Bleach activates a redox-regulated chaperone by oxidative protein unfolding

Functional diversity of YbbN/CnoX proteins: Insights from a comparative analysis of three thioredoxin-like oxidoreductases from Pseudomonas aeruginosa, Xylella fastidiosa and Escherichia coli

YbbN/CnoX are proteins that display a Thioredoxin (Trx) domain linked to a tetratricopeptide domain. YbbN from Escherichia coli (EcYbbN) displays a co-chaperone (holdase) activity that is induced by HOCl. Here, we compared EcYbbN with YbbN proteins from Xylella fastidiosa (XfYbbN) and from Pseudomonas aeruginosa (PaYbbN). EcYbbN presents a redox active Cys residue at Trx domain (Cys63), 24 residues away from SQHC motif (SQHC[N24]C) that can form mixed disulfides with target proteins. In contrast, XfYbbN and PaYbbN present two Cys residues in the CXXC (CAPC) motif, while only PaYbbN shows the Cys residue equivalent to Cys63 of EcYbbN. Our phylogenetic analysis revealed that most of the YbbN proteins are in the bacteria domain of life and that their members can be divided into four groups according to the conserved Cys residues. EcYbbN (SQHC[N24]C), XfYbbN (CAPC[N24]V) and PaYbbN (CAPC[N24]C) are representatives of three sub-families. In contrast to EcYbbN, both XfYbbN and PaYbbN: (1) reduced an artificial disulfide (DTNB) and (2) supported the peroxidase activity of Peroxiredoxin Q from X. fastidiosa, suggesting that these proteins might function similarly to the canonical Trx enzymes. Indeed, XfYbbN was reduced by XfTrx reductase with a high catalytic efficiency (kcat/Km = 1.27 x 107 M-1 s-1), similar to the canonical XfTrx (XfTsnC). Furthermore, EcYbbN and XfYbbN, but not PaYbbN displayed HOCl-induced holdase activity. Remarkably, EcYbbN gained disulfide reductase activity while lost the HOCl-activated chaperone function, when the SQHC was replaced by CQHC. In contrast, the XfYbbN CAPA mutant lost the disulfide reductase activity, while kept its HOCl-induced chaperone function. In all cases, the induction of the holdase activity was accompanied by YbbN oligomerization. Finally, we showed that deletion of ybbN gene did not render in P. aeruginosa more sensitive stressful treatments. Therefore, YbbN/CnoX proteins display distinct properties, depending on the presence of the three conserved Cys residues.

YabJ from Staphylococcus aureus entraps chlorides within its pocket

Chlorination is a potent disinfectant against various microorganisms, including bacteria and viruses, by inducing protein modifications and functional changes. Chlorine, in the form of sodium hypochlorite, stands out as the predominant sanitizer choice due to its cost-effectiveness and powerful antimicrobial properties. Upon exposure to chlorination, proteins undergo modifications, with amino acids experiencing alterations through the attachment of chloride or oxygen atoms. These modifications lead to shifts in protein function and the modulation of downstream signaling pathways, ultimately resulting in a bactericidal effect. However, certain survival proteins, such as chaperones or transcription factors, aid organisms in overcoming harsh chlorination conditions. The expression of YabJ, a highly conserved protein from Staphylococcus aureus, is regulated by a stress-activated sigma factor called sigma B (σB). This research revealed that S. aureus YabJ maintains its structural integrity even under intense chlorination conditions and harbors sodium hypochlorite molecules within its surface pocket. Notably, the pocket of S. aureus YabJ is primarily composed of amino acids less susceptible to chlorination-induced damage, rendering it resistant to such effects. This study elucidates how S. aureus YabJ evades the detrimental effects of chlorination and highlights its role in sequestering sodium hypochlorite within its structure. Consequently, this process enhances resilience and facilitates adaptation to challenging environmental conditions.

Resistance or tolerance? Highlighting the need for precise terminology in the field of disinfection

The terms resistance and tolerance are well defined in the context of antibiotic research. However, in the field of disinfection, these terms are often used synonymously, which creates ambiguity and can lead to misunderstandings and misconceptions. In addition, this inconsistency in terminology makes it difficult to assess the risk of a disinfectant resistance. This general review aims to discuss existing definitions of the terms adaptation, susceptibility, tolerance, persistence, and resistance in the light of disinfectants. The most ambiguity is found between tolerance and resistance. Whereas the former describes the not necessarily heritable survival of transient exposure to usually lethal concentrations, resistance is the strictly heritable ability to survive otherwise lethal concentrations of an antimicrobial agent, regardless of exposure time. A simple transfer of experience from antibiotic research is not recommended when assessing the risk of resistance to disinfectants, as there are important differences between antibiotics and disinfectants, although both are antimicrobials: (i) disinfectants are usually applied at concentrations that exceed the minimum inhibitory concentration by orders of magnitude, (ii) the exposure times of disinfectants are in the range of seconds, minutes, or a few hours, (iii) the mode of action of disinfectants is less specific, and (iv) disinfectants often contain more than one active agent with additive or synergistic effects. It is important to recognise that disinfectants, like other antimicrobial agents such as antibiotics, have a dualistic nature and should be used correctly and with caution.

Modern optical approaches in redox biology: Genetically encoded sensors and Raman spectroscopy

The objective of the current review is to summarize the current state of optical methods in redox biology. It consists of two parts, the first is dedicated to genetically encoded fluorescent indicators and the second to Raman spectroscopy. In the first part, we provide a detailed classification of the currently available redox biosensors based on their target analytes. We thoroughly discuss the main architecture types of these proteins, the underlying engineering strategies for their development, the biochemical properties of existing tools and their advantages and disadvantages from a practical point of view. Particular attention is paid to fluorescence lifetime imaging microscopy as a possible readout technique, since it is less prone to certain artifacts than traditional intensiometric measurements. In the second part, the characteristic Raman peaks of the most important redox intermediates are listed, and examples of how this knowledge can be implemented in biological studies are given. This part covers such fields as estimation of the redox states and concentrations of Fe-S clusters, cytochromes, other heme-containing proteins, oxidative derivatives of thiols, lipids, and nucleotides. Finally, we touch on the issue of multiparameter imaging, in which biosensors are combined with other visualization methods for simultaneous assessment of several cellular parameters.

Roles of Nucleic Acids in Protein Folding, Aggregation, and Disease

The role of nucleic acids in protein folding and aggregation is an area of continued research, with relevance to understanding both basic biological processes and disease. In this review, we provide an overview of the trajectory of research on both nucleic acids as chaperones and their roles in several protein misfolding diseases. We highlight key questions that remain on the biophysical and biochemical specifics of how nucleic acids have large effects on multiple proteins' folding and aggregation behavior and how this pertains to multiple protein misfolding diseases.

3D Printers in Hospitals: Bacterial Contamination of Common and Antimicrobial 3D-Printed Material

COVID-19 has presented hospitals with unique challenges. A SHEA Research Network survey showed that 40% reported "limited" or worse levels of personal protective equipment (PPE), and 13% were self-producing PPE to address those deficits, including 3D-printed items. However, we do not know how efficiently, if at all, 3D-printed materials can be disinfected. Additionally, two filaments, PLACTIVE and BIOGUARD, claim to be antimicrobial; they use copper nanocomposites and silver ions to reduce bacterial populations. We assess how PLACTIVE and BIOGUARD may be contaminated and how well they reduce contamination, and how readily Polylactic Acid (PLA), a standard 3D-printed material, may be disinfected. 3D-printed materials, including PLACTIVE and BIOGUARD, are readily contaminated with bacteria that are common in hospitals and can sustain that contamination. Our findings reveal that the levels of contamination on PLACTIVE and BIOGUARD can vary under specific conditions such as layer height or bacterial contact time, sometimes surpassing or falling short of PLA. However, disinfected disks had lower overall CFU averages than those that were not, but the level of disinfection was variable, and bacterial populations recovered hours after disinfection application. Proper disinfection and using appropriate 3D-printed materials are essential to limit bacterial contamination. 3D printers and their products can be invaluable for hospitals, especially when supplies are low, and healthcare worker safety is paramount. Environmental services should be made aware of the presence of antimicrobial 3D-printed materials, and patients should be discouraged from printing their own items for use in hospital environments.

Building an Understanding of Proteostasis in Reproductive Cells: The Impact of Reactive Carbonyl Species on Protein Fate

Significance: Stringent regulation of protein homeostasis pathways, under both physiological and pathological conditions, is necessary for the maintenance of proteome fidelity and optimal cell functioning. However, when challenged by endogenous or exogenous stressors, these proteostasis pathways can become dysregulated with detrimental consequences for protein fate, cell survival, and overall organism health. Most notably, there are numerous somatic pathologies associated with a loss of proteostatic regulation, including neurodegenerative disorders, type 2 diabetes, and some cancers. Recent Advances: Lipid oxidation-derived reactive carbonyl species (RCS), such as 4-hydroxynonenal (4HNE) and malondialdehyde, are relatively underappreciated purveyors of proteostatic dysregulation, which elicit their effects via the nonenzymatic post-translational modification of proteins. Emerging evidence suggests that a subset of germline proteins can serve as substrates for 4HNE modification. Among these, prevalent targets include succinate dehydrogenase, heat shock protein A2 and A-kinase anchor protein 4, all of which are intrinsically associated with fertility. Critical Issues: Despite growing knowledge in this field, the RCS adductomes of spermatozoa and oocytes are yet to be comprehensively investigated. Furthermore, the manner by which RCS-mediated adduction impacts protein fate and drives cellular responses, such as protein aggregation, requires further examination in the germline. Given that RCS-protein adduction has been attributed a role in infertility, there has been sparked research investment into strategies to prevent lipid peroxidation in germ cells. Future Directions: An increased depth of knowledge regarding the mechanisms and substrates of RCS-mediated protein modification in reproductive cells may reveal important targets for the development of novel therapies to improve fertility and pregnancy outcomes for future generations.

Hypochlorous acid derived from microglial myeloperoxidase could mediate high-mobility group box 1 release from neurons to amplify brain damage in cerebral ischemia-reperfusion injury

Myeloperoxidase (MPO) plays critical role in the pathology of cerebral ischemia-reperfusion (I/R) injury via producing hypochlorous acid (HOCl) and inducing oxidative modification of proteins. High-mobility group box 1 (HMGB1) oxidation, particularly disulfide HMGB1 formation, facilitates the secretion and release of HMGB1 and activates neuroinflammation, aggravating cerebral I/R injury. However, the cellular sources of MPO/HOCl in ischemic brain injury are unclear yet. Whether HOCl could promote HMGB1 secretion and release remains unknown. In the present study, we investigated the roles of microglia-derived MPO/HOCl in mediating HMGB1 translocation and secretion, and aggravating the brain damage and blood-brain barrier (BBB) disruption in cerebral I/R injury. In vitro, under the co-culture conditions with microglia BV cells but not the single culture conditions, oxygen-glucose deprivation/reoxygenation (OGD/R) significantly increased MPO/HOCl expression in PC12 cells. After the cells were exposed to OGD/R, MPO-containing exosomes derived from BV2 cells were released and transferred to PC12 cells, increasing MPO/HOCl in the PC12 cells. The HOCl promoted disulfide HMGB1 translocation and secretion and aggravated OGD/R-induced apoptosis. In vivo, SD rats were subjected to 2 h of middle cerebral artery occlusion (MCAO) plus different periods of reperfusion. Increased MPO/HOCl production was observed at the reperfusion stage, accomplished with enlarged infarct volume, aggravated BBB disruption and neurological dysfunctions. Treatment of MPO inhibitor 4-aminobenzoic acid hydrazide (4-ABAH) and HOCl scavenger taurine reversed those changes. HOCl was colocalized with cytoplasm transferred HMGB1, which was blocked by taurine in rat I/R-injured brain. We finally performed a clinical investigation and found that plasma HOCl concentration was positively correlated with infarct volume and neurological deficit scores in ischemic stroke patients. Taken together, we conclude that ischemia/hypoxia could activate microglia to release MPO-containing exosomes that transfer MPO to adjacent cells for HOCl production; Subsequently, the production of HOCl could mediate the translocation and secretion of disulfide HMGB1 that aggravates cerebral I/R injury. Furthermore, plasma HOCl level could be a novel biomarker for indexing brain damage in ischemic stroke patients.

The role of metals in hypothiocyanite resistance in Escherichia coli

The innate immune system employs a variety of antimicrobial oxidants to control and kill host-associated bacteria. Hypothiocyanite/hypothiocyanous acid (-OSCN/HOSCN) is one such antimicrobial oxidant that is synthesized by lactoperoxidase, myeloperoxidase, and eosinophil peroxidase at sites throughout the human body. HOSCN has potent antibacterial activity while being largely non-toxic towards human cells. The molecular mechanisms by which bacteria sense and defend themselves against HOSCN have only recently begun to be elaborated, notably by the discovery of bacterial HOSCN reductase (RclA), an HOSCN-degrading enzyme widely conserved among bacteria that live on epithelial surfaces. In this paper, I show that Ni2+ sensitizes Escherichia coli to HOSCN by inhibiting glutathione reductase, and that inorganic polyphosphate protects E. coli against this effect, probably by chelating Ni2+ ions. I also found that RclA is very sensitive to inhibition by Cu2+ and Zn2+, metals that are accumulated to high levels by innate immune cells, and that, surprisingly, thioredoxin and thioredoxin reductase are not involved in HOSCN stress resistance in E. coli. These results advance our understanding of the contribution of different oxidative stress response and redox buffering pathways to HOSCN resistance in E. coli and illustrate important interactions between metal ions and the enzymes bacteria use to defend themselves against oxidative stress.

Plasma-Droplet Fusion-Mass Spectrometry Reveals Sub-Millisecond Protein Unfolding Dynamics Induced by Reactive Oxygen Species

Investigating the connection between reactive oxygen species (ROS) and oxidative protein unfolding is critical to reveal the mechanisms underlying disease involving elevated ROS and protein misfolding. This could inform the development of therapeutics targeting cells based on their redox status. In this study, we developed a plasma-droplet fusion-mass spectrometry platform to rapidly assess protein resilience to ROS. This home-built system fuses ROS generated from the microplasma source with protein microdroplets from a tunable nanospray source. At the droplet-plasma intersection, ROS interact with proteins before entering the mass spectrometer for mass identification and structural characterization. Benefiting from the small-sized microdroplet with adjustable traveling velocity, the platform enables the first sub-millisecond kinetic study of ROS-induced protein unfolding, with a rate constant of approximately 1.81 ms-1. Capturing ROS-induced protein unfolding intermediates and the resultant ligand release dynamics can be extended to many more protein systems. We foresee broad applications for establishing previously undetected protein unfolding events when biologically impactful ROS are enriched in time and space with functional proteins and complexes.

Cationic fluorescent carbon dots with solution ultra-stability and its rapid/on-site sensing application for HClO

Carbon dots (CDs) as a remarkable fluorescent nanomaterial have the advantages of easy preparation, good photostability and high sensitivity. However, the poor aqueous solution stability of carbon dots largely limited their practical application due to the characteristic of easily forming precipitation for long time storage. Here, a kind of cationic fluorescent carbon dots CDs-P(Ph)3 was designed by introducing a cationic compound, (4-carboxybutyl) triphenyl phosphonium bromide, to construct an electrostatic shell outside the dots. Such electrostatic shell could highly improve carbon dots stability in an aqueous solution to make CDs-P(Ph)3 stable for long-term storage with negligible aggregation. Meanwhile, the sensitivity of CDs-P(Ph)3 for hypochlorous acid (HClO) was also enhanced on the basis of the electron-withdrawing effect of cationic substituents on the surface of carbon dots. The limit of detection of CDs-P(Ph)3 for HClO was as low as ∼0.32 μM. Additionally, the fluorescence of CDs-P(Ph)3 could be rapid quenched by HClO with a quenching efficiency of more than 80% within 30 s. The excellent stability of CDs-P(Ph)3 in an aqueous solution made it suitable for on-site detecting HClO in real samples, such as tap, well and lake water. Such designed fluorescent nanomaterial would provide a practical application pathway for optical sensing detection in environmental samples.

Depigmentation of Melanin-containing Tissues Using Hypochlorous Acid to Enhance Hematoxylin-eosin and Immunohistochemical Staining

Pathologists diagnose diseases by observing the histologic and cellular morphology microscopically. However, the high pigmentation in melanin-containing tumors can hide the tumor cell structures, making diagnosing challenging. Previously, hydrogen peroxide and potassium permanganate were utilized for melanin bleaching with several limitations. For instance, hydrogen peroxide has a weak bleaching ability, and the process is time-consuming (12 h). Meanwhile, potassium permanganate affects the antigenicity of antigens and is unsuitable for immunohistochemical (IHC) staining. In this study, the hypochlorous acid (HClO) solution was applied to hematoxylin-eosin and IHC staining of melanin tissue sections. The study discovered that 1% HClO could completely bleach melanin particles in tumor tissues in a short period (19.95 ± 2.53 min) without compromising the hematoxylin-eosin staining. In addition, 2% HClO was utilized for bleaching at room temperature for 61.17 ± 4.32 minutes after the tissue was incubated with 3,3'-diaminobenzidine in IHC staining. This treatment effectively removed melanin without negatively impacting 3,3'-diaminobenzidine signal expression, thus ensuring that the sections met the necessary diagnostic requirements. Therefore, this method could facilitate pathologists in disease diagnosis of melanin-containing tissues.

The neutrophil oxidant hypothiocyanous acid causes a thiol-specific stress response and an oxidative shift of the bacillithiol redox potential in Staphylococcus aureus

IMPORTANCE

Staphylococcus aureus colonizes the skin and the airways but can also lead to life-threatening systemic and chronic infections. During colonization and phagocytosis by immune cells, S. aureus encounters the thiol-reactive oxidant HOSCN. The understanding of the adaptation mechanisms of S. aureus toward HOSCN stress is important to identify novel drug targets to combat multi-resistant S. aureus isolates. As a defense mechanism, S. aureus uses the flavin disulfide reductase MerA, which functions as HOSCN reductase and protects against HOSCN stress. Moreover, MerA homologs have conserved functions in HOSCN detoxification in other bacteria, including intestinal and respiratory pathogens. In this work, we studied the comprehensive thiol-reactive mode of action of HOSCN and its effect on the reversible shift of the E BSH to discover new defense mechanisms against the neutrophil oxidant. These findings provide new leads for future drug design to fight the pathogen at the sites of colonization and infections.

Candida albicans resistance to hypochlorous acid

IMPORTANCE

Hypochlorous acid (HOCl), commonly known as bleach, is generated during the respiratory burst by phagocytes and is a key weapon used to attack Candida albicans and other microbial pathogens. However, the effects of hypochlorous acid on C. albicans have been less well studied than H2O2, a different type of oxidant produced by phagocytes. HOCl kills C. albicans more effectively than H2O2 and results in disruption of the plasma membrane. HOCl induced a very different transcriptional response than H2O2, and there were significant differences in the susceptibility of mutant strains of C. albicans to these oxidants. Altogether, these results indicate that HOCl has distinct effects on cells that could be targeted in novel therapeutic strategies to enhance the killing of C. albicans and other pathogens.

Antimicrobial Efficiency of Hypochlorous Acid and Its Effect on Some Properties of Alginate Impression Material

Dental clinicians and professionals need an affordable, nontoxic, and effective disinfectant against infectious microorganisms when dealing with the contaminated dental impressions. This study evaluated the efficiency of hypochlorous acid (HOCl) as an antimicrobial disinfectant by spraying technique for the alginate impression materials, compared with sodium hypochlorite, and its effect on dimensional stability and reproduction of details. HOCl with a concentration of 200 ppm for 5 and 10 min was compared with the control group (no treatment) as a negative control and with sodium hypochlorite (% 0.5) as a positive control. Candida albicans, Staphylococcus aureus, and Pseudomonas aeruginosa were selected to assess the antimicrobial activity with the colony forming unit test in addition to the dimensional stability and reproduction of details tests. The results revealed that HOCl had significant antimicrobial activity against all tested microorganisms and experimental time. Interestingly, HOCl showed no impact on the dimensional stability of alginate impression material. HOCl could be an effective antimicrobial agent for alginate impression material without interfering with their surface details and dimensional stability.

Expression of RcrB confers resistance to hypochlorous acid in uropathogenic Escherichia coli

To eradicate bacterial pathogens, neutrophils are recruited to the sites of infection, where they engulf and kill microbes through the production of reactive oxygen and chlorine species (ROS/RCS). The most prominent RCS is the antimicrobial oxidant hypochlorous acid (HOCl), which rapidly reacts with various amino acid side chains, including those containing sulfur and primary/tertiary amines, causing significant macromolecular damage. Pathogens like uropathogenic Escherichia coli (UPEC), the primary causative agent of urinary tract infections, have developed sophisticated defense systems to protect themselves from HOCl. We recently identified the RcrR regulon as a novel HOCl defense strategy in UPEC. Expression of the rcrARB operon is controlled by the HOCl-sensing transcriptional repressor RcrR, which is oxidatively inactivated by HOCl resulting in the expression of its target genes, including rcrB. The rcrB gene encodes a hypothetical membrane protein, deletion of which substantially increases UPEC's susceptibility to HOCl. However, the mechanism behind protection by RcrB is unclear. In this study, we investigated whether (i) its mode of action requires additional help, (ii) rcrARB expression is induced by physiologically relevant oxidants other than HOCl, and (iii) expression of this defense system is limited to specific media and/or cultivation conditions. We provide evidence that RcrB expression is sufficient to protect E. coli from HOCl. Furthermore, RcrB expression is induced by and protects from several RCS but not from ROS. RcrB plays a protective role for RCS-stressed planktonic cells under various growth and cultivation conditions but appears to be irrelevant for UPEC's biofilm formation. IMPORTANCE Bacterial infections pose an increasing threat to human health, exacerbating the demand for alternative treatments. Uropathogenic Escherichia coli (UPEC), the most common etiological agent of urinary tract infections (UTIs), are confronted by neutrophilic attacks in the bladder, and must therefore be equipped with powerful defense systems to fend off the toxic effects of reactive chlorine species. How UPEC deal with the negative consequences of the oxidative burst in the neutrophil phagosome remains unclear. Our study sheds light on the requirements for the expression and protective effects of RcrB, which we recently identified as UPEC's most potent defense system toward hypochlorous acid (HOCl) stress and phagocytosis. Thus, this novel HOCl stress defense system could potentially serve as an attractive drug target to increase the body's own capacity to fight UTIs.

Self-repair and resuscitation of viable injured bacteria in chlorinated drinking water: Achromobacter as an example

Chlorine disinfection for the treatment of drinking water can cause injury to the membrane and DNA of bacterial cells and may induce the surviving injured bacteria into a viable but non-culturable (VBNC) state. It is difficult to monitor viable injured bacteria by heterotrophic plate counting (HPC), and their presence is also easily miscalculated in flow cytometry intact cell counting (FCM-ICC). Viable injured bacteria have a potential risk of resuscitation in drinking water distribution systems (DWDSs) and pose a threat to public health when drinking from faucets. In this study, bacteria with injured membranes were isolated from chlorinated drinking water by FCM cell sorting. The culture rate of injured bacteria varied from 0.08% to 2.6% on agar plates and 0.39% to 6.5% in 96-well plates. As the dominant genus among the five identified genera, as well as an opportunistic pathogen with multiple antibiotic resistance, Achromobacter was selected and further studied. After treatment with chlorine at a concentration of 1.2 mg/L, Achromobacter entered into the intermediate injured state on the FCM plot, and the injury on the bacterial surface was observed by electron microscopy. However, the CTC respiratory activity assay showed that 75.0% of the bacteria were still physiologically active, and they entered into a VBNC state. The injured VBNC Achromobacter in sterile drinking water were resuscitated after approximately 25 h. The cellular repair behavior of injured bacteria was studied by Fourier transform infrared attenuated total reflectance (FTIR-ATR) and comet assays. It was found that DNA injury rather than membrane injury was repaired first. The expression of Ku and ligD increased significantly during the DNA repair period, indicating that non-homologous end-joining (NHEJ) played an important role in repairing DNA double-strand breaks. This study deepened the understanding of the effect of chlorine disinfection on bacterial viability in drinking water and will provide support for the improvement of the chlorine disinfection process for the treatment of drinking water.

The cold atmospheric pressure plasma-generated species superoxide, singlet oxygen and atomic oxygen activate the molecular chaperone Hsp33

Cold atmospheric pressure plasmas are used for surface decontamination or disinfection, e.g. in clinical settings. Protein aggregation has been shown to significantly contribute to the antibacterial mechanisms of plasma. To investigate the potential role of the redox-activated zinc-binding chaperone Hsp33 in preventing protein aggregation and thus mediating plasma resistance, we compared the plasma sensitivity of wild-type E. coli to that of an hslO deletion mutant lacking Hsp33 as well as an over-producing strain. Over-production of Hsp33 increased plasma survival rates above wild-type levels. Hsp33 was previously shown to be activated by plasma in vitro. For the PlasmaDerm source applied in dermatology, reversible activation of Hsp33 was confirmed. Thiol oxidation and Hsp33 unfolding, both crucial for Hsp33 activation, occurred during plasma treatment. After prolonged plasma exposure, however, unspecific protein oxidation was detected, the ability of Hsp33 to bind zinc ions was decreased without direct modifications of the zinc-binding motif, and the protein was inactivated. To identify chemical species of potential relevance for plasma-induced Hsp33 activation, reactive oxygen species were tested for their ability to activate Hsp33 in vitro. Superoxide, singlet oxygen and potentially atomic oxygen activate Hsp33, while no evidence was found for activation by ozone, peroxynitrite or hydroxyl radicals.

Functional changes of OsTrxm from reductase to molecular chaperone under heat shock stress

Ubiquitous disulfide reductases, thioredoxins (Trxs), function in the redox balance of all living organisms. Although the roles of the rice (Oryza sativa) Trx m-type isoform (OsTrxm) in chloroplast development have been already published, biochemical and molecular functions of OsTrxm remain to be elucidated for decades. The OsTrxm and its two conserved active cysteine mutant (OsTrxm C95S/C98S, referred to as OsTrxmC/S) proteins in Arabidopsis thaliana were overexpressed to characterize in vivo roles of active cysteines of OsTrxm. Interestingly, the OsTrxm overexpressed variant plants were resistant to heat shock treatment. Especially OsTrxmC/S with higher molecular weight (HMW) complexes showed higher heat tolerance than OsTrxm with lower molecular weight (LMW) structure in Arabidopsis thaliana. To confirm the importance of active cysteines on structural changes under heat stress, OsTrxm and OsTrxmC/S proteins were bacterially expressed and isolated. This study found that two proteins have various structures ranging from LMW to HMW complexes and have potential functions as a disulfide reductase and a molecular chaperone, which has never been reported anywhere. The function of molecular chaperone predominated in the HMW complexes, whereas the disulfide reductase function was observed in LMW forms. These results suggest that the active cysteines of OsTrxm play a critical role in protein structural change as well as heat tolerance in plants.

Conformational exchange at a C2H2 zinc-binding site facilitates redox sensing by the PML protein

The promyelocytic leukemia protein, PML, plays a vital role in the cellular response to oxidative stress; however, the molecular mechanism of its action remains poorly understood. Here, we identify redox-sensitive sites of PML. A molecule of PML is cysteine-rich and contains three zinc-binding domains including RING, B-box1, and B-box2. Using in vitro assays, we have compared the sensitivity of the isolated RING and B-box1 domains and shown that B-box1 is more sensitive to oxidation. NMR studies of PML dynamics showed that one of the Zn-coordination sites within the B-box1 undergoes significant conformational exchange, revealing a hotspot for exposure of reactive cysteines. In agreement with the in vitro data, enhancement of the B-box1 Zn-coordination dynamics led to more efficient recruitment of PML into PML nuclear bodies in cells. Overall, our results suggest that the increased sensitivity of B-box1 to oxidative stress makes this domain an important redox-sensing component of PML.

Surface Inactivation of a SARS-CoV-2 Surrogate with Hypochlorous Acid is Impacted by Surface Type, Contact Time, Inoculum Matrix, and Concentration

Indirect contact with contaminated surfaces is a potential transmission route for COVID-19. Therefore, it is necessary to investigate convenient and inexpensive surface sanitization methods, such as HOCl, against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The SARS-CoV-2 surrogate, Phi6 (~ 7 log PFU/mL), was prepared in artificial saliva and tripartite matrices, spot inoculated on coupons of either stainless steel or vinyl, and allowed to dry. The coupons were sprayed with either 500 ppm or 1000 ppm HOCl, and remained on the surface for 0 s (control), 5 s, 30 s, or 60 s. Samples were enumerated via the double agar overlay assay. Statistical analysis was completed in R using a generalized linear model with Quasipoisson error approximations. Time, concentration, surface type, and inoculum matrix were all significant contributors to log reduction at P = 0.05. Significant three-way interactions were observed for 1000 ppm, vinyl, and 60 s (P = 0.03) and 1000 ppm, tripartite, and 60 s (P = 0.0121). A significant two-way interaction between vinyl and 60 s was also observed (P = 0.0168). Overall, increased HOCl concentration and exposure time led to increased Phi6 reduction. Notably, the highest estimated mean log reduction was 3.31 (95% CI 3.14, 3.49) for stainless steel at 60 s and 1000 ppm HOCl in artificial saliva, indicating that this method of sanitization may not adequately reduce enveloped viruses to below infective thresholds.

Expression of RcrB confers resistance to hypochlorous acid in uropathogenic Escherichia coli

To eradicate bacterial pathogens, neutrophils are recruited to the sites of infection, where they engulf and kill microbes through the production of reactive oxygen and chlorine species (ROS/RCS). The most prominent RCS is antimicrobial oxidant hypochlorous acid (HOCl), which rapidly reacts with various amino acids side chains, including those containing sulfur and primary/tertiary amines, causing significant macromolecular damage. Pathogens like uropathogenic Escherichia coli (UPEC), the primary causative agent of urinary tract infections (UTIs), have developed sophisticated defense systems to protect themselves from HOCl. We recently identified the RcrR regulon as a novel HOCl defense strategy in UPEC. The regulon is controlled by the HOCl-sensing transcriptional repressor RcrR, which is oxidatively inactivated by HOCl resulting in the expression of its target genes, including rcrB . rcrB encodes the putative membrane protein RcrB, deletion of which substantially increases UPEC's susceptibility to HOCl. However, many questions regarding RcrB's role remain open including whether (i) the protein's mode of action requires additional help, (ii) rcrARB expression is induced by physiologically relevant oxidants other than HOCl, and (iii) expression of this defense system is limited to specific media and/or cultivation conditions. Here, we provide evidence that RcrB expression is sufficient to E. coli 's protection from HOCl and induced by and protects from several RCS but not from ROS. RcrB plays a protective role for RCS-stressed planktonic cells under various growth and cultivation conditions but appears to be irrelevant for UPEC's biofilm formation.

IMPORTANCE

Bacterial infections pose an increasing threat to human health exacerbating the demand for alternative treatment options. UPEC, the most common etiological agent of urinary tract infections (UTIs), are confronted by neutrophilic attacks in the bladder, and must therefore be well equipped with powerful defense systems to fend off the toxic effects of RCS. How UPEC deal with the negative consequences of the oxidative burst in the neutrophil phagosome remains unclear. Our study sheds light on the requirements for the expression and protective effects of RcrB, which we recently identified as UPEC's most potent defense system towards HOCl-stress and phagocytosis. Thus, this novel HOCl-stress defense system could potentially serve as an attractive drug target to increase the body's own capacity to fight UTIs.

Hypochlorite-induced oxidation promotes aggregation and reduces toxicity of amyloid beta 1-42

Exacerbated hypochlorite (OCl^-) production is linked to neurodegenerative processes, but there is growing evidence that lower levels of hypochlorite activity are important to protein homeostasis. In this study we characterise the effects of hypochlorite on the aggregation and toxicity of amyloid beta peptide 1-42 (Aβ_1-42), a major component of amyloid plaques that form in the brain in Alzheimer's disease. Our results demonstrate that treatment with hypochlorite promotes the formation of Aβ_1-42 assemblies ≥100 kDa that have reduced surface exposed hydrophobicity compared to the untreated peptide. This effect is the result of the oxidation of Aβ_1-42 at a single site as determined by mass spectrometry analysis. Although treatment with hypochlorite promotes the aggregation of Aβ_1-42, the solubility of the peptide is enhanced and amyloid fibril formation is inhibited as assessed by filter trap assay, thioflavin T assay and transmission electron microscopy. The results of in vitro assays using SH-SY5Y neuroblastoma cells show that pre-treatment of Aβ_1-42 with a sub-stoichiometric amount of hypochlorite substantially reduces its toxicity. The results of flow cytometry analysis and internalisation assays indicate that hypochlorite-induced modification of Aβ_1-42 reduces its toxicity via at least two-distinct mechanism, reducing the total binding of Aβ_1-42 to the surface of cells and facilitating the cell surface clearance of Aβ_1-42 to lysosomes. Our data is consistent with a model in which tightly regulated production of hypochlorite in the brain is protective against Aβ-induced toxicity.

Redox-regulated chaperones in cell stress responses

Proteostasis and redox homeostasis are tightly interconnected and most protein quality control pathways are under direct redox regulation which allow cells to immediately respond to oxidative stress conditions. The activation of ATP-independent chaperones serves as a first line of defense to counteract oxidative unfolding and aggregation of proteins. Conserved cysteine residues evolved as redox-sensitive switches which upon reversible oxidation induce substantial conformational rearrangements and the formation of chaperone-active complexes. In addition to harnessing unfolding proteins, these chaperone holdases interact with ATP-dependent chaperone systems to facilitate client refolding and restoring proteostasis during stress recovery. This minireview gives an insight into highly orchestrated mechanisms regulating the stress-specific activation and inactivation of redox-regulated chaperones and their role in cell stress responses.

Lysine and Arginine Reactivity and Transformation Products during Peptide Chlorination

Chlorine reactions with peptide-bound amino acids form disinfection byproducts and contribute to pathogen inactivation by degrading protein structure and function. Peptide-bound lysine and arginine are two of the seven chlorine-reactive amino acids, but their reactions with chlorine are poorly characterized. Using N-acetylated lysine and arginine as models for peptide-bound amino acids and authentic small peptides, this study demonstrated conversion of the lysine side chain to mono- and dichloramines and the arginine side chain to mono-, di-, and trichloramines in ≤0.5 h. The lysine chloramines formed lysine nitrile and lysine aldehyde at ∼6% yield over ∼1 week. The arginine chloramines formed ornithine nitrile at ∼3% yield over ∼1 week but not the corresponding aldehyde. While researchers hypothesized that the protein aggregation observed during chlorination arises from covalent Schiff base cross-links between lysine aldehyde and lysine on different proteins, no evidence for Schiff base formation was observed. The rapid formation of chloramines and their slow decay indicate that they are more relevant than the aldehydes and nitriles to byproduct formation and pathogen inactivation over timescales relevant to drinking water distribution. Previous research has indicated that lysine chloramines are cytotoxic and genotoxic to human cells. The conversion of lysine and arginine cationic side chains to neutral chloramines should alter protein structure and function and enhance protein aggregation by hydrophobic interactions, contributing to pathogen inactivation.

The MerR-family regulator NmlR is involved in the defense against oxidative stress in Streptococcus pneumoniae

Streptococcus pneumoniae has to cope with the strong oxidant hypochlorous acid (HOCl), during host-pathogen interactions. Thus, we analyzed the global gene expression profile of S. pneumoniae D39 towards HOCl stress. In the RNA-seq transcriptome, the NmlR, SifR, CtsR, HrcA, SczA and CopY regulons and the etrx1-ccdA1-msrAB2 operon were most strongly induced under HOCl stress, which participate in the oxidative, electrophile and metal stress response in S. pneumoniae. The MerR-family regulator NmlR harbors a conserved Cys52 and controls the alcohol dehydrogenase-encoding adhC gene under carbonyl and NO stress. We demonstrated that NmlR senses also HOCl stress to activate transcription of the nmlR-adhC operon. HOCl-induced transcription of adhC required Cys52 of NmlR in vivo. Using mass spectrometry, NmlR was shown to be oxidized to intersubunit disulfides or S-glutathionylated under oxidative stress in vitro. A broccoli-FLAP-based assay further showed that both NmlR disulfides significantly increased transcription initiation at the nmlR promoter by RNAP in vitro, which depends on Cys52. Phenotype analyses revealed that NmlR functions in the defense against oxidative stress and promotes survival of S. pneumoniae during macrophage infections. In conclusion, NmlR was characterized as HOCl-sensing transcriptional regulator, which activates transcription of adhC under oxidative stress by thiol switches in S. pneumoniae.

Roles of methionine and cysteine residues of the Escherichia coli sensor kinase HprS in reactive chlorine species sensing

Sensor histidine kinase HprS, an oxidative stress sensor of Escherichia coli, senses reactive oxygen species (ROS) and reactive chlorine species (RCS), and is involved in the induction of oxidatively damaged protein repair periplasmic enzymes. We reinvestigated the roles of six methionine and four cysteine residues of HprS in the response to HClO, an RCS. The results of site-directed mutagenesis revealed that methionine residues in periplasmic and cytoplasmic regions (Met225) are involved in HprS activation. Interestingly, the Cys165Ser substitution reduced HprS activity, which was recovered by an additional Glu22Cys substitution. Our results demonstrate that the position of the inner membrane cysteine residues influences the extent of HprS activation in HClO sensing.

Activity of a hypochlorous acid-producing electrochemical bandage as assessed with a porcine explant biofilm model

The activity of a hypochlorous acid-producing electrochemical bandage (e-bandage) in preventing methicillin-resistant Staphylococcus aureus infection (MRSA) infection and removing biofilms formed by MRSA was assessed using a porcine explant biofilm model. e-Bandages inhibited S. aureus infection (p = 0.029) after 12 h (h) of exposure and reduced 3-day biofilm viable cell counts after 6, 12, and 24 h exposures (p = 0.029). Needle-type microelectrodes were used to assess HOCl concentrations in explant tissue as a result of e-bandage treatment; toxicity associated with e-bandage treatment was evaluated. HOCl concentrations in infected and uninfected explant tissue varied between 30 and 80 µM, decreasing with increasing distance from the e-bandage. Eukaryotic cell viability was reduced by an average of 71% and 65% in fresh and day 3-old explants, respectively, when compared to explants exposed to nonpolarized e-bandages. HOCl e-bandages are a promising technology that can be further developed as an antibiotic-free treatment for wound biofilm infections.

HslO ameliorates arrested ΔrecA polA cell growth and reduces DNA damage and oxidative stress responses

Chromosome damage combined with defective recombinase activity has been widely considered to render cells inviable, owing to deficient double-strand break repair. However, temperature-sensitive recAts polA cells grow well upon induction of DNA damage and supplementation with catalase at restrictive temperatures. These treatments reduce intracellular reactive oxygen species (ROS) levels, which suggests that recAts polA cells are susceptible to ROS, but not chronic chromosome damage. Therefore, we investigated whether polA cells can tolerate a complete lack of recombinase function. We introduced a ΔrecA allele in polA cells in the presence or absence of the hslO-encoding redox molecular chaperon Hsp33 expression plasmid. Induction of the hslO gene with IPTG resulted in increased cell viability in ΔrecA polA cells with the hslO expression plasmid. ΔrecA polA cells in the absence of the hslO expression plasmid showed rich medium sensitivity with increasing ROS levels. Adding catalase to the culture medium considerably rescued growth arrest and decreased ROS. These results suggest that hslO expression manages oxidative stress to an acceptable level in cells with oxidative damage and rescues cell growth. Overall, ROS may regulate several processes, from damage response to cell division, via ROS-sensitive cell metabolism.

The MarR/DUF24-Family QsrR Repressor Senses Quinones and Oxidants by Thiol Switch Mechanisms in Staphylococcus aureus

Aims: The MarR/DUF24-family QsrR and YodB repressors control quinone detoxification pathways in Staphylococcus aureus and Bacillus subtilis. In S. aureus, the QsrR regulon also confers resistance to antimicrobial compounds with quinone-like elements, such as rifampicin, ciprofloxacin, and pyocyanin. Although QsrR was shown to be inhibited by thiol-S-alkylation of its conserved Cys4 residue by 1,4-benzoquinone, YodB senses quinones and diamide by the formation of reversible intermolecular disulfides. In this study, we aimed at further investigating the redox-regulation of QsrR and the role of its Cys4, Cys29, and Cys32 residues under quinone and oxidative stress in S. aureus. Results: The QsrR regulon was strongly induced by quinones and oxidants, such as diamide, allicin, hypochlorous acid (HOCl), and AGXX^® in S. aureus. Transcriptional induction of catE2 by quinones and oxidants required Cys4 and either Cys29' or Cys32' of QsrR for redox sensing in vivo. DNA-binding assays revealed that QsrR is reversibly inactivated by quinones and oxidants, depending on Cys4. Using mass spectrometry, QsrR was shown to sense diamide by an intermolecular thiol-disulfide switch, involving Cys4 and Cys29' of opposing subunits in vitro. In contrast, allicin caused S-thioallylation of all three Cys residues in QsrR, leading to its dissociation from the operator sequence. Further, the QsrR regulon confers resistance against quinones and oxidants, depending on Cys4 and either Cys29' or Cys32'. Conclusion and Innovation: QsrR was characterized as a two-Cys-type redox-sensing regulator, which senses the oxidative mode of quinones and strong oxidants, such as diamide, HOCl, and the antimicrobial compound allicin via different thiol switch mechanisms.

The Catalase KatA Contributes to Microaerophilic H2O2 Priming to Acquire an Improved Oxidative Stress Resistance in Staphylococcus aureus

Staphylococcus aureus has to cope with oxidative stress during infections. In this study, S. aureus was found to be resistant to 100 mM H₂O₂ during aerobic growth. While KatA was essential for this high aerobic H₂O₂ resistance, the peroxiredoxin AhpC contributed to detoxification of 0.4 mM H₂O₂ in the absence of KatA. In addition, the peroxiredoxins AhpC, Tpx and Bcp were found to be required for detoxification of cumene hydroperoxide (CHP). The high H₂O₂ tolerance of aerobic S. aureus cells was associated with priming by endogenous H₂O₂ levels, which was supported by an oxidative shift of the bacillithiol redox potential to −291 mV compared to −310 mV in microaerophilic cells. In contrast, S. aureus could be primed by sub-lethal doses of 100 µM H₂O₂ during microaerophilic growth to acquire an improved resistance towards the otherwise lethal triggering stimulus of 10 mM H₂O₂. This microaerophilic priming was dependent on increased KatA activity, whereas aerobic cells showed constitutive high KatA activity. Thus, KatA contributes to the high H₂O₂ resistance of aerobic cells and to microaerophilic H₂O₂ priming in order to survive the subsequent lethal triggering doses of H₂O₂, allowing the adaptation of S. aureus under infections to different oxygen environments.

Redox-Mediated Inactivation of the Transcriptional Repressor RcrR is Responsible for Uropathogenic Escherichia coli's Increased Resistance to Reactive Chlorine Species

The ability to overcome stressful environments is critical for pathogen survival in the host. One challenge for bacteria is the exposure to reactive chlorine species (RCS), which are generated by innate immune cells as a critical part of the oxidative burst. Hypochlorous acid (HOCl) is the most potent antimicrobial RCS and is associated with extensive macromolecular damage in the phagocytized pathogen. However, bacteria have evolved defense strategies to alleviate the effects of HOCl-mediated damage. Among these are RCS-sensing transcriptional regulators that control the expression of HOCl-protective genes under non-stress and HOCl stress. Uropathogenic Escherichia coli (UPEC), the major causative agent of urinary tract infections (UTIs), is particularly exposed to infiltrating neutrophils during pathogenesis; however, their responses to and defenses from HOCl are still completely unexplored. Here, we present evidence that UPEC strains tolerate higher levels of HOCl and are better protected from neutrophil-mediated killing compared with other E. coli. Transcriptomic analysis of HOCl-stressed UPEC revealed the upregulation of an operon consisting of three genes, one of which encodes the transcriptional regulator RcrR. We identified RcrR as a HOCl-responsive transcriptional repressor, which, under non-stress conditions, is bound to the operator and represses the expression of its target genes. During HOCl exposure, however, the repressor forms reversible intermolecular disulfide bonds and dissociates from the DNA resulting in the derepression of the operon. Deletion of one of the target genes renders UPEC significantly more susceptible to HOCl and phagocytosis indicating that the HOCl-mediated induction of the regulon plays a major role for UPEC’s HOCl resistance.

A systematic review on chlorine tolerance among bacteria and standardization of their assessment protocol in wastewater

Though chlorine is a cost-effective disinfectant for water and wastewaters, the bacteria surviving after chlorination pose serious public health and environmental problems. This review critically assesses the mechanism of chlorine disinfection as described by various researchers; factors affecting chlorination efficacy; and the re-growth potential of microbial contaminations in treated wastewater post chlorination to arrive at meaningful doses for ensuring health safety. Literature analysis shows procedural inconsistencies in the assessment of chlorine tolerant bacteria, making it extremely difficult to compare the tolerance characteristics of different reported tolerant bacteria. A comparison of logarithmic reduction after chlorination and the concentration-time values for prominent pathogens led to the generation of a standard protocol for the assessment of chlorine tolerance. The factors that need to be critically monitored include applied chlorine doses, contact time, determination of chlorine demands of the medium, and the consideration of bacterial counts immediately after chlorination and in post chlorinated samples (regrowth). The protocol devised here appropriately assesses the chlorine-tolerant bacteria and urges the scientific community to report the regrowth characteristics as well. This would increase the confidence in data interpretation that can provide a better understanding of chlorine tolerance in bacteria and aid in formulating strategies for effective chlorination.

Diversity, Antimicrobial Activity, and Antibiotic Susceptibility Pattern of Endophytic Bacteria Sourced From Cordia dichotoma L

Endophytic bacteria isolated from medicinal plants are crucial for the production of antimicrobial agents since they are capable of possessing bioactive compounds with diverse structures and activities. Cordia dichotoma, a plant of medicinal importance native to the Jammu region of India, was selected for the isolation and characterization of culturable endophytic bacteria and evaluation of their antimicrobial activities. Standardized surface sterilization methods were employed to isolate thirty-three phenotypically distinguishable endophytic bacteria from the root, stem, and leaf parts of the plant. Shannon Wiener diversity index clearly divulged diverse endophytes in roots (0.85), stem (0.61), and leaf (0.54) tissues. Physio-biochemical features of the isolates differentiated the distinct variations in their carbohydrate utilization profile and NaCl tolerance. The endophytes produced an array of enzymes, namely, catalase, oxidase, amylase, cellulase, nitrate reductase, and lipase. The bacterial isolates belong to the genera Bacillus, Pseudomonas, Paenibacillus, Acidomonas, Streptococcus, Ralstonia, Micrococcus, Staphylococcus, and Alcalignes predominantly. However, the antibiotic susceptibility pattern indicated that the isolates were mostly sensitive to erythromycin and streptomycin, while they were resistant to rifampicin, amoxicillin, and bacitracin. Interestingly, majority of the bacterial endophytes of C. dichotoma showed antimicrobial activity against Bacillus subtilis followed by Klebsiella pneumoniae. The 16S rRNA sequence of Bacillus thuringiensis has been deposited in the NCBI GenBank database under accession number OM320575. The major compounds of the crude extract derived from endophytic B. thuringiensis OM320575, according to the metabolic profile examination by GC-MS, are dibutyl phthalate, eicosane, tetrapentacontane, heneicosane, and hexadecane, which possessed antibacterial activities. In conclusion, results indicated the potential of C. dichotoma to host a plethora of bacterial endophytes that produce therapeutic bioactive metabolites.

An increase in surface hydrophobicity mediates chaperone activity in N-chlorinated RidA

Under physiological conditions, Escherichia coli RidA is an enamine/imine deaminase, which promotes the release of ammonia from reactive enamine/imine intermediates. However, when modified by hypochlorous acid (HOCl), it turns into a potent chaperone-like holdase that can effectively protect E. coli's proteome during oxidative stress. However, it is unknown, which residues need to be chlorinated for activation. Here, we employ a combination of LC-MS/MS analysis, a chemo-proteomic approach, and a mutagenesis study to identify residues responsible for RidA's chaperone-like function. Through LC-MS/MS of digested RidA_HOCl, we obtained direct evidence of the chlorination of one arginine residue. To overcome the instability of the N-chloramine modification, we established a chemoproteomic approach using 5-(dimethylamino) naphthalene-1-sulfinic acid (DANSO₂H) as a probe to label N-chlorinated lysines. Using this probe, we were able to detect the N-chlorination of six additional lysine residues. Moreover, using a mutagenesis study to genetically probe the role of single arginine and lysine residues, we found that the removal of arginines R105 and/or R128 led to a substantial reduction of RidA_HOCl's chaperone activity. These results, together with structural analysis, confirm that the chaperone activity of RidA is concomitant with the loss of positive charges on the protein surface, leading to an increased overall protein hydrophobicity. Molecular modelling of RidA_HOCl and the rational design of a RidA variant that shows chaperone activity even in the absence of HOCl further supports our hypothesis. Our data provide a molecular mechanism for HOCl-mediated chaperone activity found in RidA and a growing number of other HOCl-activated chaperones.

Copper Induces Protein Aggregation, a Toxic Process Compensated by Molecular Chaperones

Copper is well known for its antimicrobial and antiviral properties. Under aerobic conditions, copper toxicity relies in part on the production of reactive oxygen species (ROS), especially in the periplasmic compartment. However, copper is significantly more toxic under anaerobic conditions, in which ROS cannot be produced. This toxicity has been proposed to arise from the inactivation of proteins through mismetallations. Here, using the bacterium Escherichia coli, we discovered that copper treatment under anaerobic conditions leads to a significant increase in protein aggregation. In vitro experiments using E. coli lysates and tightly controlled redox conditions confirmed that treatment with Cu⁺ under anaerobic conditions leads to severe ROS-independent protein aggregation. Proteomic analysis of aggregated proteins revealed an enrichment of cysteine- and histidine-containing proteins in the Cu⁺-treated samples, suggesting that nonspecific interactions of Cu⁺ with these residues are likely responsible for the observed protein aggregation. In addition, E. coli strains lacking the cytosolic chaperone DnaK or trigger factor are highly sensitive to copper stress. These results reveal that bacteria rely on these chaperone systems to protect themselves against Cu-mediated protein aggregation and further support our finding that Cu toxicity is related to Cu-induced protein aggregation. Overall, our work provides new insights into the mechanism of Cu toxicity and the defense mechanisms that bacteria employ to survive.

Formation of Calprotectin-Derived Peptides in the Airways of Children with Cystic Fibrosis

Calprotectin is released by activated neutrophils along with myeloperoxidase (MPO) and proteases. It plays numerous roles in inflammation and infection, and is used as an inflammatory biomarker. However, calprotectin is readily oxidized by MPO-derived hypohalous acids to form covalent dimers of its S100A8 and S100A9 subunits. The dimers are susceptible to degradation by proteases. We show that detection of human calprotectin by ELISA declines markedly because of its oxidation by hypochlorous acid and subsequent degradation. Also, proteolysis liberates specific peptides from oxidized calprotectin that is present at inflammatory sites. We identified six calprotectin-derived peptides by mass spectrometry and detected them in the bronchoalveolar lavage fluid of children with cystic fibrosis (CF). We assessed the peptides as biomarkers of neutrophilic inflammation and infection. The content of the calprotectin peptide ILVI was related to calprotectin (r = 0.72, p = 0.01, n = 10). Four of the peptides were correlated with the concentration of MPO (r > 0.7, p ≤ 0.01, n = 21), while three were higher (p < 0.05) in neutrophil elastase-positive (n = 14) than -negative samples (n = 7). Also, five of the peptides were higher (p < 0.05) in the bronchoalveolar lavage fluid from children with CF with infections (n = 21) than from non-CF children without infections (n = 6). The specific peptides liberated from calprotectin will signal uncontrolled activity of proteases and MPO during inflammation. They may prove useful in tracking inflammation in respiratory diseases dominated by neutrophils, including coronavirus disease 2019.

Molecular Characterization of an Intrinsically Disordered Chaperone Reveals Net-Charge Regulation in Chaperone Action

Molecular chaperones are diverse biomacromolecules involved in the maintenance of cellular protein homeostasis (proteostasis). Here we demonstrate that in contrast to most chaperones with defined three-dimensional structures, the acid-inducible protein Asr in Escherichia coli is intrinsically disordered and exhibits varied aggregation-preventing or aggregation-promoting activities, acting as a "conditionally active chaperone". Bioinformatics and experimental analyses of Asr showed that it is devoid of hydrophobic patches but rich in positive charges and local polyproline II backbone structures. Asr contributes to the integrity of the bacterial outer membrane under mildly acidic conditions in vivo and possesses chaperone activities toward model clients in vitro. Notably, its chaperone activity is dependent on the net charges of clients: on the one hand, it inhibits the aggregation of clients with similar net charges; on the other hand, it stimulates the aggregation of clients with opposite net charges. Mutational analysis confirmed that positively charged residues in Asr are essential for the varied effects on protein aggregation, suggesting that electrostatic interactions are the major driving forces underlying Asr's proteostasis-related activity. These findings present a unique example of an intrinsically disordered molecular chaperone with distinctive dual functions-as an aggregase or as a chaperone-depending on the net charges of clients.

Synergistic interaction of tap water-based neutral electrolyzed water combined with UVA irradiation to enhance microbial inactivation on stainless steel

As an emerging electrolyzed water (EW) technology, tap water-based neutral electrolyzed water (TNEW) is an attractive alternative to other types of conventional EW for sterilization of food contact surfaces. In this study, we sought to identify strategies for improving TNEW inactivation efficiencies of major foodborne pathogenic bacteria. We investigated the synergistic antimicrobial effect of TNEW and ultraviolet-A light (UVA) combination treatment against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on stainless steel. The data confirmed that simultaneous TNEW and UVA treatment for 60 min reduced E. coli O157:H7, S. Typhimurium, and L. monocytogenes population by 2.15, 1.55, and 2.65 log CFU/cm², respectively. The synergistic cell count reductions in E. coli O157:H7, S. Typhimurium, and L. monocytogenes in the combination treatment group were 1.17, 0.59, and 1.62 log units, respectively. Additionally, the mechanisms of the synergistic bactericidal effects of TNEW and UVA were identified through several approaches. Mechanistic investigations suggested that the synergistic effect was associated with intracellular reactive oxygen species generation, bacterial cell membrane damage, and inactivation of dehydrogenase. These findings demonstrate that treatment with TNEW and UVA light can enhance the microbiological safety of food contact surfaces during food processing.

Molecular Effects of Elongation Factor Ts and Trigger Factor on the Unfolding and Aggregation of Elongation Factor Tu Induced by the Prokaryotic Molecular Chaperone Hsp33

Simple Summary

Proteins are versatile biological macromolecules involved in most biological processes. However, because of the highly labile nature of protein structures, protein quality control (PQC) to ensure proteostasis (i.e., protein homeostasis)is difficult. Therefore, proteins of a specialized class (i.e., molecular chaperones) are required that assist in proper folding and prevent aberrant folding of other proteins. Hsp33 was originally discovered as a holding chaperone that is overexpressed upon heat shock and activated by oxidation to prevent the misfolding of client proteins. Recently, an unfoldase/aggregase activity of Hsp33 was identified in its reduced state against a specific substrate, EF-Tu, which plays a key role in protein biosynthesis in cells. The present study demonstrates that EF-Tu unfolding/aggregation by Hsp33 can be accelerated by another molecular chaperone trigger factor. Given that the unfolded/aggregated EF-Tu is finally degraded by another chaperone, Lon protease, it is likely that a chaperone network dysregulating EF-Tu operates in heat shock to attenuate protein biosynthesis, which is harmful to cell survival under stressed conditions. Therefore, the apparently contradictory chaperone function (i.e., promotion of client misfolding) of Hsp33 can also be associated with the PQC processes to ensure proteostasis in cells.

Abstract

Hsp33, a prokaryotic redox-regulated holding chaperone, has been recently identified to be able to exhibit an unfoldase and aggregase activity against elongation factor Tu (EF-Tu) in its reduced state. In this study, we investigated the effect of elongation factor Ts (EF-Ts) and trigger factor (TF) on Hsp33-mediated EF-Tu unfolding and aggregation using gel filtration, light scattering, circular dichroism, and isothermal titration calorimetry. We found that EF-Tu unfolding and subsequent aggregation induced by Hsp33 were evident even in its complex state with EF-Ts, which enhanced EF-Tu stability. In addition, although TF alone had no substantial effect on the stability of EF-Tu, it markedly amplified the Hsp33-mediated EF-Tu unfolding and aggregation. Collectively, the present results constitute the first example of synergistic unfoldase/aggregase activity of molecular chaperones and suggest that the stability of EF-Tu is modulated by a sophisticated network of molecular chaperones to regulate protein biosynthesis in cells under stress conditions.

Oxidative Stress Response in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a Gram-negative environmental and human opportunistic pathogen highly adapted to many different environmental conditions. It can cause a wide range of serious infections, including wounds, lungs, the urinary tract, and systemic infections. The high versatility and pathogenicity of this bacterium is attributed to its genomic complexity, the expression of several virulence factors, and its intrinsic resistance to various antimicrobials. However, to thrive and establish infection, P. aeruginosa must overcome several barriers. One of these barriers is the presence of oxidizing agents (e.g., hydrogen peroxide, superoxide, and hypochlorous acid) produced by the host immune system or that are commonly used as disinfectants in a variety of different environments including hospitals. These agents damage several cellular molecules and can cause cell death. Therefore, bacteria adapt to these harsh conditions by altering gene expression and eliciting several stress responses to survive under oxidative stress. Here, we used PubMed to evaluate the current knowledge on the oxidative stress responses adopted by P. aeruginosa. We will describe the genes that are often differently expressed under oxidative stress conditions, the pathways and proteins employed to sense and respond to oxidative stress, and how these changes in gene expression influence pathogenicity and the virulence of P. aeruginosa. Understanding these responses and changes in gene expression is critical to controlling bacterial pathogenicity and developing new therapeutic agents.

Hypochlorous acid solution is a potent antiviral agent against SARS-CoV-2

Aim

A novel coronavirus, termed severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) suddenly appeared in Wuhan, China, and has caused pandemic. In this study, we evaluated antiviral activity of purified hypochlorous acid (HClO) against coronaviruses such as SARS‐CoV‐2 and transmissible gastroenteritis virus (TGEV) responsible for pig diseases.

Materials and Results

In a suspension test, 28.1 ppm HClO solution inactivated SARS‐CoV‐2 in phosphate‐buffered saline with the reduction of 10⁴ of 50% tissue culture infectious dose per ml (TCID₅₀ per ml) within 10 s. When its concentration increased to 59.4 ppm, the virus titre decreased to below the detection limit (reduction of 5 logs TCID₅₀) within 10 s even in the presence of 0.1% foetal bovine serum. In a carrier test, incubation with 125 ppm HClO solution for 10 min or 250 ppm for 5 min inactivated SARS‐CoV‐2 by more than 4 logs TCID₅₀ per ml or below the detection limit. Because the titre of TGEV was 10‐fold higher, TGEV was used for SARS‐CoV‐2 in a suspension test. As expected, 56.3 ppm HClO solution inactivated TGEV by 6 logs TCID₅₀ within 30 s.

Conclusions

In a carrier test, 125 ppm HClO solution for 10 min incubation is adequate to inactivate 4 logs TCID₅₀ per ml of SARS‐CoV‐2 or more while in a suspension test 56.3 ppm HClO is adequate to inactivate 5 logs TCID₅₀ per ml of SARS‐CoV‐2 when incubated for only 10 s regardless of presence or absence of organic matter.

Significance and Impact of the Study

Effectiveness of HClO solution against SARS‐CoV‐2 was demonstrated by both suspension and carrier tests. HClO solution inactivated SARS‐CoV‐2 by 5 logs TCID₅₀ within 10 s. HClO solution has several advantages such as none toxicity, none irritation to skin and none flammable. Thus, HClO solution can be used as a disinfectant for SARS‐CoV‐2.

Exploration of correlation of oral hygiene and condition with influenza infection

Influenza viruses are known to be infected through epithelial cells of the upper respiratory tract. The oral cavity is in close anatomical proximity to the upper respiratory tract, and it is conceivable that the viruses could pass through the oral cavity and infect to the upper respiratory tract. Several researchers have suggested that colonization of certain pathogenic bacteria such as Staphylococcus aureus or Streptococcus pneumoniae might affect the risk of influenza viral disease, indicating that oral hygiene and/or condition might play an important role in respiratory viral infection. Therefore, the purpose of this study was to investigate whether an oral hygiene/condition might impact influenza infection. We conducted a retrospective observational study of Japanese citizens' regional cohort (N = 2,904) consisting of National Health Insurance beneficiaries who underwent annual health/dental examination with data entries in the Kokuho database (KDB). Trained dentists checked the oral hygiene/condition, and saliva specimens were examined using the LION dental saliva multi-test (SMT) kit. Influenza infection was identified from the diagnosis recorded in the KDB. The correlations between influenza infection and oral hygiene, dryness of the mouth, or various salivary test results were examined by a multivariate analysis adjusting for confounding factors such as gender, age, recent smoking, alcohol drinking, BMI, HbA1c, RBC for influenza infection. The logistic regression model showed that age significantly correlated with influenza infection. In addition, oral hygiene status had a nearly significant impact on influenza infection (p = 0.061), whereby, the subjects with poor oral hygiene had a higher risk of influenza infection than those with good oral hygiene (odds ratio: 1.63, 95% confidence interval: 0.89-2.95). Further, the prevalence of influenza infection was lower in the subjects with saliva weakly acidic and/or containing higher protein level. The results of this study suggested that the maintenance of oral health conditions might be one of the pivotal factors for preventing and reducing influenza infection.

Efficacy of Hypochlorite as a Disinfestant Against Fungal Pathogens in Agricultural and Horticultural Plant Production: A Systematic Review and Meta-Analysis

Hypochlorite is often used as a disinfestant of fungal pathogens in a range of agricultural and horticultural settings. However, reports of its effectiveness are variable across studies and it is unclear what factors could potentially influence the reported estimates of its efficacy. A systematic review and meta-analysis was conducted to assess the efficacy of hypochlorite against fungal pathogens and explore factors that may explain the observed heterogeneity in estimates of efficacy. Standardized mean effect size, Hedges' g, was calculated for each of the 109 selected studies, published from 1972 to 2019, that met the criteria defined for the systematic review. A random-effects model was used to estimate the overall mean effect size ([Formula: see text]) and determine the heterogeneity in g among studies. Hypochlorite resulted in a significant (P < 0.001) reduction in either disease intensity or propagule viability with [Formula: see text]= 2.25, suggesting a large overall effect. However, 95% prediction intervals ranged from -0.18 to 4.68, indicating that hypochlorite could be ineffective against some fungi or when targeting some substrate materials. An estimate of the within-study variability, τ², was 1.48 and the proportion of heterogeneity in g among studies due to true effects was 71.5%. Inclusion of categorical moderator variables in the random effects model showed that hypochlorite treatments were significantly (P < 0.0062) more effective when used to disinfest spores in an aqueous solution ([Formula: see text]= 4.58) than when used on plastic ([Formula: see text]= 2.13), plant ([Formula: see text]= 2.13), and wood ([Formula: see text]= 0.79). Similarly, hypochlorite treatments were significantly (P < 0.0083) more effective in disinfesting fungal propagules of Thielaviopsis spp. ([Formula: see text]= 2.51) than those of Verticillium spp. ([Formula: see text]= 1.21). A meta-regression indicated that the effect of dose (β = -3.54; P = 0.0398) and contact time (β = -0.05; P = 0.0001) on [Formula: see text] were highly significant. Further, [Formula: see text]was significantly affected by the dose × time interaction (β = -0.017; P = 0.0269). In the meta-regression models, dose and time explained 0 and 16% of the variance in true effects, respectively. In meta-regression models with a continuous variable of dose or time, a categorical variable of target or genus and their interaction term, genus and target explained an additional 7 to 19% of the variance in true effects. These results show that although the current recommended dose and contact time for commercial bleach products are expected to result in effective disinfestation, the target material and genera of the fungal pathogen of interest will likely influence their efficacy.

The Central Role of Redox-Regulated Switch Proteins in Bacteria

Bacteria possess the ability to adapt to changing environments. To enable this, cells use reversible post-translational modifications on key proteins to modulate their behavior, metabolism, defense mechanisms and adaptation of bacteria to stress. In this review, we focus on bacterial protein switches that are activated during exposure to oxidative stress. Such protein switches are triggered by either exogenous reactive oxygen species (ROS) or endogenous ROS generated as by-products of the aerobic lifestyle. Both thiol switches and metal centers have been shown to be the primary targets of ROS. Cells take advantage of such reactivity to use these reactive sites as redox sensors to detect and combat oxidative stress conditions. This in turn may induce expression of genes involved in antioxidant strategies and thus protect the proteome against stress conditions. We further describe the well-characterized mechanism of selected proteins that are regulated by redox switches. We highlight the diversity of mechanisms and functions (as well as common features) across different switches, while also presenting integrative methodologies used in discovering new members of this family. Finally, we point to future challenges in this field, both in uncovering new types of switches, as well as defining novel additional functions.

A Bacterial Inflammation Sensor Regulates c-di-GMP Signaling, Adhesion, and Biofilm Formation

Bacteria that colonize animals must overcome, or coexist, with the reactive oxygen species products of inflammation, a front-line defense of innate immunity. Among these is the neutrophilic oxidant bleach, hypochlorous acid (HOCl), a potent antimicrobial that plays a primary role in killing bacteria through nonspecific oxidation of proteins, lipids, and DNA. Here, we report that in response to increasing HOCl levels, Escherichia coli regulates biofilm production via activation of the diguanylate cyclase DgcZ. We identify the mechanism of DgcZ sensing of HOCl to be direct oxidation of its regulatory chemoreceptor zinc-binding (CZB) domain. Dissection of CZB signal transduction reveals that oxidation of the conserved zinc-binding cysteine controls CZB Zn²⁺ occupancy, which in turn regulates the catalysis of c-di-GMP by the associated GGDEF domain. We find DgcZ-dependent biofilm formation and HOCl sensing to be regulated in vivo by the conserved zinc-coordinating cysteine. Additionally, point mutants that mimic oxidized CZB states increase total biofilm. A survey of bacterial genomes reveals that many pathogenic bacteria that manipulate host inflammation as part of their colonization strategy possess CZB-regulated diguanylate cyclases and chemoreceptors. Our findings suggest that CZB domains are zinc-sensitive regulators that allow host-associated bacteria to perceive host inflammation through reactivity with HOCl.