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

Soil microorganisms play an important role in the detrimental impact of biodegradable microplastics on plants

Biodegradable plastics were developed to mitigate environmental pollution caused by conventional plastics. Research indicates that biodegradable microplastics still have effects on plants and microorganisms as their non-biodegradable counterparts, yet the effects on vegetable crops are not well-documented. Additionally, the function of soil microorganisms affected by biodegradable microplastics on the fate of microplastics remains unverified. In this study, Brassica chinensis was cultivated in soil previously incubated for one year with low-density polyethylene (LDPE-MPs) and poly (butylene adipate-co-terephthalate) microplastics (PBAT-MPs) at 0.05 % and 2 % concentrations. High concentrations of PBAT-MPs significantly reduced the biomass to 5.83 % of the control. The abundance of Methyloversatilis, IS-44, and UTCFX1 in the rhizosphere bacterial community increased significantly in the presence of PBAT-MPs. Moreover, these microplastics significantly enhanced soil enzyme activity. Incubation tests were performed with three PBAT plastic sheets to assess the function of the altered bacterial community in the soil of control (Control-soil) and soil treated with high concentrations of PBAT-MPs (PBAT-MPs-soil). Scanning Electron Microscopy and Atomic Transfer Microscopy (SEM/ATM) results confirmed enhanced PBAT degradation in the PBAT-MPs-soil. PICRUST2 analysis revealed that pathways related to substance degradation were upregulated in the PBAT-MPs-soil. Furthermore, a higher percentage of strains with PBAT-MPs-degrading ability was found in PBAT-MPs-soil. Our results confirm that PBAT-MPs significantly inhibit the growth of vegetable crops and that soil bacterial communities affected by PBAT-MPs are instrumental in degrading them.

The fate of pharmaceuticals and personal care products (PPCPs) in sewer sediments:Adsorption triggering resistance gene proliferation

In recent years, large quantities of pharmaceuticals and personal care products (PPCPs) have been discharged into sewers, while the mechanisms of PPCPs enrichment in sewer sediments have rarely been revealed. In this study, three PPCPs (tetracycline, sulfamethoxazole, and triclocarban) were added consecutively over a 90-day experimental period to reveal the mechanisms of PPCPs enrichment and the transmission of resistance genes in sewer sediments. The results showed that tetracycline (TC) and triclocarban (TCC) have higher adsorption concentration in sediments compared to sulfamethoxazole (SMX). The absolute abundance of Tets and suls genes increased in sediments under PPCPs pressure. The increase in secretion of extracellular polymeric substances (EPS) and the loosening of the structure exposed a large number of hydrophobic functional groups, which promoted the adsorption of PPCPs. The absolute abundance of antibiotic resistance genes (ARGs), EPS and the content of PPCPs in sediments exhibited significant correlations. The enrichment of PPCPs in sediments was attributed to the accumulation of EPS, which led to the proliferation of ARGs. These findings contributed to further understanding of the fate of PPCPs in sewer sediments and opened a new perspective for consideration of controlling the proliferation of resistance genes.

Insights into the role of extracellular polymeric substances (EPS) in the spread of antibiotic resistance genes

Antibiotic resistance genes (ARG) are prevalent in aquatic environments. Discharge from wastewater treatment plants is an important point source of ARG release into the environment. It has been reported that biological treatment processes may enhance rather than remove ARG because of their presence in sludge. Attenuation of ARG in biotechnological processes has been studied in depth, showing that many microorganisms can secrete complex extracellular polymeric substances (EPS). These EPS can serve as multifunctional elements of microbial communities, involving aspects, such as protection, structure, recognition, adhesion, and physiology. These aspects can influence the interaction between microbial cells and extracellular ARG, as well as the uptake of extracellular ARG by microbial cells, thus changing the transformative capability of extracellular ARG. However, it remains unclear whether EPS can affect horizontal ARG transfer, which is one of the main processes of ARG dissemination. In light of this knowledge gap, this review provides insight into the role of EPS in the transmission of ARGs; furthermore, the mechanism of ARG spread is analyzed, and the molecular compositions and functional properties of EPS are summarized; also, how EPS influence ARG mitigation is addressed, and factors impacting how EPS facilitate ARG during wastewater treatment are summarized. This review provides comprehensive insights into the role of EPS in controlling the transport and fate of ARG during biodegradation processes at the mechanistic level.

Different fates of extracellular and intracellular antibiotic resistance genes in flocs, granular and biofilm nitrification systems under the stress of acetaminophen

The spread of antibiotic resistance genes (ARGs), including intracellular ARGs (i-ARGs) and extracellular ARGs (e-ARGs), has become a global problem that cannot be ignored. This study clarified the fates of e-ARGs and i-ARGs in floc sludge reactor (FS), granular sludge reactor (GS) and biofilm reactor (BF) under the stress of acetaminophen (APAP). The results showed that the risk of ARGs transmission, especially for e-ARGs, in FS and BF could increase with the increasing times of APAP treatment, except for that in GS. The fates of i-ARGs in three different systems were similar, which were mainly clustered as the efflux pumps mechanism. The secretion and disintegration of extracellular polymeric substances mainly affected the fates of e-ARGs. In the three systems, the complexity of network relationships between ARGs and microbial communities was FS, GS and BF. Partial least-squares path model analysis indicated that bacterial community directly contributed to the variations of e-ARGs and i-ARGs under APAP treatment in the three systems, playing a leading role. And i-ARGs and protein secondary structure showed direct effects on e-ARGs. This study indicated that e-ARGs in complex systems were more susceptible to be influenced, which should be paid more attention to prevent further propagation of ARGs.

Effect of micropollutants on disinfection byproducts and antibiotic resistance genes in drinking water in the process of biological activated carbon treatment

The biofilm stress response of biological activated carbon (BAC) was investigated under prolonged exposure to sulfadiazine and 2,4-Dichlorophenoxyacetic acid, simulating complex emerging organic contaminants (EOCs) that are mainly involved in the formation of nitrogenous disinfection byproducts (N-DBPs) and antibiotic resistance genes (ARGs). Under trace complex EOCs condition (2 µg/L), N-DBP precursors and abundance of ARGs increased significantly in BAC effluent. The total formation potential of haloacetonitriles (HANs) and halonitromethanes (HNMs) was 751.47 ± 2.98 ng/L, which was much higher than the control group (440.67 ± 13.38 ng/L without EOCs). Similarly, the relative abundance of ARGs was more than twice that in the control group. The complex EOCs induce excessive extracellular polymeric substance secretion (EPS), thereby causing more N-DBP precursors and stronger horizontal gene transfer. Metagenome analysis revealed that functional amino acid and protein biosynthesis genes were overexpressed compared to the control group, causing more EPS to be secreted into the external environment. Complex EOCs promote Cobetia, Clostridium, and Streptomyces dominance, contributing to the production of N-DBP precursors and ARGs. For the first time, in addition to the direct hazards of the EOCs, this study successfully revealed the indirect water quality risks of complex EOCs from the microbial stress response during BAC treatment. Synergistic regulation of EOCs and microorganisms is important for tap water security.

Comprehensive response of microbes to Ag and Ag2S nanoparticles and silver spatial distribution in constructed wetlands

This study investigated functional bacteria, key enzymes, and nitrogen metabolism in vertical flow constructed wetlands (CWs) after exposing to silver, silver sulfide nanoparticles (Ag NPs and Ag2S NPs), and silver iron (Ag+), and silver spatial distribution in CWs for 155 days. Ag NPs and Ag2S NPs affected species richness and diversity whereas Ag+ showed the higher the species diversity indices. Sequencing analysis exhibited that Ag NPs or Ag+ significantly inhibited nitrogen metabolic process by hindering the relative activity of functional enzymes, downregulating relative abundances of nrfA, norB and napA for Ag NPs, nxrA gene for Ag+, while Ag2S NPs inhibited relative abundance of nirA. The above results confirmed that NPs or Ag+ significantly reduced nitrogen removal and Ag NPs mainly inhibited NO3--N removal while Ag+ significantly suppressed NH4+-N removal. This study also found that CWs could effectively remove NPs or Ag+ (about 98 %), and nanoparticles showed higher translocation factors (TFs) values (0.81-1.15 or 0.36), indicating nanoparticles transported easily through substrate layers.

Deciphering the distribution and microbial secretors of extracellular polymeric substances associated antibiotic resistance genes in tube wall biofilm

Antibiotics and disinfectants have both been proposed to exert selective pressures on the biofilm as well as affecting the emergence and spread of antibiotic resistance genes (ARGs). However, the transfer mechanism of ARGs in drinking water distribution system (DWDS) under the coupling effect of antibiotics and disinfectants has not been completely understood. In the current study, four lab-scale biological annular reactors (BARs) were constructed to evaluate the effects of sulfamethoxazole (SMX) and NaClO coupling in DWDS and reveal the related mechanisms of ARGs proliferation. TetM was abundant in both the liquid phase and the biofilm, and redundancy analysis showed that the total organic carbon (TOC) and temperature were significantly correlated with ARGs in the water phase. There was a significant correlation between the relative abundance of ARGs in the biofilm phase and extracellular polymeric substances (EPS). Additionally, the proliferation and spread of ARGs in water phase were related to microbial community structure. Partial least-squares path modeling showed that antibiotic concentration may influence ARGs by affecting MGEs. These findings help us to better understand the diffusion process of ARGs in drinking water and provide a theoretical support for technologies to control ARGs at the front of pipeline.

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.

P, N, and C-related functional genes in SBR system promoted antibiotics resistance gene transmission under polystyrene microplastics stress

Wastewater treatment plants (WWTPs) are important sinks of microplastics (MPs) and antibiotics resistance genes (ARGs). Information regarding connections between functional modules of WWTPs and spread of ARGs under MPs stress is still lacking. In this study, correlations between P-, N-, and C-related functional genes and ARGs in a sequencing batch reactor (SBR) system were evaluated under polystyrene (PS) MPs stress. Total P and chemical oxygen demand (COD) in effluent showed no significant changes under 0.5-50 mg L^-1 PS MPs stress within 32 cycle treatment periods of SBR, while 0.5 mg L^-1 PS MPs affected the N cycling process. PS MPs (0.5-50 mg L^-1) promoted the richness and diversity of microbial community in SBR, and the denitrification process was exuberant. PS MPs with a low dosage (0.5-5 mg L^-1) enhanced secretion of extracellular polymeric substances and promoted expression levels of functional genes related to C fixation, C degradation, P cycling, and N cycling. Simultaneously, aac(3)-II, bla_TEM-1, and tetW increased by 27.13%, 38.36%, and 9.57% under low dosages of PS MPs stress; more importantly, the total absolute abundance of intI1 nearly doubled. 78.4% of these P-, N-, and C-related functional genes were positively correlated with intI1, thus favoring transmission of ARGs. This study firstly disclosed the underlying correlations between functional modules of WWTPs and spread of ARGs under MPs stress.

Insights into the enhanced effect of biochar on cadmium removal in vertical flow constructed wetlands

Biochar has been increasingly applied in constructed wetlands (CWs) to remediate heavy metal (HM)-polluted water. Nevertheless, only few studies have elucidated the enhanced mechanism and potential synergies related to the HM removal from biochar-based CWs (BC-CWs) for HMs removal. This study used cadmium (Cd) as the target HM and added biochar into CWs to monitor physicochemical parameters, plant' physiological responses, substrate accumulation, and microbial metabolites and taxa. In comparison with the biochar-free CW (as CWC), a maximum Cd²⁺ removal of 99.7% was achieved in the BC-CWs, associated with stable physicochemical parameters. Biochar preferentially adsorbed the available Cd²⁺ and significantly accumulated Fe/Mn oxides-bond and the exchangeable Cd fraction. Moreover, biochar alleviated the lipid peroxidation (decreased by 36.4%) of plants, resulting in improved growth. In addition, extracellular polymeric substances were increased by 376.9-396.8 mg/L in BC-CWs than compared to CWC, and N and C cycling was enhanced through interspecific positive connectivity. In summary, this study explored comprehensively the performance and mechanism of BC-CWs in the treatment of Cd²⁺-polluted water, suggesting a promising approach to promote the plant-microbe-substrate synergies under HM toxicity.

Ahmed E, Battah B, Abd Ellah NH, Zanetti S, Donadu MG. Nanotechnology as a Promising Approach to Combat Multidrug Resistant Bacteria: A Comprehensive Review and Future Perspectives

The wide spread of antibiotic resistance has been alarming in recent years and poses a serious global hazard to public health as it leads to millions of deaths all over the world. The wide spread of resistance and sharing resistance genes between different types of bacteria led to emergence of multidrug resistant (MDR) microorganisms. This problem is exacerbated when microorganisms create biofilms, which can boost bacterial resistance by up to 1000-fold and increase the emergence of MDR infections. The absence of novel and potent antimicrobial compounds is linked to the rise of multidrug resistance. This has sparked international efforts to develop new and improved antimicrobial agents as well as innovative and efficient techniques for antibiotic administration and targeting. There is an evolution in nanotechnology in recent years in treatment and prevention of the biofilm formation and MDR infection. The development of nanomaterial-based therapeutics, which could overcome current pathways linked to acquired drug resistance, is a hopeful strategy for treating difficult-to-treat bacterial infections. Additionally, nanoparticles' distinct size and physical characteristics enable them to target biofilms and treat resistant pathogens. This review highlights the current advances in nanotechnology to combat MDR and biofilm infection. In addition, it provides insight on development and mechanisms of antibiotic resistance, spread of MDR and XDR infection, and development of nanoparticles and mechanisms of their antibacterial activity. Moreover, this review considers the difference between free antibiotics and nanoantibiotics, and the synergistic effect of nanoantibiotics to combat planktonic bacteria, intracellular bacteria and biofilm. Finally, we will discuss the strength and limitations of the application of nanotechnology against bacterial infection and future perspectives.

Extracellular polymeric substances-antibiotics interaction in activated sludge: A review

Antibiotics, the most frequently prescribed drugs, have been widely applied to prevent or cure human and veterinary diseases and have undoubtedly led to massive releases into sewer networks and wastewater treatment systems, a hotspot where the occurrence and transformation of antibiotic resistance take place. Extracellular polymeric substances (EPS), biopolymers secreted via microbial activity, play an important role in cell adhesion, nutrient retention, and toxicity resistance. However, the potential roles of sludge EPS related to the resistance and removal of antibiotics are still unclear. This work summarizes the composition and physicochemical characteristics of state-of-the-art microbial EPS, highlights the critical role of EPS in antibiotics removal, evaluates their defense performances under different antibiotics exposures, and analyzes the typical factors that could affect the sorption and biotransformation behavior of antibiotics. Next, interactions between microbial EPS and antibiotic resistance genes are analyzed. Future perspectives, especially the engineering application of microbial EPS for antibiotics toxicity detection and defense, are also emphatically stressed.

A rational strategy of combining Fenton oxidation and biological processes for efficient nitrogen removal in toxic coking wastewater

Effective removal of nitrogen from coking wastewaters is a great challenge, since conventional biological technologies commonly suffer from concentrated bio-toxic components such as phenolic compounds and thiocyanide (SCN^-). This study has successfully developed a novel ternary process for efficiently removing nitrogen from a practical coking wastewater, by rationally combined biological pretreatment, Fenton sub-pretreatment and final partial nitrification-denitrification (PN) process. It was noted that the oxic biological pretreatment (OP) could degrade above 80 % of COD and SCN^- in the wastewater, by adopting the pristine coking wastewater sludge. Fenton sub-pretreatment would further degrade the residual toxic organics and protect the metabolic activity of nitrobacteria and denitrobacteria, realizing the efficient removal of NH₄⁺-N and TN that occurred in the final PN process with self-cultivated sludge. This work can provide an interesting strategy by rationally combining biological-physicochemical processes for nitrogen removal in toxic industrial wastewaters.

Metal and Metal Oxide Nanomaterials for Fighting Planktonic Bacteria and Biofilms: A Review Emphasizing on Mechanistic Aspects

The misuse and mismanagement of antibiotics have made the treatment of bacterial infections a challenge. This challenge is magnified when bacteria form biofilms, which can increase bacterial resistance up to 1000 times. It is desirable to develop anti-infective materials with antibacterial activity and no resistance to drugs. With the rapid development of nanotechnology, anti-infective strategies based on metal and metal oxide nanomaterials have been widely used in antibacterial and antibiofilm treatments. Here, this review expounds on the state-of-the-art applications of metal and metal oxide nanomaterials in bacterial infective diseases. A specific attention is given to the antibacterial mechanisms of metal and metal oxide nanomaterials, including disrupting cell membranes, damaging proteins, and nucleic acid. Moreover, a practical antibiofilm mechanism employing these metal and metal oxide nanomaterials is also introduced based on the composition of biofilm, including extracellular polymeric substance, quorum sensing, and bacteria. Finally, current challenges and future perspectives of metal and metal oxide nanomaterials in the anti-infective field are presented to facilitate their development and use.

Exploring the impact of intensity and duration of Cu (II) depression on aniline-degrading biosystem: Performance, sludge activity and microbial diversity

To evaluate the ecological risk of aniline wastewater biodegradation, the aniline wastewater (200 mg/L) was treated in this work under the stress of Cu (II) at 3, 6 and 10 mg/L, respectively. The slight fluctuation of aniline-degrading performance and the significant inhibition of nitrogen removal was caused by the Cu (II) stress at below 6 mg/L. Meanwhile, the tolerance of nitrifying performance to Cu (II) was higher than denitrifying. The collapse of biosystem was caused by the Cu (II) stress at 10 mg/L and the decontamination function was disabled within 8 days. The activity and stability of sludge declined under the increase of Cu (II) content. Microbial diversity results demonstrated that the genera with heavy-metal tolerance represented by Zoogloea and Azospira significantly dominated under the continuously Cu (II) stress. Whereas, the biosystem with these dominant genera did not achieve the comparable aniline and nitrogen removal performance as the control group.

Hot-pressed membrane assemblies enhancing the biofilm formation and nitrogen removal in a membrane-aerated biofilm reactor

Membrane-aerated biofilm reactor (MABR) is gaining popularity in wastewater treatment as a result of the low-energy delivery of oxygen from the carrier side and reduced sludge waste production, although its wider application suffers from the difficulty in microbial colonization on the smooth, hydrophobic membrane surface. In this study, a newly designed membrane/non-woven fabric assembly, prepared via a facile hot-pressing method, is demonstrated to be efficient in promoting the biofilm formation and nitrogen removal in MABR. The assembly achieved rough surface structure to retain biomass whilst sustained the surface hydrophobicity for a high oxygen transfer ability, which is crucial to support a resilient biofilm. Compared with the slower biomass growth and severe detachment of biofilm in the control, a thicker biofilm was quickly developed on the hot-pressed membrane assembly. High loading rates of organic matter, ammonia nitrogen and total nitrogen (TN) in the MABR using the hot-pressed membrane were 154.9 ± 5.4 g COD/(m²·d), 25.5 ± 0.6 g N/(m²·d) and 22.6 ± 0.7 g N/(m²·d), respectively. Particularly, the removal efficiency of TN was up to 82.8%, which was 2.5 times higher than the control. Furthermore, the biofilm grown on the hot-pressed membrane assembly organized a stable microbial community structure with a steady evolution to achieve a synergistic denitrifying function. Among the bacterial phylotypes, OLB8 might be crucial in denitrification. This study highlighted the significance of this facile membrane modification method to improve the process performance of MABR in wastewater treatment.

Unveiling changes of microbial community involved in N and P removal in constructed wetlands with exposing to silver nanoparticles

Constructed wetlands (CWs) are environmentally friendly engineered systems to purify wastewater, with low-cost and easy maintenance. However, it is not clear on responses of functional microbes for nitrogen (N) and phosphorus (P) biotransformation in CWs to silver nanoparticles (Ag NPs). The high throughput sequencings were employed to reveal microbial communities in vertical flow subsurface CWs with stable operation for 120 days. The results indicated that NH₄⁺-N, TN and TP removal of soil layer decreased by 43.56%, 15.7% and 22.7% under stress of Ag NPs. Microbial richness index and compositions were affected, and control wetland enriched Sulfurospirillum, Desulfarculaceae and Flavobacterium whereas CWs exposed to Ag NPs enriched Desulfosporosinus and Desulfurispora from LEfSe analysis. Moreover, after dosing Ag NPs, relative abundances of functional genes amoA and hao for nitrification, nirK and norB for denitrification and ppx and phoA/phoD for phosphorus conversions in upper soil were significantly downregulated. Inhibition on functional bacteria and genes of Ag NPs explained poor removal efficiencies of nitrogen and phosphorus pollutants in CWs. Our findings give an insight into ecological toxicity of Ag NPs on CWs with N and P bioconversions and provide the understanding of response of nitrifiers, denitrifies and PAOs.

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.

Antibiotic Resistance in the Drinking Water: Old and New Strategies to Remove Antibiotics, Resistant Bacteria, and Resistance Genes

Bacterial resistance is a naturally occurring process. However, bacterial antibiotic resistance has emerged as a major public health problem in recent years. The accumulation of antibiotics in the environment, including in wastewaters and drinking water, has contributed to the development of antibiotic resistant bacteria and the dissemination of antibiotic resistance genes (ARGs). Such can be justified by the growing consumption of antibiotics and their inadequate elimination. The conventional water treatments are ineffective in promoting the complete elimination of antibiotics and bacteria, mainly in removing ARGs. Therefore, ARGs can be horizontally transferred to other microorganisms within the aquatic environment, thus promoting the dissemination of antibiotic resistance. In this review, we discuss the efficiency of conventional water treatment processes in removing agents that can spread/stimulate the development of antibiotic resistance and the promising strategies for water remediation, mainly those based on nanotechnology and microalgae. Despite the potential of some of these approaches, the elimination of ARGs remains a challenge that requires further research. Moreover, the development of new processes must avoid the release of new contaminants for the environment, such as the chemicals resulting from nanomaterials synthesis, and consider the utilization of green and eco-friendly alternatives such as biogenic nanomaterials and microalgae-based technologies.

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.

Enhanced effects of walnut green husk solution on the phytoextraction of soil Cd and Zn and corresponding microbial responses

Walnut green husk (WGH) is a common agricultural waste, but it may be conducive to phytoremediation of heavy metals owing to its abundant phenolic hydroxyl, carboxyl, and other functional groups. In this study, WGH solution was used as an enhancer in the phytoextraction process via Sedum plumbizincicola, a hyperaccumulator of Zn and Cd. Microbial responses in the soil and plants were seamlessly analyzed to determine the underlying mechanisms of heavy metal extraction in this process. The results showed that the addition of 0.05 g/mL WGH solution increased the accumulation of Cd (by 153%) and Zn (by 220%) in plants as well as the availabilities of Cd (by 29.46%) and Zn (by 9.71%) in the soil, which can be attributed to an increase in the relative abundance of plant growth-promoting rhizobacteria that benefit phytoextraction. Furthermore, co-occurrence network analysis indicated the keystone taxa in the microbial community. Particularly, one of the keystone taxa, Pseudomonas, was also identified as distinct taxon in soil, and it was dominant among the endophytic bacteria. These results indicated that Pseudomonas, a taxon responded to WGH solution, may play a key role in enhanced phytoextraction in both soil and plant root. These results help to a better understanding of the microbial mechanisms for heavy metal accumulation in hyperaccumulator.