Application of genetically encoded redox biosensors to measure dynamic changes in the glutathione, bacillithiol and mycothiol redox potentials in pathogenic bacteria

Nicotine promotes Staphylococcus aureus-induced osteomyelitis by activating the Nrf2/Slc7a11 signaling axis

Although smoking is a significant risk factor for osteomyelitis, there is limited experimental evidence that nicotine, a key tobacco constituent, is associated with this condition, leaving its mechanistic implications uncharacterized. This study revealed that nicotine promotes Staphylococcus aureus-induced osteomyelitis by increasing Nrf2 and Slc7a11 expression in vivo and in vitro. Inhibition of Slc7a11 using Erastin augmented bacterial phagocytosis/killing capabilities and fortified antimicrobial responses in an osteomyelitis model. Moreover, untargeted metabolomic analysis demonstrated that Erastin mitigated the effects of nicotine on S. aureus-induced osteomyelitis by altering glutamate/glutathione metabolism. These findings suggest that nicotine aggravates S. aureus-induced osteomyelitis by activating the Nrf2/Slc7a11 signaling pathway and that Slc7a11 inhibition can counteract the detrimental health effects of nicotine.

Diverse roles of low-molecular weight thiol GSH in Francisella's virulence, location sensing and GSH-stealing from host

Low-molecular weight (LMW) thiols, encompassing peptides and small proteins with active cysteine residue(s), are important to bacteria as they are involved in a wide range of redox reactions. They include the tripeptide glutathione (GSH) and the small redox proteins, thioredoxins and glutaredoxins. We review the low MW thiols and related molecules in Francisella species and what role they may play in growth and virulence. Genes for GSH biosynthesis, metabolism and thioredoxins are present in all strains of Francisella, including the fully human-virulent strains. GSH and cysteine (CSH) are the major LMW thiols in Francisella extracts. We explore the potential role of the LMW thiols to overcome the nutritional challenges of intracellular growth (high GSH conditions) as well as the nutritional challenges of planktonic growth (low GSH conditions), and their contribution to Francisella's sensing its environmental location. Francisella may also use GSH as a source of CSH, for which it is auxotrophic. "Glutathione stealing" from the host may be an important part of Francisella's success strategy as a facultative intracellular pathogen both to detect its location and obtain CSH. An understanding of GSH metabolism in Francisella provides insights into the interaction of this pathogen with its host and may reveal additional targets for therapeutic intervention for tularemia infections.

Phenotypic and genomic characterization provide new insights into adaptation to environmental stressors and biotechnological relevance of mangrove Alcaligenes faecalis D334

Alcaligenes faecalis D334 was determined in this study as a salt-tolerant bacterium isolated from mangrove sediment. In response to 6% (w/v) NaCl, strain D334 produced the highest ectoines of 14.14 wt%. To understand adaptive features to mangrove environment, strain D334 was sequenced using Pacific BioScience platform, resulting in a circular chromosome of 4.23 Mb. Of note, D334 genome harbored 81 salt-responsive genes, among which two membrane-associated genes ompc and eric were absent in 3 selected A. faecalis genomes. Apart from that, a complete pathway for ectoine and 5-hydroxyectoine synthesis was predicted. To resist 40 mM H₂O₂, 46 genetic determinants contributing to oxidative stress response were employed. Moreover, two operons involved in polyhydroxyalkanoate (PHA) production were identified in the D334 genome, resulting in maximum PHA content of 5.03 ± 0.04 wt% and PHA concentration of 0.13 ± 0.001 g/L. A large flagellar biosynthesis operon contributing to swimming motility was found to be conserved in D334 and 8 other A. faecalis genomes. These findings shed light for the first time on the high versatility of A. faecalis D334 genome to adapt to mangrove lifestyle and the possibility to develop D334 as an industrial platform for PHA and 5-hydroxyectoine production.

Genomic and physiological traits provide insights into ecological niche adaptations of mangrove endophytic Streptomyces parvulus VCCM 22513

Purpose

Endophytic Streptomyces parvulus VCCM 22513 isolated from Bruguiera gymnorrhiza in Quang Ninh mangrove forest, northern Vietnam showed abiotic stress tolerance consisting of antioxidant, salt-tolerant, and aromatic-compound degrading activities. The goal of this study was to shed light on genomic bases rendering mangrove endophytic S. parvulus more resilient to environmental stressors.

Methods

Phenotypic analysis including antioxidant activities, hydrogen peroxide and sodium chloride resistance, and aromatic compound utilization were evaluated. The genome of strain VCCM 22513 was sequenced using Illumina Miseq sequencing platform and assembled using SPAdes.

Results

Out of 15 endophytic actinomycetes associated with B. gymnorrhiza in Quang Ninh mangrove, northern Vietnam, VCCM 22513 extract showed remarkable antioxidant activities through (1,1-diphenyl-2-picrylhydrazyl) DPPH and superoxide radical scavenging assays of 72.1 ± 0.04% and 38.3 ± 0.16% at 1.6 mg/ml, respectively. The genome consists of a 7,688,855 bp linear chromosome, 6782 protein-coding sequences, and 68 tRNAs. Genomic analysis identified strain VCCM 22513 as Streptomyces parvulus and confirmed a highly conserved core genome and stability of S. parvulus under natural selection. Genome mining revealed the presence of genetic determinants involved in mycothiol and ergothioneine biosynthesis (26 genes), oxidative stress resistance (43 genes), osmoadaptation (87 genes), heat and cold stress (34 genes), aromatic compound degradation (55 genes). Further genome-wide comparison between S. parvulus VCCM 22513 and 11 Streptomyces genomes showed that VCCM 22513 possesses significantly higher copies of genes involved in mycothiol and ergothioneine biosynthesis. In support of this finding, the strain exhibited much resistance to 0.6–1.0 M H2O2 and 6% (w/v) NaCl as compared to Streptomyces cavourensis YBQ59 isolated from Cinnamomum cassia Prels. In addition, the complete pathways for degradation of aromatic compounds including protocatechuate, gentisate, 4-hydroxyphenylpyruvate, cinnamate, 3-phenylpropionate, and styrene were only identified in the genome of VCCM 22513.

Conclusions

The present study revealed for the first time adaptive responses of mangrove endophytic S. parvulus VCCM 22513 to survive in hostile environment. The information shown here provided better understanding of underlying mechanisms related to adaptation and partially plant-microbe interaction of Streptomyces associated with mangrove plants.

Salmonella Typhimurium outer membrane protein A (OmpA) renders protection from nitrosative stress of macrophages by maintaining the stability of bacterial outer membrane

Bacterial porins are highly conserved outer membrane proteins used in the selective transport of charged molecules across the membrane. In addition to their significant contributions to the pathogenesis of Gram-negative bacteria, their role(s) in salmonellosis remains elusive. In this study, we investigated the role of outer membrane protein A (OmpA), one of the major outer membrane porins of Salmonella, in the pathogenesis of Salmonella Typhimurium (STM). Our study revealed that OmpA plays an important role in the intracellular virulence of Salmonella. An ompA deficient strain of Salmonella (STM ΔompA) showed compromised proliferation in macrophages. We found that the SPI-2 encoded virulence factors such as sifA and ssaV are downregulated in STM ΔompA. The poor colocalization of STM ΔompA with LAMP-1 showed that disruption of SCV facilitated its release into the cytosol of macrophages, where it was assaulted by reactive nitrogen intermediates (RNI). The enhanced recruitment of nitrotyrosine on the cytosolic population of STM ΔompAΔsifA and ΔompAΔssaV compared to STM ΔsifA and ΔssaV showed an additional role of OmpA in protecting the bacteria from host nitrosative stress. Further, we showed that the generation of greater redox burst could be responsible for enhanced sensitivity of STM ΔompA to the nitrosative stress. The expression of several other outer membrane porins such as ompC, ompD, and ompF was upregulated in STM ΔompA. We found that in the absence of ompA, the enhanced expression of ompF increased the outer membrane porosity of Salmonella and made it susceptible to in vitro and in vivo nitrosative stress. Our study illustrates a novel mechanism for the strategic utilization of OmpA by Salmonella to protect itself from the nitrosative stress of macrophages.

Salmonella Typhimurium majorly uses SPI-1 and SPI-2 encoded T3SS and virulence factors for thriving in the host macrophages. But the role of non-SPI genes in Salmonella pathogenesis remains unknown. This article illustrates a novel mechanism of how a non-SPI virulent protein, OmpA, helps Salmonella Typhimurium to survive in murine macrophages. Our data revealed that Salmonella lacking OmpA (STM ΔompA) is deficient in producing SPI-2 effector proteins and has a severe defect in maintaining the stability of its outer membrane. It is released into the cytosol of macrophages during infection after disrupting the SCV membrane. STM ΔompA was severely challenged with reactive nitrogen intermediates in the cytosol, which reduced their proliferation in macrophages. We further showed that the deletion of OmpA increased the expression of other larger porins (ompC, ompD, and ompF) on the surface of Salmonella. It was observed that the enhanced expression of OmpF in STM ΔompA increased the outer membrane permeability and made the bacteria more susceptible to in vitro and in vivo nitrosative stress. Altogether our study proposes new insights into the role of Salmonella OmpA as an essential virulence factor.

Digital models in biotechnology: Towards multi-scale integration and implementation

Industrial biotechnology encompasses a large area of multi-scale and multi-disciplinary research activities. With the recent megatrend of digitalization sweeping across all industries, there is an increased focus in the biotechnology industry on developing, integrating and applying digital models to improve all aspects of industrial biotechnology. Given the rapid development of this field, we systematically classify the state-of-art modelling concepts applied at different scales in industrial biotechnology and critically discuss their current usage, advantages and limitations. Further, we critically analyzed current strategies to couple cell models with computational fluid dynamics to study the performance of industrial microorganisms in large-scale bioprocesses, which is of crucial importance for the bio-based production industries. One of the most challenging aspects in this context is gathering intracellular data under industrially relevant conditions. Towards comprehensive models, we discuss how different scale-down concepts combined with appropriate analytical tools can capture intracellular states of single cells. We finally illustrated how the efforts could be used to develop digitals models suitable for both cell factory design and process optimization at industrial scales in the future.

Catechin Mediates Ferroptosis to Exert an Anti-Inflammatory Effect on RAW 264.7 Cells

Catechin possesses a potential anti-inflammatory activity, but its anti-inflammatory mechanism is still unclear. Herein, the analysis of network pharmacology showed that catechin might mediate ferroptosis on macrophages to exhibit a significant anti-inflammatory effect on RAW264.7. The metabolomics further indicated that catechin might influence ferroptosis by activating two pathways of cysteine and methionine metabolism and glutathione metabolism, and inhibiting the pathway of ferroptosis to promote the reduction of l-methionine-s-oxide and s-glutathionyl-l-cysteine, and the reduction and synthesis of γ-glutamylcysteine. Furthermore, related proteins (MSRA, CDR, GSR and GCL) in three metabolic pathways and ferroptosis-related proteins (GPX4 and SLC7A11) might be relevant to catechin through molecular docking. Thus, we speculate that catechin plays an anti-inflammatory effect through mediating ferroptosis on RAW264.7, which still needs further focus on the detailed molecular mechanism.

Redox-sensitive fluorescent biosensors detect Sinorhizobium meliloti intracellular redox changes under free-living and symbiotic lifestyles

Reactive oxygen species such as hydrogen peroxide (H₂O₂) are key signaling molecules that control the setup and functioning of Rhizobium-legume symbiosis. This interaction results in the formation of a new organ, the root nodule, in which bacteria enter the host cells and differentiate into nitrogen (N₂)-fixing bacteroids. The interaction between Sinorhizobium meliloti and Medicago truncatula is a genetic model to study N₂-fixing symbiosis. In previous work, S. meliloti mutants impaired in the antioxidant defense, showed altered symbiotic properties, emphasizing the importance of redox-based regulation in the bacterial partner. However, direct measurements of S. meliloti intracellular redox state have never been performed. Here, we measured dynamic changes of intracellular H₂O₂ and glutathione redox potential by expressing roGFP2-Orp1 and Grx1-roGFP2 biosensors in S. meliloti. Kinetic analyses of redox changes under free-living conditions showed that these biosensors are suitable to monitor the bacterial redox state in real-time, after H₂O₂ challenge and in different genetic backgrounds. In planta, flow cytometry and confocal imaging experiments allowed the determination of sensor oxidation state in nodule bacteria. These cellular studies establish the existence of an oxidative shift in the redox status of S. meliloti during bacteroid differentiation. Our findings open up new possibilities for in vivo studies of redox dynamics during N₂-fixing symbiosis.

A Fluorescent Probe to Detect Quick Disulfide Reductase Activity in Bacteria

The Trx and Grx systems, two disulfide reductase systems, play critical roles in various cell activities. There are great differences between the thiol redox systems in prokaryotes and mammals. Though fluorescent probes have been widely used to detect these systems in mammalian cells. Very few methods are available to detect rapid changes in the redox systems of prokaryotes. Here we investigated whether Fast-TRFS, a disulfide-containing fluorescent probe utilized in analysis of mammalian thioredoxin reductase, could be used to detect cellular disulfide reducibility in bacteria. Fast-TRFS exhibited good substrate qualities for both bacterial thioredoxin and GSH-glutaredoxin systems in vitro, with Trx system having higher reaction rate. Moreover, the Fast-TRFS was used to detect the disulfide reductase activity in various bacteria and redox-related gene null E. coli. Some glutaredoxin-deficient bacteria had stronger fast disulfide reducibility. The Trx system was shown to be the predominant disulfide reductase for fast disulfide reduction rather than the Grx system. These results demonstrated that Fast-TRFS is a viable probe to detect thiol-dependent disulfide reductases in bacteria. It also indicated that cellular disulfide reduction could be classified into fast and slow reaction, which are predominantly catalyzed by E. coli Trx and Grx system, respectively.

In Vivo Imaging with Genetically Encoded Redox Biosensors

Redox reactions are of high fundamental and practical interest since they are involved in both normal physiology and the pathogenesis of various diseases. However, this area of research has always been a relatively problematic field in the context of analytical approaches, mostly because of the unstable nature of the compounds that are measured. Genetically encoded sensors allow for the registration of highly reactive molecules in real-time mode and, therefore, they began a new era in redox biology. Their strongest points manifest most brightly in in vivo experiments and pave the way for the non-invasive investigation of biochemical pathways that proceed in organisms from different systematic groups. In the first part of the review, we briefly describe the redox sensors that were used in vivo as well as summarize the model systems to which they were applied. Next, we thoroughly discuss the biological results obtained in these studies in regard to animals, plants, as well as unicellular eukaryotes and prokaryotes. We hope that this work reflects the amazing power of this technology and can serve as a useful guide for biologists and chemists who work in the field of redox processes.

Redox regulation in host-pathogen interactions: thiol switches and beyond

Our organism is exposed to pathogens on a daily basis. Owing to this age-old interaction, both pathogen and host evolved strategies to cope with these encounters. Here, we focus on the consequences of the direct encounter of cells of the innate immune system with bacteria. First, we will discuss the bacterial strategies to counteract powerful reactive species. Our emphasis lies on the effects of hypochlorous acid (HOCl), arguably the most powerful oxidant produced inside the phagolysosome of professional phagocytes. We will highlight individual examples of proteins in gram-negative bacteria activated by HOCl via thiol-disulfide switches, methionine sulfoxidation, and N-chlorination of basic amino acid side chains. Second, we will discuss the effects of HOCl on proteins of the host. Recent studies have shown that both host and bacteria address failing protein homeostasis by activation of chaperone-like holdases through N-chlorination. After discussing the role of individual proteins in the HOCl-defense, we will turn our attention to the examination of effects on host and pathogen on a systemic level. Recent studies using genetically encoded redox probes and redox proteomics highlight differences in redox homeostasis in host and pathogen and give first hints at potential cellular HOCl signaling beyond thiol-disulfide switch mechanisms.

The Industrial Organism Corynebacterium glutamicum Requires Mycothiol as Antioxidant to Resist Against Oxidative Stress in Bioreactor Cultivations

In aerobic environments, bacteria are exposed to reactive oxygen species (ROS). To avoid an excess of ROS, microorganisms are equipped with powerful enzymatic and non-enzymatic antioxidants. Corynebacterium glutamicum, a widely used industrial platform organism, uses mycothiol (MSH) as major low molecular weight (LMW) thiol and non-enzymatic antioxidant. In aerobic bioreactor cultivations, C. glutamicum becomes exposed to oxygen concentrations surpassing the air saturation, which are supposed to constitute a challenge for the intracellular MSH redox balance. In this study, the role of MSH was investigated at different oxygen levels (pO₂) in bioreactor cultivations in C. glutamicum. Despite the presence of other highly efficient antioxidant systems, such as catalase, the MSH deficient ΔmshC mutant was impaired in growth in bioreactor experiments performed at pO₂ values of 30%. At a pO₂ level of 20%, this growth defect was abolished, indicating a high susceptibility of the MSH-deficient mutant towards elevated oxygen concentrations. Bioreactor experiments with C. glutamicum expressing the Mrx1-roGFP2 redox biosensor revealed a strong oxidative shift in the MSH redox potential (E_MSH) at pO₂ values above 20%. This indicates that the LMW thiol MSH is an essential antioxidant to maintain the robustness and industrial performance of C. glutamicum during aerobic fermentation processes.

The role of thiols in antioxidant systems

The sulfur biochemistry of the thiol group endows cysteines with a number of highly specialized and unique features that enable them to serve a variety of different functions in the cell. Typically highly conserved in proteins, cysteines are predominantly found in functionally or structurally crucial regions, where they act as stabilizing, catalytic, metal-binding and/or redox-regulatory entities. As highly abundant low molecular weight thiols, cysteine thiols and their oxidized disulfide counterparts are carefully balanced to maintain redox homeostasis in various cellular compartments, protect organisms from oxidative and xenobiotic stressors and partake actively in redox-regulatory and signaling processes. In this review, we will discuss the role of protein thiols as scavengers of hydrogen peroxide in antioxidant enzymes, use thiol peroxidases to exemplify how protein thiols contribute to redox signaling, provide an overview over the diverse set of low molecular weight thiol-based redox systems found in biology, and illustrate how thiol-based redox systems have evolved not only to protect against but to take full advantage of a world full of molecular oxygen.

Utilizing redox-sensitive GFP fusions to detect in vivo redox changes in a genetically engineered prokaryote

Understanding the in vivo redox biology of cells is a complex albeit important biological problem. Studying redox processes within living cells without physical disruption or chemical modifications is essential in determining the native redox states of cells. In this study, the previously characterized reduction-oxidation sensitive green fluorescent protein (roGFP2) was used to elucidate the redox changes of the genetically engineered Escherichia coli strain, SHuffle. SHuffle cells were demonstrated to be under constitutive oxidative stress and responding transcriptionally in an OxyR-dependent manner. Using roGFP2 fused to either glutathione (GSH)- or hydrogen peroxide (H₂O₂)- sensitive proteins (glutaredoxin 1 or Orp1), the cytosolic redox state of both wild type and SHuffle cells based on GSH/GSSG and H₂O₂ pools was measured. These probes open the path to in vivo studies of redox changes and genetic selections in prokaryotic hosts.

Staphylococcus aureus Uses the Bacilliredoxin (BrxAB)/Bacillithiol Disulfide Reductase (YpdA) Redox Pathway to Defend Against Oxidative Stress Under Infections

Staphylococcus aureus is a major human pathogen and has to cope with reactive oxygen and chlorine species (ROS, RCS) during infections. The low molecular weight thiol bacillithiol (BSH) is an important defense mechanism of S. aureus for detoxification of ROS and HOCl stress to maintain the reduced state of the cytoplasm. Under HOCl stress, BSH forms mixed disulfides with proteins, termed as S-bacillithiolations, which are reduced by bacilliredoxins (BrxA and BrxB). The NADPH-dependent flavin disulfide reductase YpdA is phylogenetically associated with the BSH synthesis and BrxA/B enzymes and was recently suggested to function as BSSB reductase (Mikheyeva et al., 2019). Here, we investigated the role of the complete bacilliredoxin BrxAB/BSH/YpdA pathway in S. aureus COL under oxidative stress and macrophage infection conditions in vivo and in biochemical assays in vitro. Using HPLC thiol metabolomics, a strongly enhanced BSSB level and a decreased BSH/BSSB ratio were measured in the S. aureus COL ΔypdA deletion mutant under control and NaOCl stress. Monitoring the oxidation degree (OxD) of the Brx-roGFP2 biosensor revealed that YpdA is required for regeneration of the reduced BSH redox potential (E_BSH) upon recovery from oxidative stress. In addition, the ΔypdA mutant was impaired in H₂O₂ detoxification as measured with the novel H₂O₂-specific Tpx-roGFP2 biosensor. Phenotype analyses further showed that BrxA and YpdA are required for survival under NaOCl and H₂O₂ stress in vitro and inside murine J-774A.1 macrophages in infection assays in vivo. Finally, NADPH-coupled electron transfer assays provide evidence for the function of YpdA in BSSB reduction, which depends on the conserved Cys14 residue. YpdA acts together with BrxA and BSH in de-bacillithiolation of S-bacillithiolated GapDH. In conclusion, our results point to a major role of the BrxA/BSH/YpdA pathway in BSH redox homeostasis in S. aureus during recovery from oxidative stress and under infections.

Molecular Mechanisms of Glutaredoxin Enzymes: Versatile Hubs for Thiol-Disulfide Exchange between Protein Thiols and Glutathione

The tripeptide glutathione (GSH) and its oxidized form glutathione disulfide (GSSG) constitute a key redox couple in cells. In particular, they partner protein thiols in reversible thiol-disulfide exchange reactions that act as switches in cell signaling and redox homeostasis. Disruption of these processes may impair cellular redox signal transduction and induce redox misbalances that are linked directly to aging processes and to a range of pathological conditions including cancer, cardiovascular diseases and neurological disorders. Glutaredoxins are a class of GSH-dependent oxidoreductase enzymes that specifically catalyze reversible thiol-disulfide exchange reactions between protein thiols and the abundant thiol pool GSSG/GSH. They protect protein thiols from irreversible oxidation, regulate their activities under a variety of cellular conditions and are key players in cell signaling and redox homeostasis. On the other hand, they may also function as metal-binding proteins with a possible role in the cellular homeostasis and metabolism of essential metals copper and iron. However, the molecular basis and underlying mechanisms of glutaredoxin action remain elusive in many situations. This review focuses specifically on these aspects in the context of recent developments that illuminate some of these uncertainties.

The AGXX® Antimicrobial Coating Causes a Thiol-Specific Oxidative Stress Response and Protein S-bacillithiolation in Staphylococcus aureus

Multidrug-resistant pathogens, such as methicillin-resistant Staphylococcus aureus (MRSA) pose an increasing health burden and demand alternative antimicrobials to treat bacterial infections. The surface coating AGXX® is a novel broad-spectrum antimicrobial composed of two transition metals, silver and ruthenium that can be electroplated on various surfaces, such as medical devices and implants. AGXX® has been shown to kill nosocomial and waterborne pathogens by production of reactive oxygen species (ROS), but the effect of AGXX® on the bacterial redox balance has not been demonstrated. Since treatment options for MRSA infections are limited, ROS-producing agents are attractive alternatives to combat multi-resistant strains. In this work, we used RNA-seq transcriptomics, redox biosensor measurements and phenotype analyses to study the mode of action of AGXX® microparticles in S. aureus USA300. Using growth and survival assays, the growth-inhibitory amount of AGXX® microparticles was determined as 5 μg/ml. In the RNA-seq transcriptome, AGXX® caused a strong thiol-specific oxidative stress response and protein damage as revealed by the induction of the PerR, HypR, QsrR, MhqR, CstR, CtsR, and HrcA regulons. The derepression of the Fur, Zur, and CsoR regulons indicates that AGXX® also interferes with the metal ion homeostasis inducing Fe²⁺- and Zn²⁺-starvation responses as well as export systems for toxic Ag⁺ ions. The induction of the SigB and GraRS regulons reveals also cell wall and general stress responses. AGXX® stress was further shown to cause protein S-bacillithiolation, protein aggregation and an oxidative shift in the bacillithiol (BSH) redox potential. In phenotype assays, BSH and the HypR-controlled disulfide reductase MerA were required for protection against ROS produced under AGXX® stress in S. aureus. Altogether, our study revealed a strong thiol-reactive mode of action of AGXX® in S. aureus USA300 resulting in an increased BSH redox potential and protein S-bacillithiolation.

Stable integration of the Mrx1-roGFP2 biosensor to monitor dynamic changes of the mycothiol redox potential in Corynebacterium glutamicum

Mycothiol (MSH) functions as major low molecular weight (LMW) thiol in the industrially important Corynebacterium glutamicum. In this study, we genomically integrated an Mrx1-roGFP2 biosensor in C. glutamicum to measure dynamic changes of the MSH redox potential (E_MSH) during the growth and under oxidative stress. C. glutamicum maintains a highly reducing intrabacterial E_MSH throughout the growth curve with basal E_MSH levels of ~- 296 mV. Consistent with its H₂O₂ resistant phenotype, C. glutamicum responds only weakly to 40 mM H₂O₂, but is rapidly oxidized by low doses of NaOCl. We further monitored basal E_MSH changes and the H₂O₂ response in various mutants which are compromised in redox-signaling of ROS (OxyR, SigH) and in the antioxidant defense (MSH, Mtr, KatA, Mpx, Tpx). While the probe was constitutively oxidized in the mshC and mtr mutants, a smaller oxidative shift in basal E_MSH was observed in the sigH mutant. The catalase KatA was confirmed as major H₂O₂ detoxification enzyme required for fast biosensor re-equilibration upon return to non-stress conditions. In contrast, the peroxiredoxins Mpx and Tpx had only little impact on E_MSH and H₂O₂ detoxification. Further live imaging experiments using confocal laser scanning microscopy revealed the stable biosensor expression and fluorescence at the single cell level. In conclusion, the stably expressed Mrx1-roGFP2 biosensor was successfully applied to monitor dynamic E_MSH changes in C. glutamicum during the growth, under oxidative stress and in different mutants revealing the impact of Mtr and SigH for the basal level E_MSH and the role of OxyR and KatA for efficient H₂O₂ detoxification under oxidative stress.