Application of humic acid changes the microbial communities and inhibits the expression of tetracycline resistance genes in 4-chlorophenol wastewater treatment

Ultrasound enhanced destruction of tetracycline hydrochloride with peroxydisulfate oxidation over FeS/NBC catalyst: Governing factors, strengthening mechanism and degradation pathway

In this study, FeS/N-doped biochar (NBC) derived from the co-pyrolysis of birch sawdust and Mohr's salt was applied to evaluate the efficiency of catalyzed peroxydisulfate (PDS) oxidation for tetracycline (TC) degradation. It is found that the combination of ultrasonic irradiation can distinctly enhance the removal of TC. This study investigated the effects of control factors such as PDS dose, solution pH, ultrasonic power, and frequency on TC degradation. Within the applied ultrasound intensity range, TC degradation increases with increasing frequency and power. However, excessive power can lead to a reduced efficiency. Under the optimized experimental conditions, the observed reaction kinetic constant of TC degradation increased from 0.0251 to 0.0474 min-1, with an increase of 89%. The removal ratio of TC also increased from ∼85% to ∼99% and the mineralization level from 45% to 64% within 90 min. Through the decomposition testing of PDS, reaction stoichiometric efficiency calculation, and electron paramagnetic resonance experiments, it is shown that the increase in TC degradation of the ultrasound-assisted FeS/NBC-PDS system was attributed to the increase in PDS decomposition and utilization, as well as the increase in SO4•- concentration. The radical quenching experiments showed that SO4•-, •OH, and O2•- radicals were the dominant active species in TC degradation. TC degradation pathways were speculated according to intermediates from HPLC-MS analysis. The test of simulated actual samples showed that dissolved organic matter, metal ions, and anions in waters can undercut the TC degradation in FeS/NBC-PDS system, but ultrasound can significantly reduce the negative impact of these factors.

Improvement of carbon source composition reduces antibiotic resistance genes in the ectopic fermentation system

Effectively reduce antibiotic resistance genes (ARGs) in ectopic fermentation system (EFS) is essential for practical production. In this study, three experiments were performed to explore how to remove ARGs in EFS effectively. Results demonstrated that ARGs were easily enriched in rice-husk-sawdust padding; simultaneous addition of laccase and cellulase suppressed the ARGs, mainly by increasing soluble carbohydrate concentration and promoting humic acid concentration; addition of corn stalks into rice-husk-sawdust decreased the abundance of ARGs by improving the carbon source structure and enhancing cellulase activity. In conclusion, the present study provides a guidance to reduce the threat of ARGs in EFS, which paved a potential pathway to safely utilize manure resources.

Effects of different cathodic potentials on performance, microbial community structure and function for bioelectrochemical-stimulated dechlorination of 2,4,6-trichlorophenol in sediments

Bioelectrochemical systems with biocathodes constitute a promising means to enhance the biological dechlorination of 2,4,6-trichlorophenol (2,4,6-TCP) in constructed wetland (CW) sediments. However, the effect of different cathodic potentials on the structure and function of 2,4,6-TCP-reducing biocathode communities in CW sediments is largely unknown. Here, we evaluated the performance and microbial community structure of 2,4,6-TCP-reducing biocathode systems at different cathodic potentials (- 0.5, - 0.7, - 0.9, and - 1.1 V vs. saturated calomel electrode). The dechlorination efficiency of 2,4,6-TCP with the biocathode relatively increased by 16.02%-33.17% compared to that in the open circuit. The highest 2,4,6-TCP dechlorination efficiency (92.34 ± 0.86%) was observed at - 0.7 V in sediment, which may be due to the highest abundance of functional genera (e.g., Pseudomonas, Spirochaeta) at - 0.7 V. Metagenomic analysis provided new insights into the metabolic potential of microorganisms in CW sediments and suggested possible 2,4,6-TCP conversion pathways in sediments. 2,4,6-TCP was gradually dechlorinated to form 4-chlorophenol, followed by a ring-opening step via the activities of chlorophenol reductive dehalogenase and oxygenase (e.g., cprA, tfdB). Interestingly, micro-electrical stimulation enhanced the expression of chlorophenol reductive dehalogenase (cprA). Therefore, our findings at the molecular and gene expression levels provide insights into the effects of different cathodic potentials on the performance and community structure of 2,4,6-TCP-reducing biocathode systems in CW sediments.

Natural organic matters promoted conjugative transfer of antibiotic resistance genes: Underlying mechanisms and model prediction

Dissemination of antibiotic resistance gene (ARG) is a huge challenge around the world. Natural organic matter (NOM) is one of the most commonly components in aquatic systems. Information regarding ARG transfer induced by NOM is still lacking. In this study, experimental exploration and model prediction on RP4 plasmid conjugative transfer between bacteria under NOM exposure was conducted. Compared with no exposure, the conjugative transfer frequency of RP4 plasmid increased 7.1-fold and 3.2-fold under exposure to 10 kDa and 100 kDa NOM exposure, respectively. NOM exposure with a lower molecular weight and higher concentration promoted gene expressions related to reactive oxygen species generation, cell membrane permeability, intercellular contact, quorum sensing, and energy driving force. Concurrently, the expressions of conjugation genes in RP4 plasmid were also upregulated. Moreover, model prediction demonstrated that the maintenance of the acquired plasmid was shortened to 133 h under 10 kDa NOM exposure compared with the control (200 h). Long-term NOM exposure enhanced transfer frequency and transfer rate of ARG. This study firstly theoretically and experimentally revealed the underlying mechanisms for promoting ARG transfer by NOM.

Combined physiological and metabolomic analysis reveals the effects of different biostimulants on maize production and reproduction

Plant biostimulants (PBs) are a potential strategy to improve crop growth and grain quality. In the present study, 100 mg/L trehalose, chitosan, humic acid and gamma-aminobutyric acid treatments were applied to analyze the effects of maize production and reproductive characteristics. The contents of nitrogen, phosphorus and potassium and grain quality were significantly affected by the PBs, but not yield. The seed germination rate of all PB treatments was significantly reduced, but the drought resistance of progeny seedlings was significantly improved, with humic acid having the strongest effect. Liquid chromatography mass spectrometry analysis indicated that the disruption of the tricarboxylic acid cycle, probably due to the blockage of intermediate anabolism, reduced the supply of energy and nutrients in the early stages of germination, thus inhibiting seed germination, while the increased resistance of the offspring seedlings may be due to the up-regulation of the synthesis of unsaturated fatty acids and alkaloids by humic acid treatment. This study revealed the similarity and heterogeneity of the effects of different PBs on nutrient accumulation, yield characteristics and grain quality of maize, providing guidance for the application of PBs in intensive and sustainable agricultural production.

Interaction of Antibiotics and Humic Substances: Environmental Consequences and Remediation Prospects

The occurrence and distribution of antibiotics in the environment has received increasing attention due to their potential adverse effects on human health and ecosystems. Humic substances (HS) influence the mobility, reactivity, and bioavailability of antibiotics in the environment significantly due to their interaction. As a result, HS can affect the dissemination of antibiotic-resistance genes, which is one of the main problems arising from contamination with antibiotics. The review provides quantitative data on the binding of HS with fluoroquinolones, macrolides, sulfonamides, and tetracyclines and reports the proposed mechanisms of their interaction. The main issues of the quantification of antibiotic-HS interaction are discussed, which are a development of standard approaches and the accumulation of a dataset using a standard methodology. This would allow the implementation of a meta-analysis of data to reveal the patterns of the binding of antibiotics to HS. Examples of successful development of humic-based sorbents for fluoroquinolone and tetracycline removal from environmental water systems or polluted wastewaters were given. Data on the various effects of HS on the dissemination of antibiotic-resistance genes (ARGs) were summarized. The detailed characterization of HS properties as a key point of assessing the environmental consequences of the formation of antibiotic-HS complexes, such as the dissemination of antibiotic resistance, was proposed.

Effects of Mn2+ and humic acid on microbial community structures, functional genes for nitrogen and phosphorus removal, and heavy metal resistance genes in wastewater treatment

Considering the wide occurrence of Mn²⁺ and humic acid (HA) in environmental media, the effects of Mn²⁺ (5-16 mg/L) and HA (10 mg/L) on microbial community structures, functional genes for nitrogen and phosphorus removal, and heavy metal resistance genes (HMRGs) were investigated in wastewater treatment using sequencing batch bioreactors (SBRs). The treatment efficiencies of influent chemical oxygen demands (COD), NH₄⁺-N, and PO₄^3--P were unaffected during the entire operational processes irrespective of whether Mn²⁺ and HA were supplied. Although the functional prediction of genetic information via sequencing analysis showed that the microbial activity was not influenced by Mn²⁺ and HA from different SBRs, the abundance of dominant phyla (Proteobacteria, Actinobacteriota, Firmicutes, and Bacteroidota), classes (Saccharimonadia, Gammaproteobacteria, and Bacilli), and genera (unidentified_Chloroplast, TM7a, Micropruina, Candidatus_Competibacter, Lactobacillus, OLB12, and Pediococcus) was different. Compared to the SBR without Mn²⁺ and HA supplementation, the abundance of functional genes for nitrogen and phosphorus removal (narG, nirS, nosZ, ppk, and phoD) and HMRGs (corA and mntA) significantly increased under Mn²⁺ stress, but significantly decreased with the addition of HA except for genes nirS and ppk. The abundance of genes corA and mntA was related to the partially dominant microbes and functional genes, and might be reduced by supplying HA. This study provides insight into the effects of Mn²⁺ and HA on functional genes for nitrogen and phosphorus removal and HMRGs in wastewater treatment.

Trace antibiotics increase the risk of antibiotic resistance genes transmission by regulating the biofilm extracellular polymeric substances and microbial community in the sewer

Sewer is considered a potential hotspot for antibiotic resistance, but the occurrence and proliferation of antibiotic resistance genes (ARGs) under trace antibiotics exposure have received little attention. This work evaluated the effects of tetracycline (TC) and sulfamethoxazole (SMX) individually and in combination in the sewer system and revealed the related mechanisms of ARG proliferation. The relative abundance of tetA and sul1 increased the most under TC and SMX stress, respectively, whereas sul1 increased the most under combined stress. Intl1 was abundant in both the liquid phase and the biofilm, and redundancy analysis confirmed that horizontal gene transfer was the main reason for the proliferation of ARGs. The increase in extracellular polymeric substances (EPS) secretion and the enhancement of the main hydrophobic functional groups facilitated the accumulation of biofilms, which promoted the proliferation of ARGs in biofilms. The relative abundance of most ARGs in the liquid phase was significantly correlated with EPS, protein and tryptophan-like substances. Furthermore, the microbial community structure and diversity affected the proliferation and spread of ARGs in the sewer. These findings contribute to our further understanding of the proliferation and development of ARGs in the sewer and lay the foundation for the front-end control of ARGs.

Impact of microbial inoculants combined with humic acid on the fate of estrogens during pig manure composting under low-temperature conditions

To investigate the efficiency of psychrotrophic cellulose-degrading fungal strains (PCDFSs) and estrogen-degrading bacteria (EDBs) combined with humic acid (HA) on estrone (E1) and 17-β-estradiol (E2) degradation, five compost groups (T, HA, EDB, PCDFS, and CK) were prepared and composted for 32 days at 11-14°C. The results indicated that inoculation increased the temperature to 62.2°C and promoted E1 degradation to the lowest level of 100.1 ng/kg, while E2 was undetected from day 16. Metagenomic analysis revealed that inoculation altered the microbial community structure by increasing the abundance of cellulose-degrading fungi, especially Meyerozyma (16.7%) (among PCDFSs), and of estrogen-degrading bacteria, particularly Microbacterium (13.4%) (involved in EDBs). Moreover, inoculation increased the levels (>0.500%) of Gene Ontology (GO) associated with estrogen degradation, like 3-β-hydroxy-delta 5-steroid dehydrogenase and monooxygenase. Redundancy analysis demonstrated that temperature and Microbacterium were positively correlated with estrogen degradation. Structural equation model indicated that temperature and estrogen-degrading bacterial genera exhibited positive, significant (p < 0.001) and direct impacts on estrogen degradation. This is the first study to suggest that applying microbial inoculants and HA could accelerate estrogen degradation during composting in cold regions. The research outcomes offer a practical reference for managing compost safety, thereby decreasing its potential environmental and human health impacts.

Effects of combined 4-chlorophenol and Cu2+ on functional genes for nitrogen and phosphorus removal and heavy metal resistance genes in sequencing batch bioreactors

The effects of combined 4-chlorophenol (4-CP) and Cu²⁺ on microbial community structures, functional genes for nitrogen and phosphorus removal, and heavy metal resistance genes (HMRGs) were explored in wastewater treatment using sequencing batch bioreactors (SBRs). Compared to influent 4-CP (2.3-4.5 mg/L), the removal of pollutants including chemical oxygen demands (COD), NH₄⁺-N, PO₄^3--P, and 4-CP was inhibited under Cu²⁺ stress (5 mg/L). The effects of Cu²⁺ on microbial community structures were more significant than those of 4-CP with respect to operational time, while the dominant function from gene information was not affected with or without influent 4-CP and Cu²⁺ via sequencing analysis. The influent 4-CP and Cu²⁺ largely influenced the dynamic changes of functional genes and HMRGs, and the abundance of partial HMRGs was correlated to the functional genes and dominant genera. This study provides insights into the treatment of combined chlorophenols and Cu²⁺ in wastewater.

Ozone oxidation of 2,4,6-TCP in the presence of halide ions: Kinetics, degradation pathways and toxicity evaluation

2,4,6-Trichlorophenol (2,4,6-TCP) is extensively consumed in industrial production and may cause environmental damages. The effect of halide ions on the decomposition of 2,4,6-TCP has often been overlooked. In this study, the bromide ion was found to have a stronger negative impact on 2,4,6-TCP degradation than chloride ion in the O₃ system, and led to the formation of adsorbable organic halogens (AOX). Kinetic modeling demonstrated that the concentration of various radicals was largely depended on the solution pH, and stronger basicity not only contributed to the mineralization of 2,4,6-TCP, but also inhibited the formation of halogenated by-products. Combining the intermediate identification and quantum chemical calculation, the degradation pathways of 2,4,6-TCP during ozone oxidation process were proposed. The toxicity test and ECOSAR simulation demonstrated that the acute toxicity of some 2,4,6-TCP degradation intermediates was relatively higher than their parent compound. With high concentrations of halide ions, the ozone-treated solution showed greater toxicity than the originator 2,4,6-TCP solution. These results illustrate that the ozone treatment of the halide-containing wastewater may cause potential ecological hazards and its application needs to be more cautious.

Response of extracellular polymeric substances and microbial community structures on resistance genes expression in wastewater treatment containing copper oxide nanoparticles and humic acid

The extracellular polymeric substances (EPS) and microbial community structures were investigated in wastewater treatment containing copper oxide nanoparticles (CuO NPs) (reactor R1) and CuO NPs and humic acid (HA) (reactor R2) using both sequencing batch bioreactors (SBRs), and their response on resistance genes expression was analyzed. The removal of influent chemical oxygen demands (COD) and NH₄⁺-N was moderately influenced under CuO NPs (5 mg/L) stress, while the function of HA (10 mg/L) was not reflected. However, the EPS production and microbial community were affected by the HA addition. The expression of different antibiotic resistance genes (ARGs), metal-resistance genes (MRGs), and intI1 was related to the primary compositions of polysaccharides and proteins in EPS and different microbial communities at the genus level. Furthermore, the expression of resistance genes was not stimulated under CuO NPs stress, and supplying HA was suggested to reduce their expression in wastewater treatment.

Effects of emerging pollutants on the occurrence and transfer of antibiotic resistance genes: A review

The emergence and spread of antibiotic resistance genes (ARGs) have become major concerns for both public health and environmental ecosystems. Emerging pollutants (EPs) that accumulate in environmental compartments also pose a potential risk for the enrichment of ARGs in indigenous microorganisms. This paper presents a comprehensive review of the effects and intrinsic mechanisms of EPs, including microplastics, engineered nanomaterials, disinfection byproducts, pharmaceuticals, and personal care products, on the occurrence and dissemination of ARGs. State-of-the-art methods for identifying culture-independent ARG-host interactions and monitoring horizontal gene transfer (HGT) processes in real-time are first reviewed. The contributions of EPs to the abundance and diversity of ARGs are then summarized. Finally, we discussed the underlying mechanisms related to the regulation of HGT, increased mutagenesis, and the evolution of microbial communities. Further details of three HGT (i.e., conjugation, transformation, and transduction) frequency patterns in response to various EPs are also examined. This review contemplates and reassesses the risks of ARG evolution posed by the manufacture and application of EPs.

Effect of immobilized anthraquinone-2-sulfonate on antibiotic resistance genes and microbial community in biofilms of anaerobic reactors

Quinone compounds could significantly accelerate anaerobic biotransformation of refractory pollutants. However, the effect of quinone compounds application on the propagation of antibiotic resistance genes (ARGs) in the bio-treatment of these pollutants-containing wastewater is not available. In this study, the catalytic performance of anthraquinone-2-sulfonate immobilized on polyurethane foam (AQS-PUF), changes of ARGs, mobile gene elements (MGEs) and microbial community structure attached on AQS-PUF and PUF in the up-flow anaerobic bioreactors were investigated. The results showed that AQS-PUF could significantly accelerate the decolorization of azo dye RR X-3B. Meanwhile, metagenomics analysis showed that the total absolute abundance of ARGs increased in the presence of the immobilized AQS. Among ARGs, the number of the efflux pump-encoding ARGs in the biofilm of AQS-PUF accounted for 35.7% of the total ARGs, which was slightly higher than that of PUF (32.1%) due to the presence of the immobilized AQS. The relative abundances of ARGs conferring resistance to MLS (macrolide, lincosamide and streptogramin), tetracycline and sulfonamide, which were deeply concerned, reduced 10%, 21.7% and 7.3% in the presence of the immobilized AQS, respectively. Moreover, the immobilized AQS resulted in the decreased relative abundance of plasmids, transposons and class I integrons. Among the detected 31 ARG subtypes located in MGEs, the relative abundances of only lnuF, msrE and mphD in the biofilm of AQS-PUF were over 2-fold higher compared with those in the biofilm of PUF. However, the three ARGs and their host Gammaproteobacteria was not dominant in microbial community. The relative abundances of more ARGs including MLS (lnuB and EreA), tetracycline (tetH) resistance genes located in MGEs decreased, which was attributed to the decreased relative abundance of their hosts. These studies showed that the addition of the immobilized AQS (around 0.25 mM) had a beneficial effect on reducing the spread of ARGs during dyeing wastewater bio-treatment.

Effects of 2,4,6-trichlorophenol and its intermediates on acute toxicity of sludge from wastewater treatment and functional gene expression

Considering the extensive usage of chlorophenols as well as their refractory and toxic characteristics, 2,4,6-trichlorophenol (2,4,6-TCP) and its metabolic intermediates that cause the acute toxicity of sludge were comprehensively evaluated using a bioassay including Photobacterium phosphoreum in a sequencing batch bioreactor (SBR), and the effects of 2,4,6-TCP wastewater treatment on mRNA expression were explored. The results showed that acute toxicity of sludge and effluent chemical oxygen demand greatly exceeded that of the other SBR without 2,4,6-TCP acclimation when 2,4,6-TCP wastewater treatment in the range of 10-50 mg/L was used. The identified intermediates and 2,4,6-TCP largely contributed to the acute toxicity of sludge, which favorably fitted the Fit Exponential Decay (R² > 0.93). During the stable stages for treating 50 mg/L 2,4,6-TCP in the influent, the mRNA expression for encoding functional proteins based on the genus Pseudomonas was markedly inhibited after the completion of the SBR operation.

Effects of humic acid on sludge performance, antibiotics resistance genes propagation and functional genes expression during Cu(II)-containing wastewater treatment via metagenomics analysis

The humic acid (HA) function on the sludge performance, antibiotics resistance genes (ARGs) propagation and functional genes expression during Cu(II)-containing wastewater treatment was comprehensively investigated via metagenomics analysis. Results showed that the pollutants removal was significantly inhibited after long-term exposure of 5 mg/L Cu(II), while the inhibitory effects were moderately alleviated after addition of 10 mg/L HA. The extracellular polymeric substances (EPS) production with Cu(II) acclimation was higher than the sludge with Cu(II) and HA acclimation. The microbial community was significantly affected by the HA addition, while the relative abundance of dominant ARGs had no distinct differences with or without HA addition under Cu(II) stress. The functional genes were largely implemented for microbial metabolism, while no significant differences were found with HA addition under Cu(II) stress. Thus, the HA function for ARGs propagation and functional genes expression needed to be further research under Cu(II) stress in wastewater treatment.