Sensitive Method for Reliable Quantification of Sulfane Sulfur in Biological Samples

Enterobacter sp. HIT-SHJ4 isolated from wetland with carbon, nitrogen and sulfur co-metabolism and its implication for bioremediation

Both autotrophic and heterotrophic denitrification are known as important bioprocesses of microbe-mediated nitrogen cycle in natural ecosystems. Actually, mixotrophic denitrification co-driven by organic matter and reduced sulfur substances are also common, especially in hypoxic environments such as estuarine sediments. However, carbon, nitrogen and sulfur co-metabolism during mixotrophic denitrification in natural water ecosystems has rarely been reported in detail. Therefore, this study investigated the co-metabolism of carbon, nitrogen and sulfur using samples collected from four distinct natural water ecosystems. Results demonstrated that samples from various sources all exhibited the ability for co-metabolism of carbon, nitrogen and sulfur. Microbial community analysis showed that Pseudomonas and Paracoccus were dominant bacteria ranging from 65.6% to 75.5% in mixotrophic environment. Enterobacter sp. HIT-SHJ4, a mixotrophic denitrifying strain which owned the capacity for co-metabolism of carbon, nitrogen and sulfur, was isolated and reported here for the first time. The strain preferred methanol as its carbon source and demonstrated remarkable efficiency for removing sulfide and nitrate with below 100 mg/L sulfide. Under weak acid conditions (pH 6.5-7.0), it exhibited enhanced capability in converting sulfide to elemental sulfur. Its bioactivity was evident within a temperature from 25 °C to 40 °C and C/N ratios from 0.75 to 3. This study confirmed the widespread presence of microbial-mediated synergistic carbon, nitrogen and sulfur metabolism in natural aquatic ecosystems. HIT-SHJ4 emerges as a novel strain, shedding light on carbon, nitrogen and sulfur co-metabolism in natural water bodies. Furthermore, it also serves as a promising candidate microorganism for in-situ ecological remediation, particularly in dealing with contamination posed by nitrate, sulfide, and organic matter.

MarR family proteins sense sulfane sulfur in bacteria

Members of the multiple antibiotic resistance regulator (MarR) protein family are ubiquitous in bacteria and play critical roles in regulating cellular metabolism and antibiotic resistance. MarR family proteins function as repressors, and their interactions with modulators induce the expression of controlled genes. The previously characterized modulators are insufficient to explain the activities of certain MarR family proteins. However, recently, several MarR family proteins have been reported to sense sulfane sulfur, including zero-valent sulfur, persulfide (R-SSH), and polysulfide (R-SnH, n ≥ 2). Sulfane sulfur is a common cellular component in bacteria whose levels vary during bacterial growth. The changing levels of sulfane sulfur affect the expression of many MarR-controlled genes. Sulfane sulfur reacts with the cysteine thiols of MarR family proteins, causing the formation of protein thiol persulfide, disulfide bonds, and other modifications. Several MarR family proteins that respond to reactive oxygen species (ROS) also sense sulfane sulfur, as both sulfane sulfur and ROS induce the formation of disulfide bonds. This review focused on MarR family proteins that sense sulfane sulfur. However, the sensing mechanisms reviewed here may also apply to other proteins that detect sulfane sulfur, which is emerging as a modulator of gene regulation.

The Activity of YCA1 Metacaspase Is Regulated by Reactive Sulfane Sulfur via Persulfidation in Saccharomyces cerevisiae

YCA1, the only metacaspase in Saccharomyces cerevisiae, plays important roles in the regulation of chronological lifespan, apoptosis, and cytokinesis. YCA1 has protein hydrolase activity and functions by cleaving itself and target proteins. However, there are few reports about the regulation of YCA1 activity. In this study, we observed that reactive sulfane sulfur (RSS) can inhibit the activity of YCA1. In vitro experiments demonstrated that RSS reacted with the Cys276 of YCA1, the residue central to its protein hydrolase activity, to form a persulfidation modification (protein-SSH). This modification inhibited both its self-cleavage and the cleavage of its substrate protein, BIR1. To investigate further, we constructed a low-endogenous-RSS mutant of S. cerevisiae, BY4742 Δcys3, in which the RSS-producing enzyme cystathionine-γ-lyase (CYS3) was knocked out. The activity of YCA1 was significantly increased by the deletion of CYS3. Moreover, increased YCA1 activity led to reduced chronological lifespan (CLS) and CLS-driven apoptosis. This study unveils the first endogenous factor that regulates YCA1 activity, introduces a novel mechanism of how yeast cells regulate chronological lifespan, and broadens our understanding of the multifaceted roles played by RSS.

Microorganisms uptake zero-valent sulfur via membrane lipid dissolution of octasulfur and intracellular solubilization as persulfide

Zero-valent sulfur, commonly utilized as a fertilizer or fungicide, is prevalent in various environmental contexts. Its most stable and predominant form, octasulfur (S8), plays a crucial role in microbial sulfur metabolism, either through oxidation or reduction. However, the mechanism underlying its cellular uptake remains elusive. We presented evidence that zero-valent sulfur was adsorbed to the cell surface and then dissolved into the membrane lipid layer as lipid-soluble S8 molecules, which reacted with cellular low-molecular thiols to form persulfide, e.g., glutathione persulfide (GSSH), in the cytoplasm. The process brought extracellular zero-valent sulfur into the cells. When persulfide dioxygenase is present in the cells, GSSH will be oxidized. Otherwise, GSSH will react with another glutathione (GSH) to produce glutathione disulfide (GSSG) and hydrogen sulfide (H2S). The mechanism is different from simple diffusion, as insoluble S8 becomes soluble GSSH after crossing the cytoplasmic membrane. The uptake process is limited by physical contact of insoluble zero-valent sulfur with microbial cells and the regeneration of cellular thiols. Our findings elucidate the cellular uptake mechanism of zero-valent sulfur, which provides critical information for its application in agricultural practices and the bioremediation of sulfur contaminants and heavy metals.

Rhodobacteraceae methanethiol oxidases catalyze methanethiol degradation to produce sulfane sulfur other than hydrogen sulfide

Methanethiol (MT) is a sulfur-containing compound produced during dimethylsulfoniopropionate (DMSP) degradation by marine bacteria. The C-S bond of MT can be cleaved by methanethiol oxidases (MTOs) to release a sulfur atom. However, the cleaving process remains unclear, and the species of sulfur product is uncertain. It has long been assumed that MTOs produce hydrogen sulfide (H2S) from MT. Herein, we studied the MTOs in the Rhodobacteraceae family-whose members are important DMSP degraders ubiquitous in marine environments. We identified 57 MTOs from 1,904 Rhodobacteraceae genomes. These MTOs were grouped into two major clusters. Cluster 1 members share three conserved cysteine residues, while cluster 2 members contain one conserved cysteine residue. We examined the products of three representative MTOs both in vitro and in vivo. All of them produced sulfane sulfur other than H2S from MT. Their conserved cysteines are substrate-binding sites in which the MTO-S-S-CH3 complex is formed. This finding clarified the sulfur product of MTOs and enlightened the MTO-catalyzing process. Moreover, this study connected DMSP degradation with sulfane sulfur metabolism, filling a critical gap in the DMSP degradation pathway and representing new knowledge in the marine sulfur cycle field.

IMPORTANCE

This study overthrows a long-time assumption that methanethiol oxidases (MTOs) cleave the C-S bond of methanethiol to produce both H2S and H2O2-the former is a strong reductant and the latter is a strong oxidant. From a chemistry viewpoint, this reaction is difficult to happen. Investigations on three representative MTOs indicated that sulfane sulfur (S0) was the direct product, and no H2O2 was produced. Finally, the products of MTOs were corrected to be S0 and H2O. This finding connected dimethylsulfoniopropionate (DMSP) degradation with sulfane sulfur metabolism, filling a critical gap in the DMSP degradation pathway and representing new knowledge in the marine sulfur cycle field.

Visualization diagnosis of acute cerebral ischemia via sulfane sulfur-activated photoacoustic imaging

A photoacoustic (PA) imaging probe, HCy-SH, was designed and synthesized. This probe can react rapidly and specifically with sulfane sulfur to produce a strong PA signal. This probe also exhibited low cytotoxicity and biotoxicity. Thus, HCy-SH has been used for visual diagnosis of acute cerebral ischemia.

Transcription factor OxyR regulates sulfane sulfur removal and L-cysteine biosynthesis in Corynebacterium glutamicum

Sulfane sulfur, a collective term for hydrogen polysulfide and organic persulfide, often damages cells at high concentrations. Cells can regulate intracellular sulfane sulfur levels through specific mechanisms, but these mechanisms are unclear in Corynebacterium glutamicum. OxyR is a transcription factor capable of sensing oxidative stress and is also responsive to sulfane sulfur. In this study, we found that OxyR functioned directly in regulating sulfane sulfur in C. glutamicum. OxyR binds to the promoter of katA and nrdH and regulates its expression, as revealed via in vitro electrophoretic mobility shift assay analysis, real-time quantitative PCR, and reporting systems. Overexpression of katA and nrdH reduced intracellular sulfane sulfur levels by over 30% and 20% in C. glutamicum, respectively. RNA-sequencing analysis showed that the lack of OxyR downregulated the expression of sulfur assimilation pathway genes and/or sulfur transcription factors, which may reduce the rate of sulfur assimilation. In addition, OxyR also affected the biosynthesis of L-cysteine in C. glutamicum. OxyR overexpression strain Cg-2 accumulated 183 mg/L of L-cysteine, increased by approximately 30% compared with the control (142 mg/L). In summary, OxyR not only regulated sulfane sulfur levels by controlling the expression of katA and nrdH in C. glutamicum but also facilitated the sulfur assimilation and L-cysteine synthesis pathways, providing a potential target for constructing robust cell factories of sulfur-containing amino acids and their derivatives. IMPORTANCE C. glutamicum is an important industrial microorganism used to produce various amino acids. In the production of sulfur-containing amino acids, cells inevitably accumulate a large amount of sulfane sulfur. However, few studies have focused on sulfane sulfur removal in C. glutamicum. In this study, we not only revealed the regulatory mechanism of OxyR on intracellular sulfane sulfur removal but also explored the effects of OxyR on the sulfur assimilation and L-cysteine synthesis pathways in C. glutamicum. This is the first study on the removal of sulfane sulfur in C. glutamicum. These results contribute to the understanding of sulfur regulatory mechanisms and may aid in the future optimization of C. glutamicum for biosynthesis of sulfur-containing amino acids.

The Rhodanese PspE Converts Thiosulfate to Cellular Sulfane Sulfur in Escherichia coli

Hydrogen sulfide (H₂S) and its oxidation product zero-valent sulfur (S⁰) play important roles in animals, plants, and bacteria. Inside cells, S⁰ exists in various forms, including polysulfide and persulfide, which are collectively referred to as sulfane sulfur. Due to the known health benefits, the donors of H₂S and sulfane sulfur have been developed and tested. Among them, thiosulfate is a known H₂S and sulfane sulfur donor. We have previously reported that thiosulfate is an effective sulfane sulfur donor in Escherichia coli; however, it is unclear how it converts thiosulfate to cellular sulfane sulfur. In this study, we showed that one of the various rhodaneses, PspE, in E. coli was responsible for the conversion. After the thiosulfate addition, the ΔpspE mutant did not increase cellular sulfane sulfur, but the wild type and the complemented strain ΔpspE::pspE increased cellular sulfane sulfur from about 92 μM to 220 μM and 355 μM, respectively. LC-MS analysis revealed a significant increase in glutathione persulfide (GSSH) in the wild type and the ΔpspE::pspE strain. The kinetic analysis supported that PspE was the most effective rhodanese in E. coli in converting thiosulfate to glutathione persulfide. The increased cellular sulfane sulfur alleviated the toxicity of hydrogen peroxide during E. coli growth. Although cellular thiols might reduce the increased cellular sulfane sulfur to H₂S, increased H₂S was not detected in the wild type. The finding that rhodanese is required to convert thiosulfate to cellular sulfane sulfur in E. coli may guide the use of thiosulfate as the donor of H₂S and sulfane sulfur in human and animal tests.

Redox and Nucleophilic Reactions of Naphthoquinones with Small Thiols and Their Effects on Oxidization of H2S to Inorganic and Organic Hydropolysulfides and Thiosulfate

Naphthoquinone (1,4-NQ) and its derivatives (NQs, juglone, plumbagin, 2-methoxy-1,4-NQ, and menadione) have a variety of therapeutic applications, many of which are attributed to redox cycling and the production of reactive oxygen species (ROS). We previously demonstrated that NQs also oxidize hydrogen sulfide (H₂S) to reactive sulfur species (RSS), potentially conveying identical benefits. Here we use RSS-specific fluorophores, mass spectroscopy, EPR and UV-Vis spectrometry, and oxygen-sensitive optodes to examine the effects of thiols and thiol-NQ adducts on H₂S-NQ reactions. In the presence of glutathione (GSH) and cysteine (Cys), 1,4-NQ oxidizes H₂S to both inorganic and organic hydroper-/hydropolysulfides (R₂S_n, R=H, Cys, GSH; n = 2-4) and organic sulfoxides (GS_nOH, n = 1, 2). These reactions reduce NQs and consume oxygen via a semiquinone intermediate. NQs are also reduced as they form adducts with GSH, Cys, protein thiols, and amines. Thiol, but not amine, adducts may increase or decrease H₂S oxidation in reactions that are both NQ- and thiol-specific. Amine adducts also inhibit the formation of thiol adducts. These results suggest that NQs may react with endogenous thiols, including GSH, Cys, and protein Cys, and that these adducts may affect both thiol reactions as well as RSS production from H₂S.

Investigating the debrominations of a subset of brominated flame retardants by biogenic reactive sulfur species

Brominated flame retardants (BFRs) are persistent organic pollutants. Many bacteria are able to debrominate BFRs, but the underlying mechanism is unclear. Herein, we discovered that reactive sulfur species (RSS), which have strong reductive activity and are commonly present in bacteria, might be one of the reasons leading to such ability. Experiments performed with RSS (H₂S and HSSH) and BFRs indicated that RSS can debrominate BFRs via two different mechanisms simultaneously: the substitutive debromination that generates thiol-BFRs and the reductive debromination that generates hydrogenated BFRs. Debromination reactions rapidly happened under neutral pH and ambient temperature, and the debromination degree was around 30% - 55% in one hour. Two Pseudomonas strains, Pseudomonas sp. C27 and Pseudomonas putida B6-2 both produced extracellular RSS and showed debromination activity. C27 debrominated HBCD, TBECH, and TBP by 5.4%, 17.7%, and 15.9% in two days. Whereas, B6-2 debrominated the three BFRs by 0.4%, 0.6%, and 0.3% in two days. The two bacteria produced different amounts and species of RSS, which were likely responsible for the contrasted degrees of the debromination. Our finding unveiled a novel, non-enzymatic debromination mechanism that many bacteria may possess. RSS producing bacteria have potentials to contribute to bioremediation of BFRs-polluted environments.

A sulfide-sensor and a sulfane sulfur-sensor collectively regulate sulfur-oxidation for feather degradation by Bacillus licheniformis

Bacillus licheniformis MW3 degrades bird feathers. Feather keratin is rich in cysteine, which is metabolized to produce hazardous sulfide and sulfane sulfur. A challenge to B. licheniformis MW3 growing on feathers is to detoxify them. Here we identified a gene cluster in B. licheniformis MW3 to deal with these toxicity. The cluster contains 11 genes: the first gene yrkD encodes a repressor, the 8^th and 9^th genes nreB and nreC encode a two-component regulatory system, and the 10th and 11th genes encode sulfide: quinone reductase (SQR) and persulfide oxygenase (PDO). SQR and PDO collectively oxidize sulfide and sulfane sulfur to sulfite. YrkD sensed sulfane sulfur to derepress the 11 genes. The NreBC system sensed sulfide and further amplified the transcription of sqr and pdo. The two regulatory systems synergistically controlled the expression of the gene cluster, which was required for the bacterium to grow on feather. The findings highlight the necessity of removing sulfide and sulfane sulfur during feather degradation and may help with bioremediation of feather waste and sulfide pollution.

The Pleiotropic Regulator AdpA Regulates the Removal of Excessive Sulfane Sulfur in Streptomyces coelicolor

Reactive sulfane sulfur (RSS), including persulfide, polysulfide, and elemental sulfur (S₈), has important physiological functions, such as resisting antibiotics in Pseudomonas aeruginosa and Escherichia coli and regulating secondary metabolites production in Streptomyces spp. However, at excessive levels it is toxic. Streptomyces cells may use known enzymes to remove extra sulfane sulfur, and an unknown regulator is involved in the regulation of these enzymes. AdpA is a multi-functional transcriptional regulator universally present in Streptomyces spp. Herein, we report that AdpA was essential for Streptomyces coelicolor survival when facing external RSS stress. AdpA deletion also resulted in intracellular RSS accumulation. Thioredoxins and thioredoxin reductases were responsible for anti-RSS stress via reducing RSS to gaseous hydrogen sulfide (H₂S). AdpA directly activated the expression of these enzymes at the presence of excess RSS. Since AdpA and thioredoxin systems are widely present in Streptomyces, this finding unveiled a new mechanism of anti-RSS stress by these bacteria.

Detection of sulfane sulfur species in biological systems

Sulfane sulfur species such as hydropersulfides (RSSH), polysulfides (RSnR), and hydrogen polysulfides (H2Sn) are critically involved in sulfur-mediated redox signaling, but their detailed mechanisms of action need further clarification. Therefore, there is a need to develop selective and sensitive sulfane sulfur detection methods to gauge a better understanding of their functions. This review summarizes current detection methods that include cyanolysis, chemical derivatization and mass spectrometry, proteomic analysis, fluorescent probes, and resonance synchronous/Raman spectroscopic methods. The design principles, advantages, applications, and limitations of each method are discussed, along with suggested directions for future research on these methods. The development of robust detection methods for sulfane sulfur species will help to elucidate their mechanisms and functions in biological systems.

Naphthoquinones Oxidize H2S to Polysulfides and Thiosulfate, Implications for Therapeutic Applications

1,4-Napththoquinones (NQs) are clinically relevant therapeutics that affect cell function through production of reactive oxygen species (ROS) and formation of adducts with regulatory protein thiols. Reactive sulfur species (RSS) are chemically and biologically similar to ROS and here we examine RSS production by NQ oxidation of hydrogen sulfide (H2S) using RSS-specific fluorophores, liquid chromatography-mass spectrometry, UV-Vis absorption spectrometry, oxygen-sensitive optodes, thiosulfate-specific nanoparticles, HPLC-monobromobimane derivatization, and ion chromatographic assays. We show that NQs, catalytically oxidize H2S to per- and polysulfides (H2Sn, n = 2−6), thiosulfate, sulfite and sulfate in reactions that consume oxygen and are accelerated by superoxide dismutase (SOD) and inhibited by catalase. The approximate efficacy of NQs (in decreasing order) is, 1,4-NQ ≈ juglone ≈ plumbagin > 2-methoxy-1,4-NQ ≈ menadione >> phylloquinone ≈ anthraquinone ≈ menaquinone ≈ lawsone. We propose that the most probable reactions are an initial two-electron oxidation of H2S to S0 and reduction of NQ to NQH2. S0 may react with H2S or elongate H2Sn in variety of reactions. Reoxidation of NQH2 likely involves a semiquinone radical (NQ·−) intermediate via several mechanisms involving oxygen and comproportionation to produce NQ and superoxide. Dismutation of the latter forms hydrogen peroxide which then further oxidizes RSS to sulfoxides. These findings provide the chemical background for novel sulfur-based approaches to naphthoquinone-directed therapies.

The role of sulfur compounds in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a common respiratory disease that brings about great social and economic burden, with oxidative stress and inflammation affecting the whole disease progress. Sulfur compounds such as hydrogen sulfide (H₂S), thiols, and persulfides/polysulfides have intrinsic antioxidant and anti-inflammatory ability, which is engaged in the pathophysiological process of COPD. Hydrogen sulfide mainly exhibits its function by S-sulfidation of the cysteine residue of the targeted proteins. It also interacts with nitric oxide and acts as a potential biomarker for the COPD phenotype. Thiols’ redox buffer such as the glutathione redox couple is a major non-enzymatic redox buffer reflecting the oxidative stress in the organism. The disturbance of redox buffers was often detected in patients with COPD, and redressing the balance could delay COPD exacerbation. Sulfane sulfur refers to a divalent sulfur atom bonded with another sulfur atom. Among them, persulfides and polysulfides have an evolutionarily conserved modification with antiaging effects. Sulfur compounds and their relative signaling pathways are also associated with the development of comorbidities in COPD. Synthetic compounds which can release H₂S and persulfides in the organism have gradually been developed. Naturally extracted sulfur compounds with pharmacological effects also aroused great interest. This study discussed the biological functions and mechanisms of sulfur compounds in regulating COPD and its comorbidities.

A novel intra- and extracellular distribution pattern of elemental sulfur in Pseudomonas sp. C27-driven denitrifying sulfide removal process

Pseudomonas sp. C27 can achieve the conversion of toxic sulfide to economical elemental sulfur (S⁰) with various electron acceptors. In this study the distribution pattern of S⁰ produced by C27 in denitrifying sulfide removal (DSR) process was explored. The SEM observation identified that the particle size of the biogenic S⁰ was at micron level. Strikingly, a novel distribution pattern of S⁰ was revealed that the produced S⁰ was not directly secreted extracellularly, but be stored temporarily in the cell interior. Pyrolysis at 65 °C for 20 min were recommended prior to S⁰ recovery, which could maximize the separation of extracellular polymeric substances (EPS) from C27. Furthermore, the effects of N/S molar ratio, initial sulfide concentration, and micro-oxygen condition were investigated to improve the production of S⁰ by C27. The highest S⁰ production was obtained at S/N of 3 and anaerobic condition seemed to favor the S⁰ production by C27. This study would provide a theoretical support for highly efficient sulfide removal as well as S⁰ recovery in sulfide-laden wastewater treatment.

Sulfane Sulfur Is an Intrinsic Signal for the Organic Peroxide Sensor OhrR of Pseudomonas aeruginosa

Sulfane sulfur, including organic persulfide and polysulfide, is a normal cellular component, and its level varies during growth. It is emerging as a signaling molecule in bacteria, regulating the gene regulator MarR in Escherichia coli, MexR in Pseudomonas aeruginosa, and MgrA of Staphylococcus aureus. They are MarR-family regulators and are often repressors for multiple antibiotic resistance genes. Here, we report that another MarR-type regulator OhrR that represses the expression of itself and a thiol peroxidase gene ohr in P. aeruginosa PAO1 also responded to sulfane sulfur. PaOhrR formed disulfide bonds between three Cys residues within a dimer after polysulfide treatment. The modification reduced its affinity to its cognate DNA binding site. An Escherichia coli reporter system, in which mKate was under the repression of OhrR, showed that PaOhrR derepressed its controlled gene when polysulfide was added, whereas the mutant PaOhrR with two Cys residues changed to Ser residues did not respond to polysulfide. The expression of the PaOhrR-repressed mKate was significantly increased when the cells enter the late log phase when cellular sulfane sulfur reached a maximum, but the mKate expression under the control of the PaOhrR-C9SC19S double mutant was not increased. Furthermore, the expression levels of ohrR and ohr in P. aeruginosa PAO1 were significantly increased when cellular sulfane sulfur was high. Thus, PaOhrR senses both exogenous and intrinsic sulfane sulfur to derepress its controlled genes. The finding also suggests that sulfane sulfur may be a common inducer of the MarR-type regulators, which may confer the bacteria to resist certain stresses without being exposed to the stresses.

Synechococcus sp. PCC7002 Uses Peroxiredoxin to Cope with Reactive Sulfur Species Stress

Cyanobacteria are a widely distributed group of microorganisms in the ocean, and they often need to cope with the stress of reactive sulfur species, such as sulfide and sulfane sulfur. Sulfane sulfur refers to the various forms of zero-valent sulfur, including persulfide, polysulfide, and element sulfur (S₈). Although sulfane sulfur participates in signaling transduction and resistance to reactive oxygen species in cyanobacteria, it is toxic at high concentrations and induces sulfur stress, which has similar effects to oxidative stress. In this study, we report that Synechococcus sp. PCC7002 uses peroxiredoxin to cope with the stress of cellular sulfane sulfur. Synechococcus sp. PCC7002 contains six peroxiredoxins, and all were induced by S₈. Peroxiredoxin I (PrxI) reduced S₈ to H₂S by forming a disulfide bond between residues Cys⁵³ and Cys¹⁵³ of the enzyme. A partial deletion strain of Synechococcus sp. PCC7002 with decreased copy numbers of the prxI gene was more sensitive to S₈ than was the wild type. Thus, peroxiredoxin is involved in maintaining the homeostasis of cellular sulfane sulfur in cyanobacteria. Given that peroxiredoxin evolved before the occurrence of O₂ on Earth, its original function could have been to cope with reactive sulfur species stress, and that function has been preserved. IMPORTANCE Cyanobacteria are the earliest microorganisms that perform oxygenic photosynthesis, which has played a key role in the evolution of life on Earth, and they are the most important primary producers in the modern oceans. The cyanobacterium Synechococcus sp. PCC7002 uses peroxiredoxin to reduce high levels of sulfane sulfur. That function is possibly the original role of peroxiredoxin, as the enzyme evolved before the appearance of O₂ on Earth. The preservation of the reduction of sulfane sulfur by peroxiredoxin5-type peroxiredoxins may offer cyanobacteria an advantage in the complex environment of the modern oceans.

Reactive Species in Progeroid Syndromes and Aging-Related Processes

Significance: Reactive species have been classically considered causative of age-related degenerative processes, but the scenario appears considerably more complex and to some extent counterintuitive than originally anticipated. The impact of reactive species in precocious aging syndromes is revealing new clues to understand and perhaps challenge the resulting degenerative processes. Recent Advances: Our understanding of reactive species has considerably evolved, including their hormetic effect (beneficial at a certain level, harmful beyond this level), the occurrence of diverse hormetic peaks in different cell types and organisms, and the extended type of reactive species that are relevant in biological processes. Our understanding of the impact of reactive species has also expanded from the dichotomic damaging/signaling role to modulation of gene expression. Critical Issues: These new concepts are affecting the study of aging and diseases where aging is greatly accelerated. We discuss how notions arising from the study of the underlying mechanisms of a progeroid disease, Cockayne syndrome, represent a paradigm shift that may shed a new light in understanding the role of reactive species in age-related degenerative processes. Future Issues: Future investigations urge to explore established and emerging notions to elucidate the multiple contributions of reactive species in degenerative processes linked to pathophysiological aging and their possible amelioration. Antioxid. Redox Signal. 37, 208-228.

Optimization of a Method for Detecting Intracellular Sulfane Sulfur Levels and Evaluation of Reagents That Affect the Levels in Escherichia coli

Sulfane sulfur is a class of compounds containing zero-valent sulfur. Most sulfane sulfur compounds are reactive and play important signaling roles. Key enzymes involved in the production and metabolism of sulfane sulfur have been characterized; however, little is known about how to change intracellular sulfane sulfur (iSS) levels. To accurately measure iSS, we optimized a previously reported method, in which reactive iSS reacts with sulfite to produce thiosulfate, a stable sulfane sulfur compound, before detection. With the improved method, several factors were tested to influence iSS in Escherichia coli. Temperature, pH, and osmotic pressure showed little effect. At commonly used concentrations, most tested oxidants, including hydrogen peroxide, tert-butyl hydroperoxide, hypochlorous acid, and diamide, did not affect iSS, but carbonyl cyanide m-chlorophenyl hydrazone increased iSS. For reductants, 10 mM dithiothreitol significantly decreased iSS, but tris(2-carboxyethyl)phosphine did not. Among different sulfur-bearing compounds, NaHS, cysteine, S₂O₃²⁻ and diallyl disulfide increased iSS, of which only S₂O₃²⁻ did not inhibit E. coli growth at 10 mM or less. Thus, with the improved method, we have identified reagents that may be used to change iSS in E. coli and other organisms, providing tools to further study the physiological functions of iSS.

Sulfane Sulfur Posttranslationally Modifies the Global Regulator AdpA to Influence Actinorhodin Production and Morphological Differentiation of Streptomyces coelicolor

The transcription factor AdpA is a key regulator controlling both secondary metabolism and morphological differentiation in Streptomyces. Due to its critical functions, its expression undergoes multilevel regulations at transcriptional, posttranscriptional, and translational levels, yet no posttranslational regulation has been reported. Sulfane sulfur, such as hydro polysulfide (HS_nH, n ≥ 2) and organic polysulfide (RS_nH, n ≥ 2), is common inside microorganisms, but its physiological functions are largely unclear. Here, we discovered that sulfane sulfur posttranslationally modifies AdpA in Streptomyces coelicolor via specifically reacting with Cys⁶² of AdpA to form a persulfide (Cys⁶²-SSH). This modification decreases the affinity of AdpA to its self-promoter P_adpA, allowing increased expression of adpA, further promoting the expression of its target genes actII-4 and wblA. ActII-4 activates actinorhodin biosynthesis, and WblA regulates morphological development. Bioinformatics analyses indicated that AdpA-Cys⁶² is highly conserved in Streptomyces, suggesting the prevalence of such modification in this genus. Thus, our study unveils a new type of regulation on the AdpA activity and sheds a light on how sulfane sulfur stimulates the production of antibiotics in Streptomyces.

Sulfane Sulfur Compounds as Source of Reappearance of Reductive Off-Odors in Wine

Reactive compounds with one or more sulfane sulfur atoms can be an important source of reductive off-odors in wine. These substances contain labile sulfur, which can participate in microbiological (enzymatic) and chemical transformations (including in the post-bottling period), releasing malodorous hydrogen sulfide (H2S) and its derivatives (MeSH, EtSH, etc.). The following sulfane sulfur compounds were considered in this review as important precursors in the wine chemistry of reductive aromas: elemental sulfur (S8), persulfides (R-S-S-H), polysulfanes (R-Sn-R(′)), polythionates (−O3S-Sn-SO3−), thiosulfate (S2O32−) and derivatives of (poly)sulfane monosulfonic acids (R-Sn-SO3H). This review discusses the formation of these compounds, their reactivity and chemical transformations in wine, including reactions of nucleophilic substitution. In particular, the reactions of thiolysis, thiosulfatolysis and sulfitolysis of sulfane sulfur compounds are described, which lead in the end to reductive aroma compounds. In this way, the review attempts to shed light on some of the mysteries in the field of sulfur chemistry in wine and the reappearance of reductive off-odors after bottling.

Lipoic Acid Does Not Affect The Growth of Mycoplasma hominis Cells In Vitro

Mycoplasma hominis is associated with various infections, for which the treatment can be complex. Lipoic acid (LA) plays a role as a cofactor in eukaryotes, most Bacteria, and some Archea. Research of recent years has increasingly pointed to the therapeutic properties of exogenously supplemented LA. The present study was conducted on 40 strains of M. hominis cultured with the following LA concentrations: 1,200 μg/ml, 120 μg/ml, and 12 μg/ml. The bacterial colonies of each strain were counted and expressed as the number of colony-forming units/ml (CFU). The number of CFU in M. hominis strains obtained in the presence of LA was compared with the number of CFU in the strains grown in the media without LA. The obtained results indicated that the presence of LA in the medium did not affect the growth of M. hominis. The investigation of the influence of LA on the growth and survival of microbial cells not only allows for obtaining an answer to the question of whether LA has antimicrobial activity and, therefore, can be used as a drug supporting the treatment of patients infected with a given pathogenic microorganism. Such studies are also crucial for a better understanding of LA metabolism in the microbial cells, which is also important for the search for new antimicrobial drugs. This research is, therefore, an introduction to such further studies.

Sulfane Sulfur Is a Strong Inducer of the Multiple Antibiotic Resistance Regulator MarR in Escherichia coli

Sulfane sulfur, including persulfide and polysulfide, is produced from the metabolism of sulfur-containing organic compounds or from sulfide oxidation. It is a normal cellular component, participating in signaling. In bacteria, it modifies gene regulators to activate the expression of genes involved in sulfur metabolism. However, to determine whether sulfane sulfur is a common signal in bacteria, additional evidence is required. The ubiquitous multiple antibiotic resistance regulator (MarR) family of regulators controls the expression of numerous genes, but the intrinsic inducers are often elusive. Recently, two MarR family members, Pseudomonas aeruginosa MexR and Staphylococcus aureus MgrA, have been reported to sense sulfane sulfur. Here, we report that Escherichia coli MarR, the prototypical member of the family, also senses sulfane sulfur to form one or two disulfide or trisulfide bonds between two dimers. Although the tetramer with two disulfide bonds does not bind to its target DNA, our results suggest that the tetramer with one disulfide bond does bind to its target DNA, with reduced affinity. An MarR-repressed mKate reporter is strongly induced by polysulfide in E. coli. Further investigation is needed to determine whether sulfane sulfur is a common signal of the family members, but three members sense cellular sulfane sulfur to turn on antibiotic resistance genes. The findings offer additional support for a general signaling role of sulfane sulfur in bacteria.

Sulfide-quinone oxidoreductase is required for cysteine synthesis and indispensable to mitochondrial health

Mitochondrial dysfunction is related to common age-related disorders, including neurodegenerative diseases, metabolic syndrome, and carcinogenesis. Therefore, maintaining the functionality and integrity of mitochondria is important for human health. Herein, we found that sulfide:quinone oxidoreductase (Sqr), which oxidizes hydrogen sulfide to reactive sulfur species (RSS), was indispensable to mitochondria health in the eukaryotic model microorganism Schizosaccharomyces pombe. Sqr knock-out led to morphological changes and functional deficiencies of mitochondria and apoptosis in S. pombe. The Sqr knock-out strain displayed the same phenotypes as the cysteine-synthesis-deficient strain, and cysteine addition complemented the effects caused by Sqr knock-out. In S. pombe, Sqr was the main RSS producer in mitochondria, and RSS instead of H₂S was used by cysteine synthase to synthesize cysteine. This finding rewrites the cysteine biosynthesis route in S. pombe and may also in other eukaryotes and prokaryotes, and highlights the importance of cysteine and RSS in maintaining mitochondrial health.

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Sqr is an important RSS producer in mitochondria.

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RSS is involved in cysteine de novo biosynthesis. It is the de facto substrate of cysteine synthase.

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Sqr is required for maintaining the health of mitochondria, might be a new target for inhibiting cell proliferation.

Sulfane Sulfur Regulates LasR-Mediated Quorum Sensing and Virulence in Pseudomonas aeruginosa PAO1

Sulfane sulfur, such as inorganic and organic polysulfide (HS_n^- and RS_n^-, n > 2), is a common cellular component, produced either from hydrogen sulfide oxidation or cysteine metabolism. In Pseudomonas aeruginosa PAO1, LasR is a quorum sensing master regulator. After binding its autoinducer, LasR binds to its target DNA to activate the transcription of a suite of genes, including virulence factors. Herein, we report that the production of hydrogen sulfide and sulfane sulfur were positively correlated in P. aeruginosa PAO1, and sulfane sulfur was able to modify LasR, which generated Cys¹⁸⁸ persulfide and trisulfide and produced a pentasulfur link between Cys²⁰¹ and Cys²⁰³. The modifications did not affect LasR binding to its target DNA site, but made it several-fold more effective than unmodified LasR in activating transcription in both in vitro and in vivo assays. On the contrary, H₂O₂ inactivates LasR via producing a disulfide bond between Cys²⁰¹ and Cys²⁰³. P. aeruginosa PAO1 had a high cellular sulfane sulfur and high LasR activity in the mid log phase and early stationary phase, but a low sulfane sulfur and low LasR activity in the declination phase. Thus, sulfane sulfur is a new signaling factor in the bacterium, adding another level of control over LasR-mediated quorum sensing and turning down the activity in old cells.

Sulfane sulfur-activated actinorhodin production and sporulation is maintained by a natural gene circuit in Streptomyces coelicolor

Sulfane sulfur, including polysulfide and persulfide, is a newly identified cellular component present in microorganisms; however, its physiological functions are unclear. Streptomyces coelicolor M145 is a model strain of actinomycetes, which produces several polyketides, including actinorhodin. Herein, we found that both exogenously added and endogenously generated sulfane sulfur increased the actinorhodin production and accelerated spore formation of S. coelicolor M145. This bacterial species carries a natural gene circuit containing four genes that encode a CsoR-like transcription factor (ScCsoR), persulfide dioxygenase (ScPDO), rhodanese and a sulfite transporter, which were shown to be responsible for sensing and removal of excessive sulfane sulfur. ScCsoR was observed to bind to the promoters of the four genes, thus repressing their transcription. Sulfane sulfur modified Cys37 of ScCsoR, and the modified ScCSoR did not bind to the promoters, thereby activating the transcription of ScPDO. The deletion of ScCsoR decreased cellular sulfane sulfur, while the deletion of ScPDO increased its levels. The increased sulfane sulfur promoted actinorhodin production and sporulation. This study unveiled a natural gene circuit for maintaining sulfane sulfur homeostasis in bacteria. Further, we identified the trigger effect of sulfane sulfur on actinorhodin production, presenting a new approach for activating polyketide gene clusters in actinomycetes.

Sulfane Sulfur is an intrinsic signal activating MexR-regulated antibiotic resistance in Pseudomonas aeruginosa

Pseudomonas aeruginosa PAO1, an opportunistic human pathogen, deploys several strategies to resist antibiotics. It uses multidrug efflux pumps, including the MexAB-OprM pump, for antibiotic resistance, and it also produces hydrogen sulfide (H₂ S) that provides some defense against antibiotics. MexR functions as a transcriptional repressor of the mexAB-oprM operon. MexR responds to oxidative stresses caused by antibiotic exposure, and it also displays a growth phase-dependent derepression of the mexAB-oprM operon. However, the intrinsic inducer has not been identified. Here, we report that P. aeruginosa PAO1 produced sulfane sulfur, including glutathione persulfide and inorganic polysulfide, produced from either H₂ S oxidation or from L-cysteine metabolism. Sulfane sulfur directly reacted with MexR, forming di- and trisulfide cross-links between two Cys residues, to derepress the mexAB-oprM operon. Levels of cellular sulfane sulfur and mexAB-oprM expression varied during growth, and both reached the maximum during the stationary phase of growth. Thus, self-produced H₂ S and sulfane sulfur may facilitate antibiotic resistance via inducing the expression of antibiotic resistance genes.