Antibiotic and metal resistance genes are closely linked with nitrogen-processing functions in municipal solid waste landfills

Nitrogen fertilization and soil nitrogen cycling: Unraveling the links among multiple environmental factors, functional genes, and transformation rates

Anthropogenic nitrogen (N) inputs substantially influence the N cycle in agricultural ecosystems. However, the potential links among various environmental factors, nitrogen functional genes, and transformation rates under N fertilization remain poorly understood. Here, we conducted a five-year field experiment and collected 54 soil samples from three 0-4 m boreholes across different treatments: control, N-addition (nitrogen fertilizer) and NPK-addition (combined application of nitrogen, phosphorus and potassium fertilizers) treatments. Our results revealed pronounced variations in soil physiochemical parameters, metal concentrations and antibiotic levels under both N and NPK treatments. These alternations induced significant shifts in bacterial and fungal communities, altered NFG abundance and composition, and greatly enhanced rates of nitrate reduction processes. Notably, nutrients, antibiotics and bacteria exerted a more pronounced influence on NFGs and nitrate reduction under N treatment, whereas nutrients, metals, bacteria and fungi had a significant impact under NPK treatment. Furthermore, we established multidimensional correlations between nitrate reduction gene profiles and the activity rates under N and NPK treatments, contrasting with the absence of significant relationships in the control treatment. These findings shed light on the intricate relationships between microbial genetics and ecosystem functions in agricultural ecosystem, which is of significance for predicting and managing metabolic processes effectively.

Multi-omics illuminates the functional significance of previously unknown species in a full-scale landfill leachate treatment plant

Landfill leachate treatment plants (LLTPs) harbor a vast reservoir of uncultured microbes, yet limited studies have systematically unraveled their functional potentials within LLTPs. Combining 36 metagenomic and 18 metatranscriptomic datasets from a full-scale LLTP, we unveiled a double-edged sword role of unknown species in leachate biotreatment and environmental implication. We identified 655 species-level genome bins (SGBs) spanning 47 bacterial and 3 archaeal phyla, with 75.9 % unassigned to any known species. Over 90 % of up-regulated functional genes in biotreatment units, compared to the leachate influent, were carried by unknown species and actively participated in carbon, nitrogen, and sulfur cycles. Approximately 79 % of the 37,366 carbohydrate active enzymes (CAZymes), with ∼90 % novelty and high expression, were encoded by unknown species, exhibiting great potential in biodegrading carbohydrate compounds linked to human meat-rich diets. Unknown species offered a valuable genetic resource of thousands of versatile, abundant, and actively expressed metabolic gene clusters (MGCs) and biosynthetic gene clusters (BGCs) for enhancing leachate treatment. However, unknown species may contribute to the emission of hazardous N2O/H2S and represented significant reservoirs for antibiotic-resistant pathogens that posed environmental safety risks. This study highlighted the significance of considering both positive and adverse effects of LLTP microbes to optimize LLTP performance.

Nitrogen in landfills: Sources, environmental impacts and novel treatment approaches

Nitrogen (N) accumulation in landfills is a pressing environmental concern due to its diverse sources and significant environmental impacts. However, there is relatively limited attention and research focus on N in landfills as it is overshadowed by other more prominent pollutants. This study comprehensively examines the sources of N in landfills, including food waste contributing to 390 million tons of N annually, industrial discharges, and sewage treatment plant effluents. The environmental impacts of N in landfills are primarily manifested in N2O emissions and leachate with high N concentrations. To address these challenges, this study presents various mitigation and management strategies, including N2O reduction measures and novel NH4+ removal techniques, such as electrochemical technologies, membrane separation processes, algae-based process, and other advanced oxidation processes. However, a more in-depth understanding of the complexities of N cycling in landfills is required, due to the lack of long-term monitoring data and the presence of intricate interactions and feedback mechanisms. To ultimately achieve optimized N management and minimized adverse environmental impacts in landfill settings, future prospects should emphasize advancements in monitoring and modeling technologies, enhanced understanding of microbial ecology, implementation of circular economy principles, application of innovative treatment technologies, and comprehensive landfill design and planning.

NO3- as an electron acceptor elevates antibiotic resistance gene and human bacterial pathogen risks in managed aquifer recharge (MAR): A comparison with O2

Managed aquifer recharge (MAR) stands out as a promising strategy for ensuring water resource sustainability. This study delves into the comparative impact of nitrate (NO3-) and oxygen (O2) as electron acceptors in MAR on water quality and safety. Notably, NO3-, acting as an electron acceptor, has the potential to enrich denitrifying bacteria, serving as hosts for antibiotic resistance genes (ARGs) and enriching human bacterial pathogens (HBPs) compared to O2. However, a direct comparison between NO3- and O2 remains unexplored. This study assessed risks in MAR effluent induced by NO3- and O2, alongside the presence of the typical refractory antibiotic sulfamethoxazole. Key findings reveal that NO3- as an electron acceptor resulted in a 2 times reduction in dissolved organic carbon content compared to O2, primarily due to a decrease in soluble microbial product production. Furthermore, NO3- significantly enriched denitrifying bacteria, the primary hosts of major ARGs, by 747%, resulting in a 66% increase in the overall abundance of ARGs in the effluent of NO3- MAR compared to O2. This escalation was predominantly attributed to horizontal gene transfer mechanisms, as evidenced by a notable 78% increase in the relative abundance of mobile ARGs, alongside a minor 27% rise in chromosomal ARGs. Additionally, the numerous denitrifying bacteria enriched under NO3- influence also belong to the HBP category, resulting in a significant 114% increase in the abundance of all HBPs. The co-occurrence of ARGs and HBPs was also observed to intensify under NO3- influence. Thus, NO3- as an electron acceptor in MAR elevates ARG and HBP risks compared to O2, potentially compromising groundwater quality and safety.

Response characteristics and functional predictions of soil microorganisms to heavy metals, antibiotics, and their resistance genes originating from different animal farms amended with Herbaspirillum huttiense

Current understanding is limited regarding technologies that use biochar and microorganisms to simultaneously treat soils contaminated with both veterinary antibiotics (VAs) and heavy metals (HMs) from different animal farms. The contributions of the keystone taxa and their similarities from different animal farms under VA and HM stresses before and after soil remediation should be further investigated as well. An innovative treatment of Herbaspirillum huttiense (HHS1) inoculated waste fungus chaff-based (WFCB) biochar was designed for immobilization of copper (Cu) and zinc (Zn), and the removal of oxytetracycline (OTC), enrofloxacin (ENR), and a subsequent reduction in their resistance genes in soils from pig, cow, and chicken farms. Roles of indigenous microorganisms which can treat soils contaminated with VAs and HMs were summarized. Results showed that available Cu and Zn were reduced by 19.5% and 28.1%, respectively, while 49.8% of OTC and 85.1% of ENR were removed by WFCB-HHS1. The decrease in ENR improved overall microbial community diversity, and the increases in genera HHS1, Pedobacter, Flavobacterium and Aequorivita, along with the decreases of genera Bacillus, Methylobacter, and Fermentimonas were indirectly favorable to treat HMs and VAs in soils from different animal farms. Bacterial communities in different animal farm soils were predominantly influenced by stochastic processes. The regulations of functional genes associated with metabolism and environmental information processing, which contribute to HM and VA defense, were altered when using WFCB-HHS1. Furthermore, the spread of their antibiotic resistance genes was restricted.

Characterization of heavy metal, antibiotic pollution, and their resistance genes in paddy with secondary municipal-treated wastewater irrigation

Secondary municipal-treated wastewater irrigation may introduce residual antibiotics into the agricultural systems contaminated with certain heavy metals, ultimately leading to the coexistence of antibiotics and heavy metals. The coexistence may induce synergistic resistance to both in the microbial community. Here, we investigated the effects of long-term municipal-treated irrigation for rice on the microbiome and resistome. The results showed that the target antibiotics were undetectable in edible grains, and the heavy metal concentrations did not exceed the standard in edible rice grains. Heavy metal resistance genes (MRGs) ruvB and acn antibiotic resistance genes (ARGs) sul1 and sul2 were the dominating resistant genes. The coexistence of antibiotics and heavy metals affected the microbial community and promoted metal and antibiotic resistance. Network analysis revealed that Proteobacteria were the most influential hosts for MRGs, ARGs, and integrons, and co-selection may serve as a potential mechanism for resistance maintenance. MRG czcA and ARG sul1 can be recommended as model genes to study the co-selection of ARGs and MRGs in environments. The obtained results highlight the importance of considering the co-occurrence of heavy metals and antibiotics while developing effective methods to prevent the transmission of ARGs. These findings are critical for assessing the possible human health concerns associated with secondary municipal-treated wastewater irrigation for agriculture and improving the understanding of the coexistence of heavy metals and antibiotics.

Antibiotic resistance genes and heavy metals in landfill: A review

Landfill is reservoir containing antibiotic resistance genes (ARGs) that pose a threat to human life and health. Heavy metals impose lasting effects on ARGs. This review investigated and analyzed the distribution, composition, and abundance of heavy metals and ARGs in landfill. The abundance ranges of ARGs detected in refuse and leachate were similar. The composition of ARG varied with sampling depth in refuse. ARG in leachate varies with the distribution of ARG in the refuse. The ARG of sulI was associated with 11 metals (Co, Pb, Mn, Zn, Cu, Cr, Ni, Sb, As, Cd, and Al). The effects of the total metal concentration on ARG abundance were masked by many factors. Low heavy metal concentrations showed positive effects on ARG diffusion; conversely, high heavy metal concentrations showed negative effects. Organic matter had a selective pressure effect on microorganisms and could provide energy for the diffusion of ARGs. Complexes of heavy metals and organic matter were common in landfill. Therefore, the hypothesis was proposed that organic matter and heavy metals have combined effects on the horizontal gene transfer (HGT) of ARGs during landfill stabilization. This work provides a new basis to better understand the HGT of ARGs in landfill.

Distribution, removal and ecological risk assessment of antibiotics in leachate from municipal solid waste incineration plants in Shanghai, China

Leachate from Municipal Solid Waste (MSW) incineration plants contains multiple antibiotics. However, current knowledge of antibiotics in such leachate is very limited compared to landfill leachate. In this study, the distribution, removal and ecological risks of 8 sulfonamides (SAs), 4 quinolones (FQs), and 4 macrolides (MLs) antibiotics in leachate from three MSW incineration plants in Shanghai were investigated. The results showed that 12 types of target antibiotics were detected at high concentrations (7737.3-13,758.7 ng/L) in the fresh leachate, exceeding the concentrations reported for landfill leachate. FQs were the dominant antibiotics detected in all three fresh leachates, accounting for >60 % of the total detected concentrations. The typical "anaerobic-anoxic/aerobic-anoxic/aerobic-ultrafiltration" treatment process removed the target antibiotics effectively (89.0 %-93.4 %), of which the anaerobic unit and the primary anoxic/aerobic unit were the most important antibiotic removal units. Biodegradation was considered to be the dominant removal mechanism, removing 78.11 %-92.37 % of antibiotics, whereas sludge adsorption only removed 1.02 %-10.89 %. Antibiotic removal was significantly correlated with leachate COD, pH, TN, and NH3-N, indicating that they may be influential factors for antibiotic removal. Ecological risk assessment revealed that ofloxacin (OFX) and enrofloxacin (EFX) in the treated leachate still posed high risks to algae and crustaceans. This research provides insights into the fate of antibiotics in leachate.

The concentration-dependent physiological damage, oxidative stress, and DNA lesions in Caenorhabditis elegans by subacute exposure to landfill leachate

The leakage of landfill leachate (LL) into environmental media would be happened even in the sanitary/controlled landfill, due to the deterioration of geomembrane and the blockage of drainage system after long-term operation. Considering the complex composition and high concentration of pollutants in LL, its toxicity assessment should be conducted as a whole liquid contaminant. Therefore, the impacts of LL on Caenorhabditis elegans (C. elegans) were investigated under the condition of different exposure time and exposure volume fraction (EVF). The stimulating effects on locomotion behavior and growth of C. elegans were observed after acute (24 h) exposure to LL, which were increased firstly and then decreased with the increase of EVF. Meanwhile, the intestinal barrier was not affected by LL, and levels of reactive oxygen species (ROS) and cell apoptosis significantly decreased. However, stimulation and inhibition effects on locomotion behavior and growth of C. elegans were observed when subacute (72 h) exposure to 0.25%-0.5% and 1%-4% of LL, respectively. The intestinal injury index and levels of ROS and cell apoptosis significantly increased when EVF were 2% and 4%. Although the acute exposure of LL had resulted in obviously biological adaptability and antioxidant defense in C. elegans, the protective mechanisms failed to be induced as the exposure time increased (subacute exposure). The toxic effects were confirmed by the down-regulation of genes associated with antioxidant defense and neurobehavior, accompanied by the up-regulation of intestinal injury and cell apoptosis related genes. Moreover, the disturbance of metabolic pathways that associated with locomotion behaviors, growth, and antioxidant defense provided good supplementary evidence for the confirmation of oxidative stress in C. elegans. The research results verified the potential of C. elegans as model organism to determine the complex toxic effects of LL.

Batch-fed composting of food waste: Microbial diversity characterization and removal of antibiotic resistance genes

The aim of this work was to study the impact of batch-fed strategies on bacterial communities and ARGs in compost. The findings demonstrate that batch-feeding helped maintain high temperatures in the compost pile for an extended period (above 50 °C for 18 days), which in turn facilitated water dissipation. High-throughput sequencing showed that Firmicutes played a significant role in batch-fed composting (BFC). They had a high relative abundance at the beginning (98.64%) and end (45.71%) of compost. Additionally, BFC showed promising results in removing ARGs, with reductions of 3.04-1.09 log copies/g for Aminoglycoside and 2.26-2.44 log copies/g for β_Lactamase. This study provides a comprehensive survey of BFC and demonstrates its potential for eliminating resistance contamination in compost.

Characteristics of antibiotic resistance genes and microbial community distribution in Wanfeng Lake, upper Pearl River, China

Wanfeng Lake, a highland lake in the upper part of the Pearl River Basin, China, has long been disturbed by aquaculture and human activities, resulting in the accumulation of antibiotics and antibiotic resistance genes (ARGs), which pose a major threat to humans and animals. In this study, 20 antibiotics, 9 ARGs, 2 mobile genetic elements (intl1 and intl2), and microbial community structure were investigated in Wanfeng Lake. The results of the study showed that the total concentration of antibiotics in surface water was 372.72 ng/L, with ofloxacin (OFX) having the highest concentration (169.48 ng/L), posing a high ecological risk to aquatic organisms. The total concentration of antibiotics in sediments was 235.86 ng/g, with flumequine (FLU) having the highest concentration (122.54 ng/g). This indicates that the main type of antibiotics in Wanfeng Lake are quinolones. QPCR analysis results of the relative abundance of ARGs in both surface water and sediments showed that sulfonamide resistance genes > macrolide resistance genes > tetracycline resistance genes > quinolone resistance genes, indicating that sulfonamide resistance genes were the dominant type. The metagenomic results showed that the predominant microorganisms in the sediment under the phylum level were Planctomycetes, Proteobacteria, Euryarchaeota, and Chloroflexi. Pearson's correlation analysis showed a significantly positive correlation between antibiotics and environmental factors with ARGs in Wanfeng Lake and a significant positive correlation between antibiotics and ARGs with microorganisms in sediments. This suggests that there is a potential pressure of antibiotics on ARGs, while microorganisms provide the driving force for the evolution and spread of ARGs. This study provides a basis for further research on the occurrence and spread of antibiotics and ARGs in Wanfeng Lake. A total of 14 antibiotics were detected in surface water and sediments. OFX poses a high ecological risk in all points of surface water. Antibiotics and ARGs were significantly positively correlated in Wanfeng Lake. Antibiotics and ARGs in sediments were positively correlated with microorganisms.

Co-occurrence pattern of ARGs and N-functional genes in the aerobic composting system with initial elevated temperature

Animal manure is known to harbor antibiotic resistance genes (ARGs). Aerobic composting is a prevalent cost-effective and sustainable method to treat animal waste. However, the effect of initially elevated temperature on antibiotic resistome during the composting process is unclear. In this study composting was subjected to initial external heating (EHC) for a period of 5 days compared to conventional composting (CC). After composting ARGs abundance was significantly reduced by 2.43 log in EHC and 1.95 log in CC. Mobile genetic elements (MGEs) also exhibited a reduction of 1.95 log in EHC and 1.49 log in CC. However, during the cooling phase, the genes resisting macrolide lincosamide and streptogramin B (MLSB) rebounded by 0.04 log in CC. The potential human pathogenic bacteria Pseudomonas (41.5-61.5%) and Actinobacteria (98.4-98.8%) were significantly reduced in both treatments and the bulk of targeted antibiotics were eliminated by 80.74% in EHC and 68.98% in CC. ARGs and N-functional genes (NFGs), mainly denitrification genes, were carried by the same microbial species, such as Corynebacterium sp. and Bacillus sp., of the dominant phylum. Redundancy analysis (RDA) revealed that CC microbial communities played a key role in the enrichment of ARGs while in EHC the variation of ARGs was attributed to the composting temperature. The number of high-risk ARGs was also lower in EHC (4) compared with CC (6) on day 30. These results provide insight into the effects of an initially enhanced temperature on ARGs removal and the relationship between ARGs and NFGs during the composting process.

Unexpected enrichment of antibiotic resistance genes and organic remediation genes in high-altitude lakes at Eastern Tibetan Plateau

Elevation has a strong effect on aquatic microbiome. However, we know little about the effects of elevation on functional genes, especially antibiotic resistance genes (ARGs) and organic remediation genes (ORGs) in freshwater ecosystems. In this study, we analyzed five classes of functional genes including ARGs, metal resistance genes (MRGs), ORGs, bacteriophages, and virulence genes between two high-altitude lakes (HALs) and two low-altitude lakes (LALs) in Mountain Siguniang at Eastern Tibetan Plateau by means of GeoChip 5.0. No differences (Student's t-test, p > 0.05) of gene richness including ARGs, MRGs, ORGs, bacteriophages, and virulence genes in HALs and LALs were found. The abundance of most ARGs and ORGs was higher in HALs than in LALs. For MRGs, the abundance of macro metal resistance genes of potassium, calcium, and aluminum was higher in HALs than in LALs (Student's t-test, p < 0.05; all Cohen's d > 0.8). The abundance of some heavy metal resistance genes of lead and mercury was lower in HALs than in LALs (Student's t-test, p < 0.05; all Cohen's d < -0.8). The composition of these functional genes in HALs differed significantly from in LALs. The functional gene network in HALs was also more complex than that in LALs. We speculate that enrichment of ARGs and ORGs in HALs is related to different microbial communities, exogenous ARGs, and enriched persistent organic pollutants through long-range atmospheric transport driven by the Indian monsoon. This study highlights the unexpected enrichment of ARGs, MRGs, and ORGs in remote lakes at high elevations.

Comparative insight into the effects of different carbon source supplement on antibiotic resistance genes during whole-run and short-cut nitrification-denitrification processes

Mature landfill leachate is known for nitrogen-removal challenging and meantime was considered as an important sink of antibiotic resistance genes (ARGs). The added external carbon sources, enabling the short-cut nitrification and denitrification, may facilitate the proliferation of bacteria that possibly carry ARGs. However, this speculation has yet to be studied. Here, we explored the effects of glucose, sodium acetate, and methanol supplements on ARGs during whole-run and short-cut treatment processes. The results showed that sodium acetate supplement during short-cut process efficiently reduced the abundances of total ARGs (0.84-1.99 copies/16S rRNA) and integrons (0.59-1.20 copies/16S rRNA), which were highly enhanced by methanol addition during whole-run treatment process (total ARGs: 3.60-11.01 copies/16S rRNA, integrons: 1.20-4.69 copies/16S rRNA). Indirect gradient analysis showed that the variation of ARGs was not correlated with the supplement of different external carbon source. Correlation analysis indicated that dominant intl1 (55.99 ± 17.61% of integrons) showed positively significant correlations with all detected ARGs expect for sul2 and ermB (p < 0.05), suggesting the significant role on ARGs dissemination. Redundancy analysis illustrated that the potential hosts of intl1, intl2, sul1, tetQ, tetM, mefA, and mexF were dominant Bacteroidetes and Actinobacteria. Interestingly, the numbers and significant extent of correlations under the supplement of sodium acetate during short-cut denitrification process were obviously declined, and it was in accordance with ARGs reduced by sodium acetate supplement, suggesting sodium acetate displayed the efficient ARGs reduction during short-cut process. In summary, this study provides a comparative understanding of the effects on ARGs by different carbon source supplements during nitrification-denitrification processes of leachate; sodium acetate is the optimal carbon source.

Antibiotic and heavy metal resistance genes in sewage sludge survive during aerobic composting

Municipal sewage sludge has been generated in increasing amounts with the acceleration of urbanization and economic development. The nutrient rich sewage sludge can be recycled by composting that has a great potential to produce stabilized organic fertilizer and substrate for plant cultivation. However, little is known about the metals, pathogens and antibiotic resistance transfer risks involved in applying the composted sludge in agriculture. We studied changes in and relationships between heavy metal contents, microbial communities, and antibiotic resistance genes (ARGs), heavy metal resistance genes (HMRGs) and mobile genetic elements (MGEs) in aerobic composting of sewage sludge. The contents of most of the analyzed heavy metals were not lower after composting. The bacterial α-diversity was lower, and the community composition was different after composting. Firmicutes were enriched, and Proteobacteria and potential pathogens in the genera Arcobacter and Acinetobacter were depleted in the composted sludge. The differences in bacteria were possibly due to the high temperature phase during the composting which was likely to affect temperature-sensitive bacteria. The number of detected ARGs, HMRGs and MGEs was lower, and the relative abundances of several resistance genes were lower after composting. However, the abundance of seven ARGs and six HMRGs remained on the same level after composting. Co-occurrence analysis of bacterial taxa and the genes suggested that the ARGs may spread via horizontal gene transfer during composting. In summary, even though aerobic composting is effective for managing sewage sludge and to decrease the relative abundance of potential pathogens, ARGs and HMRGs, it might include a potential risk for the dissemination of ARGs in the environment.

Sulfamethoxazole degradation by Aeromonas caviae and co-metabolism by the mixed bacteria

Sulfamethoxazole (SMX) is a frequently detected antibiotic in the environment and has attracted much attention. Aeromonas caviae strain GLB-10 was isolated, which could degrade SMX to Aniline and 3-Amino-5-methylisoxazole. Compared to the single bacteria, the mixed bacteria including stain GLB-10, Vibrio diabolicus strain L2-2, Zobellella taiwanensis, Microbacterium testaceum, Methylobacterium, etc, had an ultrahigh degradation efficiency to SMX, with 250 mg/L SMX being degraded in 3 days. In addition to bioproducts of single bacteria, SMX bioproducts by the mixed bacteria also included acetanilide and hydroquinone which were not detected in the single bacteria. The SMX degradation mechanism of the mixed bacteria was more complicated including acetylation, sulfur reduction 4S pathway, and ipso-hydrolysis. The molecular mechanism of the mixed bacteria degrading SMX was also investigated, revealing that the resistance mechanism related to protein outer membrane protein and catalase peroxidase were overexpressed, meanwhile, 6-hydroxynicotinate 3-monooxygenase and ammonia monooxygenase might be the key proteins in SMX degradation. The mixed bacteria could efficiently degrade SMX in different real environments including tap water, river water, artificial lake water, estuary, and, marine water, and have very great research value in bacterial co-metabolism and biodegradation of sulfonamides antibiotics in the environment.

Application of spray-dried erythromycin fermentation residue as a soil amendment: antibiotic resistance genes, nitrogen cycling, and microbial community structure

Erythromycin fermentation residue (EFR) after spray drying could be reused as a soil amendment. However, the effects of spray-dried EFR on antibiotic resistance genes (ARGs), nitrogen cycling, and microbial community structure in soil are rarely reported. In this study, a pot experiment was conducted by adding spray-dried EFR to soil. For the application of 1.0% spray-dried EFR, the residual erythromycin (ERY) could be rapidly removed with the half-life of 22.2 d; the total relative abundance of ARGs increased at first, but decreased to the initial level of the control group in the end; genes related to ammonium assimilation (glnA, gltB, gltD), ammonification (gdhA, gudB, cynT, cynS, ncd2), denitrification (narI, narG, narH), assimilatory nitrate reduction (nirA, nasA), and dissimilatory nitrate reduction (nirD) were enriched; soil microbial community structure presented temporary variation. Network analysis showed significant negative correlations between ARGs and nitrogen cycling genes. The addition of 6.0% spray-dried EFR resulted in the amplification of ARGs and inhibition of nitrogen cycling. This work provides new insights into the effects of spray-dried EFR on ARGs, nitrogen cycling, and microbial community structure within the fertilized soil.

Exploring antibiotic resistance load in paddy-upland rotation fields amended with commercial organic and chemical/slow release fertilizer

Agricultural fertilization caused the dissemination of antibiotic resistance genes (ARGs) in agro-ecological environment, which poses a global threat to crop-food safety and human health. However, few studies are known about the influence of different agricultural fertilization modes on antibiotic resistome in the paddy-upland rotation soils. Therefore, we conducted a field experiment to compare the effect of different fertilization (chemical fertilizer, slow release fertilizer and commercial organic fertilizer replacement at various rates) on soil antibiotic resistome in paddy-upland rotation fields. Results revealed that a total of 100 ARG subtypes and 9 mobile genetic elements (MGEs) occurred in paddy-upland rotation soil, among which MDR-ARGs, MLSB-ARGs and tet-ARGs were the dominant resistance determinants. Long-term agricultural fertilization remarkably facilitated the vertical accumulation of ARGs, in particular that bla _ampC and tetO in relative abundance showed significant enrichment with increasing depth. It's worth noting that slow release fertilizer significantly increased soil ARGs, when comparable to manure with 20% replacing amount, but chemical fertilizer had only slight impact on soil ARGs. Fertilization modes affected soil microbial communities, mainly concentrated in the surface layer, while the proportion of Proteobacteria with the highest abundance decreased gradually with increasing depth. Furthermore, microbial community and MGEs were further proved to be essential factors in regulating the variability of ARGs of different fertilization modes by structural equation model, and had strong direct influence (λ = 0.61, p < 0.05; λ = 0. 55, p < 0.01). The results provided scientific guidance for reducing the spreading risk of ARGs and control ARG dissemination in agricultural fertilization.

Removal of antibiotic resistance genes during livestock wastewater treatment processes: Review and prospects

Antibiotic resistance genes (ARGs) are emerging pollutants that have received extensive attention. Many different types of ARGs exist in livestock wastewater. If not effectively treated, they can threaten animal production, public health and the ecological safety of the surrounding environment. To address the high risk of livestock wastewater contamination by ARGs, the effects of different wastewater treatment processes on ARGs and their influencing factors and mechanisms are reviewed herein. Additionally, the current problems associated with removal of ARGs are discussed, and future research is proposed.

Structure and function response of bacterial communities towards antibiotic contamination in hyporheic zone sediments

Bacterial communities are crucial for processing and degrading contaminants in hyporheic zones (HZ). However, the effects of antibiotics on HZ bacterial communities have seldom been addressed. Here, using MiSeq 16S amplicon sequencing technology, the effects of acute exposure to Enrofloxacin, Sulfathiazole, Tetracycline hydrochloride, and Penicillin V potassium on HZ bacterial communities were investigated. Results revealed that HZ sediment communities responded differently to different classes of antibiotics, reflecting the distinct selection stress of antibiotics on HZ bacterial communities. Besides, HZ communities from the locations with more severe antibiotic contamination backgrounds (∼150 μg kg^-1) were more resistant towards antibiotic treatment. Compared with small/non-significant changes in HZ community diversity and composition treated with ng L^-1∼ug L^-1 level antibiotics compared to the control group, treatments with antibiotics over mg L^-1 level significantly reduced the diversity and changed the structures of HZ bacterial communities, and enhanced the resistance of the community to antibiotics by enriching antibiotic resistant bacteria. The exposure to mg L^-1 level antibiotics also changed community functions by restricting the growth of functional bacteria, such as ammonia oxidizing bacteria (AOB) Nitrosomonas, resulting in ammonia accumulation in sediments. The results implied that at field-relevant concentrations, there was no or minor effect of antibiotics on HZ bacterial community structure and functions, and only those areas with high antibiotic concentrations would have effects.

Damage and elimination of soil and water antibiotic and heavy metal pollution caused by livestock husbandry

The combination of antibiotics and heavy metals (HMs) increases the toxicity range of influence and requires additional research attention. This article analyzed the toxicity mechanisms and damage of combined pollution. Cross-resistance, co-resistance, and co-regulation are the primary toxicity mechanisms. Combined pollution increases antibiotic resistance genes (ARGs), increases bacterial resistance, and promotes the horizontal transfer of ARGs, affecting the types and distribution of microorganisms. The hazard of combined pollution varies with concentration and composition. The physicochemical and biological technologies for eliminating combined pollution are primarily elaborated. Adsorption, photocatalytic degradation, and microbial treatment show high removal rates and good recyclability, indicating good application potential. This review provides a basis and reference for the further study the elimination of combined antibiotic and HM pollution.

Removal of carbamazepine, venlafaxine and iohexol from wastewater effluent using coupled microalgal-bacterial biofilm

We evaluated the removal capacity of a coupled microalgal-bacterial biofilm (CMBB) to eliminate three recalcitrant pharmaceuticals. The CMBB's efficiency, operating at different biofilm concentrations, with or without light, was compared and analyzed to correlate these parameters to pharmaceutical removal and their effect on the microorganism community. Removal rates changed with changing pharmaceutical and biofilm concentrations: higher biofilm concentrations presented higher removal. Removal of 82-94% venlafaxine and 18-51% carbamazepine was obtained with 5 days of CMBB treatment. No iohexol removal was observed. Light, microorganism composition, and dissolved oxygen concentration are essential parameters governing the removal of pharmaceuticals and ammonia. Chlorophyll concentration increased with time, even in the dark. Three bacterial phyla were dominant: Proteobacteria, Bacteroidetes and Firmicutes. The dominant eukaryotic supergroups were Archaeplastida, Excavata and SAR. A study of the microorganisms' community indicated that not only do the species in the biofilm play an important role; environment, concentration and interactions among them are also important. CMBB has the potential to provide low-cost and sustainable treatment for wastewater and recalcitrant pharmaceutical removal. The microenvironments on the biofilm created by the microalgae and bacteria improved treatment efficiency.

Metagenomic insights into the spatiotemporal responses of antibiotic resistance genes and microbial communities in aquaculture sediments

The dissemination of antibiotic resistance genes (ARGs) in aquaculture systems is a potential threat to environmental safety and human health. However, the spatiotemporal distribution pattern of ARGs and key factors associated with their dissemination in aquaculture sediments remain unclear. In this study, ARGs, mobile genetic elements, microbial community composition, heavy metal contents, and nutrient contents of samples collected from a whole culture cycle of fish in a representative aquaculture farm were characterized. The distribution patterns of nine subtypes of ARGs (tetW, tetM, tetA, ermC, ermB, sul1, sul2, floR, and qnrS) showed clear spatiotemporal differences. The absolute abundance of ARGs in aquaculture sediments was higher in winter and in rivers of the aquaculture farm. Proteobacteria was the dominant phylum in all sediment samples. The results of network and redundancy analyses confirmed that the Dechloromonas, Candidatus Accumulibacter, Smithella, Geobacter, and Anaeromyxobacter belonging to Proteobacteria were positively correlated with ARGs, suggesting that these microbial species are potential hosts of corresponding ARGs. Our study highlights that the microbial community is the determining factor for ARG dissemination. Strategies for inhibiting these potential hosts of ARGs should be developed based on controllable factors.

Dissemination of antibiotic resistance genes from landfill leachate to groundwater

Landfill leachate, a highly concentrated organic wastewater containing diverse microorganisms and various heavy metals, has become an important reservoir of antibiotic resistance genes (ARGs). In this study, a total of 203 unique ARGs and 10 mobile genetic elements (MGEs) were identified from collected landfill leachate and groundwater. The number and abundance (normalized and absolute) of antibiotic resistome in effluent of leachate treatment plants decreased significantly compared to influent. The abundance of ARGs in groundwater increased as the distance from the leachate basin decreased. Fast expectation-maximization microbial source tracking (FEAST) showed that up to 96 % of ARGs in groundwater (GW3) may originate from nearby leachate, suggesting that ARGs in leachate can penetrate and spread into the groundwater environment. A significant correlation between ARGs and bacterial communities was identified. Together with network analysis showing the 12 bacterial taxa co-occurring with seven classes of antibiotic-associated ARGs, our results revealed the diverse potential microbial hosts of ARGs in water samples around the landfill sites. Heavy metals, bacterial community and MGEs were the driving factors shaping the ARGs patterns in the water samples, with their interactions explaining 57 % of ARGs variations. Our results provide an understanding of the distribution and dissemination of ARGs from landfill leachate to the nearby groundwater and suggest a comprehensive impact assessment of ARGs in aquatic environments of landfills.

Metagenomic analysis of microbial community structure and distribution of resistance genes in Daihai Lake, China

The emergence of resistance genes is a global phenomenon that poses a significant threat to both animals and humans. Lakes are important reservoirs of genes that confer resistant to antibiotics and metals. In this study, we investigated the distribution and diversity of antibiotic resistance genes (ARGs) and metal resistance genes (MRGs) in the sediment of Daihai Lake using high-throughput sequencing and metagenomic analysis. The results indicated that all sampling sites had similar bacterial community structures, with Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes being the most abundant. A total of 16 ARG types containing 111 ARG subtypes were deposited in the sediment. Among the resistance genes to bacitracin, multidrug, macrolide-lincosamide-streptogramin (MLS), tetracycline, beta-lactam, and sulfonamide were the dominant ARG types, accounting for 89.9-94.3% of the total ARGs. Additionally, 15 MRG types consisting of 146 MRG subtypes were identified. In all samples, MRGs of the same type presented resistance to Pb, Ni, Hg, W, Zn, Ag, Cr, Fe, As, Cu, and multimetals. Overall, the distribution and diversity of antibiotic and metal resistance genes showed no significant differences in the samples. Plasmids (91.03-91.82%) were the most dominant mobile genetic elements in the sediments of Daihai Lake. Network analysis indicated that the target ARGs and MRGs were significantly positively correlated with the microorganisms. Potential hosts for various ARGs and MRGs include Proteobacteria, Euryarchaeota, Actinobacteria, Chloroflexi, and Bacteroidetes.

Recovery of the Structure and Function of the Pig Manure Bacterial Community after Enrofloxacin Exposure

A stable intestinal bacterial community balance is beneficial for animal health. Enrofloxacin is widely used in animal husbandry as a therapeutic drug, but it can cause intestinal environmental imbalance.

The panorama of antibiotics and the related antibiotic resistance genes (ARGs) in landfill leachate

Landfill leachate is an important source and sink of antibiotics and antibiotic resistance genes (ARGs), which poses a potential threat to human health and ecological environment. Ten antibiotics and 8 ARGs in leachates collected from Zhejiang Province, China, were systematically investigated. The effects of multiple factors were considered: leachate age, season when the leachate was sampled (dry or rainy), heavy metal concentrations, and leachate quality parameters. Leachate age was crucial to the profile of the detectable antibiotics and ARGs. The total concentration of antibiotics were in the order of macrolides > sulfonamides > tetracyclines and they decreased significantly with leachate age. Similarly, fewer ARGs were harbored in aged leachate; the order of abundance of the ARGs was mexF (11.92 ± 0.22 log₁₀ gene copies/L) > sul2 > Intl1 > sul1 > ermB > mefA > tetM > tetQ (9.57 ± 1.32 log₁₀ gene copies/L). The extreme abundances (i.e., the maxima and minima) of ARGs relating to the same class of antibiotic were always surprisingly similar and appeared in leachate of the same age. Seasonal variation greatly affected the concentrations of antibiotics in the leachate-the concentration difference between the dry and rainy seasons could reach two orders of magnitude. Heavy metal concentrations and leachate quality parameters also had important effects on the distribution of antibiotics and ARGs. Overall, the profile of antibiotics and ARGs in leachates was influenced by numerous factors, and the pollution of antibiotics and ARGs may be reduced and controlled by adjusting the environmental factors.

Short-term biodrying achieves compost maturity and significantly reduces antibiotic resistance genes during semi-continuous food waste composting inoculated with mature compost

Food waste (FW) is important object of resource utilization and source of antibiotic resistance genes (ARGs). This study investigated the effects of biodrying combined with inoculating mature compost (B&M) on the composting efficiency, succession of bacterial communities and their links with metabolism functions as well as the fate of ARGs during FW composting. The results showed that B&M could rapidly raise and maintain high relative abundance of Bacillaceae (66.59-94.44%) as well as composting temperature (45.86-65.86 ℃), so as to achieve the final maturity of FW composting in a short time by regulating microbial carbohydrate (14.02-15.31%) and amino acid metabolism (10.33-12.47%). Network analysis demonstrated that high temperature could effectively inhibit the proliferation and spread of potential bacterial hosts of ARGs and integrons including Lactobacillaceae, Enterobacteriaceae, Leuconostocaceae and Corynebacteriaceae during the first two days of composting. As a result, B&M significantly reduced the absolute (72.09-99.47%) and relative abundances (0.31-2.44 logs) of nearly all ARGs especially ermB, tetM, bla_CTX-M and bla_OXA. Present study deepened the knowledge of ARGs variation, succession and metabolism functions of bacterial communities when B&M processes were used for FW composting, suggesting a promising technology for reducing the transmission risk of ARGs and reaching maturity of FW composting.

Behaviors of antibiotic resistance genes (ARGs) and metal resistance genes (MRGs) during the pilot-scale biophysical drying treatment of sewage sludge: Reduction of ARGs and enrichment of MRGs

Biophysical drying (BPD) is one of the best alternatives for reducing the moisture content from sewage sludge by utilizing biological heat from aerobic reactions. However, the fate of emerging pollutants during BPD process is largely unknown. In this study, the fates of antibiotic resistance genes (ARGs) and metal resistance genes (MRGs) were investigated during a pilot-scale BPD treatment of sewage sludge. A total of 20 types (388 subtypes) of ARGs and 16 types (364 subtypes) of MRGs were detected by metagenomic sequencing and annotation. The total abundance of ARGs decreased from 1.78 ± 0.13 copies/16S rRNA to 0.55 ± 0.01 copies/16S rRNA while the total abundance of MRGs increased from 3.81 ± 0.01 copies/16S rRNA to 6.30 ± 0.02 copies/16S rRNA, showing the distinct behaviors of ARGs and MRGs during BPD process. The ARGs were effectively reduced during the mesophilic and thermophilic stages of BPD process and the reduction of ARGs fitted the first-order kinetic model (p < 0.01). Microbial community analysis showed that the abundance of potential pathogens also decreased during BPD process. On the contrary, the abundances of most MRG subtypes (78.3%) were enriched during BPD process with up to 122-fold change, implying the potential threats for the end product of BPD process. These results together indicate that although the ARGs and potential pathogens can be effectively reduced during BPD process, the safety for the end product still needs to be considered due to the enrichment of MRGs.

Metatranscriptomic insight into the effects of antibiotic exposure on performance during anaerobic co-digestion of food waste and sludge

Antibiotics are inevitably entered into anaerobic co-digestion (AcoD) system of food waste (FW) and sludge along with the addition of abundant antibiotic-containing activated sludge. However, the in-depth insights into antibiotics affecting AcoD performance have not comprehensively studied. In present study, the results showed that tetracycline (TC), sulfamethoxazole (SMZ) and erythromycin (ERY) inhibited and delayed methane production except for 5 mg/L ERY. By comparison, TC and SMZ significantly inhibited the cumulative methane yields (one-way ANOVA, p < 0.01), and the inhibition effects were magnified as the antibiotic level increased. Physicochemical and methane yield analysis indicated antibiotics inhibited hydrolysis process and delayed methanogenesis process, which was in line with the declined abundance of acetogenic Proteiniphilum and hydrogenotrophic Methanobacterium during AcoD. Furthermore, metatranscriptomic analysis demonstrated the microbial activities of major organic and energy metabolism were down-regulated under antibiotics exposure, thereby down-regulating the expressions of key coenzymes (coenzymes M, F420, methanofuran) biosynthesis for methanogenesis and methane metabolism. The declined methanogenesis activity was completely consistent with the inhibited activity of dominant Methanosarcina and methane production, proving the importance of Methanosarcina on methane production. This study provides new metatranscriptomic evidence into the effects of antibiotics on methanogenesis during AcoD.

The vertical migration of antibiotic-resistant genes and pathogens in soil and vegetables after the application of different fertilizers

The prevalence of bacterial resistance caused by the application of animal manure has become an important environmental issue. Herein, the vertical migration of antibiotic resistance genes (ARGs) and pathogens in soil and vegetables after the application of different fertilizers was explored. The results showed that the application of composted manure considerably enhanced the abundance of most ARGs and pathogens, especially in surface soil and pakchoi roots. Moreover, the soil ARGs increased partially from log 1.93 to log 4.65 after the application of composted manure, and six pathogens were simultaneously detected. It was observed that the increase in soil depth decreased most ARGs and pathogens by log 1.04-2.24 and 53.98 %~85.54 %, respectively. This indicated that ARGs and pathogens still existed in the deep soil (80-100 cm). Moreover, total organic carbon had a significant influence on the pathogen distribution, whereas bacterial communities primarily drove the vertical migration of ARGs rather than environmental factors. Although most of the ARG-host associations observed in the surface soil were disappeared in deep soil as revealed by network analysis, some co-occurrence pattern still occurred in deep soil, suggesting that some ARGs might be carried to deep soil by their host bacteria. These results were novel in describing the vertical migration of ARGs in the environment after the application of different fertilizers, providing ideas for curbing their migration to crops.

Dissemination of antibiotic resistance under antibiotics pressure during anaerobic co-digestion of food waste and sludge: Insights of driving factors, genetic expression, and regulation mechanism

This study revealed the effects and regulation mechanisms on antibiotic resistance genes (ARGs) dissemination during anaerobic co-digestion (AcoD) of food waste and sludge under the exposure of tetracycline, sulfamethoxazole (SMZ) and erythromycin (ERY). Results indicated antibiotics significantly increased the abundance of ARGs, and selectively enriched integron gene, suggesting antibiotics promoted the dissemination of ARGs. Procrustes analysis indicated that bacterial community, integrons and physicochemical properties displayed significant correlations with ARGs, and they respectively contributed 10.61%, 6.94% and 2.97% of explanations on ARGs variation. Especially, the maximum combined contribution (48.6%) of bacterial community and integrons, implying their significances on ARGs alteration. Metatranscriptomic analysis further demonstrated antibiotics upregulated the expressions of total ARGs and virulence factors, raising potential risks. The proposed mechanisms for ARGs dissemination facilitated by antibiotics might be attributed to the changes of ARGs-regulated functions for inducing DNA/cell damage and DNA conjugation during AcoD.

Response of microbial nitrogen transformation processes to antibiotic stress in a drinking water reservoir

Effects of antibiotics on microbial nitrogen transformation processes in natural aquatic ecosystems are largely unknown. In this study, we utilized the ¹⁵N stable isotope tracers and metagenomic sequencing to identify how antibiotics drive nitrogen transformation processes in Danjiangkou Reservoir, which is the largest artificial drinking water reservoir in China. We retrieved 51 nitrogen functional genes, and found that the highest abundances of nitrate reduction and denitrification-related genes occurred in dissimilatory nitrogen transformation pathways. ¹⁵N-labelling analysis substantiated that denitrification was the main pathway for nitrogen removal, accounting for 57.1% of nitrogen loss. Nitrogen functional genes and antibiotic resistance genes co-occurred in Danjiangkou Reservoir, and they were mainly carried by the denitrifying bacteria such as Rhodoferax, Polaromonas, Limnohabitans, Pararheinheimera, Desulfobulbus, and Pseudopelobacter. Genome annotation revealed that antibiotic deactivation, Resistance-Nodulation-Division and facilitator superfamily efflux pumps were responsible for the multiple-resistance to antibiotics in these bacteria. Moreover, antibiotics showed non-significant effects on nitrogen transformation processes. It is speculated that denitrifying bacteria harboring ARGs played crucial roles in protecting nitrogen transformation from low-level antibiotics stress in the reservoir. Our results highlight that denitrifying bacteria are important hosts of ARGs, which provides a novel perspective for evaluating the effects of antibiotics on nitrogen cycle in natural aquatic ecosystems.

An Ohio State Scenic River Shows Elevated Antibiotic Resistance Genes, Including Acinetobacter Tetracycline and Macrolide Resistance, Downstream of Wastewater Treatment Plant Effluent

The entry of antibiotic resistance genes (ARGs) into aquatic systems has been documented for large municipal wastewater treatment plants (WWTPs), but there is less study of the impact of smaller plants that are situated on small rural rivers. We sampled water metagenomes for ARGs and taxa composition from the Kokosing River, a small rural river in Knox County, Ohio, which has been designated an Ohio State Scenic River for retention of natural character. Samples were obtained 1.0 km upstream, 120 m downstream, and 6.4 km downstream from the effluent release of the Mount Vernon WWTP. ARGs were identified in metagenomes using ShortBRED markers from the comprehensive antibiotic resistance database (CARD) screened against UniPROT. Through all seasons, the metagenome just downstream of the WWTP effluent showed a substantial elevation of at least 15 different ARGs, including 6 ARGs commonly associated with Acinetobacter baumannii, such as msrE, mphE (macrolide resistance), and tet(39) (tetracycline resistance). The ARGs most prevalent near the effluent pipe persisted 6.4 km downriver. Using metagenomic phylogenetic analysis (MetaPhlAn2) clade-specific marker genes, the taxa distribution near the effluent showed elevation of reads annotated as Acinetobacter species as well as gut-associated taxa, Bacteroides and Firmicutes. The ARG levels and taxa prevalence showed little dependence on seasonal chlorination of the effluent. Nitrogen and phosphorus were elevated near the effluent pipe but had no consistent correlation with ARG levels. We show that in a rural river microbiome, year-round wastewater effluent substantially elevates ARGs, including those associated with multidrug-resistant A. baumannii.

IMPORTANCE Antibiotic resistance is a growing problem worldwide, with frequent transmission between pathogens and environmental organisms. Rural rivers can support high levels of recreational use by people unaware of inputs from treated wastewater, while wastewater treatment plants (WWTPs) can generate a small but significant portion of flow volume into a river surrounded by forest and agriculture. There is little information on the rural impacts of WWTP effluent on the delivery and transport of antibiotic resistance genes. In our study, the river water proximal to wastewater effluent shows evidence for the influx of multidrug-resistant Acinetobacter baumannii, an opportunistic pathogen of concern for hospitals but also widespread in natural environments. Our work highlights the importance of wastewater effluent in management of environmental antibiotic resistance, even in high quality, rural river systems.

Annual trends and health risks of antibiotics and antibiotic resistance genes in a drinking water source in East China

The extensive pollution of antibiotics and antibiotic resistance genes (ARGs) in drinking water has aroused worldwide concern. Successive monitoring of these pollutants has noteworthy significance for drinking water safety. Accordingly, this study conducted successive monitoring of antibiotics and ARGs from 2015 to 2017 in a drinking water source in East China. The total antibiotic concentration ranged from 19.68 ng/L to 497.00 ng/L, and decreased slightly from 2015 to 2017. Eighteen out of forty-one ARG subtypes showing resistance to six antibiotic classes and one class I integrase gene intI1, were detected in the drinking water source at concentrations ranging from 6.5 × 10⁴ copies/mL to 1.6 × 10⁶ copies/mL. Importantly, the total ARG concentration increased on an annual basis from 2015 to 2017 with an average annual increment of 0.25 orders of magnitude, which was mainly attributed to the increase in specific ARG subtypes, such as sul1, sul2, sul3, tetA, qnrB, and ermB. Most ARGs was positively correlated with the intI1 genes (r = 0.47-0.55, P < 0.01). Furthermore, the variation of antibiotics and ARGs appeared to be related to the water indices, particularly of the values of COD, BOD_5, NO₂-N (P < 0.05). This study provides basic data on antibiotic and ARG pollution in the studied drinking water source. Importantly, the findings expound that although the residual antibiotics in this drinking water source decreased slightly from 2015 to 2017, while its biological effect, the antibiotic resistance, increased annually, which give a warning of the antibiotic resistance pollution in the drinking water source.

Bacterial Community Structure and Dynamic Changes in Different Functional Areas of a Piggery Wastewater Treatment System

Chemicals of emerging concern (CEC) in pig farm breeding wastewater, such as antibiotics, will soon pose a serious threat to public health. It is therefore essential to consider improving the treatment efficiency of piggery wastewater in terms of microorganisms. In order to optimize the overall piggery wastewater treatment system from the perspective of the bacterial community structure and its response to environmental factors, five samples were randomly taken from each area of a piggery’s wastewater treatment system using a random sampling method. The bacterial communities’ composition and their correlation with wastewater quality were then analyzed using Illumina MiSeq high-throughput sequencing. The results showed that the bacterial community composition of each treatment unit was similar. However, differences in abundance were significant, and the bacterial community structure gradually changed with the process. Proteobacteria showed more adaptability to an anaerobic environment than Firmicutes, and the abundance of Tissierella in anaerobic zones was low. The abundance of Clostridial (39.02%) and Bacteroides (20.6%) in the inlet was significantly higher than it was in the aerobic zone and the anoxic zone (p < 0.05). Rhodocyclaceae is a key functional microbial group in a wastewater treatment system, and it is a dominant microbial group in activated sludge. Redundancy analysis (RDA) showed that chemical oxygen demand (COD) had the greatest impact on bacterial community structure. Total phosphorus (TP), total nitrogen (TN), PH and COD contents were significantly negatively correlated with Sphingobacteriia, Betaproteobacteria and Gammaproteobacteria, and significantly positively correlated with Bacteroidia and Clostridia. These results offer basic data and theoretical support for optimizing livestock wastewater treatment systems using bacterial community structures.

The variation of antibiotic resistance genes and their links with microbial communities during full-scale food waste leachate biotreatment processes

The prevalence of antibiotic resistance genes (ARGs) has been widely reported in various environments. However, little is known of them in food waste (FW) leachate with high organic content and how their distribution is influenced by biotreatment processes. Here, twelve ARGs, two integrase genes and bacterial communities were investigated during two full-scale FW biotreatment processes. High ARGs abundances (absolute: 1.03 × 10⁷-2.82 × 10⁹copies/mL; relative: 0.076-2.778copies/16S rRNA) were observed across all samples. Although biotreatment effectively reduced absolute abundance of ARGs, additional bacteria acquiring ARGs caused an increase in their relative abundance, which further increased the transmission risk of ARGs. mexF, blaCTX-M, sul1 played crucial roles and sul1 might be considered as an indicator for the prediction of total ARGs. It is worrying that the discharge (effluent and sludge) included highly abundant ARGs (5.09 × 10¹⁴-4.83 × 10¹⁵copies/d), integrons (1.11 × 10¹⁴-6.04 × 10¹⁴copies/d) and potential pathogens (such as Pseudomonas and Streptococcus), which should be given more attentions. blaCTX-M and tetQ possessed most potential hosts, Proteobacteria-L and Firmicutes-W were predominant contributors of ARGs-hosts at genus level. This study suggested FW leachate biotreatment systems could be reservoirs of ARGs and facilitated the proliferation of them. The exploration of effective removal methods and formulation of emission standard are necessary for future ARGs mitigation.

Bacterial community compositions and nitrogen metabolism function in a cattle farm wastewater treatment plant revealed by Illumina high-throughput sequencing

Bacteria play an important role in pollutant transformation in activated sludge-based wastewater treatment plants (WWTPs). Exploring the microbial community structure and diversity is essential to improving the performance of wastewater treatment processes. This study employed Illumina MiSeq high-throughput sequencing to investigate the microbial community composition and diversity in a cattle farm wastewater treatment plant (Cf-WWTP). The results showed that the dominant phyla in the whole process were Proteobacteria, Bacteroidetes, and Firmicutes. The principal coordinate analysis (PCoA) indicated that the different stages had a significant impact on the microbial community structure; Bacteroidetes was the dominant phylum in the anearobic stage and Proteobacteria was the dominant phylum in the anoxic-oxic stage. Redundancy analysis (RDA) revealed that total phosphorus (TP) was the most significant factor that regulated the microbial community composition, followed by chemical oxygen demand (COD), total nitrogen (TN), and pH. Proteobacteria, Patescibacteria, and Chloroflexi were simultaneously negatively correlated with TN, COD, and TP. Nitrogen metabolic pathway and transformation mechanism was elucidated by a complete denitrification function predicted with phylogenetic investigation of communities with reconstruction of unobserved states (PICRUSt), as well as detection of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB). These results provide new insights into our understanding of microbial community and metabolic functions of Cf-WWTP.

Insight into the evolution of microbial community and antibiotic resistance genes in anammox process induced by copper after recovery from oxytetracycline stress

The influence of copper ion (Cu²⁺) on anaerobic ammonium oxidation (anammox) performance and microbial community structures after oxytetracycline (OTC) stress recovery were assessed. Experimental results demonstrated that anammox performance were stressed by 1.0 mg L^-1 Cu²⁺ and inhibitions were reversible with total nitrogen removal rate higher than 3.08 ± 0.2 kg N m^-3 d^-1. The residual OTC in the anammox sludge could combine with Cu²⁺ introduced and thereby retarded inhibition on performance in the presence of 2.0 mg L^-1 Cu²⁺. Moreover, the positive relation of dominant bacterium Ca. Anammoxoglobus with the abundance of functional genes and parts of antibiotic resistance genes were observed, suggesting that regain of performance was the results of the gradual domestication of latent resistant species after inhibition. This investigation reveals new insights into resistance of anammox performance for Cu²⁺ and OTC.