Determining the Contribution of Micro/Nanoplastics to Antimicrobial Resistance: Challenges and Perspectives.

Microorganisms colonizing the surfaces of microplastics form a plastisphere in the environment, which captures miscellaneous substances. The plastisphere, owning to its inherently complex nature, may serve as a "Petri dish" for the development and dissemination of antibiotic resistance genes (ARGs), adding a layer of complexity in tackling the global challenge of both microplastics and ARGs. Increasing studies have drawn insights into the extent to which the proliferation of ARGs occurred in the presence of micro/nanoplastics, thereby increasing antimicrobial resistance (AMR). However, a comprehensive review is still lacking in consideration of the current increasingly scattered research focus and results. This review focuses on the spread of ARGs mediated by microplastics, especially on the challenges and perspectives on determining the contribution of microplastics to AMR. The plastisphere accumulates biotic and abiotic materials on the persistent surfaces, which, in turn, offers a preferred environment for gene exchange within and across the boundary of the plastisphere. Microplastics breaking down to smaller sizes, such as nanoscale, can possibly promote the horizontal gene transfer of ARGs as environmental stressors by inducing the overgeneration of reactive oxygen species. Additionally, we also discussed methods, especially quantitatively comparing ARG profiles among different environmental samples in this emerging field and the challenges that multidimensional parameters are in great necessity to systematically determine the antimicrobial dissemination risk in the plastisphere. Finally, based on the biological sequencing data, we offered a framework to assess the AMR risks of micro/nanoplastics and biocolonizable microparticles that leverage multidimensional AMR-associated messages, including the ARGs' abundance, mobility, and potential acquisition by pathogens.

Single cell protein production from methane in a gas-delivery membrane bioreactor.

Single cell protein (SCP, or microbial protein) is one of the emerging alternative protein sources to address the global challenge of food insecurity. Recently, the SCP produced from methane has attracted substantial attention since methane is a renewable resource attainable from anaerobic digestion. However, the supply of methane, an insoluble gas in water, is one of the major challenges in producing methane-based SCP. This work developed a novel bioreactor configuration, in which hollow fiber membrane was used for efficient methane supply while microorganisms were growing in the suspended form favourable for the biomass harvest. Over a 312-day operation, the impacts of three critical parameters on the SCP production were investigated, including the ratio of methane loading to ammonium loading, the ratio of methane loading to oxygen loading, and the sludge retention time (SRT). Under the condition of 4 g CH4/g NH4+, 4 g O2/g CH4, and SRT of 4 days, the highest SCP production yield was observed and determined to be 1.36 g SCP/g CH4 and 5.05 g SCP/g N, respectively. The protein content was up to 67 %, which is higher than the majority of reported values to date. Moreover, the methane and ammonium utilization efficiencies were both close to 100 %, suggesting the highly efficient utilization of substrates in this new bioreactor configuration. A high relative abundance of essential amino acids (EAA) above 42 % was achieved, representing the highest EAA content reported. These findings provide valuable insights into SCP production using methane as a feedstock.

Superior mainstream partial nitritation in an acidic membrane-aerated biofilm reactor.

Shortcut nitrogen removal holds significant economic appeal for mainstream wastewater treatment. Nevertheless, it is too difficult to achieve the stable suppression of nitrite-oxidizing bacteria (NOB), and simultaneously maintain the activity of ammonia-oxidizing bacteria (AOB). This study proposes to overcome this challenge by employing the novel acid-tolerant AOB, namely "Candidatus Nitrosoglobus", in a membrane-aerated biofilm reactor (MABR). Superior partial nitritation was demonstrated in low-strength wastewater from two aspects. First, the long-term operation (256 days) under the acidic pH range of 5.0 to 5.2 showed the successful NOB washout by the in situ free nitrous acid (FNA) of approximately 1 mg N/L. This was evidenced by the stable nitrite accumulation ratio (NAR) close to 100 % and the disappearance of NOB shown by 16S rRNA gene amplicon sequencing and fluorescence in situ hybridization. Second, oxygen was sufficiently supplied in the MABR, leading to an unprecedentedly high ammonia oxidation rate (AOR) at 2.4 ± 0.1 kg N/(m3 d) at a short hydraulic retention time (HRT) of a mere 30 min. Due to the counter diffusion of substrates, the present acidic MABR displayed a significantly higher apparent oxygen affinity (0.36 ± 0.03 mg O2/L), a marginally lower apparent ammonia affinity (14.9 ± 1.9 mg N/L), and a heightened sensitivity to FNA and pH variations, compared with counterparts determined by flocculant acid-tolerant AOB. Beyond supporting the potential application of shortcut nitrogen removal in mainstream wastewater, this study also offers the attractive prospect of intensifying wastewater treatment by markedly reducing the HRT of the aerobic unit.

Bioreduction of chromate in a syngas-based membrane biofilm reactor.

This study leveraged synthesis gas (syngas), a renewable resource attainable through the gasification of biowaste, to achieve efficient chromate removal from water. To enhance syngas transfer efficiency, a membrane biofilm reactor (MBfR) was employed. Long-term reactor operation showed a stable and high-level chromate removal efficiency > 95%, yielding harmless Cr(III) precipitates, as visualised by scanning electron microscopy and energy dispersive X-ray analysis. Corresponding to the short hydraulic retention time of 0.25 days, a high chromate removal rate of 80 µmol/L/d was attained. In addition to chromate reduction, in situ production of volatile fatty acids (VFAs) by gas fermentation was observed. Three sets of in situ batch tests and two groups of ex situ batch tests jointly unravelled the mechanisms, showing that biological chromate reduction was primarily driven by VFAs produced from in situ syngas fermentation, whereas hydrogen originally present in the syngas played a minor role. 16 S rRNA gene amplicon sequencing has confirmed the enrichment of syngas-fermenting bacteria (such as Sporomusa), who performed in situ gas fermentation leading to the synthesis of VFAs, and organics-utilising bacteria (such as Aquitalea), who utilised VFAs to drive chromate reduction. These findings, combined with batch assays, elucidate the pathways orchestrating synergistic interactions between fermentative microbial cohorts and chromate-reducing microorganisms. The findings facilitate the development of cost-effective strategies for groundwater and drinking water remediation and present an alternative application scenario for syngas.

Preparation of blast furnace dust particle electrodes and their application in synergistic electrochemical degradation of saline polyvinyl alcohol wastewater.

Polyvinyl alcohol (PVA) has been widely used as a water-soluble plastic in laundry and dish detergent pods, yet wastewater contaminated with PVA is too difficult to be treated due to its high salinity and foaming. Here, we fabricated blast furnace dust (BFD) particle electrodes, and developed a three-dimensional electrocatalytic system (3DEC) to treat saline PVA wastewater. The optimum preparation condition for BFD particle electrode was iron carbon ratio of 2:1 doping with TiO2. The optimal parameters of 3DECs for PVA wastewater degradation were thoroughly investigated, with current density of 30 mA/cm2, electrode distance of 30 mm, pH value of 7.0, and particle electrode filling rate of 50%. PVA wastewater degradation rate could reach 89.33% within 120 min. The underlying mechanism of iron-carbon micro electrolysis and electrocatalytic system was further studied. PVA wastewater was degraded by direct catalytic oxidation from electrodes. A scavenger experiment showed that free radicals consisting of •OH and HClO mainly contributed to the PVA wastewater degradation. HClO was generated by Cl- at the electrocatalysis and micro electrolysis of particles. In addition, the lifetime of the prepared BFD particle electrode was 120 h, which exhibited electrochemical stability. These findings highlight that the 3DECs coupled with BFD particle electrode is a promising electrocatalysis process for the removal of PVA wastewater.

Mechanistic toxicity assessment of differently sized and charged polystyrene nanoparticles based on human placental cells.

Nanoplastics, as emerging contaminants, may be degraded from microplastics and released into aquatic systems globally, which pose threats to human health via ingestion with food or water. Although plastic fragments have been isolated from placental tissues in pregnant women, little is known about the direct toxicity of nanoplastics on human placental cells that plays a critical role in maintaining healthy growth of fetus. This study explored the mechanistic toxicity of polystyrene nanoplastics (PS-NPs) with different sizes (25, 50, 100 and 500 nm) and surface charges (-NH2, -COOH and unlabeled) on human placental cells. Results showed that PS-NPs had size- and surface charge-specific toxicity pattern. The smaller the PS-NP size was, the greater the toxicity induced on human placental cells. In terms of surface charges, NH2-labeled PS-NPs caused greater effects on cytotoxicity, inhibition of protein kinase A (PKA) activity, oxidative stress, and cell cycle arrest compared to COOH-labeled and unmodified PS-NPs. PS-NPs also induced size- and surface charge-dependent expression profiles of genes involved in various and interrelated toxicity pathways. In particular, PS-NPs increased intracellular reactive oxygen species in human placental cells, which can induce DNA damage and lead to cell cycle arrest in G1or G2 phase, inflammation and apoptosis. Our findings provide empirical evidences that the negative effects of nanoplastics on human placental cells, and highlight the necessity to conduct risk assessment of nanoplastics on female reproduction and fetal development.

Microplastics as potential carriers of viruses could prolong virus survival and infectivity.

Microplastics are emerging contaminants in various aquatic environments, leading to human and environmental health concerns. Viruses have also been ubiquitously detected in aquatic environments, and there is an unknown risk of microplastics-mediated virus migration through adsorption. This study applied polystyrene microplastics as the carrier and the T4 bacteriophage (or phage) as the virus model, and a violet side scatter/green fluorescence double-gated flow cytometry approach to investigate the adsorption capacity of viruses on microplastics. Our results show that up to 98.6±0.2% of the dosed viruses can be adsorbed by microplastics, and such adsorptions are dependent on size and surface functional groups. Both Fourier-transform infrared spectroscopy and fluorescence-labelled confocal microscopy confirmed that the virus can successfully adsorb onto microplastics. Zeta potential characterisation revealed that the electrostatic interaction is the primary adsorption mechanism associated with the adsorption of viruses. UV-aging was found to enhance the adsorption capacities of viruses on microplastics. Both pristine and UV-aged microplastics were found to significantly prolong the infectivity of the adsorbed viruses, even under elevated temperatures. Collectively, our findings highlight that microplastics are associated with the biological risks of water-borne viral transmission through virus adsorption.

Unraveling individual and combined toxicity of nano/microplastics and ciprofloxacin to Synechocystis sp. at the cellular and molecular levels.

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.

Evaluating the Role of Microbial Internal Storage Turnover on Nitrous Oxide Accumulation During Denitrification.

Biological wastewater treatment processes under a dynamic regime with respect to carbon substrate can result in microbial storage of internal polymers (e.g., polyhydroxybutyrate (PHB)) and their subsequent utilizations. These storage turnovers play important roles in nitrous oxide (N2O) accumulation during heterotrophic denitrification in biological wastewater treatment. In this work, a mathematical model is developed to evaluate the key role of PHB storage turnovers on N2O accumulation during denitrification for the first time, aiming to establish the key relationship between N2O accumulation and PHB storage production. The model is successfully calibrated and validated using N2O data from two independent experimental systems with PHB storage turnovers. The model satisfactorily describes nitrogen reductions, PHB storage/utilization, and N2O accumulation from both systems. The results reveal a linear relationship between N2O accumulation and PHB production, suggesting a substantial effect of PHB storage on N2O accumulation during denitrification. Application of the model to simulate long-term operations of a denitrifying sequencing batch reactor and a denitrifying continuous system indicates the feeding pattern and sludge retention time would alter PHB turnovers and thus affect N2O accumulation. Increasing PHB utilization could substantially raise N2O accumulation due to the relatively low N2O reduction rate when using PHB as carbon source.

Destruction and reconstruction of the robust [Cu2(OOCR)4] unit during crystal structure transformations between two coordination polymers.

This work first demonstrates that the robust [Cu(2)(OOCR)(4)] unit can be destroyed and reconstructed in the solid state, as observed in water-induced structural interconversion of two distinct coordination polymers with 5-bromonicotinate.