Antibacterial Mechanisms of Reduced Iron-Containing Smectite-Illite Clay Minerals

Mineral-Based Advanced Oxidation Processes for Enhancing the Removal of Antibiotic Resistance Genes from Domestic Wastewater

Wastewater treatment plants (WWTPs) release antibiotic-resistant bacteria (ARB) and antibiotic-resistant genes (ARGs) into the environment. Advanced oxidation processes (AOPs) can remove ARB and ARGs, but they often require impractically high chemical or energy use. Here, we explore a low-energy AOP that uses Fe-bearing clay mineral (NAu-1) either combined with H2O2 (H2O2/NAu-1) or as prereduced structural Fe (rNAu-1) to degrade selected ARGs (i.e., tetM, tetQ, and bla OXA-10), int1 (a mobile genetic element), and the 16S rRNA gene in postsecondary WWTP effluents. Addition of H2O2/NAu-1 significantly increased tetM and int1 removals relative to UV irradiation and H2O2/UV (p ≤ 0.02). Removals increased with greater H2O2 doses and contact times, reaching maximum values of 1.2 and 2.3 log units at H2O2 doses of 0.26 and 10 mM and contact times of 4 and 8 h, respectively. Bacterial regrowth after 24 h of contact was probably due to H2O2 depletion. However, the addition of rNAu-1 achieved the highest removals, up to 2.9 log units after 0.5 h, and suppressed bacterial regrowth over 24 h. Similar removals were observed with rNAu-1 under oxic and anoxic conditions. Results show that mineral-based AOPs offer the potential for elevated ARG removal and lower chemical and energy demands in tertiary wastewater treatment.

Phosphate modified zerovalent iron enhances the interfacial hydrogen bond mediated adhesion and inactivation of Escherichia coli

The microbe-surface interaction plays essential roles in various natural and anthropogenic water processes, and it is of great benefit to tailor their interfacial contact. For instance, zero-valent iron (ZVI) holds great promise as an emerging disinfection agent, but its efficiency remains limited due to the insufficient ZVI-bacteria contact. Herein we modified the surface of ZVI with potassium dihydrogen phosphate (KH2PO4) by ball milling (P-ZVIbm) to facilitate the close adhesion and inactivation of Escherichia coli (E. coli). ExDLVO simulation indicated the significantly alleviated Lewis acid-base repulsion between P-ZVIbm and E. coli due to the enhanced hydrogen bonding. ATR-FTIR spectra and DFT calculation suggested that the surface phosphate moiety could form dual hydrogen bonds with the amide domain of bacterial proteins (e.g., membrane proteins, pili, flagella, etc.), significantly shortening the length of hydrogen bonds from 1.784 to 1.781 and 1.646 Å. The enhanced adhesion of E. coli on P-ZVIbm lead to more pronounced oxidative stress and inactivation of the cells. Impressively, P-ZVIbm exhibited superior bactericidal efficiency of 99.2% in batch experiments, far surpassing that of ZVIbm (33.9%, p < 0.001). As a prototype of application, the sand column packed with P-ZVIbm continuously removed E. coli to below 100 CFU/mL from simulated groundwater. This study provided an effective and facile strategy of phosphorylation to modulate the ZVI-bacterium adhesion for contact sterilization, and may shed light on the development of novel disinfection techniques, and the design of biofilm carriers for wastewater treatment, etc.

Antibacterial and therapeutic potential of historic deposits of silesian healing clay - terra sigillataSilesiaca

ETHNOPHARMACOLOGICAL RELEVANCE

The increasing evolution of pathogen resistance is a global problem that requires novel solutions. Recently, an increased interest in ethnomedicinal sources can be observed in the derivation of new medicines. The return to traditional medicinal formulations handed down for generations is being followed, but it is necessary to revise them again, taking into account the generally accepted research protocol.

AIM OF THE STUDY

We aimed to evaluate the antimicrobial potential of historical deposits of Silesian healing clay (SHC), used in ethnomedicine against Gram-positive bacteria and to assess their biological activity using a primary dermal fibroblast line (NHDF) and a model monocyte line (THP1).

MATERIALS AND METHODS

Information on medicinal clay deposits that occur in Silesia and are traditionally used in ethnomedicine or ancient medicine and known as terra sigillata Silesiaca or SHC, was selected on available source materials and old prints and maps from the archives of the Polish Geological Institute (Wrocław, Poland). Subsequently, their places of occurrence were identified and traced in the field by taking three deposits from the Silesia territory: Upper Silesia (D1), Opole Silesia (D2), and Lower Silesian (D3) Voivodeships for analysis. Their basic parameters and antimicrobial efficacy against pathogenic bacteria, Gram-positive streptococci and staphylococci, including methicillin-resistant strains, were examined. The study evaluated the effects of clays on growth and vitality using a primary dermal fibroblast line (NHDF) and a monocytic line (THP1). Studies were performed on a cell culture model to determine the effects on tissue regeneration (fibroblasts) and anti-inflammatory effects (monocytes). The study attempted to identify the mechanism of antimicrobial action, especially the textural characteristics and geochemical composition, as well as the environmental reaction (pH).

RESULTS

SHCs were classified into the following textural classes: clay loam (D1), clay (D2), and sand (D3). The tested deposits have antimicrobial properties that reduce the bacterial population (104 CFU) compared to the control (108 CFU). The antimicrobial effect depends on the type of clay and the species or strain of bacteria used. In-house studies clearly showed that Staphylococcus aureus Pcm 2054 and Staphylococcus epidermidis MRSE ATCC 2538 cells were completely adsorbed by clay minerals from clay D3.13. Furthermore, 10% leachates also showed an antimicrobial effect, as a reduction in bacterial populations was observed ranging from 91 to 100%. The results showed stimulation of fibroblast culture proliferation and inhibition of the growth of inflammatory cells (monocytes).

CONCLUSION

SHCs tested have antimicrobial potential, in particular D2.7, D2.11, and D3.13. The D3.13 deposit had a bactericidal effect against the staphylococci tested. Aqueous solutions of clays also showed bacteriostatic effect. The results obtained in cell culture model tests indicate properties that modulate the healing process - stimulation of fibroblast growth (NHDF line) and inhibition of monocyte growth (THP1 line).

pH dependence of reactive oxygen species generation and pollutant degradation in Fe(II)/O2/tripolyphosphate system

It has been reported that tripolyphosphate (TPP) can effectively enhance the activation of O2 by Fe(II) to remove organic pollutants in the environment. However, the influence of solution pH on the generation and conversion of reactive oxygen species (ROS) and their degradation of pollutants in the Fe(II)/O2/TPP system needs further investigation. In this study, we demonstrated that O2•- and •OH were the main ROS responsible for degradation in the system at different pH conditions, and their formation rates were calculated using a steady-state model. Experiments combined with density functional theory (DFT) calculations showed that the p-nitrophenol (PNP) degradation pathway in the Fe(II)/O2/TPP system is regulated by solution pH. Specifically, at pH = 3, the existence of Fe(II) in the solution is dominated by [Fe(II)(HTPP)2]2-, which leads to a rapid conversion from O2 and HO2• to generate •OH, and PNP is primarily oxidatively degraded. However, at pH = 5/7, [Fe(II)(TPP)2]4- is taking the lead with which O2•- is accumulated in the solution due to the slow conversion to •OH in this condition, and the PNP is mainly reductively degraded. This study proposes a new strategy to achieve the targeted oxidative/reductive removal of different types of pollutants by simply varying the solution pH in the Fe(II)/O2/TPP system.

The successive reduction of iodate to iodide driven by iron redox cycling

Ferrous iron (Fe(II)) produced by microbial Fe(III) reduction and reactive oxygen species (ROS) generated from aerobic Fe(II) oxidation can mediate iodate (IO3-) reduction and iodide (I-) oxidation, respectively. Nevertheless, how Fe redox cycling under redox fluctuating conditions drives transformation of iodine species remain unclear. In this study, Shewanella oneidensis MR-1 wildtype (WT) and its mutant △dmsEFAB, which lost the ability to enzymatically reduce IO3-, were chosen to conduct ferrihydrite/goethite/nontronite culture experiments under consecutive cycles of anoxic reduction of Fe(III) and re-oxidation of Fe(II) by O2 to reveal the role of Fe redox cycling in the transformation of iodine species. The results showed that both surface-adsorbed and mineral structural Fe(II) chemically reduced IO3-. Chemical IO3- reduction by biogenic Fe(II) was slower than enzymatic IO3- reduction by WT. Compared to △dmsEFAB cultures, WT cultures all showed higher Fe(II) concentrations under anoxic conditions but lower cumulative •OH under oxic conditions, which imply the chemical reaction between I- and ROS. I- oxidation by ROS, however, did not lead to a significant production of IO3- compared with I- formed under anoxic conditions. Consequently, Fe redox cycling successively reduced IO3- to I-, which highlights vital roles of Fe(III)-reducing bacteria in I- formation and mobilization in environments.

VMT/ACP/Dextran composite nanosheets against dental caries through promoting mineralization of dentin tubules, pH buffering, and antibacterial

Dental caries is a worldwide public healthcare concern, and is closely related to the acidic environment that caused by bacterial decomposition of food. In this study, a two-step ion exchange liquid-phase stripping method was applied to strip out vermiculite (VMT) nanosheets, then amorphous calcium phosphate (ACP) and dextran were inserted between the VMT nanosheets interlayer to obtain a composite two-dimension nanosheets (VMT/ACP/Dextran). VMT/ACP/Dextran composite nanosheets exhibited excellent biocompatibility and could provide exogenous Ca2+and PO43- from ACP, provide SiO44-, Mg2+, Fe2+ and obtain buffering pH and antibacterial properties from VMT, as well as improve suspension stability and targeting Streptococcus mutans through glucan. The in vitro study showed that the composite materials could promote the mineralization and sealing of dentin tubules by releasing active ions, buffer pH 4.5 (a value close to the pH in the dental plaque environment) to pH 6.6-7.1 (values close to the pH in human saliva) through ion exchange, and exert antibacterial effects by targeting Streptococcus mutans and exerting oxidase like and peroxidase like activities to produce reactive oxygen species (ROS). The in vivo animal study showed that daily cleaning teeth using VMT/ACP/Dextran composite nanosheets could effectively reduce the incidence rate and severity of dental caries in rats. Taking together, the developed VMT/ACP/Dextran composite nanosheets, which integrated the excellent properties of VMT, ACP and dextran, can effectively prevent dental caries through a combination of factors such as buffering acids, antibacterial properties, and promoting calcification, and may be used as an active ingredient for daily oral hygiene or filling materials to prevent and treat dental caries.

Nanoclay Hydrogel Microspheres with a Sandwich-Like Structure for Complex Tissue Infection Treatment

Addressing complex tissue infections remains a challenging task because of the lack of effective means, and the limitations of traditional bioantimicrobial materials in single-application scenarios hinder their utility for complex infection sites. Hence, the development of a bioantimicrobial material with broad applicability and potent bactericidal activity is necessary to treat such infections. In this study, a layered lithium magnesium silicate nanoclay (LMS) is used to construct a nanobactericidal platform. This platform exhibits a sandwich-like structure, which is achieved through copper ion modification using a dopamine-mediated metallophenolic network. Moreover, the nanoclay is encapsulated within gelatin methacryloyl (GelMA) hydrogel microspheres for the treatment of complex tissue infections. The results demonstrate that the sandwich-like micro- and nanobactericidal hydrogel microspheres effectively eradicated Staphylococcus aureus (S. aureus) while exhibiting excellent biocompatibility with bone marrow-derived mesenchymal stem cells (BMSCs) and human umbilical vein endothelial cells (HUVECs). Furthermore, the hydrogel microspheres upregulated the expression levels of osteogenic differentiation and angiogenesis-related genes in these cells. In vivo experiments validated the efficacy of sandwich-like micro- and nanobactericidal hydrogel microspheres when injected into deep infected tissues, effectively eliminating bacteria and promoting robust vascular regeneration and tissue repair. Therefore, these innovative sandwich-like micro- and nanobacteriostatic hydrogel microspheres show great potential for treating complex tissue infections.

Critical Role of Mineral Fe(IV) Formation in Low Hydroxyl Radical Yields during Fe(II)-Bearing Clay Mineral Oxygenation

In subsurface environments, Fe(II)-bearing clay minerals can serve as crucial electron sources for O2 activation, leading to the sequential production of O2•-, H2O2, and •OH. However, the observed •OH yields are notably low, and the underlying mechanism remains unclear. In this study, we investigated the production of oxidants from oxygenation of reduced Fe-rich nontronite NAu-2 and Fe-poor montmorillonite SWy-3. Our results indicated that the •OH yields are dependent on mineral Fe(II) species, with edge-surface Fe(II) exhibiting significantly lower •OH yields compared to those of interior Fe(II). Evidence from in situ Raman and Mössbauer spectra and chemical probe experiments substantiated the formation of structural Fe(IV). Modeling results elucidate that the pathways of Fe(IV) and •OH formation respectively consume 85.9-97.0 and 14.1-3.0% of electrons for H2O2 decomposition during oxygenation, with the Fe(II)edge/Fe(II)total ratio varying from 10 to 90%. Consequently, these findings provide novel insights into the low •OH yields of different Fe(II)-bearing clay minerals. Since Fe(IV) can selectively degrade contaminants (e.g., phenol), the generation of mineral Fe(IV) and •OH should be taken into consideration carefully when assessing the natural attenuation of contaminants in redox-fluctuating environments.

Mineral-mediated stability of organic carbon in soil and relevant interaction mechanisms

Soil, the largest terrestrial carbon reservoir, is central to climate change and relevant feedback to environmental health. Minerals are the essential components that contribute to over 60% of soil carbon storage. However, how the interactions between minerals and organic carbon shape the carbon transformation and stability remains poorly understood. Herein, we critically review the primary interactions between organic carbon and soil minerals and the relevant mechanisms, including sorption, redox reaction, co-precipitation, dissolution, polymerization, and catalytic reaction. These interactions, highly complex with the combination of multiple processes, greatly affect the stability of organic carbon through the following processes: (1) formation or deconstruction of the mineral-organic carbon association; (2) oxidative transformation of the organic carbon with minerals; (3) catalytic polymerization of organic carbon with minerals; and (4) varying association stability of organic carbon according to the mineral transformation. Several pieces of evidence related to the carbon turnover and stability during the interaction with soil minerals in the real eco-environment are then demonstrated. We also highlight the current research gaps and outline research priorities, which may map future directions for a deeper mechanisms-based understanding of the soil carbon storage capacity considering its interactions with minerals.

Differential interactions between natural clay minerals and dissolved organic matter affect reactive oxygen species formation

Naturally occurring reactive oxygen species (ROS) are widely involved in many environmental processes. Here we investigated the ROS generation associated with the interaction between complexed natural clay minerals (CMs) and dissolved organic matter (DOM). Our results showed that among the nine chemical-reduced CMs (CR-CMs), the light brown CR-CM (CR-CM 7) generated the highest ROS via oxygenation, relying on the reactive structural Fe(II) (Fe species that can transfer electrons to oxygen) instead of total structural Fe(II) as previously reported. Moreover, DOM affected the oxygenation of CR-CMs differently. The tight interaction between DOM and CR-CM 7 formed DOM-complexed Fe, while the weak interaction between DOM and the dark gold CR-CM (CR-CM 1) and the black CR-CM (CR-CM 5) exhibited decreased efficiencies. Mechanism studies revealed that ROS were generated through three pathways but all followed a similar one-electron transfer process in the presence of DOM. We further developed a three-layer geobattery model system and demonstrated that long electron transfer driven by CR-CMs/DOM could extend ROS generation to several centimetres across the oxic-anoxic interface, even without redox switching. These findings offer new insights into CMs-involved ROS generation and associated organic matter transformation in natural environments.

Mineral Phase Reconfiguration Enables the High Enzyme-like Activity of Vermiculite for Antibacterial Application

Phyllosilicates-based nanomaterials, particularly iron-rich vermiculite (VMT), have wide applications in biomedicine. However, the lack of effective methods to activate the functional layer covered by the external inert layer limits their future applications. Herein, we report a mineral phase reconfiguration strategy to prepare novel nanozymes by a molten salt method. The peroxidase-like activity of the VMT reconfiguration nanozyme is 10 times that of VMT, due to the electronic structure change of iron in VMT. Density-functional theory calculations confirmed that the upward shifted d-band center of the VMT reconfiguration nanozyme promoted the adsorption of H2O2 on the active iron sites and significantly elongated the O-O bond lengths. The reconfiguration nanozyme exhibited nearly 100% antibacterial activity toward Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), much higher than that of VMT (E. coli 10%, S. aureus 21%). This work provides new insights for the rational design of efficient bioactive phyllosilicates-based nanozyme.

Unrecognized Role of Organic Acid in Natural Attenuation of Pollutants by Mackinawite (FeS): The Significance of Carbon-Center Free Radicals

Organic acid is prevalent in underground environments and, against the backdrop of biogeochemical cycles on Earth, holds significant importance in the degradation of contaminants by redox-active minerals. While earlier studies on the role of organic acid in the generation of reactive oxygen species (ROS) primarily concentrated on electron shuttle or ligand effects, this study delves into the combined impacts of organic acid decomposition and Mackinawite (FeS) oxidation in contaminant transformation under dark aerobic conditions. Using bisphenol A (BPA) as a model, our findings showed that oxalic acid (OA) notably outperforms other acids in enhancing BPA removal, attaining a rate constant of 0.69 h-1. Mass spectrometry characterizations, coupled with anaerobic treatments, advocate for molecule-O2 activation as the principal mechanism behind pollutant transformation. Comprehensive results unveiled that carbon center radicals, initiated by hydroxyl radical (•OH) attack, serve as the primary agents in pollutant oxidation, accounting for at least 93.6% of the total •OH generation. This dynamic, driven by the decomposition of organic acids and the concurrent formation of carbon-centered radicals, ensures a steady supply of electrons for ROS generation. The obtained information highlights the importance of OA decomposition in the natural attenuation of pollutants and offers innovative strategies for FeS and organic acid-coupled decontamination.

Structural and mineralogical variation upon reoxidation of reduced Fe-bearing clay minerals during thermal activation

The hydroxyl radicals (OH) produced from Fe(II) oxidation upon reoxidation of reduced Fe-bearing clay minerals (RFC) have received increased attention and thermal activation was used to enhance Fe(II) oxidation to improve OH production. However, changes in mineral morphology and structure during thermally-activated RFC reoxidation are not yet clear. Herein, the Fe(II) oxidation extent was measured by chemical analysis during the reoxidation of model RFC (reduced nontronite (rNAu-2) at elevated temperatures. Mineralogical variation of rNAu-2 particles was observed by scanning electron microscopy (SEM), Mössbauer spectra, and X-ray photoelectron spectroscopy (XPS). The structural Fe(II) oxidation in rNAu-2 was accelerated with increasing temperature, accompanied by the transformation of structural entities and the dissolution of Fe and Si, while the overall structure of rNAu-2 minerals was relatively intact. The surface microstructure of particles showed the dissolved holes, net-shape flocs, and even large pore channels after Fe(II) oxidation by thermal activation. Moreover, the rearrangement of structural Fe(II) entities, the regeneration of edge Fe(II), and the electron transport from the interior to the edge were enhanced during rNAu-2 reoxidation by thermal activation. The increasing electron transfer at elevated temperatures could possibly be owing to the increasing number of reactive sites by increasing the internal disorder of rNAu-2. This work provides novel insights into the structural and mineralogical changes in promoting electron transfer upon RFC reoxidation.

Pyrogenic Carbon Improves Cd Retention during Microbial Transformation of Ferrihydrite under Varying Redox Conditions

Fe(III) (oxyhydr)oxides are ubiquitous in paddy soils and play a key role in Cd retention. Recent studies report that pyrogenic carbon (PC) may largely affect the microbial transformation processes of Fe(III) (oxyhydr)oxides, yet the impact of PC on the fate of Fe(III) (oxyhydr)oxide-associated Cd during redox fluctuations remains unclear. Here, we investigated the effects of PC on Cd retention during microbial (Shewanella oneidensis MR-1) transformation of Cd(II)-bearing ferrihydrite under varying redox conditions. The results showed that in the absence of PC, microbial reduction of ferrihydrite resulted in Cd release under anoxic conditions and Fe(II) oxidation by oxygen resulted in Cd retention under subsequent oxic conditions. The presence of PC facilitated microbial ferrihydrite reductive dissolution under anoxic conditions, promoted Fe(II) oxidative precipitation under oxic conditions, and inhibited Cd release under both anoxic and oxic conditions. The presence of PC and frequent shifts in redox conditions (i.e., redox cycling) inhibited the transformation of ferrihydrite to highly crystalline goethite and magnetite that exhibited less Cd adsorption. As a result, PC enhanced Cd retention by 41-59% and 55-77% after the redox shift and redox cycling, respectively, while in the absence of PC, Cd retention decreased by 5% after the redox shift and increased by 11% after redox cycling. Sequential extraction analysis revealed that 63-78% of Cd was associated with Fe minerals, while 3-12% of Cd was bound to PC, indicating that PC promoted Cd retention mainly through inhibiting ferrihydrite transformation. Our results demonstrate the great impacts of PC on improving Cd retention under dynamic redox conditions, which is essential for applying PC in remediating Cd-contaminated paddy soils.

Effects of Organic Ligands on the Antibacterial Activity of Reduced Iron-Containing Clay Minerals: Higher Extracellular Hydroxyl Radical Production Yet Lower Bactericidal Activity

Reduced iron-containing clay (RIC) minerals have been documented to exhibit antibacterial activity through a synergistic action of extracellular membrane attack and intracellular oxidation of cellular components. However, the relative importance between extracellular and intracellular processes has remained elusive. Here, metal-chelating organic ligands (lactate, oxalate, citrate, and ethylene diaminetetraacetic acid (EDTA)) were amended to the bactericidal assays such that the importance of the two processes could be evaluated. Reduced nontronite (rNAu-2) was used as a model clay mineral to produce extracellular hydroxyl radical (^•OH) upon oxygenation. The presence of Fe-chelating ligands increased ^•OH yield by 3-5 times. Consequently, bacterial cell membrane attack was enhanced, yet the antibacterial activity of RIC diminished. Additional experiments revealed that the ligands inhibited soluble metal ions from adsorption onto the bacterial cell membrane and/or penetration into the cytoplasm. Consequently, intracellular Fe concentration for the ligand-treated group was nearly 2 orders of magnitude lower than that for no-ligand control, which greatly decreased intracellular accumulation of reactive oxygen species (ROS) and increased cell survival. These results highlight that destruction of intracellular contents (proteins and DNA) is more important than oxidative degradation of membrane lipids and cell envelope proteins in causing bacterial cell death by RIC.

Novel Non-Toxic Highly Antibacterial Chitosan/Fe(III)-Based Nanoparticles That Contain a Deferoxamine—Trojan Horse Ligands: Combined Synthetic and Biological Studies

In this study, we prepared chitosan/Fe(III)/deferoxamine nanoparticles with unimodal size distribution (hydrodynamic diameter ca. 250 nm, zeta potential ca. 32 mV). The elaborated nanoparticles are characterized by outstanding in vitro and in vivo antibacterial activity, which exceeds even that of commercial antibiotics ampicillin and gentamicin. Moreover, the nanoparticles are non-toxic. We found that the introduction of iron ions into the chitosan matrix increases the ability of the resulting nanoparticles to disrupt the integrity of the membranes of microorganisms in comparison with pure chitosan. The introduction of deferoxamine into the obtained nanoparticles sharply expands their effect of destruction the bacterial membrane. The obtained antibacterial nanoparticles are promising for further preclinical studies.

Inhibition of Extracellular Enzyme Activity by Reactive Oxygen Species upon Oxygenation of Reduced Iron-Bearing Minerals

The dual roles of minerals in inhibiting and prolonging extracellular enzyme activity in soils and sediments are governed by enzyme adsorption to mineral surfaces. Oxygenation of mineral-bound Fe(II) generates reactive oxygen species (ROS), yet it is unknown whether and how this process alters the activity and functional lifespan of extracellular enzymes. Here, the effect of mineral-bound Fe(II) oxidation on the hydrolytic activity of a cellulose-degrading enzyme β-glucosidase (BG) was studied using two pre-reduced Fe-bearing clay minerals (nontronite and montmorillonite) and one pre-reduced iron oxide (magnetite) at pH 5 and 7. Under anoxic conditions, BG adsorption to mineral surfaces decreased its activity but prolonged its lifespan. Under oxic conditions, ROS was produced, with the amount of •OH, the most abundant ROS, being positively correlated with the extent of structural Fe(II) oxidation in reduced minerals. •OH decreased BG activity and shortened its lifespan via conformational change and structural decomposition of BG. These results suggest that under oxic conditions, the ROS-induced inhibitory role of Fe(II)-bearing minerals outweighed their adsorption-induced protective role in controlling enzyme activity. These results disclose a previously unknown mechanism of extracellular enzyme inactivation, which have pivotal implications for predicting the active enzyme pool in redox-oscillating environments.

Prospects of coupled iron-based nanostructures in preclinical antibacterial therapy

Bacterial infections can threaten human health. Drug-resistant bacteria have become a challenge because of the excessive use of drugs. We summarize the current metallic antibacterial materials, especially Fe-based materials, for efficiently killing bacteria. The possible antibacterial mechanisms of metallic antibacterial agents are classified into interactions with bacterial proteins, iron metabolism, catalytic activity, and combinations of magnetic, photodynamic, and photothermal effects. This review will inspire the development of novel Fe-based antibacterial agents for clinical settings.

In-situelectrochemical fabrication of Ag@AgCl NW-PET film with superior photocatalytic bactericidal activity

Constructing a composite photocatalyst with efficient charge-transfer pathways is contribute to improving charge separation, which has attracted wide attention owing to its availability in photocatalysis applications. In this work, three-dimensional (3D) silver@silver chloride (Ag@AgCl) network structures are fabricated for photocatalytic inactivation ofEscherichia coli(E. coli) by thein situelectrochemical introducing AgCl shell on the surface of Ag nanowire (NW) networks that are coated on a polyethylene terephthalate (PET) substrate. The obtained Ag@AgCl NW-PET films exhibit good photocatalytic bactericidal activity againstE. coliunder simulated Sunlight irradiation, mainly due to their efficient charge-transport channel constructed by the Ag NWs network. It is worth noting that the content of converted AgCl shell is positively correlated with their photocatalytic bactericidal efficiency. The experimental results also demonstrate that the synergistic contribution of Ag⁺sustained release, rough surfaces and energy band structure optimization in photocatalytic sterilization. Besides, the prepared Ag@AgCl NW-PET film can be recycled, and the photocatalytic sterilization efficiency can still keep above 99% after three cycles. This work might provide new and more diverse opportunities for the development of excellent charge-transport, recyclable photocatalysts for photocatalytic sterilization.

Cr(VI) Reduction by Siderophore Alone and in Combination with Reduced Clay Minerals

Siderophores and iron-containing clays are known to influence the transformation of chromium in the environment. The role of clays in hexavalent chromium [Cr(VI)] reduction has been reported extensively. However, the mechanisms of Cr(VI) reduction by siderophores and their combination with iron-bearing clays are poorly known. Herein, we report the kinetics and products of Cr(VI) reduction by a siderophore alone or in combination with reduced clays. Results showed that Cr(VI) reduction by a tri-hydroxamate siderophore─desferrioxamine B (DFOB)─at a pH of 6 was achieved by one-electron transfer via the formation of Cr(V) intermediate. The formed Cr(V) was further reduced to organically complexed Cr(III). The Cr(VI) reduction rate and extent in the presence of both DFOB and reduced clays unexpectedly decreased relative to that with reduced clays alone, despite both serving as Cr(VI) reductants. The interaction between DFOB and clays (e.g., adsorption/intercalation, dissolution, and/or oxidation) was primarily responsible for Cr(VI) reduction inhibition. The extent of inhibition increased at higher DFOB concentrations in the presence of iron-rich nontronite but decreased in the presence of iron-poor montmorillonite, which may be related to their different Cr(VI) reduction mechanisms. This study highlights the importance of siderophores in chromium transformation and its impact on the reactivity of iron-bearing clays toward heavy metal reduction in the environment.