Effects of chlorination and combined UV/Cl2 treatment on endotoxin activity and inhalation toxicity of lipopolysaccharide, gram-negative bacteria and reclaimed water

Intrinsic mechanisms underlying the highly efficient removal of bacterial endotoxin and related risks in tailwater by dielectric barrier discharge plasma

Endotoxin is widely present in aquatic environments and can induce adverse health effects. In this study, dielectric barrier discharge (DBD) plasma was used to remove bacterial endotoxin from the tailwater of a wastewater treatment plant. The removal efficiency of total endotoxin activity was up to 92% with low electrical energy consumption (0.43 J mL^-1%^-1) after 180 s of the DBD plasma treatment, which was better than other previously reported methods. In the early stage of DBD plasma oxidation, the expression of genes related to cell morphology and bacterial antioxidant enzyme synthesis was distinctly down-regulated, suggesting that cell integrity was destroyed, leading to endotoxin release into the solution. Additionally, endotoxin synthesis in the cells was suppressed. The endotoxin in the solution was effectively removed by ·OH, ¹O₂, and O₂·^-generated by the DBD plasma, with second-order reaction rates of 2.69 × 10¹⁰, 2.20 × 10⁷, and 8.60 × 10⁸ mol^-1 L s^-1, respectively. The core toxic component of endotoxin (lipid A) was attacked by these strong oxidative species, generating smaller molecular fragments with low toxicity. Consequently, the inflammatory factors IL-6, IL-β, and TNF-α of endotoxin decreased by 3.4-4.8 folds after the DBD plasma treatment, implying that the health risks posed by endotoxin were greatly reduced. This study revealed the intrinsic mechanisms of the highly efficient removal of bacterial endotoxin by DBD plasma oxidation.

Recovery of microbiological quality of long-term stagnant tap water in university buildings during the COVID-19 pandemic

Stagnant water can cause water quality deterioration and, in particular, microbiological contaminations, posing potential health risks to occupants. University buildings were unoccupied with little water usage during the COVID-19 pandemic. It's an opportunity to study microbiological quality of long-term stagnant water (LTSW) in university buildings. The tap water samples were collected for three months from four types of campus buildings to monitor water quality and microbial risks after long-term stagnation. Specifically, the residual chlorine, turbidity, and iron/zinc were disqualified, and the heterotrophic plate counts (HPC) exceeded the Chinese national standard above 100 times. It took 4-54 days for these parameters to recover to the routine levels. Six species of pathogens were detected with high frequency and levels (10¹-10⁵ copies/100 mL). Remarkably, L. pneumophilia occurred in 91% of samples with turbidity > 1 NTU. The absence of the culturable cells for these bacteria possibly implied their occurrence in a viable but non-culturable (VBNC) status. The bacterial community of the stagnant tap water differed significantly and reached a steady state in more than 50 days. Furthermore, a high concentration of endotoxin (>10 EU/mL) was found in LTSW, which was in accordance with the high proportion of dead bacteria. The results suggested that the increased microbiological risks require more attention and the countermeasures before the building reopens should be taken.

The influence of UV irradiation on PAHs in wastewater

Studies were carried out on the impact of UV radiation contact time and UV/chlorination processes on changes in polycyclic aromatic hydrocarbons (PAHs) content in treated wastewater in order to obtain environmentally safe water. The research showed that the optimal time of UV irradiation for both processes was 30 min. After irradiation, the total concentration of PAH decreased by 66%, and after the UV/chlorination process by 78%. Following UV irradiation, the reduction ranged from 74% to 81% for 3-ring PAHs, 4-ring benzo(a)anthracene and 5-ring dibenzo(a,h)anthracene. Using the UV/chlorination process, the greatest changes were observed for acenaphthene (93 ± 4%), anthracene (90 ± 4%), pyrene (87% ± 3) and acenaphthylene (83 ± 4%). Due to limited information on the mechanisms which can be responsible for the observed decrease in PAH content in wastewater after the UV and UV/chlorination processes, it cannot be clearly stated to what extent the methods used affect the actual reduction of the concentration, therefore further research is required.

Modified bone char with C-MgO as a green antibacterial household water treatment filter: Comparing the microbial quality with refrigerator cartridge filters

The present study examines the efficiency of modified bone char (BC) with C-MgO nanoparticles (MBC-C-MgO) as media in a cartridge filter as an antibacterial agent to produce a new filter. The filters were operated in a continuous mode using a pre-static pump. MBC-C-MgO were produced and modified with sucrose through the co-precipitation method. The microbial quality of effluent water samples was compared with commercial refrigerator cartridge filters using a heterotrophic plate count (HPC) test and SEM analysis. The results showed that the effluent water from the filter with MBC-C-MgO media had the lowest HPC (177 CFU/mL) compared to bioceramic (271 CFU/mL) and carbon (500 CFU/mL) under similar experimental conditions after 4 months of operation. Maximum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) tests were determined using the broth dilution method on Escherichia coli (ATCC 25922) and Enterococcus faecalis (ACC 29212). The MIC results for E. faecalis and E. coli were 156.25 and 312.5 µg/mL, respectively. Furthermore, the MBC results for E. faecalis and E. coli were 312.5 and 625 µg/mL. The experimental results obviously showed the antibacterial properties of C-MgO nanoparticles and the MBC-C-MgO.

TLR4-MyD88 signaling pathway is responsible for acute lung inflammation induced by reclaimed water

Previous research found that inhalation exposure of reclaimed water could cause severe pulmonary inflammation, and the endotoxin was proposed to be the key risk factor. To further support this view, the toxic effects of different reclaimed water induced by acute inhalation exposure were compared between wildtype C57BL/6J and TLR4 signaling pathway defect mice. It was found that reclaimed water with high levels of endotoxin could induce strong inflammation in wildtype mice, but not in Tlr4^-/- and MyD88^-/- mutants. The mixed bacterial culture from the reclaimed water showed very weak response in wildtype mice and no response in TLR4-signaling pathway deficient mice, which further suggested that the cell-bound endotoxins contribute little in the inflammation induced by reclaimed water. In addition, conditional knockout of the Tlr4 gene in myeloid cells resulted in a significant reduction of sensitivity to the reclaimed water in mutants, which indicates that myeloid cells play the most important role in the defensive immune system against the pollutants in the water. In general, this study demonstrated that the TLR4-MyD88 signaling pathway is responsible for the acute lung inflammation induced by reclaimed water, which excludes the possibility of other signaling pathway dependent inflammation inducers in reclaimed water.

Characterization for the transformation of dissolved organic matters during ultraviolet disinfection by differential absorbance spectroscopy

The transformation of dissolved organic matter (DOM) during various disinfection processes has raised great concerns due to the generation of carcinogenic disinfection by-products (DBPs). Ultraviolet (UV) irradiation is an effective method for drinking water disinfection, during which DOM undergoes changes in functional groups and molecular weight. In this study, the spectrophotometric titration and gel permeation chromatography (GPC) determination were employed to investigate the changes in oxygenated groups and weight-averaged molecular weight (M_w) of two typical DOM during UV irradiation. The differential absorbance spectra (DAS) of DOM could be deconvoluted into six Gaussian bands. The change of relative band intensity was attributed to the change of oxygenated groups (carboxylic and phenolic groups), which was confirmed by combining DAS data and revised Non-Ideal Competitive Adsorption -Donnan model. The GPC result demonstrated that the M_w of DOM decreased after UV disinfection. Moreover, a linear correlation between M_w and the intensity of deconvoluted Gaussian band from DAS was established, which might be served as an alternative approach to estimate M_w and predict the hydrophobicity and DBPs formation potential of DOM in drinking water treatment and monitoring.

Epigenetic induction of tumor stemness via the lipopolysaccharide-TET3-HOXB2 signaling axis in esophageal squamous cell carcinoma

BACKGROUND

Esophageal squamous cell cancer (ESCC) is one kind of frequent digestive tumor. The inflammatory environment plays an important role in the tumorigenesis and development of ESCC. Cancer stem cells are a small group of tumor cells with stem cell characteristics, which can potentially hinder the tumor management and treatment.

METHODS

ELISA was performed to detect the lipopolysaccharide concentration in cancer tissues. qPCR, Western blot, FACS, Immunohistochemistry, Immunofluorescence and Dot blot were applied to detect target genes expression. CCK-8, Colony-formation, Transwell, Sphere and Xenograft were conducted to investigate the function of cells, influenced by risk factors. The survival curve was drawn with the Kaplan-Meier product limit estimator. Nano-hmC-Seal-seq was utilized to detect the downstream target of TET3. ChIP-qPCR was adopted to demonstrate the transcriptional regulation of stem cell-associated genes by HOXB2.

RESULTS

Lipopolysaccharide concentration was significantly up-regulated in ESCC. High concentration of lipopolysaccharide stimulation induced the stemness of ESCC cells. TET3 expression was elevated with lipopolysaccharide stimulation via p38/ERK-MAPK pathway in ESCC and negatively correlated with patients' survival. TET3 induced the stemness of ESCC cells. Nano-hmC-Seal-seq showed that TET3 overexpression led to a significant increase in 5hmC levels of HOXB2 gene region, which was thus identified as the downstream target of TET3. The binding of HOXB2 to NANOG and cMYC was verified by ChIP-qPCR.

CONCLUSIONS

Lipopolysaccharide served as a tumor promotor in ESCC by inducing cancer cell stemness through the activation of a LPS-TET3-HOXB2 signaling axis, which might provide a novel therapeutic strategy for ESCC. Video Abstract.

Bioassay: A useful tool for evaluating reclaimed water safety

Wastewater reclamation and reuse has been proved to be an effective way to relieve the fresh water crisis. However, toxic contaminants remaining in reclaimed water could lead to potential risk for reuse, and the conventional water quality standards have difficulty guaranteeing the safety of reclaimed water. Bioassays can vividly reflect the integrated biological effects of multiple toxic substances in water as a whole, and could be a powerful tool for evaluating the safety of reclaimed water. Therefore, in this study, the advantages and disadvantages of using bioassays for evaluating the safety of reclaimed water were compared with those of conventional water quality standards. Although bioassays have been widely used to describe the toxic effects of reclaimed water and treatment efficiency of reclamation techniques, a single bioassay cannot reflect the complex toxicity of reclaimed water, and a battery of bioassays involving multiple biological effects or in vitro tests with specific toxicity mechanisms would be recommended. Furthermore, in order to evaluate the safety of reclaimed water based on bioassay results, various methods including potential toxicology, the toxicity unit classification system, and a potential eco-toxic effects probe are summarized as well. Especially, some integrated ranking methods based on a bioassay battery involving multiple toxicity effects are recommended as useful tools for evaluating the safety of reclaimed water, which will benefit the promotion and guarantee the rapid development of the reclamation and reuse of wastewater.

Simultaneous solid-liquid separation and wastewater disinfection using an electrochemical dynamic membrane filtration system

An electrochemical dynamic membrane filtration (EDMF) system for simultaneous solid-liquid separation (also protecting electrodes against fouling) and sewage disinfection was developed. At a low voltage of 2.5 V, efficient disinfection performance was achieved in the EDMF, with ~100% log removal efficiency (no detectable bacteria in the effluent). Results also demonstrated that the EDMF system, operated at membrane flux of 100 L/(m² h), could maintain long-lasting bacterial disinfection efficiency of real wastewater (~100% log removal) in continuous flow tests. Transmembrane pressure (TMP) increased from 0.8 kPa to 22 kPa within 80 d (one operation cycle), and cleaning of EDMF could effectively restore TMP and biocidal behaviors for subsequent filtration cycles. In contrast, without dynamic membrane, the disinfection efficiency was decreased from initial ~100% log removal (with no detectable live bacteria) to ~44.4% log removal within 7 d. Reactive oxygen species (ROS)-mediated oxidation was responsible for bacteria disinfection in the EDMF, and HO• and H₂O₂ generated in this system played a dominant role, causing damage to cell membranes and K⁺ leakage from cytosol. Moreover, catalase and superoxide dismutase for intracellular ROS attenuation were inhibited, resulting in the increase of intracellular oxidative stress and thus high-efficient disinfection. These results highlight the potential of EDMF system to be used for wastewater treatment and disinfection.