Changes of bacterial diversity and tetracycline resistance in sludge from AAO systems upon exposure to tetracycline pressure

The proliferation of antibiotic resistance genes (ARGs) and microbial communities in industrial wastewater treatment plant treating N,N-dimethylformamide (DMF) by AAO process

The excessive use of antibiotics has resulted in the contamination of the environment with antibiotic resistance genes (ARGs), posing a significant threat to public health. Wastewater treatment plants (WWTPs) are known to be reservoirs of ARGs and considered to be hotspots for horizontal gene transfer (HGT) between bacterial communities. However, most studies focused on the distribution and dissemination of ARGs in hospital and urban WWTPs, and little is known about their fate in industrial WWTPs. In this study, collected the 15 wastewater samples containing N,N-dimethylformamide (DMF) from five stages of the anaerobic anoxic aerobic (AAO) process in an industrial WWTPs. The findings revealed a stepwise decrease in DMF and chemical oxygen demand (COD) content with the progression of treatment. However, the number and abundances of ARGs increase in the effluents of biological treatments. Furthermore, the residues of DMF and the treatment process altered the structure of the bacterial community. The correlation analysis indicated that the shift in bacterial community structures might be the main driver for the dynamics change of ARGs. Interestingly, observed that the AAO process may acted as a microbial source and increased the total abundance of ARGs instead of attenuating it. Additionally, found that non-pathogenic bacteria had higher ARGs abundance than pathogenic bacteria in effluents. The study provides insights into the microbial community structure and the mechanisms that drive the variation in ARGs abundance in industrial WWTPs.

Effect of antibiotic exposure on the characteristics of activated sludge in a landfill leachate biological treatment system

Changes in the activated sludge performance in an anaerobic/aerobic biological treatment system for leachate was discussed under the condition of tetracycline (TC) exposure. The results show that a low concentration of TC did not have an obvious effect on the removal of chemical oxygen demand (COD) while a high concentration of TC had a certain promoting effect. Under the stimulation of TC, the particle size distribution of anaerobic/aerobic sludge tended to be more uniform, the particle size of anaerobic sludge decreased while the settleability increased; however, the particle size of aerobic sludge increased due to bulking. With the addition of TC, the concentration of most heavy metal ions in sludge samples increased.TC exposure results in the release of a large amount of extracellular polymeric substances (EPS), thus leading to a smoother surface of anaerobic sludge and a rougher surface of aerobic sludge. The high removal efficiency of COD under the high concentration of TC was also presumed to be due to EPS promoting the microbial absorption of anaerobic substances in the leachate. The results clearly showed that TC had a bacteriostatic effect. After antibiotic exposure, the abundance and diversity index of bacteria in each reactor decreased obviously, the microbial community evolved, and the dominant species at the genus and phylum levels of anaerobic/aerobic reactors changed. This study provides a better understanding the effect of TC on activated sludge and has reference value for the management of antibiotic exposure in leachate treatment facilities.

Investigation of antibiotic resistance genotypic and phenotypic characteristics of marine aquaculture fish carried in the Dalian area of China

Due to the long-term and irrational use of antibiotics for the prevention and control of bacterial diseases in aquaculture, antibiotic resistance genes have become a new source of pollution in aquatic products. Factors such as the spread of drug-resistant strains and the horizontal transfer of drug-resistant genes have led to multi-drug resistance in fish-infecting bacteria, which seriously affects the quality and safety of aquatic products. In this study, 50 samples of horse mackerel and puffer fish sold in Dalian aquatic products market and seafood supermarket were collected, and the phenotypic characteristics of the bacteria carried by the fish for drugs such as sulfonamides, amide alcohols, quinolones, aminoglycosides and tetracyclines were tested and analyzed, and the resistance genes carried by fish samples were detected by SYBG qPCR. Our statistical analyses demonstrated that the drug resistance phenotypes and genotypes of bacteria carried by mariculture horse mackerel and puffer fish in the Dalian area of China were complex, and the multi-drug resistance rate reached 80%. Among the examined antibiotics, the resistance rates to cotrimoxazole, tetracycline, chloramphenicol, ciprofloxacin, norfloxacin, levofloxacin, kanamycin, and florfenicol exceeded 50%, whereas the resistance rates to gentamicin and tobramycin were 26 and 16%, respectively. The detection rate of the drug resistance genes tetA, sul1, sul2, qnrA, qnrS, and floR exceeded 70% and all samples carried more than three drug resistance genes. The correlation analysis of drug resistance genes and drug resistance phenotypes showed that the detection of the drug resistance genes sul1, sul2, floR, and qnrD was correlated with the detection of drug resistance phenotypes (p < 0.01). However, the correlation between the resistance genes cmlA, cfr, tetA, qnrA, qnrS, and aac(6')-Ib-cr and the corresponding resistance phenotype was not significant (p > 0.05). In general, our findings indicated that the multi-drug resistance of bacteria carried by marine horse mackerel and puffer fish in the Dalian area was serious. From the perspective of drug resistance rate and drug resistance gene detection rate, the aminoglycosides gentamicin and tobramycin are still considered effective in controlling bacterial infection in marine fish in the study area. Collectively, our findings provide a scientific basis for the management of drug use in mariculture, which can prevent the transmission of drug resistance through the food chain and minimize the associated human health risks.

Response of microbial interactions in activated sludge to chlortetracycline

Chlortetracycline (CTC) has attracted increasing attention due to its potential environmental risks. However, its effects on bacterial communities and microbial interactions in activated sludge systems remain unclear. To verify these issues, a lab-scale sequencing batch reactor (SBR) exposed to different concentrations of CTC (0, 0.05, 0.5, 1 mg/L) was carried out for 106 days. The results showed that the removal efficiencies of COD, TN, and TP were negatively affected, and the system functions could gradually recover at low CTC concentrations (≤0.05 mg/L), but high CTC concentrations (≥0.5 mg/L) caused irreversible damage. CTC significantly altered bacterial diversity and the overall bacterial community structure, and stimulated the emergence of many taxa with antibiotic resistance. Molecular ecological network analysis showed that low concentrations of CTC increased network complexity and enhanced microbial interactions, while high concentrations of CTC had the opposite effect. Sub-networks analysis of dominant phyla (Bacteriodota, Proteobacteria, and Actionobacteriota) and dominant genera (Propioniciclava, a genus from the family Pleomorphomonadaceae and WCHB1-32) also showed the same pattern. In addition, keystone species identified by Z-P analysis had low relative abundance, but they were important in maintaining the stable performance of the system. In summary, low concentrations of CTC enhanced the complexity and stability of the activated sludge system. While high CTC concentrations destabilized the stability of the overall network and then caused effluent water quality deterioration. This study provides insights into our understanding of response in the bacteria community and their network interactions under tetracycline antibiotics in activated sludge system.

High concentration of ammonia sensitizes the response of microbial electrolysis cells to tetracycline

Microbial electrolysis cell (MEC) is a promising technology for effective energy conversion of wastewater organics to biogas. Yet, in swine wastewater treatment, the complex contaminants including antibiotics may affect MEC performance, while the high ammonia concentration might increase this risk by increasing cell membrane permeability. In this work, the responses of MECs on tetracycline (TC) with low and high ammonia loadings (80 and 1000 mg L^-1) were fully investigated. The TC of 0 to 1 mg L^-1 slightly improved MEC performance in current production and electrochemical characteristics with low ammonia loading, while TC ≥ 4 mg L^-1 started to show negative effects. Generally, the high ammonia loading sensitized MECs to TC concentration, inducing the current and COD removal of MECs to sharply decline with TC ≥ 0.5 mg L^-1. The positive effect of high ammonia loading on MEC due to conductivity increase was counteracted with TC ≥ 1 mg L^-1. The co-contamination of TC and ammonia significantly decreased the bioactivity and biomass of anode biofilm. Although the high concentration of co-existing TC and ammonia inhibited MEC performance, the reactors still obtained positive energy feedback. The network analyses indicated that the effluent suspension contributed much to antibiotic resistance gene (ARG) transmission, while the microplastics (MPs) in wastewater greatly raised the risks of ARGs spreading. This work systematically examined the synergetic effects of TC and ammonia and the transmission of ARGs in MEC operation, which is conducive to expediting the application of MECs in swine wastewater treatment.

Behavior of antibiotic resistance genes in a wastewater treatment plant with different upgrading processes

Wastewater treatment plants (WWTPs) in China have been upgraded or renovated with a variety of emerging processes, but a comprehensive understanding of the behavior of antibiotic resistance genes (ARGs) in these WWTPs is still lacking. Here, the distribution of ARGs and bacterial community were investigated in a wastewater treatment plant with upgrading processes (WWTP-UP). 238 unique ARGs were detected in all samples. During the study period, the average ARGs concentration decreased by 98.4% along the entire treatment process. The removal efficiency of A²/O-membrane bioreactor (MBR) process was significantly higher than that of A²/O-high efficiency flocculent settling/cloth media filter (HEFS/CMF) process (p < 0.05), which corresponded to 3.5 and 2.1 log values on average, respectively. Notably, 35 ARGs and 14 mobile genetic elements (MGEs) were persistent in all samples. Based on the co-occurrence pattern revealed by network analysis, persistent ARGs possibly spread through the transfer of persistent MGEs among persistent bacteria. Using multiple linear regression analysis, we obtained 3 to 5 possible indicators for major ARG types, which might be served to evaluate the general distribution of ARGs or even predict the abundance of different ARG types. Our findings provide new insights into the impacts of upgrading process on ARGs and highlight the need for better strategies to improve ARGs elimination in WWTPs.

Effective degradation of tetracycline by manganese peroxidase producing Bacillus velezensis strain Al-Dhabi 140 from Saudi Arabia using fibrous-bed reactor

A tetracycline degrading bacterial strains was characterized from the municipal sludge and detected its ability to produce manganese peroxidase. The molecular weight of manganese peroxidase was determined as 46 kDa after Biogel P-100 gel filtration column chromatography purification. Maximum tetracycline degradation was observed with the manganese peroxidase from the strain Bacillus velezensis Al-Dhabi 140 and the optimum degradation process was studied. Optimization revealed the maximum removal efficacy was obtained as 87 mg/L at initial tetracycline concentration 143.75 mg/L, pH 6.94 and 8.04% inoculum. Consequently, fibrous bed reactor containing the culture of B. velezensis Al-Dhabi 140 in fibrous matrix was formed to transform tetracycline in synthetic wastewater. The transformed product of tetracycline from the fibrous bed reactor was evident by the activity of ligninolytic enzymes produced by B. velezensis Al-Dhabi 140 in reactor. The decreased level of antibacterial potency was obtained after 10 days. The zone of inhibition was 24 ± 1 mm after 1 day and it decreased as 9 ± 1 mm after 10 days. Based on the findings, fibrous bed B. velezensis Al-Dhabi 140 could be an efficient strain for tetracycline removal from artificial wastewater, even from natural wastewater.

Anaerobic digestion reduces extracellular antibiotic resistance genes in waste activated sludge: The effects of temperature and degradation mechanisms

The fate of extracellular antibiotic resistance genes (eARGs) in waste activated sludge during anaerobic digestion (AD) remained unclear. The current study investigated the changes in seven eARGs (sulI, sulII, tet(A), tet(O), tet(X), bla_TEM, and bla_SHV) and intI1 during sludge AD at 35 °C and 55 °C. First, the extracellular DNA (eDNA) extraction method from sludge was optimized by adding sodium dodecyl sulfonate, and the eDNA recovery nearly doubled. Second, analysis via qPCR showed that eARGs ranged from 1.5% to 85.1% of the total ARGs, stressing the importance of eARGs in sludge. Besides, the abundances of all detected eARGs decreased following AD, where removal rates ranged from 22.8% to 93.9% at 35 °C and 52.7% to 96.6% at 55 °C. Further analysis showed that the removal rates of eARGs were negatively correlated with their initial abundances (P < 0.05). Last, the degradation characteristics of eARGs under AD conditions were determined. The first-order degradation rate constants for different eARGs did not vary significantly, indicating that gene sequences did not cause a removal distinction, and fitted Michaelis-Menten equation confirmed the higher eARGs degradation ability at the higher temperature. Overall, this study firstly uncovered the decrease of eARGs in sludge during AD treatment, and advanced the understanding of the positive effect of AD on eARGs dissemination control.

A critical review on antibiotics and hormones in swine wastewater: Water pollution problems and control approaches

Swine wastewater (SW) is an important source of antibiotics and hormones (A&H) in the environment due to their large-scale application in swine industry. A&H in SW can be released into the water environment through the direct discharge of SW, effluent from SW treatment plants, and runoff and leaching from farmland polluted by swine wastes. The presence of A&H in the water environment has become an increasing global concern considering their adverse effects to the aquatic organism and human. This review critically discusses: (i) the occurrence of A&H in global water environment and their potential risks to water organisms and human; (ii) the management and technical approaches for reducing the emission of A&H in SW to the water environment. The development of antibiotic alternatives and the enhanced implementation of vaccination and biosecurity are promising management approaches to cut down the consumption of antibiotics during swine production. Through the comparison of different biological treatment technologies for removing A&H in SW, membrane-based bioprocesses have relatively higher and more stable removal efficiencies. Whereas, the combined system of bioprocesses and AOPs is expected to be a promising technology for elimination and mineralization of A&H in swine wastewater. Further study on this system is therefore necessary.

Contribution of antibiotics to the fate of antibiotic resistance genes in anaerobic treatment processes of swine wastewater: A review

Antibiotic resistance genes (ARGs) in water environment have become a global health concern. Swine wastewater is widely considered to be one of the major contributors for promoting the proliferation of ARGs in water environments. This paper comprehensively reviews and discusses the occurrence and removal of ARGs in anaerobic treatment of swine wastewater, and contributions of antibiotics to the fate of ARGs. The results reveal that ARGs' removal is unstable during anaerobic processes, which negatively associated with the presence of antibiotics. The abundance of bacteria carrying ARGs increases with the addition of antibiotics and results in the spread of ARGs. The positive relationship was found between antibiotics and the abundance and transfer of ARGs in this review. However, it is necessary to understand the correlation among antibiotics, ARGs and microbial communities, and obtain more knowledge about controlling the dissemination of ARGs in the environment.

Different inhibitory mechanisms of chlortetracycline and enrofloxacin on mesophilic anaerobic degradation of propionate

In anaerobic digestion, propionate is a key intermediate whose degradation is thermodynamically challenging and accumulation is detrimental to the process. Many wastewater streams contain antibiotics due to its globally increasing use, and these compounds can inhibit methane production. However, the effect of antibiotics on propionate degradation in anaerobic digestion remains unclear. In this study, the influence of two antibiotics (chlortetracycline [CTC] and enrofloxacin [EFX]) on biogas production and mesophilic propionate-degrading microbial community was investigated. CTC strongly repressed propionate oxidation, acetate utilization, and methane production, while EFX only inhibited propionate oxidation and methane production to a lesser extent. Microbial community analyses showed that syntrophic propionate-oxidizing bacteria (SPOB) Syntrophobacter had strong tolerance to both CTC and EFX. CTC inhibition mainly acted on the activity of acetate-oxidizing bacteria (Mesotoga, Geovibrio, Tepidanaerobacter, unclassified Bacteroidetes, and unclassified Clostridia) and acetoclastic methanogen, while EFX inhibition applied to the SPOB Smithella and acetoclastic methanogen. Network analysis further indicated that more complicated correlation among bacterial genera occurred in CTC treatments. These results suggested that CTC and EFX inhibited propionate degradation via different mechanisms, which was the result of joint action by antibiotics and microbial interactions.

Occurrence and ranking of pharmaceuticals in the major rivers of China

Residual pharmaceuticals have received widespread attention worldwide due to their continuous release and potential hazard to the environment. As a result of rapid development and a large population, China has become a country with high production and consumption of pharmaceuticals. This may be the main reason for the high detection frequencies and concentrations of pharmaceuticals in the aquatic environment in China. Rivers represent an important water resource and play an important role in the sustainable development of the Chinese economy and society. This study summarizes the occurrence of frequently detected pharmaceuticals in major rivers. A hazard score based on the occurrence, exposure potential, and environmental effects of pharmaceuticals was calculated and a prioritization approach was used to rank 166 pharmaceuticals that were detected in the aquatic environment of major rivers in China. The priority list provides a basis for selecting candidate pharmaceuticals for future site-specific monitoring in rivers.

Effects of tetracycline residuals on humification, microbial profile and antibiotic resistance genes during vermicomposting of dewatered sludge

Vermicomposting is a green technology used in the recycling of sewage sludge using the joint action of earthworms and microorganisms. Although tetracycline is present in abundance in sewage sludge, little attention has been given to its influence on vermicomposts. This study investigated the effects of different tetracycline concentrations (0, 100, 500 and 1000 mg/kg) on the decomposition of organic matter, microbial community and antibiotic resistance genes (ARGs) during vermicomposting of spiked sludge. The results showed that 100 mg/kg tetracycline could stimulate earthworms' growth, accompanied by the highest humification and decomposition rates of organic matter in the sludge. The abundance of active microbial cells and diversity decreased with the increase in tetracycline concentrations. The member of Bacteroidetes dominated in the tetracycline spiked treatments, especially in the higher concentration treatments. Compared to its counterparts, the addition of tetracycline significantly increased the abundances of ARGs (tetC, tetM, tetX, tetG and tetW) and Class 1 integron (int-1) by 4.7-186.9 folds and 4.25 folds, respectively. The genera of Bacillus and Mycobacterium were the possible bacterial pathogen hosts of ARGs enriched in tetracycline added group. This study suggests that higher concentration of tetracycline residual can modify microbial communities and increase the dissemination risk of ARGs for final sludge vermicompost.

The effect of tetracycline on the structure of the bacterial community in a wastewater treatment system and its effects on nitrogen removal

This study examined the impact of tetracycline at two environmentally relevant concentrations (1 μg/L and 10 μg/L) and one synthetically high concentration (500 μg/L) on the structure and function of the microbial community from the secondary treatment process of a municipal wastewater treatment plant (WWTP). Specifically, this study examined whether the introduction of tetracycline into bench scale reactors at two different replacement volume rates would cause a shift in the composition profile of the bacterial community. Furthermore concentrations of ammonia, nitrate/nitrite and total Kjeldahl nitrogen were monitored to examine the effect of the antibiotic on ammonia and nitrogen removal. At the low volume replacement rate, tetracycline was observed to have a positive impact on nitrogen removal. Total Kjeldahl nitrogen concentrations were also observed to decrease suggesting a role for tetracycline as a carbon source. However, at the higher volume replacement rate, the removal of ammonia and nitrogen were not significantly different from reactors that did not contain tetracycline. Over time, the bacterial composition profiles changed under all the conditions studied, however, the bacterial composition profiles appeared to be more influenced by the replacement volume rate than the presence of tetracycline even at concentrations many times higher than environmentally relevant amounts.

Evolution of microbial community and drug resistance during enrichment of tetracycline-degrading bacteria

Recently, the microbial degradation of tetracycline has been widely reported. However, its potential risks in treating wastewater containing high concentrations of tetracycline have not been fully evaluated. In this study, the evolution of the microbial community and drug resistance was traced during the enrichment of tetracycline-degrading bacteria. The results showed that some minor compositions such as Shewanella, Bacillus, and Pseudomonas in the seed sludge became the predominant genera in the enrichment cultures when continuously using tetracycline as the sole carbon source, especially some possible pathogenic bacteria increased significantly in this process. The abundances of most TRGs/16S rDNA were increased after enrichment, although the relative abundance of tetA and tetL genes decreased to some extent. From the enrichment culture, 7 predominant tetracycline-degrading strains were isolated, of which TD-1 (Bacillus) and TD-5 (Shewanella) presented high degradation efficiencies (6-day degradation rate > 95%, half-life period of tetracycline ≈ 24 h). In addition, multiple TRGs, mobile genetic elements (MGEs) and even gene cassettes were found in each tetracycline-degrading isolate. The findings suggested that some risks such as the pathogenicity of isolates and the spread of ARGs should be considered when the biodegradation method is used to treat wastewater polluted with high concentrations of tetracycline.

Different Concentrations of Doxycycline in Swine Manure Affect the Microbiome and Degradation of Doxycycline Residue in Soil

Antibiotic residues that enter the soil through swine manure could disturb the number, community structure and functions of microbiota which could also degrade antibiotics in soil. Five different concentrations of doxycycline (DOX) incorporated into swine manure were added to soil to explore the effects of DOX on microbiota in soil and degradation itself. The results showed that the soil microbiome evolved an adaptation to the soil containing DOX by generating resistance genes. Moreover, some of the organisms within the soil microbiome played crucial roles in the degradation of DOX. The average degradation half-life of DOX in non-sterile groups was 13.85 ± 0.45 days, which was significantly shorter than the 29.26 ± 0.98 days in the group with sterilized soil (P < 0.01), indicating that the soil microbiome promoted DOX degradation. DOX addition affected the number of tetracycline resistance genes, depending on the type of gene and the DOX concentration. Among these genes, tetA, tetM, tetW, and tetX had significantly higher copy numbers when the concentration of DOX was higher. In contrast, a lower concentration of DOX had an inhibitory effect on tetG. At the same time, the microbial compositions were affected by the initial concentration of DOX and the different experimental periods. The soil chemical indicators also affected the microbial diversity changes, mainly because some microorganisms could survive in adversity and become dominant bacterial groups, such as the genera Vagococcus and Enterococcus (which were associated with electrical conductivity) and Caldicoprobacter spp. (which were positively correlated with pH). Our study mainly revealed soil microbiota and DOX degradation answered differently under variable concentrations of DOX mixed with swine manure in soil.

Effects of tetracycline and ibuprofen on the relative abundance of microbial eukaryotic and bacterial populations in wastewater treatment

The activated sludge process in a wastewater treatment plant (WWTP) relies on the activity of microbes to reduce the organic and inorganic matter and produce effluent that is safe to discharge into receiving waters. This research examined the effects of the non-steroidal anti-inflammatory drug ibuprofen and the antibiotic tetracycline on the relative abundance and composition of eukaryotes and bacteria in the microbial population present in activated sludge from a WWTP. The current investigation was designed to observe the impact of these contaminants, at low (environmentally relevant concentrations) as well as high concentrations of the drugs. Using 16S and 18S rRNA gene primer sets and quantitative polymerase chain reaction, the abundance of each population was monitored as well as the relative ratio of the two populations under the various conditions. It was found that current environmentally relevant concentrations of ibuprofen (100 ng/mL) stimulated eukaryotic growth but higher concentrations (2,000 ng/mL, 100,000 ng/mL) reduced their numbers significantly especially in the presence of tetracycline. Finally using denaturing gradient gel electrophoresis, some of the more abundant eukaryotes were identified and it was noted that high ibuprofen and tetracycline concentrations favoured the abundance of some genera.

Fate of potential indicator antimicrobial resistance genes (ARGs) and bacterial community diversity in simulated manure-soil microcosms

The aim of this study was to investigate the fate of nine potential indicator antimicrobial resistance genes (ARGs) (sul1, sul2, tetB, tetM, ermB, ermF, fexA, cfr, intI1) and the diversity of bacterial communities in response to poultry manure applications to arable soil over a 90 day period. Quantitative real time PCR and Illumina high-throughput sequencing of 16S rDNA gene were used to quantify and trace ARG fate. The levels of all genes dramatically decreased over time and intI1, sul1, sul2 and tetM always had the greatest abundance and lowest dissipation rates. This indicated that more effort should be focused on the ARG elimination from manure rather than waiting for subsequent attenuation in the environment. Our sequencing results documented dramatic changes in the microbial community structure and diversity during these experiments. In poultry manure groups, Bacteroidetes and Actinobacteria were the two dominant phyla while Acidobacteria dominated the control groups. Moreover, the relative abundance of genera Corynebacterium, Pseudomonas, Ochrobactrum, Actinomadura and Bacillus, which contained potential opportunistic pathogens, changed over time suggesting that poultry manure not only strongly influenced bacterial community composition, but also selected specific bacterial communities. This study provides a glimpse of ARG fates and bacterial community diversity in soil after the application of poultry manure.

Degradation and characteristic changes of organic matter in sewage sludge using Vermi-biofilter system

Vermi-biofilter (VF) System could be an efficient sludge treatment unit in regard of rates and extents of total chemical oxygen demand (TCOD) removal, particularly the first 10 days earthworm-treated. This study characterized the organic matter in sludge before and after VF system treatment, with or without earthworm stage. The 60 days earthworm-treated VF system reached a TCOD removal of 10,450 mg/L, bulk DOC removal of 89.5 mg/L, and earthworm density increase from 32 g/L to 43 g/L in sludge EBOM in 60 days of VF system operation. The aromatic proteins, soluble microbial byproduct-like fluorescent compounds and carboxylic components, aliphatic components (C-H related), hydrocarbon and carbohydrate materials were identified to be principally increased by 10 days earthworm-treated and then degradation in the nest days under VF system.

Impact of selected non-steroidal anti-inflammatory pharmaceuticals on microbial community assembly and activity in sequencing batch reactors

This study covers three widely detected non-steroidal anti-inflammatory pharmaceuticals (NSAIDs), diclofenac (DCF), ibuprofen (IBP) and naproxen (NPX), as NSAIDs pollutants. The objective is to evaluate the impact of NSAIDs at their environmental concentrations on microbial community assembly and activity. The exposure experiments were conducted under three conditions (5 μg L^-1 DCF, 5 μg L^-1 DCF+5 μg L^-1 IBP and 5 μg L^-1 DCF+5 μg L^-1 IBP+ 5 μg L^-1 NPX) in sequencing batch reactors (SBRs) for 130 days. Removals of COD and NH₄⁺-N were not affected but total nitrogen (TN) removal decreased. IBP and NPX had the high removal efficiencies (79.96% to 85.64%), whereas DCF was more persistent (57.24% to 64.12%). In addition, the decreased removals of TN remained the same under the three conditions (p > 0.05). The results of oxidizing enzyme activities, live cell percentages and extracellular polymeric substances (EPS) indicated that NSAIDs damaged the cell walls or microorganisms and the mixtures of the three NSAIDs increased the toxicity. The increased Shannon-Wiener diversity index suggested that bacterial diversity was increased with the addition of selected NSAIDs. Bacterial ribosomal RNA small subunit (16S) gene sequencing results indicated that Actinobacteria and Bacteroidetes were enriched, while Micropruina and Nakamurella decreased with the addition of NSAIDs. The enrichment of Actinobacteria and Bacteroidetes indicated that both of them might have the ability to degrade NSAIDs and thereby could adapt well with the presence of NSAIDs.

Effects of oxytetracycline on archaeal community, and tetracycline resistance genes in anaerobic co-digestion of pig manure and wheat straw

In this study, the effects of different concentrations of oxytetracycline (OTC) on biogas production, archaeal community structure, and the levels of tetracycline resistance genes (TRGs) were investigated in the anaerobic co-digestion products of pig manure and wheat straw. PCR denaturing gradient gel electrophoresis analysis and real-time quantitative polymerase chain reaction (RT-qPCR) (PCR) were used to detect the archaeal community structure and the levels of four TRGs: tet(M), tet(Q), tet(W), and tet(C). The results showed that anaerobic co-digestion with OTC at concentrations of 60, 100, and 140 mg/kg (dry weight of pig manure) reduced the cumulative biogas production levels by 9.9%, 10.4%, and 14.1%, respectively, compared with that produced by the control, which lacked the antibiotic. The addition of OTC substantially modified the structure of the archaeal community. Two orders were identified by phylogenetic analysis, that is, Pseudomonadales and Methanomicrobiales, and the methanogen present during anaerobic co-digestion with OTC may have been resistant to OTC. The abundances of tet(Q) and tet(W) genes increased as the OTC concentration increased, whereas the abundances of tet(M) and tet(C) genes decreased as the OTC concentration increased.

High Levels of Antibiotic Resistance Genes and Their Correlations with Bacterial Community and Mobile Genetic Elements in Pharmaceutical Wastewater Treatment Bioreactors

To understand the diversity and abundance of antibiotic resistance genes (ARGs) in pharmaceutical wastewater treatment bioreactors, the ARGs in sludge from two full-scale pharmaceutical wastewater treatment plants (PWWTPs) were investigated and compared with sludge samples from three sewage treatment plants (STPs) using metagenomic approach. The results showed that the ARG abundances in PWWTP sludge ranged from 54.7 to 585.0 ppm, which were higher than those in STP sludge (27.2 to 86.4 ppm). Moreover, the diversity of ARGs in PWWTP aerobic sludge (153 subtypes) was higher than that in STP aerobic sludge (118 subtypes). In addition, it was found that the profiles of ARGs in PWWTP aerobic sludge were similar to those in STP aerobic sludge but different from those in PWWTP anaerobic sludge, suggesting that dissolve oxygen (DO) could be one of the important factors affecting the profiles of ARGs. In PWWTP aerobic sludge, aminoglycoside, sulfonamide and multidrug resistance genes were frequently detected. While, tetracycline, macrolide-lincosamide-streptogramin and polypeptide resistance genes were abundantly present in PWWTP anaerobic sludge. Furthermore, we investigated the microbial community and the correlation between microbial community and ARGs in PWWTP sludge. And, significant correlations between ARG types and seven bacterial genera were found. In addition, the mobile genetic elements (MGEs) were also examined and correlations between the ARGs and MGEs in PWWTP sludge were observed. Collectively, our results suggested that the microbial community and MGEs, which could be affected by DO, might be the main factors shaping the profiles of ARGs in PWWTP sludge.

Design and evaluation of universal 16S rRNA gene primers for high-throughput sequencing to simultaneously detect DAMO microbes and anammox bacteria

To develop universal 16S rRNA gene primers for high-throughput sequencing for the simultaneous detection of denitrifying anaerobic methane oxidation (DAMO) archaea, DAMO bacteria, and anaerobic ammonium oxidation (anammox) bacteria, four published primer sets (PS2-PS5) were modified. The overall coverage of the four primer pairs was evaluated in silico with the Silva SSU r119 dataset. Based on the virtual evaluation, the two best primer pairs (PS4 and PS5) were selected for further verification. Illumina MiSeq sequencing of a freshwater sediment and a culture from a DAMO-anammox reactor using these two primer pairs revealed that PS5 (341b4F-806R) was the most promising universal primer pair. This pair of primers detected both archaea and bacteria with less bias than PS4. Furthermore, an anaerobic fermentation culture and a wastewater treatment plant culture were used to verify the accuracy of PS5. More importantly, it detected DAMO archaea, DAMO bacteria, and anammox bacteria simultaneously with no false positives appeared. This universal 16S rRNA gene primer pair extends the existing molecular tools for studying the community structures and distributions of DAMO microbes and their potential interactions with anammox bacteria in different environments.