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Although nanoplastics/microplastics (NPs/MPs) may interact with co-contaminants (e.g. antibiotics) in aquatic systems, little is known about their combined toxicity. Here, we compared the individual toxicity of NPs/MPs or ciprofloxacin (CIP, a very commonly detected antibiotic) and their combined toxicity toward a unicellular cyanobacterium Synechocystis sp. in terms of the cellular responses and metabolomic analysis. We found that CIP exhibited an antagonistic effect with NPs/MPs due to its adsorption onto the surface of NPs/MPs. Particle size-dependent toxic effects of NPs/MPs were observed. Reactive oxygen species (ROS) was verified as an important factor for NPs/MPs to inhibit cell growth, other than for CIP. Metabolomics further revealed that Synechocystis sp. up-regulated glycerophospholipids, amino acids, nucleotides, and carbohydrates to tolerate CIP pressure. NPs/MPs downregulated the TCA cycle and glycerophospholipids metabolism and impaired the primary production and membrane integrity via adhesion with Synechocystis sp.. Additionally, the toxicity of NPs/MPs throughout ten growth cycles at a sublethal concentration unveiled its potential risks in interfering with metabolism. Collectively, our findings provide insights into the joint ecotoxicity of NPs/MPs and antibiotics, and highlight the potential risks of co-pollutants at environmental relevant concentrations.

The widespread use of CuO nanoparticles (NPs) results in their continuous release into the environment, which could pose risks to public health and to microbial ecosystems. Following consumption, NPs will initially enter into sewer systems and interact with and potentially influence sewer microbial communities. An understanding of the response of microbes in sewers, particularly sulfate-reducing bacteria (SRB), to the CuO NPs induced stress is important as hydrogen sulfide produced by SRB can cause sewer corrosion and odour emissions. In this study, we elucidated how the anabolic and catabolic processes of a model SRB, Desulfovibrio vulgaris Hidenborough (D. vulgaris), respond to CuO NPs. Physiological analyses indicated that the exposure of the culture to CuO NPs at elevated concentrations (>50 mg/L) inhibited both its anabolic and catabolic activities, as revealed by lowered cell proliferation and sulfate reduction rate. The antibacterial effects of CuO NPs were mainly attributed to the overproduction of reactive oxygen species. Transcriptomic analysis indicated that genes encoding for flagellar assembly and some genes involved in electron transfer and respiration were down-regulated, while genes for the ferric uptake regulator (Fur) were up-regulated. Moreover, the CuO NPs exposure significantly up-regulated genes involved in protein synthesis and ATP synthesis. These results suggest that CuO NPs inhibited energy conversion, cell mobility, and iron starvation to D. vulgaris. Meanwhile, D. vulgaris attempted to respond to the stress of CuO NPs by increasing protein and ATP synthesis. These findings offer new insights into the bacterial-nanoparticles interaction at the transcriptional level, and advance our understanding of impacts of CuO NPs on SRB in the environment. Keywords: CuO nanoparticles, Ecotoxicity, Sulfate-reducing bacteria, Genome-wide RNA sequencing

Partial nitritation-Anammox (PN/A) process has been recognized as a sustainable process for biological nitrogen removal. Although various antibiotics have been ubiquitously detected in influent of wastewater treatment plants, little is known whether functional microorganisms in the PN/A process are capable of biodegrading antibiotics. This study aimed to investigate simultaneous nitrogen and antibiotic removal in a lab-scale one-stage PN/A system treating synthetic wastewater containing a widely-used antibiotic, sulfadiazine (SDZ). Results showed that maximum total nitrogen (TN) removal efficiency of 86.1% and SDZ removal efficiency of 95.1% could be achieved when treating 5 mg/L SDZ under DO conditions of 0.5–0.6 mg/L. Compared to anammox bacteria, ammonia-oxidizing bacteria (AOB) made a major contribution to SDZ degradation through their cometabolic pathway. A strong correlation between amoA gene and SDZ removal efficiency was found (p < 0.01). In addition, the degradation products of SDZ did not exhibit any inhibitory effects on Escherichia coli. The findings suggest that it is promising to apply the PN/A process to simultaneously remove antibiotics and nitrogen from contaminated wastewater.

An innovative process coupling anaerobic ammonium oxidation (anammox) with nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) in membrane biofilm reactors (MBfRs) has been developed to achieve high-level nitrogen removal from both sidestream (i.e., anaerobic digestion liquor) and mainstream (i.e., domestic strength) wastewater. In this study, a 1D biofilm model embedding the n-DAMO and anammox reactions was developed to facilitate further understanding of the process and its optimization. The model was calibrated and validated using comprehensive data sets from two independent MBfRs, treating sidestream- and mainstream-strength wastewater, respectively. Modelling results revealed a unique biofilm stratification. While anammox bacteria dominated throughout the biofilm, n-DAMO archaea (coupling nitrate reduction with anaerobic methane oxidation) only occurred at the inner layer and n-DAMO bacteria (coupling nitrite reduction with anaerobic methane oxidation) spread more evenly with a slightly higher fraction in the outer layer. The established MBfRs were robust against dynamic influent flowrates and nitrite/ammonium ratios. Thicker biofilms were beneficial for not only the total nitrogen (TN) removal but also the system robustness. Additionally, a positive correlation between the nitrogen removal efficiency and the residual methane emission was observed, as a result of higher methane partial pressure required. However, there was a threshold of methane partial pressure, above which the residual methane increased but nitrogen removal efficiency was stable. Meanwhile, thicker biofilms were also favorable to achieve less residual methane emission. Simulation results also suggested the feasibility of methane-based MBfRs to polish mainstream anammox effluent to meet a stringent N discharge standard (e.g., TN

Background: Antibiotic resistance poses a great threat to global public health. Overuse of antibiotics is generally considered as the major factor contributing to it. However, little is known about whether non-antibiotic drugs could play potential roles in the emergence of antibiotic resistance. Objective: We aimed to investigate whether antidepressant fluoxetine induces multiple antibiotic resistances and reveal underlying mechanisms. Methodology: Escherichia coli K12 was exposed to different concentrations of fluoxetine (0, 0.5, 5, 50 and 100 mg/L) and the resistant strains were isolated by plating on antibiotic containing plates. Resistant strains were randomly selected to determine the increase of minimum inhibition concentration (MIC) of multiple antibiotics. Genome-wide DNA sequencing was performed on cells cultured in lysogeny broth (LB) without any fluoxetine or antibiotics exposure. RNA sequencing and proteomic profiling of isolated mutants grown in LB with 100 mg/L fluoxetine were analyzed to reveal the underlying mechanisms. Results: Exposure of Escherichia coli to fluoxetine at 5–100 mg/L after repeated subculture in LB for 30 days promoted its mutation frequency resulting in increased resistance against the antibiotics chloramphenicol, amoxicillin and tetracycline. This increase was up to 5.0 × 107 fold in a dose-time pattern. Isolated mutants with resistance to one of these antibiotics also exhibited multiple resistances against fluoroquinolone, aminoglycoside, β-lactams, tetracycline and chloramphenicol. According to global transcriptional and proteomic analyses, the AcrAB-TolC pump together with the YadG/YadH transporter, a Tsx channel and the MdtEF-TolC pump have been triggered to export the antibiotics to the exterior of the cell. Whole-genome DNA analysis of the mutants further revealed that ROS-mediated mutagenesis (e.g., deletion, insertion, and substitution) of DNA-binding transcriptional regulators (e.g., marR, rob, sdiA, cytR and crp) to up-regulate the expression of efflux pumps, may further enhance the antibiotic efflux. Conclusions: Our findings for the first time demonstrated that the exposure to antidepressant fluoxetine induces multiple antibiotic resistance in E. coli via the ROS-mediated mutagenesis. Keywords: Antimicrobial resistance, Multiple antibiotic resistance, AcrAB-TolC, ROS-mediated mutagenesis, Escherichia coli, Antidepressant fluoxetine

Antibiotic resistance poses a major threat to public health. Overuse and misuse of antibiotics are generally recognised as the key factors contributing to antibiotic resistance. However, whether non-antibiotic, anti-microbial (NAAM) chemicals can directly induce antibiotic resistance is unclear. We aim to investigate whether the exposure to a NAAM chemical triclosan (TCS) has an impact on inducing antibiotic resistance on Escherichia coli. Here, we report that at a concentration of 0.2 mg/L TCS induces multi-drug resistance in wild-type Escherichia coli after 30-day TCS exposure. The oxidative stress induced by TCS caused genetic mutations in genes such as fabI, frdD, marR, acrR and soxR, and subsequent up-regulation of the transcription of genes encoding beta-lactamase and multi-drug efflux pump, together with down-regulation of genes related to membrane permeability. The findings advance our understanding of the potential role of NAAM chemicals in the dissemination of antibiotic resistance in microbes, and highlights the need for controlling biocide applications.

It has been reported that microbial reduction of sulfate, nitrite/nitrate and iron/manganese could be coupled with anaerobic oxidation of methane (AOM), which plays a significant role in controlling methane emission from anoxic niches. However, little is known about microbial chromate (Cr(VI)) reduction coupling with AOM. In this study, a microbial consortium was enriched via switching nitrate dosing to chromate feeding as the sole electron acceptor under anaerobic condition in a membrane biofilm reactor (MBfR), in which methane was continuously provided as the electron donor through bubble-less hollow fiber membranes. According to long-term reactor operation and chromium speciation analysis, soluble chromate could be reduced into Cr(III) compounds by using methane as electron donor. Fluorescence in situ hybridization and high-throughput 16S rRNA gene amplicon profiling further indicated that after feeding chromate Candidatus ‘Methanoperedens’ (a known nitrate-dependent anaerobic methane oxidation archaeon) became sole anaerobic methanotroph in the biofilm, potentially responsible for the chromate bio-reduction driven by methane. Two potential pathways of the microbial AOM-coupled chromate reduction were proposed: (i) Candidatus ‘Methanoperedens’ independently utilizes chromate as electron acceptor to form Cr(III) compounds, or (ii) Candidatus ‘Methanoperedens’ oxidizes methane to generate intermediates or electrons, which will be utilized to reduce chromate to Cr(III) compounds by unknown chromate reducers synergistically. Our findings suggest a possible link between the biogeochemical chromium and methane cycles. Keywords: Microbial chromate reduction, Anaerobic oxidation of methane, Cr(III) compounds, Candidatus ‘Methanoperedens’, Membrane biofilm reactor

The spread of antibiotic resistance has become a major concern for public health. As emerging contaminants, various metallic nanoparticles (NPs) and ionic heavy metals have been ubiquitously detected in various environments. Although previous studies have indicated NPs and ionic heavy metals could exhibit co-selection effects for antibiotic resistance, little is known about whether and how they could promote antibiotic resistance spread via horizontal gene transfer across bacterial genera. This study, we report both CuO NPs and copper ions (Cu2+) could stimulate the conjugative transfer of multiple-drug resistance genes. When exposing bacteria to CuO NPs or Cu2+ at environmental-relevant and sub-inhibitory concentrations (e.g., 1–100 μmol/L), conjugation frequencies of plasmid-encoded antibiotic resistance genes across genera (i.e., from Escherichia coli to Pseudomonas putida) were significantly enhanced (p

Background: Antibiotic resistance poses an increasing threat to public health. Horizontal gene transfer (HGT) promoted by antibiotics is recognized as a significant pathway to disseminate antibiotic resistance genes (ARGs). However, it is unclear whether non-antibiotic, anti-microbial (NAAM) chemicals can directly promote HGT of ARGs in the environment. Objectives: We aimed to investigate whether triclosan (TCS), a widely-used NAAM chemical in personal care products, is able to stimulate the conjugative transfer of antibiotic multi-resistance genes carried by plasmid within and across bacterial genera. Methods: We established two model mating systems, to investigate intra-genera transfer and inter-genera transfer. Escherichia coli K-12 LE392 carrying IncP-α plasmid RP4 was used as the donor, and E. coli K-12 MG1655 or Pseudomonas putida KT2440 were the intra- and inter-genera recipients, respectively. The mechanisms of the HGT promoted by TCS were unveiled by detecting oxidative stress and cell membrane permeability, in combination with Nanopore sequencing, genome-wide RNA sequencing and proteomic analyses. Results: Exposure of the bacteria to environmentally relevant concentrations of TCS (from 0.02 μg/L to 20 μg/L) significantly stimulated the conjugative transfer of plasmid-encoded multi-resistance genes within and across genera. The TCS exposure promoted ROS generation and damaged bacterial membrane, and caused increased expression of the SOS response regulatory genes umuC, dinB and dinD in the donor. In addition, higher expression levels of ATP synthesis encoding genes in E. coli and P. putida were found with increased TCS dosage. Conclusions: TCS could enhance the conjugative ARGs transfer between bacteria by triggering ROS overproduction at environmentally relevant concentrations. These findings improve our awareness of the hidden risks of NAAM chemicals on the spread of antibiotic resistance. Keywords: Non-antibiotic antimicrobial (NAAM), Triclosan, Environmental concentration, Antibiotic resistance genes, Horizontal gene transfer