Unveiling the photoelectrocatalytic inactivation mechanism of Escherichia coli: Convincing evidence from responses of parent and anti-oxidation single gene knockout mutants

Microbiological interpretation of weak ultrasound enhanced biological wastewater treatment - using Escherichia coli degrading glucose as model system

The Escherichia coli (E.coli) degrading glucose irradiated by ultrasound irradiation (20 W, 14 min) was investigated as the model system, the glucose degradation increased by 13 % while the E.coli proliferation decreased by 10 % after culture for 18 h. It indicated a tradeoff effect between substrate degradation and cell proliferation, which drove the enhanced contaminants removal and excess sludge reduction in a weak ultrasound enhanced biological wastewater treatment. The enzymatic activities (catalase, superoxide dismutase, adenosine triphosphatases, lactic dehydrogenase, membrane permeability, intracellular reactive oxygen species and calcium ion of E. coli increased immediately by 12 %, 63 %, 124 %, 19 %, 15 %, 4-fold and 38-fold, respectively by ultrasound irradiation power of 20 W for 14 min. Furthermore, the membrane permeability of irradiated E. coli increased by 26 % even though the ultrasound stopped for 10 h. Additionally, pathways associated with glucose degradation and cell proliferation were continuously up-regulated and down-regulated, respectively.

Response mechanisms of resistance in L-form bacteria to different target antibiotics: Implications from oxidative stress to metabolism

Due to the specific action on bacterial cell wall, β-lactam antibiotics have gained widespread usage as they exhibit a high degree of specificity in targeting bacteria, but causing minimal toxicity to host cells. Under antibiotic pressure, bacteria may opt to shed their cell walls and transform into L-form state as a means to evade the antibiotic effects. In this study, we explored and identified diverse optimal conditions for both Gram-negative bacteria (E. coli DH5α (CTX)) and Gram-positive bacteria (B. subtilis ATCC6633), which were induced to L-form bacteria using lysozyme (0.5 ppm) and meropenem (64 ppm). Notably, when bacteria transformed into L-form state, both bacterial strains showed varying degrees of increased resistance to antibiotics polymyxin E, meropenem, rifampicin, and tetracycline. E. coli DH5α (CTX) exhibited the most significant enhancement in resistance to tetracycline, with a 128-fold increase, while B. subtilis ATCC6633 showed a 32-fold increase in resistance to tetracycline and polymyxin E. Furthermore, L-form bacteria maintained their normal metabolic activity, combined with enhanced oxidative stress, served as an adaptive strategy promoting the sustained survival of L-form bacteria. This study provided a theoretical basis for comprehending antibiotic resistance mechanisms, developing innovative treatment strategies, and confronting global antibiotic resistance challenges.

Kinetics and mechanism of sulfate radical-and hydroxyl radical-induced disinfection of bacteria and fungal spores by transition metal ions-activated peroxymonosulfate

Peroxymonosulfate(PMS)-based advanced oxidation process have been recognized as efficient disinfection processes. This study comprehensively investigated the role of sulfate radical (SO4•-) and hydroxyl radical (•OH)-driven disinfection of bacteria and fungal spores by the PMS/metals ions (Me(II)) systems and modeled the CT value based on the relationship between survival and ∫[Radical]dt, with the aim to provide an accurate and quantitative kinetic data of inactivation processes. The results indicated that •OH played a more central role than SO4•- in the inactivation process, and bacteria were more vulnerable to radical attack than fungal spores due to the differences in antioxidant mechanisms and external structures. The k value of •OH -induced inactivation of E. coli was approximately 3-fold higher than that of A. niger, and the shoulder length of •OH -induced inactivation of E. coli was closely 52-fold shorter than that of A. niger after treated with the PMS/Co(II) system. The morphological and biochemical changes revealed that PMS/Me(II) treatment caused membrane damage, intracellular ROS accumulation and esterase activity loss in microorganisms. This study significantly improved the understanding of the contribution of radicals in the process of microbial inactivation by PMS/Me(II) and would provide important implications for the further development of technologies to cope with the highly resistant fungal spores in drinking water.

Toxicity of Nanoscale Zero-Valent Iron to Soil Microorganisms and Related Defense Mechanisms: A Review

Soil pollution is a global environmental problem. Nanoscale zero-valent iron (nZVI) as a kind of emerging remedial material is used for contaminated soil, which can quickly and effectively degrade and remove pollutants such as organic halides, nitrates and heavy metals in soil, respectively. However, nZVI and its composites can enter the soil environment in the application process, affect the physical and chemical properties of the soil, be absorbed by microorganisms and affect the growth and metabolism of microorganisms, thus affecting the ecological environment of the entire soil. Because of the potential risks of nZVI to the environment and ecosystems, this paper summarizes the current application of nZVI in the remediation of contaminated soil environments, summarizes the various factors affecting the toxic effects of nZVI particles and comprehensively analyzes the toxic effects of nZVI on microorganisms, toxic mechanisms and cell defense behaviors to provide a theoretical reference for subsequent biosafety research on nZVI.

Photo-sterilization of groundwater by tellurium and enhancement by micro/nano bubbles

In rural areas where low-temperature groundwater is used as a drinking water source, cost-effective sterilization techniques are needed to prevent groundwater consumers from the disease risks triggered by pathogenic microorganisms like Escherichia coli and fungal spores. In this study, micro/nano bubbles (MNBs) coupled with the tellurium (Te)-based catalysts were used to considerably enhance the solar disinfection (SODIS) efficiency while overcoming the intrinsic defects of SODIS, particularly in low-temperature. Sterilization tests showed that 6.5 log₁₀ cfu/mL of E. coli K-12 and 4.0 log₁₀ cfu/mL of Aspergillus niger spores were completely inactivated within 5 min while applying this novel process for disinfection of raw groundwater, even in low-temperature. The underlying mechanisms of the extraordinary sterilization efficiency were revealed through comprehensive characterization of the catalysts and the physiological changes of the microorganisms. The localized surface plasmon resonance (LSPR) effect of the Te catalysts was identified to take advantage of photothermal synergism to achieve cell death. The integration of MNBs with the facet-engineered Te catalysts improved the photothermal catalytic effect and extracellular electron transfer, which substantially strengthened disinfection efficiency. This study provides a targeted solution into microbial inactivation in groundwater and emphasizes a cost-effective groundwater sterilization process.

Response mechanisms of different antibiotic-resistant bacteria with different resistance action targets to the stress from photocatalytic oxidation

The stress response of antibiotic-resistant bacteria (ARB) and the spread of antibiotic resistance genes (ARGs) pose a serious threat to the aquatic environment and human beings. This study mainly explored the effect of the heterogeneous photocatalytic oxidation (UVA-TiO₂ system) on the stress response mechanism of ARB with different antibiotic resistance action targets, including the cell wall, proteins, DNA, RNA, folate and the cell membrane. Results indicate that the stress response mechanism of tetracycline- and sulfamethoxazole-resistant E. coli DH5α, which targets the synthesis of protein and folate, could rapidly induce global regulators by the overexpression of relative antibiotic resistance action target genes. Different stress response systems were mediated via cross-protection mechanism, causing stronger tolerance to an adverse environment than other ARB. Moreover, the photocatalytic inactivation mechanism of bacterial cells and a graded response of cellular stress mechanism caused differences in the intensity of the stress mechanism of antibiotic resistance action targets. E. coli DH5α resistant to cefotaxime and polymyxin, targeting synthesis of the cell wall and cell membrane, respectively, could confer greater advantages to bacterial survival and higher conjugative transfer frequency than E. coli DH5α resistant to nalidixic acid and rifampicin, which target the synthesis of DNA and RNA, respectively. This new perspective provides detailed information on the practical application of photocatalytic oxidation for inactivating ARB and hampering the spreading of ARGs in the aquatic environment.

Transcriptome profiles of genes related to growth and virulence potential in Vibrio alginolyticus treated with modified clay

Vibrio alginolyticus is a globally distributed opportunistic pathogen that causes different degrees of disease in various marine organisms, such as fish, shrimp and shellfish. At present, vibriosis caused by V. alginolyticus has a wide epidemic range and causes frequent outbreaks, resulting in substantial losses in aquaculture. According to previous studies, modified clay (MC) could effectively flocculate and reduce the density of Vibrio in water, but it is still unknown whether MC inhibits growth and how it affects virulence in bottom flocs. Here, we studied the response mechanism of V. alginolyticus in flocs treated with MC at the transcriptome level and verified the transcriptomic data combined with relevant physiological experiments and reverse transcription quantitative real-time PCR (RT-qPCR) for the first time. It was found that the morphology of Vibrio in the MC flocs changed, the membrane function was damaged, the antioxidant system was activated, and the material and energy metabolism also changed. In addition, MC could inhibit the expression of virulence factors of V. alginolyticus; for example, flagella, pilus, siderophores, quorum sensing, and other related genes were significantly downregulated. In general, MC effectively inhibited the growth of Vibrio and reduced its virulence potential in flocs, which could provide theoretical support for a new model of healthy aquaculture.

Beta-Sitosterol Modulates the Migration of Vascular Smooth Muscle Cells via the PPARG/AMPK/mTOR Pathway

INTRODUCTION

The increased migration of vascular smooth muscle cells (VSMCs) is an essential pathological factor in the early development of atherosclerosis. Beta-sitosterol (BS), a natural phytosterol abundant in plant seeds, exhibits various bioactivities, including cardioprotective effects. However, its effects on VSMC migration and underlying mechanisms remain to be explored.

METHOD AND RESULT

BS inhibited the proliferation and migration of angiotensin II-induced A7r5 cells and reduced intracellular oxidative stress. Targets related to VSMC migration and the targets of BS were screened, cross-referenced, and analyzed by network pharmacology combined with molecular docking technology. The identified targets were verified at the protein and gene levels using Western blotting and quantitative PCR, respectively. BS was observed to activate peroxisome proliferator-activated receptor-γ (PPARG) and adenosine 5'-monophosphate-activated protein kinase (AMPK) and negatively regulate mammalian target of rapamycin (mTOR) expression. Furthermore, a PPARG inhibitor reversed the BS-induced activation of AMPK and mTOR.

CONCLUSION

This study indicated that regulation of the PPARG/AMPK/mTOR signaling pathway could potentially contribute to the inhibitory effects of BS on angiotensin II-induced VSMC migration.

Novel Control Strategy for Membrane Biofouling by Surface Loading of Aerobically and Anaerobically Applicable Photocatalytic Optical Fibers Based on a Z-Scheme Heterostructure Zr-MOFs/rGO/Ag3PO4 Photocatalyst

The high replacement cost of modified membranes in antibiofouling application is inevitable. Here, surface-loaded photocatalytic optical fibers (POFs) were developed as antibiofouling strategies to replace membrane modification. To prepare aerobically and anaerobically applicable POFs, novel visible light-driven zirconium-based metal-organic framework/reduced graphene oxide/Ag₃PO₄ (Zr-MOFs/rGO/Ag₃PO₄) Z-scheme heterojunctions were constructed and coated on optical fibers. After loading the POFs on the membrane surface, the antibiofouling capability of the POFs was demonstrated during membrane filtration of bacteria and foulants under visible light irradiation. The disinfection efficiencies of the POFs against Escherichia coli and Staphylococcus aureus reached 95.7 and 92.4%, respectively, by aerobic treatment and 90.3 and 85.5%, respectively, by anaerobic treatment. For the inactivated bacteria, cell membrane and membrane-associated functions were destroyed, accompanied by antioxidant enzyme decomposition, loss of cell respiration and adenosine triphosphate (ATP) synthesis capacity, and leakage and oxidation of protein, lipid, potassium, DNA, and RNA. During membrane filtration of model foulants and membrane bioreactor sludge, the POFs significantly alleviated the membrane flux decline by foulant disintegration. By qualitative and quantitative detection and quenching tests of reactive species, aerobically generated ^•O₂^- and ^•OH and anaerobically generated ^•OH from POFs played dominant roles in the antibiofouling process. This work provides unique insights into membrane fouling control based on environmentally friendly and efficient photocatalytic technology.

Photoelectrocatalytic inactivation mechanism of E. coli DH5α (TET) and synergistic degradation of corresponding antibiotics in water

The occurrence and proliferation of antibiotic-resistance genes (ARGs) / antibiotic-resistant bacteria (ARB) have been currently aggravating due to the increase of antibiotic residues in the aquatic environment. The interaction of ARB/ARGs with antibiotics inevitably occurred during water purification, yet their synergistic purification mechanism remains unclear. Herein, a systematic approach was developed to understand, in-depth, the synergistic mechanism in the coexisted E. coli DH5α (TET) inactivation and tetracycline hydrochloride (TET) degradation using photoelectrocatalysis (PEC) as a model technology. Results showed that low dosage (0 - 40 ppm) of TET exerted a negative influence on ARB inactivation with prolonged bactericidal time from 60 to 160 min. Addition of TET in environmental concentration (5 - 60 ppm) resulted in sub-lethal damage and prolonged PEC treatment time (100 - 160 min), accounting for inhibition effects on ARB inactivation. The major reactive species (RSs) involved in ARB inactivation and TET degradation were evidenced as photogenerated hole, ^•OH and O₂^•-, whereas hole and O₂^•- were demonstrated to be the major disinfectants for ARB/ARG inactivation. The bacterial defense system displayed increased antioxidative activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) to protect ARB cells against oxidative stress. Exposure to 60 ppm TET was a threshold where certain ARB cells were induced into viable but nonculturable bacterial cell (VBNC) state, as evidenced by plate counting and ATP activity analysis, together with the integral cell membranes observed by flow cytometry (FCM) and scanning electron microscope (SEM). These findings appeal for appropriate technical adjustments for water and wastewater treatment to ensure safety of water.

Photoelectrocatalytic coupling system synergistically removal of antibiotics and antibiotic resistant bacteria from aquatic environment

Antibiotics, antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) are ubiquitous in the reclaimed water, posing a potential threat to human and ecological health. Nowadays, the reuse technology of reclaimed water has been widely concerned, but the removal of antibiotics, ARB and ARGs in reclaimed water has not been sufficiently studied. This study used TiO2 nanotube arrays (TNTs) decorated with Ag/SnO2-Sb nanoparticles (TNTs-Ag/SnO2-Sb) as the anode and Ti-Pd/SnO2-Sb as the cathode to construct an efficient photoelectrocatalytic (PEC) system. In this system, 99.9% of ARB was inactivated in 20 min, meanwhile, ARGs was removed within 30 min, and antibiotics were almost completely degraded within 1 h. Furthermore, the effects of system parameters on the removals of antibiotics, ARB and ARGs were also studied. The redox performance of the system was verified by adding persulfate. Escherichia coli, as a representative microorganism in aquatic environments, was used to evaluate the ecotoxicity of PEC treated chloramphenicol (CAP) solution. The ecotoxicity of CAP solution was significantly reduced after being treated by PEC. In addition, transformation intermediates of CAP were identified using liquid chromatography-tandems mass spectrometry (LC-MS/MS) and the possible degradation pathways were proposed. This study could provide a potential alternative method for controlling antibiotic resistance and protecting the quality of reclaimed water.

Antimicrobial Effects of Novel H2O2-Ag+ Complex on Membrane Damage to Staphylococcus aureus, Escherichia coli O157:H7, and Salmonella Typhimurium

ABSTRACT

Diseases caused by harmful microorganisms pose a serious threat to human health. Safe and environmentally friendly disinfectants are, therefore, essential in preventing and controlling such pathogens. This study aimed to investigate the antimicrobial activity and mechanism of a novel hydrogen peroxide and silver (H2O2-Ag+) complex (HSC) in combatting Staphylococcus aureus ATCC 29213, Escherichia coli O157:H7 NCTC 12900, and Salmonella Typhimurium SL 1344. The MICs and MBCs against S. aureus were found to be 0.014% H2O2-3.125 mg/L Ag+, and for both E. coli O157:H7 and Salmonella Typhimurium they were 0.028% H2O2-6.25 mg/L Ag+. Results of the time-kill trial suggest that HSC could inhibit the growth of the tested bacteria, because 99.9% of viable cells were killed following treatment at 1 MIC for 3 h. The mechanism of antibacterial action of HSC was found to include the disruption of the bacterial cell membrane, followed by reduction of intracellular ATP concentration and inhibition of the activity of antioxidases, superoxide dismutase, and catalase. The enhanced bactericidal effect of hydrogen peroxide combined with silver indicates a potential for its application in environmental disinfection, particularly in the food industry.

HIGHLIGHTS

Electrocatalytic inactivation of antibiotic resistant bacteria and control of antibiotic resistance dissemination risk

Antibiotic resistance in environmental matrices becomes urgently significant for public health and has been considered as an emerging environmental contaminant. In this work, the ampicillin-resistant Escherichia coli (AR E. coli) and corresponding resistance genes (bla_TEM-1) were effectively eliminated by the electrocatalytic process, and the dissemination risk of antibiotic resistance was also investigated. All the AR E. coli (∼8 log) was inactivated and 8.17 log bla_TEM-1 was degraded by the carbon nanotubes/agarose/titanium (CNTs/AG/Ti) electrode within 30 min. AR E. coli was inactivated mainly attributing to the damage of cell membrane, which was attacked by reactive oxygen species and subsequent leakage of intracellular cytoplasm. The bla_TEM-1 was degraded owing to the strand breaking in the process of electrocatalytic degradation. Furthermore, the dissemination risk of antibiotic resistance was effectively controlled after being electrocatalytic treatment. This study provided an effective electrocatalytic technology for the inactivation of antibiotic resistant bacteria and control of antibiotic resistance dissemination risk in the aqueous environment.

Photo-assisted electrochemical advanced oxidation processes for the disinfection of aqueous solutions: A review

Disinfection is usually the final step in water treatment and its effectiveness is of paramount importance in ensuring public health. Chlorination, ultraviolet (UV) irradiation and ozone (O3) are currently the most common methods for water disinfection; however, the generation of toxic by-products and the non-remnant effect of UV and O3 still constitute major drawbacks. Photo-assisted electrochemical advanced oxidation processes (EAOPs) on the other hand, appear as a potentially effective option for water disinfection. In these processes, the synergism between electrochemically produced active species and photo-generated radicals, improve their performance when compared with the corresponding separate processes and with other physical or chemical approaches. In photo-assisted EAOPs the inactivation of pathogens takes place by means of mechanisms that occur at different distances from the anode, that is: (i) directly at the electrode's surface (direct oxidation), (ii) at the anode's vicinity by means of electrochemically generated hydroxyl radical species (quasi-direct), (iii) or at the bulk solution (away from the electrode surface) by photo-electrogenerated active species (indirect oxidation). This review addresses state of the art reports concerning the inactivation of pathogens in water by means of photo-assisted EAOPs such as photo-electrocatalytic process, photo-assisted electrochemical oxidation, photo-electrocoagulation and cathodic processes. By focusing on the oxidation mechanism, it was found that while quasi-direct oxidation is the preponderant inactivation mechanism, the photo-electrocatalytic process using semiconductor materials is the most studied method as revealed by numerous reports in the literature. Advantages, disadvantages, trends and perspectives for water disinfection in photo-assisted EAOPs are also analyzed in this work.

Modular Assembly of Ordered Hydrophilic Proteins Improve Salinity Tolerance in Escherichia coli

Most late embryogenesis abundant group 3 (G3LEA) proteins are highly hydrophilic and disordered, which can be transformed into ordered α-helices to play an important role in responding to diverse stresses in numerous organisms. Unlike most G3LEA proteins, DosH derived from Dinococcus radiodurans is a naturally ordered G3LEA protein, and previous studies have found that the N-terminal domain (position 1–103) of DosH protein is the key region for its folding into an ordered secondary structure. Synthetic biology provides the possibility for artificial assembling ordered G3LEA proteins or their analogues. In this report, we used the N-terminal domain of DosH protein as module A (named DS) and the hydrophilic domains (DrHD, BnHD, CeHD, and YlHD) of G3LEA protein from different sources as module B, and artificially assembled four non-natural hydrophilic proteins, named DS + DrHD, DS + BnHD, DS + CeHD, and DS + YlHD, respectively. Circular dichroism showed that the four hydrophile proteins were highly ordered proteins, in which the α-helix contents were DS + DrHD (56.1%), DS + BnHD (53.7%), DS + CeHD (49.1%), and DS + YLHD (64.6%), respectively. Phenotypic analysis showed that the survival rate of recombinant Escherichia coli containing ordered hydrophilic protein was more than 10% after 4 h treatment with 1.5 M NaCl, which was much higher than that of the control group. Meanwhile, in vivo enzyme activity results showed that they had higher activities of superoxide dismutase, catalase, lactate dehydrogenase and less malondialdehyde production. Based on these results, the N-terminal domain of DosH protein can be applied in synthetic biology due to the fact that it can change the order of hydrophilic domains, thus increasing stress resistance.

Simulated sunlight-induced inactivation of tetracycline resistant bacteria and effects of dissolved organic matter

The transmission of antibiotic resistance in surface water has attracted much attention due to its increasing threat to human health. The role of sunlight irradiation and the effect of dissolved organic matter (DOM) on the transmission of antibiotic resistance are still unclear. In this study, photo-inactivation of antibiotic resistant bacteria (ARB) was investigated using antibiotic resistant E. coli (AR E. coli) that contained the tetracycline resistance gene (Tc-ARG) as a representative. The results showed that AR E. coli underwent significant photo-inactivation due to the membrane damage induced by direct irradiation and by the generated reactive oxygen species. Simulated sunlight irradiation specifically suppressed the expression of tetracycline resistance, which is attributed to the destruction of tetracycline-specific efflux pump. Tetracycline inhibited the photo-inactivation of AR E. coli due to its selective pressure on tetracycline resistant E. coli and competitive light absorption effect. Suwannee River fulvic acid (SRFA), a representative DOM, promoted the inactivation of AR E. coli and further inhibited the expression of tetracycline resistance gene due to the generation of its excited triplet state, singlet oxygen, and hydroxyl radical. The extracellular Tc-ARG also underwent fast photodegradation under light irradiation and in the presence of SRFA, which leads to the decrease of its transformation efficiency. This study provided insight into the sunlight-induced inactivation of ARB, which is of significance for understanding the transmission of tetracycline resistance in surface water.

SWNTs-PAN/TPU/PANI composite electrospun nanofiber membrane for point-of-use efficient electrochemical disinfection: New strategy of CNT disinfection

Single-walled carbon nanotubes (SWNTs) can be used as 1D electrochemical disinfection material for point-of-use water treatment but are limited by their poor durability and possible cytotoxicity. Immobilizing SWNTs in nanofibers with electrospinning served as slow-release technology develop a novel with a lasting antibacterial and (eco-) toxicological alleviation of SWNTs. Hence, the single-walled carbon nanotubes-polyacrylonitrile/polyurethane/polyaniline (SWNTs-PAN/TPU/PANI, SPTP) composite electrospun nanofiber membrane was successfully fabricated by co-electrospinning process and the electrochemical filtration and disinfection system of point-of-use drinking water treatment is constructed. In the absence of electrolysis, the SPTP filter is effective for complete removal of bacteria by sieving mechanism. Concomitant electrolysis in the course of filtration results in significantly increased inactivation of sieved bacteria. Application of 3.0 V leads to complete (5 log) inactivation of bacteria within 20 min. 5-cycle experiments, membrane flux and shake flask tests prove that composite restrict the excessive release of SWNTs retaining the long-lasting antibacterial properties of SPTP membrane. At 1.0 and 2.0 V, electrolyte concentration and composition is irrelevant to electrochemical inactivation consistent with oxidation of SPTP filter. Bacterial reactive oxygen species (ROSs) also support an oxidation mechanism. At 3.0 V, electrochemical disinfection mainly relies on indirect oxidation.

Solar driven self-sustainable photoelectrochemical bacteria inactivation in scale-up reactor utilizing large-scale fabricable Ti/MoS2/MoOx photoanode

Here we present photoelectrochemical (PEC) bacterial inactivation properties of large-scale fabricable Ti/MoS₂/MoO_x photoanode with a strong solar light absorbance capacity. Specifically, by thermal oxidation of the as-prepared MoS₂/Ti film at 250 °C for 15 min in aerobic condition, the visible light performance of photocurrent generation and Escherichia coli (E. coli) inactivation are markedly enhanced. Complete inactivation of 10⁶ CFU/mL E. coli in NaCl electrolyte is achieved with 0.5 V bias in 2 h under visible light irradiation, and H₂O₂ and O₂^- have been found as key reactive oxidative species to destroy E. coli. The bacteria inactivation performance of present photoanode is comparable with reported visible light photoanodes such as Cu₂O or N-doped TiO₂. The markedly improved PEC performance and inhibited photocorrosion could be attributed to the formation of heterojunction of MoS₂/MoO_x on the surface due to thermal oxidation. Furthermore, the PEC E. coli inactivation performance and stability of the large dimensional electrode are evaluated in a scale-up reactor. As an example of self-sustainable PEC water treatment system powered by only solar panels, wastewater containing inorganic, organic, macromolecule and microbial pollutants is attempted to be treated employing the developed electrodes under illumination of LED lamps.

Bacterial response mechanism during biofilm growth on different metal material substrates: EPS characteristics, oxidative stress and molecular regulatory network analysis

Overwhelming growth of bacterial biofilms on different metal-based pipeline materials are intractable and pose a serious threat to public health when tap water flows though these pipelines. Indeed, the underlying mechanism of biofilm growth on the surface of different pipeline materials deserves detailed exploration to provide subsequent implementation strategies for biofilm control. Thus, in this study, how bacteria response to their encounters was explored, when they inhabit different metal-based pipeline substrates. Results revealed that bacteria proliferated when they grew on stainless steel (SS) and titanium sheet (Ti), quickly developing into bacterial biofilms. In contrast, the abundance of bacteria on copper (Cu) and nickel foam (Ni) substates decreased sharply by 4-5 logs within 24 h. The morphological shrinkage and shortening of bacterial cells, as well as a sudden 64-fold increase of carbohydrate content in extracellular polymeric substances (EPS), were observed on Cu substrate. Furthermore, generation of reactive oxygen species and fluctuation of enzymatic activity demonstrated the destruction of redox equilibrium in bacteria. Bacteria cultured on Cu substrate showed the strongest response, followed by Ni, SS and Ti. The oxidative stress increased quickly during the growth of bacterial biofilm, and almost all tested metal transporter-related genes were upregulated by 2-11 folds on Cu, which were higher than on other substrates (1-2 folds for SS and Ti, 2-9 folds for Ni). Finally, these behaviors were compared under the biofilm regulatory molecular network. This work may facilitate better understanding different response mechanisms during bacterial biofilm colonization on metal-based pipelines and provide implications for subsequent biofilm control.

Inactivation of antibiotic-resistant bacteria and antibiotic resistance genes by electrochemical oxidation/electro-Fenton process

Antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in the environment are of great concern due to their potential risk to human health. The effluents from wastewater treatment plants and livestock production are major sources of ARB and ARGs. Chlorination, UV irradiation, and ozone disinfection cannot remove ARGs completely. In this study, the potential of electrochemical oxidation and electro-Fenton processes as alternative treatment technologies for inactivation of ARB and ARGs in both intracellular and extracellular forms was evaluated. Results showed that the electrochemical oxidation process was effective for the inactivation of selected ARB but not for the removal of intracellular ARGs or extracellular ARGs. The electro-Fenton process was more effective for the removal of both intracellular and extracellular ARGs. The removal efficiency after 120 min of electro-Fenton treatment under 21.42 mA/cm² was 3.8 logs for intracellular tetA, 4.1 logs for intracellular ampC, 5.2 logs for extracellular tetA, and 4.8 logs for extracellular ampC, respectively in the presence of 1.0 mmol/L Fe²⁺. It is suggested that electrochemical oxidation is an effective disinfection method for ARB and the electro-Fenton process is a promising technology for the removal of both intracellular and extracellular ARGs in wastewater.

Photocatalytic Bacterial Inactivation by a Rape Pollen-MoS2 Biohybrid Catalyst: Synergetic Effects and Inactivation Mechanisms

A novel and efficient 3D biohybrid photocatalyst, defective MoS₂ nanosheets encapsulated carbonized rape pollen, was fabricated and applied to water disinfection. The rape pollen-MoS₂ (PM) biohybrid showed excellent dispersibility, high stability, and efficient charge-carrier separation and migration ability, resulting in the highly enhanced photocatalytic inactivation performance toward various waterborne bacteria under different light sources. The inactivation mechanisms were systematically investigated. Reactive species (RSs), including electrons, holes, and reactive oxygen species (•O₂^- and •OH), played major roles in inactivating bacteria. The antioxidant system of bacteria exhibited a self-protection capacity by eliminating the photogenerated RSs from PM biohybrid at the early stage of inactivation. With the accumulation of RSs, the cell membrane and membrane-associated functions were destroyed, as suggested by the collapse of cell envelope and subsequent loss of cell respiration and ATP synthesis capacity. The microscopic images further confirmed the destruction of the bacterial membrane. After losing the membrane barrier, the oxidation of cytoplasmic proteins and lipids caused by invaded RSs occurred readily. Finally, the leakage of DNA and RNA announced the irreversible death of bacteria. These results indicated that the bacterial inactivation began with the membrane rupture, followed by the oxidation and leakage of intracellular substances. This work not only provided a new insight into the combination of semiconductors with earth-abundant biomaterials for fabricating high-performance photocatalysts, but also revealed the underlying mechanisms of photocatalytic bacterial inactivation in depth.

Photoelectrocatalytic degradation of organics and formation of disinfection byproducts in reverse osmosis concentrate

The high content of organics in municipal reverse osmosis concentrate (ROC) requires proper treatment. Here, this study applied the photoelectrocatalysis (PEC) to reduce the concentration of organics in ROC. Meanwhile, the formation of disinfection byproducts (DBPs) was investigated. Participation of primary oxidants in organics removal and DBPs formation was revealed at different anodic potentials and pHs. The results showed that PEC process effectively oxidized the organics in ROC, achieving the highest mineralization rate of 63%. Increasing anodic potential from 0 to 1.0 V enhanced the oxidations of bulk organics (i.e., dissolved organic carbons (DOC), UV₂₅₄, fluorescence, large molecular weight compounds) and trace-level pharmaceuticals. Raising anodic potential to higher than 1.0 V slightly benefited the oxidations of bulk organics, owing to the relatively stable formation of hydroxyl radicals (OH•) and radical reactive chlorine species (r-RCS). The continuously rising concentration of free chlorine (FC) accelerated the decompositions of pharmaceuticals at ≥ 1.0 V. However, the generated FC raised the concentration of DBPs up to 10.36 μmol/L at 3.0 V. Lowering initial pH from 7-9 to 4-6 improved the mineralization rates by around 20% due to the higher formation of OH• at pH 4-6. Further decreasing initial pH from 6 to 4 enhanced the breakdown of large molecular weight compounds as well as the decomposition of pharmaceuticals. This came from the strengthened formation of FC and r-RCS at lower pHs. The intense participation of FC and r-RCS resulted in a higher total DBP concentration at pH 4-6 than that at pH 7-9. However, the individual species of DBPs changed differently toward the pH shift. The results of this study show that PEC could be an alternative for organics oxidation in ROC with proper control of DBPs formation.

Enhanced photocatalytic disinfection of Escherichia coli K-12 by porous g-C3N4 nanosheets: Combined effect of photo-generated and intracellular ROSs

The porous graphitic carbon nitride nanosheets (PCNSs) with high yields were synthesized by using one-step chemical exfoliation method. PCNSs accelerated separation efficiency of photo-generated electron-hole pairs in comparison to bulk graphitic carbon nitride. The PCNS5 (exfoliation for 5 h) exhibited optimal photocatalytic disinfection capability towards Escherichia coli K-12 under simulated solar light irradiation with complete disinfection of 6.5 log₁₀ cfu/mL of E. coil K-12 within 2 h. The enhanced photocatalytic activity of PCNS5 originated from mesoporous nanosheet structure. The possible mechanism of photocatalytic disinfection has proposed that intracellular reactive oxygen species levels and the activities of antioxidant enzymes (e.g., catalase and superoxide dismutase) were enhanced. Transmission electron microscope images observed during photocatalytic disinfection process suggested that the cell membrane was regarded as the first target for oxidation, resulting in a faster leakage of cytoplasmic content and finally degradation of DNA leading to bacterial death. Furthermore, the trapping experiment showed that superoxide radical (•O₂^-) and holes (h⁺) were responsible for E. coli K-12 disinfection by PCNS5.

Rapid Aerobic Inactivation and Facile Removal of Escherichia coli with Amorphous Zero-Valent Iron Microspheres: Indispensable Roles of Reactive Oxygen Species and Iron Corrosion Products

Zero valent iron (ZVI) is recently regarded as a promising alternative for water disinfection, but still suffers from low efficiency. Herein we demonstrate that amorphous zerovalent iron microspheres (A-mZVI) exhibit both higher inactivation rate and physical removal efficiency for the disinfection of Escherichia coli than conventional crystalline nanoscale ZVI (C-nZVI) under aerobic condition. The enhanced E. coli inactivation performance of A-mZVI was mainly attributed to more reactive oxygen species (ROSs), especially free •OH, generated by the accelerated iron dissolution and molecular oxygen activation in bulk solution. In contrast, C-nZVI preferred to produce surface bound •OH, and its bactericidal ability was thus hampered by the limited physical contact between C-nZVI and E. coli. More importantly, hydrolysis of dissolved iron released from A-mZVI produced plenty of loose FeOOH to wrap E. coli, increasing the dysfunction of E. coli membrane. Meanwhile, this hydrolysis process lowered the stability of E. coli colloid and caused its rapid coagulation and sedimentation, favoring its physical removal. These findings clarify the indispensable roles of ROSs and iron corrosion products during the ZVI disinfection, and also provide a promising disinfection material for water treatment.

Antibiotic-resistance gene transfer in antibiotic-resistance bacteria under different light irradiation: Implications from oxidative stress and gene expression

Due to the significant public health risks, there is substantial scientific interest in the increasing abundance of antibiotic-resistance bacteria (ARB) and the spread of antibiotic-resistance genes (ARGs) in aquatic environments. To clearly understand the mechanism of ARG transfer, this study examined the conjugative transfer of genes encoding resistance to cephalosporin (bla_CTX) and polymyxin (mcr-1) from two antibiotic-resistant donor strains, namely E. coli DH5α (CTX) and E. coli DH5α (MCR), and to a streptomycin-resistant receptor strain (E. coli C600 (Sm)). Conjugative transfer was specifically studied under different light irradiation conditions including visible light (VL), simulated sunlight (SS) and ultraviolet light (UV_254nm). Results show that the conjugative transfer frequency was not affected by VL irradiation, while it was slightly improved (2-10 fold) by SS irradiation and extremely accelerated (up to 100 fold) by UV irradiation. Furthermore, this study also explored the link between ARG transfer and stress conditions. This was done by studying physiological and biochemical changes; oxidative stress response; and functional gene expression of co-cultured AR-E. coli strains under stress conditions. When correlated with the transfer frequency results, we found that VL irradiation did not affect the physiological and biochemical characteristics of the bacteria, or induce oxidative stress and gene expression. For SS irradiation, oxidative stress occurred slowly, with a slight increase in the expression of target genes in the bacterial cells. In contrast, UV irradiation, rapidly inactivated the bacteria, the degree of oxidative stress was very severe and the expression of the target genes was markedly up-regulated. Our study could provide new insight into the underlying mechanisms and links between accelerated conjugative transfer and oxidative stress, as well as the altered expression of genes relevant to conjugation and other stress responses in bacterial cells.

Elimination of antibiotic-resistance bacterium and its associated/dissociative blaTEM-1 and aac(3)-II antibiotic-resistance genes in aqueous system via photoelectrocatalytic process

The ubiquity of antibiotic-resistance bacteria (ARB) and antibiotic-resistance genes (ARGs) in various environmental matrices is a potential threat to human and ecological health. Therefore, the inactivation of ARB E. coli S1-23 and the elimination of its associated ARGs, bla_TEM-1 and aac(3)-II, were investigated using the photoelectrocatalytic (PEC) process. Results indicate that the ARB E. coli S1-23 (1 × 10⁸ cfu mL^-1) and its ARGs (extracellular and intracellular) could be fully inactivated within 10 and 16 h PEC treatment, respectively. In contrast, photocatalytic (PC) and electrochemical (EC) treatments displayed no obvious effect; however, ARG-containing DNA extracted from E. coli S1-23, which was used as a model for dissociative naked ARGs, could be completely decomposed within a few minutes through these three treatments. Further analyses, including PCR, AFM and HPLC, proved that the structural integrity and surface topography of naked ARGs are damaged during treatment and can be completely eliminated. Furthermore, there is no generation of cytosine, guanine, adenine or thymine intermediates during the PEC, PC, and EC treatments. This study is the first report to propose the PEC treatment as a promising method for complete decomposition of ARB and ARGs in aqueous systems.

Enhanced simultaneous PEC eradication of bacteria and antibiotics by facilely fabricated high-activity {001} facets TiO2 mounted onto TiO2 nanotubular photoanode

Biohazards and coexisted antibiotics are two groups of emerging contaminants presented in various aquatic environments. They can pose serious threat to the ecosystem and human health. As a result, inactivation of biohazards, degradation of antibiotics, and simultaneous removal of them are highly desired. In this work, a novel photoanode with a hierarchical structured {001} facets exposed nano-size single crystals (NSC) TiO2 top layer and a perpendicularly aligned TiO2 nanotube array (NTA) bottom layer (NSC/NTA) was successfully fabricated. The morphology and facets of anatase TiO2 nanoparticles covered on the top of NTA layer could be controlled by adjusting precalcination temperature and heating rate as the pure NTA was clamped with glasses. Appropriate recalcination can timely remove surface F from {001} facets, and the photocatalytic activity of the resultant photoanode was subsequently activated. NSC/NTA photoanode fabricated under 500 °C precalcination with 20 °C min(-1) followed by 550 °C recalcination possessed highest photoelectrocatalytic efficiency to simultaneously remove bacteria and antibiotics. Results suggest that two-step calcination is necessary for fabrication of high photocatalytic activity NSC/NTA photoanode. The capability of simultaneous eradication of bacteria and antibiotics shows great potential for development of a versatile approach to effectively purify various wastewaters contaminated with complex pollutants.

Synergistic photocatalytic inactivation mechanisms of bacteria by graphene sheets grafted plasmonic AgAgX (X = Cl, Br, I) composite photocatalyst under visible light irradiation

By coupling graphene sheet and plasmonic photocatalysis technologies, a series of AgAgX/RGOs (X = Cl, Br, I; RGO = reduced graphene oxide) composites were prepared and found to be efficient antimicrobial agents for water disinfection upon visible light. Attributed to the efficient charge transfer by RGO sheets, the optimum AgAgBr/0.5% RGO could completely inactivate 2 × 10(7) cfu mL(-1) of Escherichia coli within 8 min, much faster than bare AgAgBr within 35 min. The synergistic antimicrobial mechanism of AgAgBr/0.5% RGO was studied by Ag(+) ions release evaluation, radical scavengers study, and radical determination. The enhanced photocatalytic activity of irradiated AgAgBr/0.5% RGO originated from the synergistic activities of its three components including Ag, AgBr and RGO, and the proposed mechanisms contained enhanced attraction by RGO followed by two pathways: primary oxidative stress caused by plasma induced reactive species like H2O2 and bactericidal effect of released Ag(+) ions. Furthermore, characterization of E. coli cells using SEM, fluorescent microscopy, and cytoplasmic substance leakage illustrated that VL irradiated AgAgBr/0.5% RGO could not only cause metabolic dysfunction but also destroy the cell envelope and biomolecular, while irradiated Ag(+) ions play a differential bactericidal action with a limited metabolic injury and no cell-membrane damage. The present work provides an efficient water disinfection technology and also opens a new idea in studying the antimicrobial mechanism of plasmonic photocatalyst.