Zhigang Yu

Biofilms are widespread in water distribution systems and consist of bacterial cells with extensive cell-to-cell contact, a prerequisite for plasmid-mediated conjugative transfer of antibiotic resistance genes (ARGs). Although plasmid-mediated conjugative ARG transfer has been extensively studied, our understanding of how conjugation occurs within spatially structured bacterial biofilms and how chlorine disinfection influences the conjugation process remains limited. This study systematically investigated the effects of chlorine exposure on biofilm disruption, resistant bacteria invasion, and the conjugative transfer of ARGs in both monoculture and multispecies biofilms composed of Escherichia coli, Pseudomonas putida, and Pseudomonas aeruginosa. Results showed that free chlorine significantly enhanced plasmid-mediated ARG transfer in biofilms at an initial dose of 5 mgCl/L. This could be due to the disruption of recipient biofilm structure, which facilitated donor colonization of the biofilms and close contact with the recipient bacteria. The hotspots for ARG conjugative transfer in the biofilms shifted from the surface (18 ± 2 μm) to the inner layer (27 ± 3 μm) under free chlorine exposure in the multispecies biofilm model. Moreover, a mathematical model was developed to simulate the long-term dynamics of gene transfer within biofilms under free chlorine exposure. The simulation results indicated that exposure to 5 mgCl/L promoted deeper colonization of donor cells and enhanced the dissemination of ARGs throughout the biofilm. Collectively, our findings provide a mechanistic link between biofilm structural disruption, bacterial invasion, and accelerated ARG horizontal transfer in biofilms under free chlorine exposure.

The role of micro/nanoplastics (M/NPs) in the dissemination of antimicrobial resistance (AMR) remains insufficiently understood. Here, we examine how polystyrene (PS) M/NPs of varying sizes and concentrations affect AMR gene (ARG) transfer in model systems with gram-negative (Escherichia coli) and gram-positive (Enterococcus faecalis) donors. In these systems, the ARG transfer frequency is higher for intrageneric pairs than for intergeneric pairs. The 20- and 120-nm-sized PS broadly facilitate conjugation, whereas the 1-μm-sized PS selectively promotes ARG transfer to E. coli recipients, in addition to altering the expression of conjugation- and pili-associated genes. Notably, an environmentally relevant (0.1 mg/L) concentration of PS M/NPs facilitates AMR transfer in the tested systems, which correlates with increased reactive oxygen species levels, ATP levels, and cell membrane permeability in both donors and recipients. Collectively, our findings underscore the role of M/NPs in facilitating AMR spread in specific bacterial systems, providing valuable insights for understanding their potential ecological risk in water environments.

This Editorial introduces the Special Issue titled “Integrated Remediation Processes toward Heavy Metal-Contaminated Environment”

Numerous disinfectants have been discharged into the environment through anthropogenic activities, leading to ubiquitous coexistence of multiple disinfectants in the real environment. Previous studies reported that individual disinfectants induce the emergence of antimicrobial resistance (AMR); however, the impacts of the coexposure to multiple disinfectants on the development of AMR and its toxicity associated with bacterial pathogenicity are still unclear. Here, we conducted a 30-day stepwise exposure experiment to investigate the impacts of the commonly used disinfectants polyhexamethylene guanidine (PHMG), benzalkonium chloride (BAC), and their combination on AMR and pathogenicity of Wild-Type Escherichia coli. Results reveal that the coexistence of dual disinfectants dramatically led to higher levels of AMR (2.0- to 14.8-fold) and pathogenicity (8.7-fold) in the evolved strains. Dual disinfectant-induced bacterial evolution is primarily driven by the alteration in the expression of key functional genes, such as those involved in biofilm formation and cell motility. In contrast, genetic mutations may not account for the increased AMR and pathogenicity in combination of dual disinfectant treatment, as similar gene mutations are responsible for both dual and single disinfectant stress. The evolved strains induced by disinfectant combination, characterized with transcriptional regulation, exhibited a synergistic or additive response on AMR and pathogenicity, which was further confirmed by a toxicology prediction model. This study demonstrated that dual disinfectants synergistically enhanced AMR and the associated pathogenicity, advancing our understanding of the risks posed by coexistence of multiple chemical pollutants in the environment.

Lutein is widely used in medicine, health care, and food processing due to its antioxidant effects; however, it is difficult for the traditional extraction of lutein using marigolds to meet the increasing market demand for lutein. To achieve high-efficiency lutein production, we investigated the effects of different conditions on the biomass accumulation and lutein yield of Chlorella vulgaris. The optimized cultivation conditions include mixotrophic cultivation using sodium nitrate as a nitrogen source, maintaining a total-organic-carbon-to-total-nitrogen ratio of 12:1, a total-nitrogen-to-total-phosphorus ratio of 10:1, and lighting duration of 24 h. The results of the study indicated that under these specific conditions, Chlorella vulgaris attained a final biomass concentration, biomass productivity, and growth yield of 6.08 g·L⁻¹, 1.00 g·L⁻¹·d⁻¹, and 1.67 g biomass/g TOC, respectively. Additionally, the concentrations of total chlorophyll, carotenoid, lutein, and protein reached 139.20 mg·L⁻¹, 31.87 mg·L⁻¹, 15.02 mg·L⁻¹, and 2.17 g·L⁻¹, respectively, and the content of lutein reached 2.47 mg·g⁻¹. This study supplies a theoretical basis for the industrial application of lutein production using Chlorella vulgaris.

In this work, the materials from different positions of 2219 aluminum‐alloy/304 stainless‐steel inertia friction–welded tank with long‐term storage of N₂O₄ are studied. The results show that the corrosion product layer composed of Fe₃O₄ and FeCr₂O₄ is covered on the surface of stainless steel. The corrosion product layer on the surface of stainless steel can effectively improve the protection effect. Severe corrosion occurred in both the sidewall and bottom aluminum alloy, with intergranular corrosion depths of about 30–50 μm observed in the cross section, accompanied by typical exfoliation corrosion. A Fe–Al‐dominated intermetallic compound layer is formed at the weld. A dynamic recrystallization zone and thermomechanical‐affected zone are included on the aluminum‐alloy side with intergranular corrosion depths of 4.3 and 13.3 μm, respectively. The granular Al matrix can be seen on the peeling surface of the aluminum alloy. Combining scanning Kelvin probe and potentiodynamic polarization curve results, the high potential of the stainless steel can further promote the corrosion of the aluminum alloy.

Biochar can effectively reduce the phytoavailability of mercury (Hg) in soil, but the mechanisms are not fully understood. In this study, the dynamic changes in Hg content adsorbed by the biochar (BC-Hg), Hg phytoavailability in the soil (P-Hg), and soil dissolved organic matter (DOM) characteristics were determined over a 60-day treatment period. Biochar obtained at 300 °C, 500 °C and 700 °C reduced the P-Hg concentration assessed by MgCl₂ extraction by 9.4%, 23.5% and 32.7%, respectively. However, biochar showed a very limited adsorption on Hg, with the maximum BC-Hg content only accounting for 1.1% of the total amount. High-resolution scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS) results showed that the proportion of Hg atoms in biochar after 60 d was barely detectable. Biochar treatment can shift soil DOM toward higher aromatic content and molecular weight. Additionally, the addition of high-temperature biochar increased more humus-like components, but low-temperature biochar increased more protein-like components. Correlation analysis and partial least squares path modeling (PLS-PM) showed that biochar promoted humus-like fractions formation to reduce the Hg phytoavailability. This research has deepened the understanding of the mechanisms by which biochar stabilizes Hg in agricultural soils.