Occurrence and the potential ecological risk of veterinary antimicrobials in swine farm wastewaters in Japan: Seasonal changes, relation to purchased quantity and after termination of oxytetracycline usage

Enhanced tetracycline removal in sequencing batch reactors by bioaugmentation using tetX-carrying strains: Efficiency and mechanisms

Tetracyclines antibiotics (TCs) pose notable environmental challenges due to their persistence in the effluent of wastewater treatment systems. Bioaugmentation offers a promising strategy for their removal, yet information is still very limited. This study aimed to assess the efficacy of bioaugmentation using wild-type (Sphingobacterium sp. WM1) and engineered tetX-carrying (PUC-tetX) strains for enhancing tetracycline (TC) removal in sequencing batch reactors (SBRs). Bioaugmentation mitigated TC's inhibitory effects on denitrification and phosphorus removal processes within SBR systems. Specifically, strain WM1 outperformed strain PUC-tetX in removing TC from sludge and maintained a longer viability. TC addition (500 μg/L, at an environmentally relevant concentration) and bioaugmentation did not significantly impact overall microbial community diversity. Notably, the introduction of these exogenous bacteria markedly increased the abundance of the tetX gene, correlating with the increase in TC degradation. Interestingly, MAGs associated with the Chloroflexi phylum in bioaugmented reactors showed the transfer of the tetX gene to autochthonous bacterial species, promoting TC removal capability. These findings underscored the potential of bioaugmentation to enhance antibiotic removal and provided insights into the dynamics of ARGs and tetX gene within activated sludge systems.

Deciphering the interplay between wastewater compositions and oxytetracycline in recovered struvite: Unveiling mechanisms and introducing control strategies

Struvite recovery from wastewater offers a sustainable phosphorus and nitrogen source, yet it harbors the challenge of variable antibiotic residues, notably oxytetracycline (OTC), increasing the ecological risk during subsequent use. Despite the need, mechanisms behind these residues and regulatory solutions remain obscure. We characterized OTC in recovered struvite and showed that increased dissolved organic matter (DOM) enhanced OTC accumulation, while PO43- suppressed it. NH4+ modulated OTC levels through the saturation index (SI), with a rise in SI significantly reducing OTC content. Additionally, excess Mg2+ formed complexes with OTC and DOM (humic acid, HA), leading to increased residue levels. Complexation was stronger at higher pH, whereas electrostatic interactions dominated at lower pH. The primary binding sites for antibiotics and DOM were Mg-OH and P-OH groups in struvite. OTC's dimethylamino, amide, and phenolic diketone groups primarily bound to struvite and DOM, with the carboxyl group of DOM serving as the main binding site. Mg2+ complexation was the primary pathway for OTC transportation, whereas electrostatic attraction of PO43- dominated during growth. Controlling magnesium (Mg) dosage and adjusting pH were effective for reducing OTC in recovered products. Our findings provided insights into the intricate interactions between struvite and antibiotics, laying the groundwork for further minimizing antibiotic residues in recovered phosphorus products.

Fate of antibiotic resistance genes and EPS defence mechanisms during simultaneous denitrification and methanogenesis, coupled with the biodegradation of multiple antibiotics under zinc stress

High-strength nitrogen and antibiotics-containing wastewater can be efficiently eliminated by simultaneous denitrification and methanogenesis (SDM). Heavy metals and antibiotics are two critical factors that can lead to horizontal transfer of antibiotic resistance genes (ARGs), which can be simultaneously detected in wastewater. Unfortunately, the impacts of heavy metals on SDM and antibiotic biodegradation have not been fully elucidated. Herein, the effects of SDM and multiple antibiotics biodegradation, extracellular polymeric substances (EPSs) and protein response mechanisms, and ARG fate under Zn(II) stress were comprehensively evaluated. The results indicated that a high level of Zn(II) (≥5 mg/L) stress significantly decreased the degradation rate of multiple antibiotics and suppressed denitrification and methanogenesis. In addition, Zn(II) exposure prompted the liberation of proteins from microbes into the EPSs, and the combination of EPSs with small molecules quenched the original fluorescent components and destroyed the protein structure. The dominant proteins can bind to both Zn(II) and multiple antibiotics through several types of chemical interactions, including metallic and hydrogen bonds, hydrophobic interactions, and salt bridges, relieving the toxicity of harmful substances. Moreover, metagenomic sequencing revealed that the abundance of zinc resistance genes (Zn-RGs), ARGs (mainly tetracyclines), and mobile genetic elements (MGEs) increased under Zn(II) stress. Mantel test illustrated that the ARGs mecD, tetT, and tetB(60) were most affected by MGEs. Moreover, molecular network analysis revealed that several MGEs can bridge metal resistance genes (MRGs) and ARGs, facilitating the horizontal transfer of ARGs. This study provides theoretical guidance for the environmental risk control of antibiotics-containing wastewater treated by an SDM system.

The contribution of swine wastewater on environmental pathogens and antibiotic resistance genes: Antibiotic residues and beyond

Swine wastewater application can introduce antibiotics, antibiotic resistance genes (ARGs) into environments. Herein, the full-scale transmission of antibiotics, ARGs and their potential carriers from an intensive swine feedlot to its surroundings were explored. Results showed that lincomycin and doxycycline hydrochloride were dominant antibiotics in this ecosystem. Lincomycin concentration were strongly associated with soil bacterial communities. According to the risk quotient (RQ), lincomycin was identified as posing higher ecological risk in aquatic environments. ARGs and mobile genetic elements (MGEs) abundance in wastewater were reduced after anaerobic treatment. Notably, ARGs composition of environmental samples were clustered into two groups based on if they were directly affected by the wastewater. However, there were no remarkable difference of ARGs abundance among environmental samples. The total abundance of ARGs was positively related to that of MGEs. Pathogens Escherichia coli and Enterococcus revealed strong connection with qnrS, tet and sul. Overall, this study highlights the importance of responsible antibiotics use in livestock production and appropriate treatment technology before agricultural application and discharge.

Exploring bacterial diversity and antimicrobial resistance gene on a southern Brazilian swine farm

The bacterial composition of and the circulation of antimicrobial resistance genes (ARGs) in waste from Brazilian swine farms are still poorly understood. Considering that antimicrobial resistance (AMR) is one of the main threats to human, animal, and environmental health, the need to accurately assess the load of ARGs released into the environment is urgent. Therefore, this study aimed to characterize the microbiota in a swine farm in southern Brazil and the resistome in swine farm wastewater treated in a series of waste stabilization ponds (WSPs). Samples were collected from farm facilities and the surrounding environment, representing all levels of swine manure within the treatment system. Total metagenomic sequencing was performed on samples from WSPs, and 16S-rDNA sequencing was performed on all the collected samples. The results showed increased bacterial diversity in WSPs, characterized by the presence of Caldatribacteriota, Cloacimonadota, Desulfobacterota, Spirochaetota, Synergistota, and Verrucomicrobiota. Furthermore, resistance genes to tetracyclines, lincosamides, macrolides, rifamycin, phenicol, and genes conferring multidrug resistance were detected in WSPs samples. Interestingly, the most abundant ARG was linG, which confers resistance to the lincosamides. Notably, genes conferring macrolide (mphG and mefC) and rifamycin (rpoB_RIF) resistance appeared in greater numbers in the late WSPs. These drugs are among the high-priority antibiotic classes for human health. Moreover, certain mobile genetic elements (MGEs) were identified in the samples, notably tnpA, which was found in high abundance. These elements are of particular concern due to their potential to facilitate the dissemination of ARGs among bacteria. In summary, the results indicate that, in the studied farm, the swine manure treatment system could not eliminate ARGs and MGEs. Our results validate concerns about Brazil's swine production system. The misuse and overuse of antimicrobials during animal production must be avoided to mitigate AMR.

Elucidating doxycycline biotransformation mechanism by Chryseobacterium sp. WX1: Multi-omics insights

Doxycycline (DOX) represents a second-generation tetracycline antibiotic that persists as a challenging-to-degrade contaminant in environmental compartments. Despite its ubiquity, scant literature exists on bacteria proficient in DOX degradation. This study marked a substantial advancement in this field by isolating Chryseobacterium sp. WX1 from an activated sludge enrichment culture, showcasing its unprecedented ability to completely degrade 50 mg/L of DOX within 44 h. Throughout the degradation process, seven biotransformation products were identified, revealing a complex pathway that began with the hydroxylation of DOX, followed by a series of transformations. Employing an integrated multi-omics approach alongside in vitro heterologous expression assays, our study distinctly identified the tetX gene as a critical facilitator of DOX hydroxylation. Proteomic analyses further pinpointed the enzymes postulated to mediate the downstream modifications of DOX hydroxylation derivatives. The elucidated degradation pathway encompassed several key biological processes, such as the microbial transmembrane transport of DOX and its intermediates, the orchestration of enzyme synthesis for transformation, energy metabolism, and other gene-regulated biological directives. This study provides the first insight into the adaptive biotransformation strategies of Chryseobacterium under DOX-induced stress, highlighting the potential applications of this strain to augment DOX removal in wastewater treatment systems containing high concentrations of DOX.

Simultaneous adsorption and biodegradation of oxytetracycline in wastewater by Mycolicibacterium sp. immobilized on magnetic biochar

Due to the adverse effects of long-term oxytetracycline (OTC) residues in aquatic environments, an effective treatment is urgently needed. Immobilized microbial technology has been widely explored in the treatment of various organic pollutants in aquatic environments with its excellent environmental adaptability. Nevertheless, studies on its application in the removal of antibiotics are relatively scarce and not in sufficient depth. Only a few studies have further investigated the final fate of antibiotics in the immobilized bacteria system. In this study, a novel kind of OTC-degrading bacteria Mycolicibacterium sp. was immobilized on straw biochar and magnetic biochar, respectively. Magnetic biochar was proved to be a more satisfactory immobilization carrier due to its superior property and the advantage of easy recycling. Compared with free bacteria, immobilized bacteria had stronger environmental adaptability under different OTC concentrations, pH, and heavy metal ions. After 5 cycles, immobilized bacteria could still remove 71.8% of OTC, indicating that it had a stable recyclability. Besides, OTC in real swine wastewater was completely removed by immobilized bacteria within 2 days. The results of FTIR showed that bacteria were successfully immobilized on biochar and O-H, N-H, and C-N groups might be involved in the removal of OTC. The fate analysis indicated that OTC was removed by simultaneous adsorption and biodegradation, while biodegradation (92.8%) played a dominant role in the immobilized bacteria system. Meanwhile, the amount of adsorbed OTC (7.20%) was rather small, which could effectively decrease the secondary pollution of OTC. At last, new degradation pathways of OTC were proposed. This study provides an eco-friendly and effective approach to remedy OTC pollution in wastewater.

Livestock wastes from family-operated farms are potential important sources of potentially toxic elements, antibiotics, and estrogens in rural areas in North China

The open-air storage and disposal of livestock waste from family-operated livestock farms can be a potential health threat to rural residents. In this study, the occurrence and seasonal distribution of 8 potentially toxic elements, 24 antibiotics, and 4 estrogens were investigated in 44 waste samples from 11 rural farms in North China. The results showed that these micropollutants were ubiquitous in livestock waste, with concentration ranges of 238.9-4555 mg/kg for potentially toxic elements, not detected (ND) to 286,672 μg/kg for antibiotics and ND to 229.5 μg/kg for estrogens. The pollutants in animal wastes showed seasonal variation. Since these wastes are directly applicable to nearby farmland without treatment, the risks those wastes pose to farmland soils were also evaluated. Risk assessment results showed that Zn, Cd, Hg, FF and DC in swine manures were at high risk, while total estrogens in chicken and dairy cattle manures were at high risk. The results will provide important data for the regulation of animal wastes produced by small-scale livestock farms in rural areas of China.

Characteristics of antimicrobial residues in manure composts from swine farms: Residual patterns, removal efficiencies, and relation to purchased quantities and composting methods in Japan

Present study provides first comprehensive results on the residual levels of 19 antimicrobial (AM) residues in 12 Japanese swine manure composting facilities that use open or enclosed types of treatment methods. Tilmicosin (14000 μg/kg d.w.) and tiamulin (15000 μg/kg d.w.) were present in the highest concentrations in manure composts. Morantel (MRT) had the highest detection frequency (100%) in compost, suggesting its ubiquitous usage and resistance to degradation during composting. Sulfamethoxazole had low detection frequencies and concentrations, likely due to limited partitioning to the solid phase. A positive correlation (p < 0.05) between purchasing quantities and residue levels in manure composts was detected for fluoroquinolones (FQs). The removal efficiencies of AMs in enclosed-type facilities were lower and more inconsistent than those in open-type facilities. Tetracyclines (TCs), lincomycin, and trimethoprim were easily removed from open-type facilities, whereas FQs and MRT persisted in both facilities. After discontinuing the usage of oxytetracycline (OTC), TCs concentrations reduced drastically in input materials, remained pseudo-persistent in composts for up to 4 months, suggesting a time lag for composting and were not detected (<10 µg/kg) after 4 months of OTC withdrawal. This study emphasizes on the effectiveness of manure composting methods in reducing AM residues in swine waste.