Active Metal Ions Research Articles

Prototype membrane electrolysis using a MFI-zeolite-coated ceramic tubular membrane provides in-line generation of two active electron mediators by eliminating active species crossover

Active ion crossover is a major obstacle in membrane electrolysis, which reduces the efficiency of the active mediator and increases operational cost. Using a prototype tubular cell divided with a MFI-zeolite-coated (shell side) ceramic tubular membrane, two active mediators, Co3+ (Co2(SO4)3) in 5 M H2SO4 at the anodic half-cell and Ni1+ ([Ni(CN)4]3-) in 9 M KOH at the cathodic half-cell, were produced. The rate of Co3+ production increased from 5.74 × 10−3 M min−1 to 7.11 × 10−3 M min−1 when the use of 9 M KOH at the cathodic half-cell instead of 5 M H2SO4 at both half-cells and controlled migration due to the pH change. The absence of a UV–visible spectral peak for cobalt or nickel ions in the other side of the electrolyzed solution supports the lack of active metal ion crossover by the MFI-zeolite-coated ceramic membrane. In high acid and base electrolyte pH, the 5.6 fold higher resistance (5.13 Ω cm−2) than in high acid electrolytes in both half-cells (0.91 Ω cm−2) prevented proton and active mediator ion crossover. SEM-EDS and XRD data profiles found no cobalt or nickel ions on the membrane, which also supports the lack of migration, whereas the Al ion concentration decreased on the lumen side (9 M KOH containing the cathodic half-cell), demonstrating the dissolution of Al2O3 in the KOH medium (uncoated MFI). The MFI-coated tubular membrane can be a good choice for the effective generation of two mediators by membrane electrolysis using high end pH electrolytes.

Redox Recycling-Triggered Peroxidase-Like Activity Enhancement of Bare Gold Nanoparticles for Ultrasensitive Colorimetric Detection of Rare-Earth Ce3+ Ion.

Although it has been demonstrated that rare-earth elements (REEs) disturb and alter the catalytic activity of numerous natural enzymes, their effects on nanomaterial-based artificial enzymes (nanozymes) have been seldom explored. In this work, the influence of REEs on the peroxidase-like activity of bare gold nanoparticles (GNPs) is investigated for the first time, and a new type of Ce3+-activated peroxidase mimetic activity of GNPs is obtained. The introduced Ce3+ can be bound to the bare GNP surface rapidly through electrostatic attraction, after which it donates its electron to the bare GNP. As H2O2 is a good electron scavenger, more •OH radicals are generated on the surfaces of the bare GNPs, which can considerably enhance TMB oxidation. Due to its redox cycling ability, the activation effect of Ce3+ is proved to be more efficient in comparison to those of the other reported metal ion activators (e.g., Bi3+, Hg2+, and Pb2+). In addition, it is determined that Ce3+ should directly contact with the gold core to trigger its activation effect. When the surface states of the bare GNPs are altered, the Ce3+-stimulated effect is strongly inhibited. Furthermore, a novel colorimetric method for Ce3+ is developed, on the basis of its enhancing effect on the peroxidase mimetic activity of bare GNPs. The sensitivity of this newly developed method for Ce3+ is excellent with a limit of detection as low as 2.2 nM. This study not only provides an effective GNP-based peroxidase mimic but also contributes in realizing new applications for nanozymes.

Enhancement of Photocatalytic Activity of Sodium Bismuth Titanate by Doping with Copper, Silver, and Tin Ions

Perovskite type oxides, sodium bismuth titanate (Na0.5Bi0.5TiO3), and Ag+, Cu2+, and Sn2+ doped Na0.5Bi0.5TiO3 were prepared by pechini and ion exchange methods, respectively. Photocatalytic activities of these catalysts were tested by decomposition of methylene blue (MB) under visible light irradiation. Results showed that the photocatalytic activity of metal ion doped Na0.5Bi0.5TiO3 was higher than undoped Na0.5Bi0.5TiO3. Relatively high photocatalytic performance of Ag+‐doped Na0.5Bi0.5TiO3 is mainly ascribed to the efficient separation of electron‐hole (e–, h+) pairs, lower bandgap energy and the creation of active hydroxyl radicals (•OH). Further, the Ag+‐doped Na0.5Bi0.5TiO3 catalyst showed good reusability up to four cycles. A possible mechanism for the enhanced photocatalytic performance was proposed. The synthesized photocatalysts were characterized by XRD, SEM, EDS, XPS, FT‐IR, and UV/Vis DRS techniques.

Interaction of Small Ionic Species With Phospholipid Membranes: The Role of Metal Coordination

In studies of the transfer, distribution and biochemical activity of metal ions it is typically assumed that the phospholipid bilayer acts as an inert barrier. Yet, there is mounting evidence that metal ions can influence the physical properties of membranes. Little is known of the basis of this effect. In this work the location and distribution of common metal ions: Na+, Mg2+ and Ca2+ in phospholipid membranes were studied. Computer simulations of lipid membrane segments in an aqueous environment showed that the ions penetrate the membrane headgroup zone and co-localize with the phosphate and the ester moieties. Analysis of the chemical environment of the ions in the simulations suggested that the co-localization is facilitated by coordination to the polar oxygen atoms of the phosphate and ester groups in typical coordination geometries of each ionic species, where the coordination shells are completed by water molecules. In contrast, the counterions do not penetrate the headgroup zone but form a layer over the membrane; this layer is also an effective metal exclusion zone. Importantly, the choline groups appear to be distributed almost exactly in the same plane as the phosphate, suggesting that the zwitterion dipole is preferentially horizontally aligned: this suggests that the distribution of the Cl- over the membrane surface is not a direct result of interaction with the choline groups, but rather an effect of the field emanating from the metal ion content of the membrane. Such a well defined ion distribution is expected to have a strong influence on membrane properties, in particular phase transition temperatures via increased in-plane cohesion; this was proven by calorimetry measurements using differential scanning calorimetry of suspended liposomes and quartz crystal microbalance-based measurements on supported single bilayer membranes. These findings shed a new light on the role metal ions play in stabilizing biological membranes.

Structurally controlled layered Ni3C/graphene hybrids using cyano-bridged coordination polymers

The wide range of oxygen-containing functional groups on the basal planes and edges of graphene oxide (GO) facilitate the anchoring of active metal ions on its surface. Previously, we have shown that these active centers allow the in situ crystallization of cyano-bridged Ni-based coordination polymers (Ni-CP) as nanoflakes on the surface of GO sheets (Angew. Chem. Int. Ed., 2016, 55, 8426). Here, in this work, by extending our previous concept, we demonstrate that Ni-CP-coated GO sheets can be made to self-assemble to form various multi-layered hybrid structures (Ni-CP/GO) by controlling the composition ratios. Ni3C/rGO with the original morphology was successfully prepared by converting the Ni-CP to Ni3C in the space between the graphene sheets by thermal treatment in an inert atmosphere. The electrochemical analyses reveal that the optimized Ni3C/rGO hybrid exhibits superior electrocatalytic performance for the oxygen reduction reaction (ORR) with good durability and stability.

Opportunistic fungal infections of ent organs. Part 2

The review of literature summarized information about main fungal pathogens and theirs proportions in infections affecting the ENT areas. Different nosological forms of fungal diseases of upper respiratory tract and ear were considered, and listed the main clinical manifestations. Microbiological diagnosis of mycoses affecting the ENT organs is based on microscopic, mycological, immunological and molecular-genetic studies. The review paid particular attention to the treatment of fungal infections of the areas. It presented the classification of modern antifungal drugs, and described regimens and duration of treatment depending on fungus type, disease severity and other patient's condition. It was noted that success of therapy of fungal infections affecting upper respiratory tract and ear now provided by using of complex antimycotics, immunotropic agents, antihistamines and probiotics. The emergence of resistant strains of micromycetes was observed as the main reason for decreased effectiveness of antifungal agents. Prospective solution of this problem were indicated by way of using of biologically active plant compounds, nanoantiseptics, metal ions, enzymes and photodynamic therapy. The review suggested relevance of increasing rates of fungal morbidity affecting the ENT areas, the necessity of early diagnosis, the search of new antifungal agents and compounds with fungicidal activity and theirs introduction into clinical practice.

Characterization of the genomically encoded fosfomycin resistance enzyme from Mycobacterium abscessus.

Mycobacterium abscessus belongs to a group of rapidly growing mycobacteria (RGM) and accounts for approximately 65-80% of lung disease caused by RGM. It is highly pathogenic and is considered the prominent Mycobacterium involved in pulmonary infection in patients with cystic fibrosis and chronic pulmonary disease (CPD). FosM is a putative 134 amino acid fosfomycin resistance enzyme from M. abscessus subsp. bolletii that shares approximately 30-55% sequence identity with other vicinal oxygen chelate (VOC) fosfomycin resistance enzymes and represents the first of its type found in any Mycobacterium species. Genes encoding VOC fosfomycin resistance enzymes have been found in both Gram-positive and Gram-negative pathogens. Given that FosA enzymes from Gram-negative bacteria have evolved optimum activity towards glutathione (GSH) and FosB enzymes from Gram-positive bacteria have evolved optimum activity towards bacillithiol (BSH), it was originally suggested that FosM might represent a fourth class of enzyme that has evolved to utilize mycothiol (MSH). However, a sequence similarity network (SSN) analysis identifies FosM as a member of the FosX subfamily, indicating that it may utilize water as a substrate. Here we have synthesized MSH and characterized FosM with respect to divalent metal ion activation and nucleophile selectivity. Our results indicate that FosM is a Mn2+-dependent FosX-type hydrase with no selectivity toward MSH or other thiols as analyzed by NMR and mass spectroscopy.

Anti-biofilm activity of two novel, borate based, bioactive glass wound dressings

Abstract Bioactive glass was first developed in the late 1960’s as a compound that would facilitate bone re-growth. In more recent years, this technology has been used to promote wound healing through its ability to stimulate soft tissue growth, angiogenesis, reduce inflammation, and prevent infection. Chronically infected wounds, which result from biofilm formation, affect millions of patients in the Unites States each year and cost billions of dollars to treat. The present studies demonstrate exposure of pre-formed biofilms to bioactive glass, under simulated body conditions, resulted in significant reduction in bacterial load. Additionally, specific therapeutically active metal ions such as copper and zinc were added to a borate bioactive glass formulation through a process of ion doping and found to further enhance the anti-biofilm activity. Based on the present findings, the antibiofilm agents released by borate bioactive glasses may prove effective to eradicate the biofilm infections that prevent healing in patients with chronic wounds.

Electrochemical-Mediated Gelation Of Catechol-Bearing Hydrogels Based On Multimodal Crosslinking.

Catechol-bearing polymers form hydrogel networks through cooperative oxidative crosslinking and coordination chemistry. Here we describe the kinetics of cation-dependent electrochemical-mediated gelation of precursor solutions composed of catechol functionalized four-arm poly(ethylene glycol) combined with select metal cations. The gelation kinetics, mechanical properties, crosslink composition, and self-healing capacity is a strong function of the valency and redox potential of metal ions in the precursor solution. Catechol-bearing hydrogels exhibit highly compliant mechanical properties with storage moduli ranging from G' = 0.1-5 kPa depending on the choice of redox active metal ions in the precursor solution. The gelation kinetics is informed by the net cell potential of redox active components in the precursor solution. Finally, redox potential of the metal ion precursor can differentially alter the effective density of crosslinks in networks and confer properties to hydrogels such as self-healing capacity. Taken together, this parametric study generates new insight to inform the design of catechol-bearing hydrogel networks formed by electrochemical-mediated multimodal crosslinking.

Synergistically well-mixed MOFs grown on nickel foam as highly efficient durable bifunctional electrocatalysts for overall water splitting at high current densities

Metal-organic framework (MOF), possessing versatile catalytic activities, remarkable structural diversity, high surface areas, and tunable pore sizes, was recently demonstrated an outstanding catalyst for electrolytic water splitting. The electrolytic performances can be much enhanced with a synergistic design of the MOFs, which was realized as uniformly well-mixed and dispersed Fe- and Ni-MOFs (termed as MFN-MOFs) in-situ grown on backbones of nickel foam (NF). The electrocatalyst thus developed exhibited ultra-high activities at high current densities for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1 M KOH, delivering 10 and 500 mA cm−2 at ultralow overpotentials of 79 and 234 mV, respectively with a small Tafel slope of 30.1 mV dec−1 for the HER and achieving ultralow overpotentials of 235 and 294 mV for the OER at 50 and 500 mA cm−2, respectively with a small Tafel slope of 55.4 mV dec−1. The inter-molecular synergistic interactions between the well-mixed and dispersed Fe- and Ni-MOFs not only facilitate the critical charge transfer for the redox reactions but also disperse the active metal ion sites to enhance their degree of utilization to achieve exceptional OER and HER performances. The MFN-MOFs/NF//MFN-MOFs/NF couple exhibited ultralow cell voltages of 1.495 V@10 mA cm−2 and 1.80 V@500 mA cm−2 with a Tafel slope of only 79.5 mV dec−1 in 1 M KOH, outperforming most of the state-of-the-art bifunctional electrode couples and benchmark couple of Pt-C/NF//IrO2/NF. More importantly, the MFN-MOFs/NF electrode exhibited ultrastability at high current densities, with a minor decay of 3.7% in a chronopotentiometric stability test conducted at a commercially viable high current density of 500 mA cm−2 for overall water-splitting over 100 h. This synergistic effect boosting design concept for electrocatalysts was successfully demonstrated, opening up a new way for catalyst design toward large-scale H2 production.

Piezophotonics: From fundamentals and materials to applications

Abstract

Electrophoretic Determination of Lactococcus lactis Modified by Zinc Ions

The developed capillary electrophoresis (CE) method was applied to evaluate the aggregation activity of divalent metal ions (zinc) on bacterial cells. In our study, the influence of the Lactococcus lactis surface modification by zinc ions at different concentration (1, 3 and 10 mM, respectively) was determined. Electrophoretic results in pseudo isotachophoretic mode indicated that using a Znaq2+ caused the uncontrolled aggregation of bacterial cells and, as a result, new signals of microbial agglomerates were observed in the electropherogram. Moreover, the observed process is strongly related with the concentration of the used Znaq2+ solution—the number of bacterial agglomerates increased with an increasing concentration of modifier. The phenomenon of L. lactis uncontrolled clumping was also evaluated by application of size distribution and spectrometric in infrared range measurements (FT-IR) measurements. The obtained data indicated that the main groups involved in the bacterial cells aggregation process are deprotonated carboxyl and amid groups derived from microbial surface proteins. As a consequence, the proposed mechanism of the L. lactis uncontrolled clumping process is presented. In addition, data from fluorescence microscopy pointed out damage cells analyzed direct after electroanalysis. Therefore, CE may be a potential method for evaluating the aggregation activity of different types of bivalent metal ions against microbial cells.

Metal ion concentrations after metal-on-metal hip arthroplasty are not correlated with habitual physical activity levels.

Metal-on-metal (MoM) hip arthroplasties have shown high clinical failure rates with many patients at risk for a revision and under surveillance for high metal ion concentrations. Implant wear releasing such ions is assumed to be a function of use, i.e. the patient's physical activity. This study aimed to assess whether habitual physical activity levels of MoM patients are correlated with metal ion concentrations and are higher in patients with high (at risk) than in patients with low (safe) metal ion concentrations. A cohort study was conducted of patients with any type of MoM hip prosthesis. Metal ion concentrations were determined using ICP-MS. Habitual physical activity of subjects was measured in daily living using an acceleration-based activity monitor. Outcome consisted of quantitative and qualitative activity parameters. In total, 62 patients were included. Mean age at surgery was 60.8 ± 9.3 years and follow-up was 6.3 ± 1.4 years. Cobalt concentrations were highly elevated overall (112.4 ± 137.9 nmol/L) and significantly more in bilateral (184.8 ± 106.5 nmol/L) than in unilateral cases (87.8 ± 139.4 nmol/L). No correlations were found between physical activity parameters and metal ion concentrations. Subgroup analysis of patients with low versus high cobalt concentration showed no significant differences in habitual physical activity. No correlation was found between physical activity levels and metal ion concentrations. Implant use by normal habitual activities of daily living seems not to influence metal ion concentrations.

An Anthraquinone/Carbon Fiber Composite as Cathode Material for Rechargeable Sodium‐Ion Batteries

AbstractThe transition from rare to natural abundant materials in rechargeable batteries is becoming a grand challenge in developing a resource sustainable power supply. Since decades, scientists attempt to circumvent the lithium's resource problem by innovating alternative active metal ions. A cost‐effective alternative to lithium is to use sodium (Na) as the carrier ion in rechargeable batteries. We present an electrode composite material comprising anthraquinone (AQ) and nanostructured carbon fibers, as a cathode material for Na‐ion batteries. These electrodes are characterized by a large surface area, ordered porous network, large pore volume and good electrical conductivity. The material is further compared to the water soluble, mono‐substituted anthraquinone derivative, sulfonated 9,10‐anthraquinone (SAQ). While the SAQ/carbon fiber composite demonstrates a moderate initial discharge capacity of ∼95 mAh g−1 accompanied by substantial, initial capacity fading, the AQ/carbon fiber composite shows a remarkably high discharge capacity of ∼307 mAh g−1 and exhibit reasonable cycling stability over 115 charge/discharge cycles in a Na containing electrolyte. This may be best explained by the well‐structured intermolecular π‐π stacking of the thermally evaporated AQ layers and with the subjacent carbon fibers. Since AQ and SAQ are widely‐used industrial pigments, they may offer a cost‐effective, abundant and environmentally benign cathode material for secondary Na‐ion and Na‐flow batteries.

A New Class of EutT ATP:Co(I)rrinoid Adenosyltransferases Found in Listeria monocytogenes and Other Firmicutes Does Not Require a Metal Ion for Activity.

ATP:Co(I)rrinoid adenosyltransferases (ACATs) are involved in de novo adenosylcobamide (AdoCba) biosynthesis and in salvaging complete and incomplete corrinoids from the environment. The ACAT enzyme family is comprised of three classes of structurally and evolutionarily distinct proteins (i.e., CobA, PduO, and EutT). The structure of EutT is unknown, and an understanding of its mechanism is incomplete. The Salmonella enterica EutT ( SeEutT) enzyme is the best-characterized member of its class and is known to be a ferroprotein. Here, we report the identification and initial biochemical characterization of an enzyme representative of a new class of EutTs that does not require a metal ion for activity. In vivo and in vitro evidence shows that the metal-free EutT homologue from Listeria monocytogenes ( LmEutT) has ACAT activity and that, unlike other ACATs, the biologically active form of LmEutT is a tetramer. In vitro studies revealed that LmEutT was more efficient than SeEutT and displayed positive cooperativity. LmEutT adenosylated cobalamin, but not cobinamide, showed specificity for ATP and 2'-deoxyATP and released a triphosphate byproduct. Bioinformatics analyses suggest that metal-free EutT ACATs are also present in other Firmicutes.

Effects of the preassembly of benzohydroxamic acid with Fe (III) ions on its adsorption on cassiterite surface

Metal ions are widely used as activators in the flotation of oxidised minerals. At the same dosage of collector, the recovery of target minerals (cassiterite, scheelite, wolframite and ilmenite) can be evidently improved with the addition of metal ion activator. Adsorption of metal ions and their hydroxides can provide attractive sites for collector attachment, contrary to bare minerals that exhibit considerably low affinity towards the collector. Iron complexes of benzohydroxamic acid (BHA) are formed during the reaction of ferric chloride with BHA in the solution. These complexes also exhibit strong collecting ability towards cassiterite in the flotation, which contradicted the classical theory that the activator must be added before the collector. However, the major active component and the underlying adsorption mechanism of the Fe-BHA complexes are still unknown. In this study, the solution chemistry calculation has been used to identify the major active components of the Fe-BHA complexes. Accordingly, a preferred adsorption model of the Fe-BHA complexes onto the cassiterite surface has been proposed and proven effective, through first-principles calculations based on density functional theory, flotation experiments and adsorption tests. Our results might shed new light on the activation mechanism of metal ions in mineral flotation.

Synergistically Enhanced Oxygen Evolution Reaction Catalysis for Multielement Transition-Metal Oxides

Transition metal oxides have been extensively investigated as novel catalysts for oxygen evolution reaction (OER). Partial elemental substitutions are effective ways to increase catalytic performance and such electronic interactions between multiple elements are known as synergistic effects. However, serious issues such as random atomic arrangement and ambiguous roles of constituent elements humper theoretical investigations for rational materials design. Herein, we describe systematic study on OER activity of AA′3B4O12-type quadruple perovskite oxides, in which multiple transition metal ions are located at distinct crystallographic sites. Electrochemical measurements demonstrate that OER catalytic activities of quadruple perovskite oxide series, CaCu3B4O12 (B = Ti, V, Cr, Mn, Fe, and Co), are all superior to those of simple perovskite counterparts CaBO3. The order of activity of B-site transition metal ions for CaBO3 (Fe4+ > Co4+ ≫ Ti4+, V4+, Cr4+, Mn4+) is retained in CaCu3B4O12, indicating that B-site ...

Metal-Binding Isosteres as New Scaffolds for Metalloenzyme Inhibitors.

The principle of isosteres or bioisosteres in medicinal chemistry is a central and essential concept in modern drug discovery. For example, carboxylic acids are often replaced by bioisosteres to mitigate issues related to lipophilicity or acidity while retaining acidic characteristics in addition to hydrogen bond donor/acceptor abilities. Separately, the development of metal-binding pharmacophores (MBPs) for binding to the active site metal ion in metalloenzymes of therapeutic interest is an emerging area in the realm of fragment-based drug discovery (FBDD). The direct application of the bioisostere concept to MBPs has not been well-described or systematically investigated. Herein, the picolinic acid MBP is used as a case study for the development of MBP isosteres (so-called MBIs). Many of these isosteres are novel compounds, and data on their physicochemical properties, metal binding capacity, and metalloenzyme inhibition characteristics are presented. The results show that MBIs of picolinic acid generally retain metal coordinating properties and exhibit predictable metalloenzyme inhibitory activity while possessing a broad range of physicochemical properties (e.g., p Ka, log P). These findings demonstrate the use of bioisosteres results in an untapped source of metal binding functional groups suitable for metalloenzyme FBDD. These MBIs provide a previously unexplored route for modulating the physicochemical properties of metalloenzyme inhibitors and improving their drug-likeness.

Porphyrin-Based Electrochemical H2 Evolution: Role of Central Metal Ion on Overpotential and Catalytic Activity

Various transition metal complexes of porphyrins, M-meso-tetrakis-(p-NH2phenyl)porphyrins [where M = Fe, Co, Ni, and Cu] have been synthesized and employed for electrochemical H2 evolution studies. The effects of nature of central metal ion in H2 evolution activity and overpotential were explored by conducting activity study in DMSO using organic acid and H2O as a proton source. In organic acid (trifluoroacetic acid, TFA), the catalysis occurs at a potential close to M2+/M1+ redox couple only for Co and Cu while at a more –ve potential (close to M1+/M0 redox event) for Fe and Ni with activity order of Co > Fe > Cu > Ni. At low acid concentration catalytic efficiency (C.E) of 85%, observed rate constant (kobs) of 240 s−1 and a current enhancement (Icat/Ip) of 29 are obtained for Co complex. In neutral aqueous solution, high activities were also observed for Co and Fe complexes than others. Based on our results, the redox potential of central metal ion and thermodynamic reduction potential of a proton source seem to play roles in tuning catalytic activity.

Anti-σ factor YlaD regulates transcriptional activity of σ factor YlaC and sporulation via manganese-dependent redox-sensing molecular switch in Bacillus subtilis.

YlaD, a membrane-anchored anti-sigma (σ) factor of Bacillus subtilis, contains a HX3CXXC motif that functions as a redox-sensing domain and belongs to one of the zinc (Zn)-co-ordinated anti-σ factor families. Despite previously showing that the YlaC transcription is controlled by YlaD, experimental evidence of how the YlaC-YlaD interaction is affected by active cysteines and/or metal ions is lacking. Here, we showed that the P yla promoter is autoregulated solely by YlaC. Moreover, reduced YlaD contained Zn and iron, while oxidized YlaD did not. Cysteine substitution in YlaD led to changes in its secondary structure; Cys3 had important structural functions in YlaD, and its mutation caused dissociation from YlaC, indicating the essential requirement of a HX3CXXC motif for regulating interactions of YlaC with YlaD. Analyses of the far-UV CD spectrum and metal content revealed that the addition of Mn ions to Zn-YlaD changed its secondary structure and that iron was substituted for manganese (Mn). The ylaC gene expression using βGlu activity from P yla :gusA was observed at the late-exponential and early-stationary phase, and the ylaC-overexpressing mutant constitutively expressed gene transcripts of clpP and sigH, an important alternative σ factor regulated by ClpXP. Collectively, our data demonstrated that YlaD senses redox changes and elicits increase in Mn ion concentrations and that, in turn, YlaD-mediated transcriptional activity of YlaC regulates sporulation initiation under oxidative stress and Mn-substituted conditions by regulating clpP gene transcripts. This is the first report of the involvement of oxidative stress-responsive B. subtilis extracytoplasmic function σ factors during sporulation via a Mn-dependent redox-sensing molecular switch.