5-8.5. An initial C/N ratio of 26 was identified as the most suitable for promoting compost degradation and microorganism activity. The present results promoted a composting strategy for producing high-quality compost.

Composting reduces the risks of antibiotic resistance genes in maize seeds posed by gentamicin fermentation waste.

Using high-throughput quantitative PCR and next generation sequencing, the impact of land application of raw and composted gentamicin fermentation waste (GFW) on antibiotic resistance genes (ARGs) in maize seeds was studied in a three-year field trial. The raw and composted GFW changed both the bacterial community composition and the ARGs diversity in the maize seeds compared to non-amended controls and chemical fertilizer. The abundance of ARGs after raw GFW amendment was significantly higher than other treatments because of a high abundance of aadA1, qacEdeltal and aph(2')-Id-02; probably induced by gentamicin selection pressure in maize tissues. Meanwhile, the potential host of these three ARGs, pathogenic bacteria Tenacibaculum, also increased significantly in maize seeds after the application of raw GFW. But our result proved that composting could weaken the risk posed by GFW. We further reveal that the key biotic driver for shaping the ARG profiles in maize seeds is bacterial community followed by heavy metal resistance genes, and ARGs are more likely located on bacterial chromosomes. Our findings provide new insight into ARGs dispersal mechanism in maize seeds after long-term GFW application, demonstrate the potential benefits of composting the GFW to reduce risks as well as the potential efficient management method to GFW.

Fate of bacterial community, antibiotic resistance genes and gentamicin residues in soil after three-year amendment using gentamicin fermentation waste.

Over a three-year field trial, the impacts of composted and raw gentamicin fermentation waste (GFW) application to land on residual soil gentamicin levels, physicochemical properties, bacterial community composition, and antibiotic resistance genes (ARGs) were assessed. In the saline-alkali soil tested, GFW application decreased electrical conductivity (EC) and pH. Importantly, there was no measurable long-term accumulation of gentamicin as a result of GFW addition. Changes in the abundance of Bacillus was primarily associated with degradation of gentamicin in soil, whereas wider (i.e. more general) shifts in bacterial communities over the treatments was linked to alteration of soil physicochemical properties, particularly pH, total nitrogen, dissolved organic carbon, EC, NO3--N and NH4+-N. Compared with other treatments, soils receiving composted GFW harbored more types of ARGs and significantly higher (P < 0.05) abundances of mobile genes elements (MGEs) (especially IncQ and Int1) and aminoglycoside ARGs (especially aminoglycoside phosphotransferases genes, APH). Finally, the abundances of ARGs in soils receiving raw and composted GFW were 59.60% and 50.26% higher than that in soils only receiving chemical fertilizer, respectively. Specifically, the abundances of APH, especially strB, were significantly higher than other kinds of ARGs (P < 0.05). The results of linear regression and partial least squares path model showed that MGEs, including plasmids, integrons, and transposons, along with soil properties (EC and NH4+-N) were the main factors associated with change in ARGs. Furthermore, different MGEs were involved in different transfer mechanisms of specific ARGs. Our findings demonstrated the potential risks of using raw and composted GFW as fertilizer, and suggest potential solutions to this problem.

In-feed antibiotic use changed the behaviors of oxytetracycline, sulfamerazine, and ciprofloxacin and related antibiotic resistance genes during swine manure composting.

The dynamics of oxytetracycline (OTC), sulfamerazine (SM1), ciprofloxacin (CIP) and related antibiotic resistance genes (ARGs) during swine manure composting were compared between manure collected from swine fed a diet containing these three antibiotics (TD) and manure directly spiked with these drugs (TS). The composting removal efficiency of OTC (94.9 %) and CIP (87.8 %) in the TD treatment was significantly higher than that of OTC (83.8 %, P < 0.01) and CIP (83.9 %, P < 0.05) in the TS treatment, while SM1 exhibited no significant difference (P > 0.05) between the two treatments. Composting effectively reduced the majority of ARGs in both TD and TS types of manure, especially tetracycline resistance genes (TRGs). Compared with the TS treatment, the abundance of some ARGs, such as tetG, qepA, sul1 and sul2, increased dramatically up to 309-fold in the TD treatment. The microbial composition of the composting system changed significantly during composting due to antibiotic feeding. Redundancy analysis suggested that the abundance of ARGs had a considerable impact on alterations in the physicochemical parameters (C/N, pH and temperature) and bacterial communities (Actinobacteria, Proteobacteria and Firmicutes) during the composting of swine manure.

Changes in microbial community structure during pig manure composting and its relationship to the fate of antibiotics and antibiotic resistance genes.

Animal manure containing veterinary antibiotics is a significant source of microbial antibiotic resistance genes (ARGs). Composting of animal manure with wheat straw and sawdust was explored as a means to reduce ARGs load in the final material. The effects of ciprofloxacin, oxytetracycline, sulfamerazine on the bacterial community composition, and how this then affected the removal of seven tetracycline resistance genes (TARGs), four sulfonamide resistance genes (SARGs), and two fluoroquinolone resistance genes (QARGs) were investigated. Treatments receiving either ciprofloxacin or the three mixed antibiotics had reduced bacterial alpha-diversity and displayed shifts in the abundance of Proteobacteria and Firmicutes. This demonstrated that different antibiotics played an important role in bacterial community composition. Furthermore, variation in the physicochemical properties of compost, particularly pH and temperature, was also strongly linked to shifts in bacterial composition over time. Based on network analysis, the reduction of TARGs were associated with loss of Pseudomonas, Pseudoxanthomonas, Pusillimonas, Aquamicrobium, Ureibacillus, Lysinibacillus, Bacillus and Brachybacterium during the thermophilic stage. However, QARGs and SARGs were more strongly affected by the presence of multiple antibiotics. Our results have important implications for reducing the spread of certain ARGs by controlling the composting temperature, pH or the antibiotics species used in husbandry.

Changes in Arsenic and Copper Bioavailability and Oxytetracycline Degradation during the Composting Process.

This research focuses on the effects of the composting process on oxytetracycline antibiotic degradation and the bioavailability of arsenic and copper. A compost experiment was conducted using cow and pig manure contaminated with oxytetracycline, and copper and arsenic salts. The changes in physicochemical properties, oxytetracycline concentration, and the germination index were measured. Copper and arsenic were estimated by sequential chemical extraction. We also detected the effects of compost properties, oxytetracycline concentration, and heavy metal (loid)s on the germination index through simple regression analysis. The results showed that the composting process positively and significantly affected heavy metal(loid)s bioavailability, oxytetracycline degradation, and the germination index. Oxytetracycline concentration declined in all treatments, and the decline was more evident in cows' manure. The copper and arsenic bioavailable fraction decreased significantly, while the low bioavailability fraction increased. The germination index increased above 50%, which showed that the compost was free of toxic substances. This result also showed that the compost properties had the most significant impact on the germination index, and their regression had the highest R2 values (0.84 and 0.99) in the cow and pig manure treatments, respectively. In conclusion, the composting process provides an economical method for oxytetracycline degradation and heavy metal(loid)s bioavailability reduction.

Fe3+ enhanced degradation of oxytetracycline in water by pseudomonas.

The application and fate of antibiotics are closely related to human health and the ecological balance, which has gradually aroused the widespread global concerns. Long-term antibiotic residues can easily induce antibiotic resistance and antibiotic resistance genes (ARGs) in the environment. Although many studies have investigated the metabolic pathways of biosynthesis or degradation of oxytetracycline (OTC) and its influencing factors under laboratory or controlled conditions, the understanding of OTC degradation pathways and influencing factors in the environment is still poor. In the present study, the role of Pseudomonas (T4) in OTC biodegradation were investigated with different carbon sources, metal ions, substrate concentrations, temperatures, and pH values, as well as the temporal changes in the relative abundance of OTC ARGs. It was found that OTC could be degraded by T4 as a sole carbon source. Comparison with Cu2+, the addition of Fe3+ could significantly promote the growth of T4, and then increased the OTC degradation percentage to 65.3%. The initial concentration of OTC, temperature, and pH had significant impacts on OTC degradation. At the initial OTC concentration of 50 mg L-1, the percentage degradation of OTC by T4 could reach 81.0% at the presence of Fe3+, and at 40 °C and pH = 7. Common tetracycline ARGs were not found during the OTC degradation by T4 in the present study. The eight main putative OTC degradation byproducts were identified by ultra-high definition accurate-mass quadrupole time-of-flight tandem mass spectrometry (QTOF/MS). Six different reaction types and seven possible degradation pathways were proposed, including enol-ketone conversion, hydroxylation, dehydration, deamination, demethylation and decarbonylation. Under optimal conditions, the OTC degradation percentages by T4 could reach to 88.2%, 91.6% and 92.0% in pond water, fish wastewater and industrial wastewater, respectively. These results demonstrate the high effectiveness of T4 at the presence of Fe3+ for the enhanced biodegradation of OTC in water environment, without resulting in the occurrence of ARGs. This has important implications for the removal of OTC from aquatic environments by the technology proposed from this study.

Uptake, translocation and distribution of three veterinary antibiotics in Zea mays L.

Frequently detected residuals of antibiotics in crops has drawn increasing attention from research community and the general public. This study was conducted under the controlled environmental conditions to investigate the uptake, translocation and distribution of three different veterinary antibiotics (VAs) in plants of Zea mays L. (maize, the third largest crop in the world, especially in China) and the associated mechanisms. The distribution color-maps of mixed-VAs showed that the highest RCF (root concentration factors) values of chlortetracycline (CTC) and sulfamethoxazole (SMZ) were found in the 0.5-2.0 mm zone (cell division zone), while the highest RCF value of sulfathiazole (ST) was in the 6.0-8.0 mm zone (elongation zone) of root tips (0.5-10.0 mm) after 120 h of exposure to VAs. The translocation factor (TF) of CTC was greater than 1.0, but the TFs of SMZ and ST were less than 1.0 under addition of single antibiotic. However, the TFs of three VAs were all greater than 1.0 at the end of exposure under addition of mixed-VAs. The dissipation of antibiotics by maize was also demonstrated by harvesting all plant parts in an enclosed system. The possible mechanisms for uptake and translocation of VAs in maize were investigated by adding multiple respiration inhibitors into the culture solution. The RCFs of VAs were suppressed heavily by salicylhydroxamic acid (SHAM) and sodium azide (NaN3), which indicates that the uptake of VAs was an active process. The results of TFs and stem concentration factors (SCFs) of CTC and SMZ in HgCl2 treatments revealed that the translocation of VAs was associated with the aquaporin activity in maize. The findings from this study will have significant implications for the management of crop food contamination by VAs and for the development of phytoremediation technology for antibiotics in the environment.

Dynamics of oxytetracycline, sulfamerazine, and ciprofloxacin and related antibiotic resistance genes during swine manure composting.

Understanding the dynamics of veterinary antibiotic and related antibiotic resistance genes (ARGs) during swine manure composting is crucial in assessing the environmental risk of antibiotics, which could effectively reduce their impact in natural environments. This study investigated the dissipation of oxytetracycline (OTC), sulfamerazine (SM1) and ciprofloxacin (CIP) as well as the behaviour of their corresponding ARGs during swine manure composting. These antibiotics were added at two concentration levels and two different methods of addition (single/mixture). The results indicated that the removal efficiency of antibiotics by composting were ≥85%, except for the single-SM1 treatment. The tetracycline resistance genes (TRGs) encoding ribosomal protection proteins (RPP) and efflux pump (EFP) and fluoroquinolone resistance genes (FRGs) could be effectively removed after 42 days. On the contrary, the TRGs encoding enzymatic inactivation (EI) and sulfonamide resistance genes (SRGs) were enriched up to 31-fold (sul 2 in single-low-SM1). Statistical analyses indicated that the behaviour of these class antibiotics and ARGs were controlled by microbial activity and significantly influenced by environmental factors (mainly C/N, moisture and pH) throughout the composting process.

A Simple, Sensitive, and Reliable Method for the Simultaneous Determination of Multiple Antibiotics in Vegetables through SPE-HPLC-MS/MS.

Antibiotics, widely used in livestock breeding, enter the environment through animal manure because of incomplete absorption in animals, especially the farmland ecosystem. Therefore, antibiotics may be adsorbed by plants and even become hazardous to human health through the food chain. In this study, a simple, sensitive, and reliable method was developed for the simultaneous determination of eleven antibiotics, including four sulfonamides, two tetracyclines, three fluoroquinolones, tylosin, and chloramphenicol in different vegetable samples using SPE-HPLC-MS/MS. Vegetable samples were extracted by acetonitrile added with hydrochloric acid (125:4, v/v). The extracts were enriched by circumrotating evaporation, and then cleaned through SPE on a hydrophilic-lipophilic balance (HLB) cartridge. All compounds were determined on a C18 reverse phase column through HPLC-MS/MS. The mean recoveries of 11 antibiotics from spiked samples of vegetables ranged from 71.4% to 104.0%. The limits of detection and quantification were 0.06⁻1.88 µg/kg and 0.20⁻6.25 µg/kg, respectively. The applicability of this technique demonstrated its good selectivity, high efficiency, and convenience by the analysis of 35 vegetable samples available from a vegetable greenhouse. Antibiotic residues in vegetables have aroused wide concern from the public. Therefore, standards should be established for antibiotic residues in vegetables to ensure food safety and human health.

Dynamics of bacterial composition and the fate of antibiotic resistance genes and mobile genetic elements during the co-composting with gentamicin fermentation residue and lovastatin fermentation residue.

Dynamics in bacterial community composition, along with 13 antibiotic resistance genes (ARGs) and eight mobile genetic elements (MGEs), were assessed during co-composting with gentamicin and lovastatin fermentation residue (GFR and LFR, respectively). Using next generation sequencing, the key bacterial taxa associated with the different stages of composting were identified. Most importantly, Bacillus, belonging to Phylum Firmicutes, was associated with enhanced degradation of gentamicin, decomposition of organic matter (OM) and dissolved organic carbon (DOC), and also extension of the thermophilic phase of the composting cycle. During the course of composting, the patterns of different ARGs/MGEs varied. However, the total and the normalized (to bacterial numbers) copies both remained high. The abundance of various ARGs was related to bacterial abundance and community composition, and the changing pattern of individual ARGs was influenced by the selectivity of MGEs and bacteria.

Quantitative models for predicting adsorption of oxytetracycline, ciprofloxacin and sulfamerazine to swine manures with contrasting properties.

Understanding antibiotic adsorption in livestock manures is crucial to assess the fate and risk of antibiotics in the environment. In this study, three quantitative models developed with swine manure-water distribution coefficients (LgKd) for oxytetracycline (OTC), ciprofloxacin (CIP) and sulfamerazine (SM1) in swine manures. Physicochemical parameters (n=12) of the swine manure were used as independent variables using partial least-squares (PLSs) analysis. The cumulative cross-validated regression coefficients (Q2cum) values, standard deviations (SDs) and external validation coefficient (Q2ext) ranged from 0.761 to 0.868, 0.027 to 0.064, and 0.743 to 0.827 for the three models; as such, internal and external predictability of the models were strong. The pH, soluble organic carbon (SOC) and nitrogen (SON), and Ca were important explanatory variables for the OTC-Model, pH, SOC, and SON for the CIP-model, and pH, total organic nitrogen (TON), and SOC for the SM1-model. The high VIPs (variable importance in the projections) of pH (1.178-1.396), SOC (0.968-1.034), and SON (0.822 and 0.865) established these physicochemical parameters as likely being dominant (associatively) in affecting transport of antibiotics in swine manures.

Biodegradation of gentamicin by bacterial consortia AMQD4 in synthetic medium and raw gentamicin sewage.

Gentamicin, a broad spectrum antibiotic of the aminoglycoside class, is widely used for disease prevention of human beings as well as animals. Nowadays the environmental issue caused by the disposal of wastes containing gentamicin attracts increasing attention. In this study, a gentamicin degrading bacterial consortia named AMQD4, including Providencia vermicola, Brevundimonas diminuta, Alcaligenes sp. and Acinetobacter, was isolated from biosolids produced during gentamicin production for the removal of gentamicin in the environment. The component and structure of gentamicin have a great influence on its degradation and gentamicin C1a and gentamicin C2a were more prone to being degraded. AMQD4 could maintain relatively high gentamicin removal efficiency under a wide range of pH, especially in an alkaline condition. In addition, AMQD4 could remove 56.8% and 47.7% of gentamicin in unsterilized and sterilized sewage in a lab-scale experiment, respectively. And among the isolates in AMQD4, Brevundimonas diminuta BZC3 performed the highest gentamicin degradation about 50%. It was speculated that aac3iia was the gentamicin degradation gene and the main degradation product was 3'-acetylgentamicin. Our results suggest that AMQD4 and Brevundimonas diminuta BZC3 could be important candidates to the list of superior microbes for bioremediation of antibiotic pollution.

Gentamicin degradation and changes in fungal diversity and physicochemical properties during composting of gentamicin production residue.

An indoor co-composting of gentamicin fermentation residues (GFR) and lovastatin fermentation residues (LFR) inoculated with gentamicin-degrading Aspergillus terreus FZC3 was conducted to remove gentamicin residues. The results showed that treatment MFZC3, consisting of a 10:1 blend of GFR and LFR (w/w), had the longest thermophilic phase (7days), quickest gentamicin degradation (t½=4.4days), and relatively higher gentamicin degradation percentage (96.7%) at the end of composting. Addition of Aspergillus terreus FZC3 affected fungal diversity of the compost and improved the removal of gentamicin during composting of the 15:1 GFR:LFR blend. By analyzing the variations of gentamicin and fungal community dynamics, it was speculated that Aspergillus terreus could accelerate gentamicin degradation. The microbial community and dynamic during composting were deeply affected by the physicochemical properties, and vice versa. In conclusion, co-composting of GFR with LFR could be a promising technology to solve the problem of gentamicin residue in GFR waste.

Gentamicin removal in submerged fermentation using the novel fungal strain Aspergillus terreus FZC3.

Social concern and awareness of the potential risk posed by environmental residues of antibiotics such as gentamicin in the development of antibiotic resistance genes have increased. The present study used laboratory-scale experiments to develop methods for gentamicin removal from the environment. A fungus, strain FZC3, which could remove gentamicin in submerged fermentation, was isolated from solid waste and sewage water from a gentamicin production factory. The fungus was identified as Aspergillus terreus by sequencing the PCR-amplified ITS fragments of its rRNA-coding genes and by its morphology. The gentamicin removal efficiency exceeded 95% by day 7 under optimized culture conditions. The results showed that both biosorption and biodegradation were involved. We speculated that Aspergillus terreus FZC3 absorbed gentamicin and subsequently degraded it. We also found that Aspergillus terreus FZC3 survived and maintained a high bioremediation efficiency over a wide pH range, indicating its potential for future use in the large-scale bioremediation of gentamicin.