OsmC proteins of Mycobacterium tuberculosis and Mycobacterium smegmatis protect against organic hydroperoxide stress

Biotransformation of Pb and As from sewage sludge and food waste by black soldier fly larvae: Migration mechanism of bacterial community and metalloregulatory protein scales

The accumulation and transformation of lead (Pb) and arsenic (As) during the digestion of sewage sludge (SS) by black soldier fly larvae (BSFL) remain unclear. In this study, we used 16 s rRNA and metagenomic sequencing techniques to investigate the correlation between the microbial community, metalloregulatory proteins (MRPs), and Pb and As migration and transformation. During the 15-day test period, BSFL were able to absorb 34-48 % of Pb and 32-45 % of As into their body. Changes in bacterial community abundance, upregulation of MRPs, and redundancy analysis (RDA) results confirmed that ZntA, EfeO, CadC, ArsR, ArsB, ArsD, and ArsA play major roles in the adsorption and stabilization of Pb and As, which is mainly due to the high contribution rates of Lactobacillus (48-59 %) and Enterococcus (21-23 %). Owing to the redox reaction, the regulation of the MRPs, and the change in pH, the Pb and As in the BSFL residue were mainly the residual fraction (F4). The RDA results showed that Lactobacillus and L.koreensis could significantly (P < 0.01) reduce the reducible fraction (F2) and F4 of Pb, whereas Firmicutes and L.fermentum can significantly (P < 0.05) promote the transformation of As to F4, thus realizing the passivation Pb and As. This study contributes to the understanding of Pb and As in SS adsorbed by BSFL and provides important insights into the factors that arise during the BSFL-mediated migration of Pb and As.

Antibiotic Resistance Diagnosis in ESKAPE Pathogens-A Review on Proteomic Perspective

Antibiotic resistance has emerged as an imminent pandemic. Rapid diagnostic assays distinguish bacterial infections from other diseases and aid antimicrobial stewardship, therapy optimization, and epidemiological surveillance. Traditional methods typically have longer turn-around times for definitive results. On the other hand, proteomic studies have progressed constantly and improved both in qualitative and quantitative analysis. With a wide range of data sets made available in the public domain, the ability to interpret the data has considerably reduced the error rates. This review gives an insight on state-of-the-art proteomic techniques in diagnosing antibiotic resistance in ESKAPE pathogens with a future outlook for evading the "imminent pandemic".

Enrichment and speciation changes of Cu and Cd in black soldier fly (Hermetia illucens) larval compost and their effects on larval growth performance

Municipal sludge (MS), rainwater sludge (RS), and kitchen waste (KW) were used as nutritional supplements for black soldier fly larvae (BSFL). Cd (52.3 %) was more easily assimilated in the BSFL body than Cu (34.8 %). After biotransformation in BSFL, the weak acid-soluble fraction (F1) of Cu and Cd increased by an average of 29.0 % and 42.7 %, respectively, whereas the reducible fraction (F2) of Cu and Cd decreased by an average of 13.8 % and 56.4 %, respectively, in the BSFL sand (BSFL feces and waste residues). A significant correlation (P < 0.01) was found between pH and the speciation of Cu and Cd. The abundance of Bacteroides had a positive correlation (P < 0.05) with the F1 of Cu, an extremely significant negative correlation (P < 0.001) with the F2 of Cd, and an extremely significant positive correlation with the F1 of Cd (P < 0.001). In addition, Cu and Cd exposures significantly (P < 0.01) reduced larval weight by 67.7 % and 45.3 %, respectively, pupation rate by 46.3 % and 26.5 %, respectively, and eclosion rate by 35.5 % and 33.4 %, respectively. Exposure to high concentrations of Cu and Cd also prolonged the development cycle (1-12 days) of BSFL and led to the failure of BSFL to complete their metamorphosis.

Ohr - OhrR, a neglected and highly efficient antioxidant system: Structure, catalysis, phylogeny, regulation, and physiological roles

Ohrs (organic hydroperoxide resistance proteins) are antioxidant enzymes that play central roles in the response of microorganisms to organic peroxides. Here, we describe recent advances in the structure, catalysis, phylogeny, regulation, and physiological roles of Ohr proteins and of its transcriptional regulator, OhrR, highlighting their unique features. Ohr is extremely efficient in reducing fatty acid peroxides and peroxynitrite, two oxidants relevant in host-pathogen interactions. The highly reactive Cys residue of Ohr, named peroxidatic Cys (C_p), composes together with an arginine and a glutamate the catalytic triad. The catalytic cycle of Ohrs involves a condensation between a sulfenic acid (C_p-SOH) and the thiol of the second conserved Cys, leading to the formation of an intra-subunit disulfide bond, which is then reduced by dihydrolipoamide or lipoylated proteins. A structural switch takes place during catalysis, with the opening and closure of the active site by the so-called Arg-loop. Ohr is part of the Ohr/OsmC super-family that also comprises OsmC and Ohr-like proteins. Members of the Ohr, OsmC and Ohr-like subgroups present low sequence similarities among themselves, but share a high structural conservation, presenting two Cys residues in their active site. The pattern of gene expression is also distinct among members of the Ohr/OsmC subfamilies. The expression of ohr genes increases upon organic hydroperoxides treatment, whereas the signals for the upregulation of osmC are entry into the stationary phase and/or osmotic stress. For many ohr genes, the upregulation by organic hydroperoxides is mediated by OhrR, a Cys-based transcriptional regulator that only binds to its target DNAs in its reduced state. Since Ohrs and OhrRs are involved in virulence of some microorganisms and are absent in vertebrate and vascular plants, they may represent targets for novel therapeutic approaches based on the disruption of this key bacterial organic peroxide defense system.

A Large-Scale Multiple Genome Comparison of Acidophilic Archaea (pH ≤ 5.0) Extends Our Understanding of Oxidative Stress Responses in Polyextreme Environments

Acidophilic archaea thrive in anaerobic and aerobic low pH environments (pH < 5) rich in dissolved heavy metals that exacerbate stress caused by the production of reactive oxygen species (ROS) such as hydrogen peroxide (H2O2), hydroxyl radical (OH) and superoxide (O2−). ROS react with lipids, proteins and nucleic acids causing oxidative stress and damage that can lead to cell death. Herein, genes and mechanisms potentially involved in ROS mitigation are predicted in over 200 genomes of acidophilic archaea with sequenced genomes. These organisms are often be subjected to simultaneous multiple stresses such as high temperature, high salinity, low pH and high heavy metal loads. Some of the topics addressed include: (1) the phylogenomic distribution of these genes and what this can tell us about the evolution of these mechanisms in acidophilic archaea; (2) key differences in genes and mechanisms used by acidophilic versus non-acidophilic archaea and between acidophilic archaea and acidophilic bacteria and (3) how comparative genomic analysis predicts novel genes or pathways involved in oxidative stress responses in archaea and likely horizontal gene transfer (HGT) events.

Genomic characterization and proteomic analysis of the halotolerant Micrococcus luteus SA211 in response to the presence of lithium

Micrococcus luteus SA211, isolated from the Salar del Hombre Muerto in Argentina, developed responses that allowed its survival and growth in presence of high concentrations of lithium chloride (LiCl). In this research, analysis of total genome sequencing and a comparative proteomic approach were performed to investigate the responses of this bacterium to the presence of Li. Through proteomic analysis, we found differentially synthesized proteins in growth media without LiCl (DM) and with 10 (D10) and 30 g/L LiCl (D30). Bi-dimensional separation of total protein extracts allowed the identification of 17 over-synthesized spots when growth occurred in D30, five in D10, and six in both media with added LiCl. The results obtained showed different metabolic pathways involved in the ability of M. luteus SA211 to interact with Li. These pathways include defense against oxidative stress, pigment and protein synthesis, energy production, and osmolytes biosynthesis and uptake. Furthermore, mono-dimensional gel electrophoresis revealed differential protein synthesis at equivalent NaCl and LiCl concentrations, suggesting that this strain would be able to develop different responses depending on the nature of the ion. Moreover, the percentage of proteins with acidic pI predicted and observed was highlighted, indicating an adaptation to saline environments. To the best of our knowledge, this is the first report showing the relationship between protein synthesis and genome sequence analysis in response to Li, showing the great biotechnological potential that native microorganisms present, especially those isolated from extreme environments.

Transformation of pig manure by passage through the gut of black soldier fly larvae (Hermetia illucens): Metal speciation, potential pathogens and metal-related functional profiling

Black soldier fly larvae (BSFL) have great potential in livestock manure disposal. However, the changes in metal speciation, microbial communities, potential pathogens during the manure transformation process by BSFL is still largely uncharacterized, as well as the underlying metal tolerance mechanism of larval gut microbiome. Here we used BSFL to convert pig manure (PM) into larval feces (BF), and investigated the metal and microbial changes in the conversion process. Physicochemical parameters (e.g. pH, electrical conductivity, total nitrogen, total phosphorus and total potassium) in PM were significantly altered compared to BF. After conversion, less than 10% of Cu and Zn were accumulated in larval bodies. The bioavailable fraction of Cu (88.3%-86.2%) and Zn (80.6%-82.3%) occupied as the primary form in PM and BF. Genera Enterococcus, Clostridium_sensu_stricto_1, Terrisporobacter and Romboutsia were substantially enriched in the final BSFL gut (GF) compared with initial gut (GI). BSFL transformation substantially reduced pathogen abundances (decreased by 89%) derived from pig manure. Functional genes involved in metal homeostasis and resistance (e.g. CutC, pcoC, cusR, zurR and zntB) were obviously strengthened (by 2.3-7.7 folds) in GF than in GI, which might partly explain the metal tolerance ability of BSFL during the livestock manure transformation process.

Ohr and OhrR Are Critical for Organic Peroxide Resistance and Symbiosis in Azorhizobium caulinodans ORS571

Azorhizobium caulinodans is a symbiotic nitrogen-fixing bacterium that forms both root and stem nodules on Sesbania rostrata. During nodule formation, bacteria have to withstand organic peroxides that are produced by plant. Previous studies have elaborated on resistance to these oxygen radicals in several bacteria; however, to the best of our knowledge, none have investigated this process in A. caulinodans. In this study, we identified and characterised the organic hydroperoxide resistance gene ohr (AZC_2977) and its regulator ohrR (AZC_3555) in A. caulinodans ORS571. Hypersensitivity to organic hydroperoxide was observed in an ohr mutant. While using a lacZ-based reporter system, we revealed that OhrR repressed the expression of ohr. Moreover, electrophoretic mobility shift assays demonstrated that OhrR regulated ohr by direct binding to its promoter region. We showed that this binding was prevented by OhrR oxidation under aerobic conditions, which promoted OhrR dimerization and the activation of ohr. Furthermore, we showed that one of the two conserved cysteine residues in OhrR, Cys₁₁, was critical for the sensitivity to organic hydroperoxides. Plant assays revealed that the inactivation of Ohr decreased the number of stem nodules and nitrogenase activity. Our data demonstrated that Ohr and OhrR are required for protecting A. caulinodans from organic hydroperoxide stress and play an important role in the interaction of the bacterium with plants. The results that were obtained in our study suggested that a thiol-based switch in A. caulinodans might sense host organic peroxide signals and enhance symbiosis.

Shotgun proteomic analysis of ESBL-producing and non-ESBL-producing Klebsiella Pneumoniae clinical isolates

Klebsiella pneumoniae is a pathogenic bacterium that is responsible for a wide range of infections in humans. An increased rate of infections caused by multi-drug-resistant K. pneumoniae has been noted in the last two decades. The association between antimicrobial resistance and virulence is an important topic of study. Genomic tools have been used widely for the detection of virulence. In our study, we used proteomic analysis with mass spectrometry and bioinformatics tools to explore the virulence factors of both ESBL-producing and non-ESBL-producing K. pneumoniae and to determine the association between virulence and antimicrobial resistance in these clinical isolates. We have revealed different proteomic profiles and different pathways between the ESBL- and non-ESBL-producing groups. Many proteins involved in stress responses have been reported in the shared proteome between ESBL-and non-ESBL producers, such as ElaB protein, Lon protease, and universal stress proteins G and A. The virulence and pathogenicity of ESBL-producing bacteria were stronger than those of the non-ESBL-producing bacteria. Several unique virulence determinants were identified in ESBL-producing K. pneumoniae, such as proteins with lyase, catalase, isochorismatase, and oxidoreductase activity.

The msaABCR Operon Regulates the Response to Oxidative Stress in Staphylococcus aureus

Staphylococcus aureus has evolved a complex regulatory network that controls a multitude of defense mechanisms against the deleterious effects of oxidative stress stimuli, subsequently leading to the pathogen's survival and persistence in the hosts. Previously, we characterized the msaABCR operon as a regulator of virulence, antibiotic resistance, and the formation of persister cells in S. aureus Deletion of the msaABCR operon resulted in the downregulation of several genes involved in resistance against oxidative stress. Notably, those included carotenoid biosynthetic genes and the ohr gene, which is involved in resistance against organic hydroperoxides. These findings led us to hypothesize that the msaABCR operon is involved in resisting oxidative stress generated in the presence of both H₂O₂ and organic hydroperoxides. Here, we report that a protein product of the msaABCR operon (MsaB) transcriptionally regulates the expression of the crtOPQMN operon and the ohr gene to resist in vitro oxidative stresses. In addition to its direct regulation of the crtOPQMN operon and ohr gene, we also show that MsaB is the transcriptional repressor of sarZ (repressor of ohr). Taken together, these results suggest that the msaABCR operon regulates an oxidative stress defense mechanism, which is required to facilitate persistent and recurrent staphylococcal infections. Moving forward, we plan to investigate the role of msaABCR in the persistence of S. aureus under in vivo conditions.IMPORTANCE This study shows the involvement of the msaABCR operon in resisting oxidative stress by Staphylococcus aureus generated under in vitro and ex vivo conditions. We show that MsaB regulates the expression and production of a carotenoid pigment, staphyloxanthin, which is a potent antioxidant in S. aureus We also demonstrate that MsaB regulates the ohr gene, which is involved in defending against oxidative stress generated by organic hydroperoxides. This study highlights the importance of msaABCR in the survival of S. aureus in the presence of various environmental stimuli that mainly exert oxidative stress. The findings from this study indicate the possibility that msaABCR is involved in the persistence of staphylococcal infections and therefore could be a potential antimicrobial target to overcome recalcitrant staphylococcal infections.

OsmC in Corynebacterium glutamicum was a thiol-dependent organic hydroperoxide reductase

Bacterial antioxidants play a vital role in the detoxification of exogenous peroxides. Several antioxidant defenses including low-molecular-weight thiols (LMWTs) and protective enzymes were developed to help the bacterium withstand the adverse stress. Although osmotically induced bacterial protein C (OsmC), classified as the organic hydroperoxide reductase (Ohr)/OsmC superfamily, has been demonstrated in some mycobacterial species, including M. tuberculosis and M. smegmatis, its physiological and biochemical functions in C. glutamicum remained elusive. Here we found the lack of C. glutamicum osmC gene resulted in decreased cell viability and increased intracellular reactive oxygen species accumulation under organic hydroperoxides (OHPs) stress conditions. The osmC expression was induced in the multiple antibiotic resistance regulator MarR-dependent manner by OHPs, and not by other oxidants or osmotic stress. Peroxide reductase activity showed that OsmC had a narrow range of substrates-only degrading OHPs, and detoxified OHPs mainly by linking the alkyl hydroperoxide reductase (AhpD) system (AhpD/dihydrolipoamide dehydrogenase (Lpd)/dihydrolipoamide acyltransferase (SucB)). Site-directed mutagenesis confirmed Cys48 was the peroxidatic cysteine, while Cys114 was the resolving Cys residue that formed an intramolecular disulfide bond with oxidized Cys48. Therefore, C. glutamicum OsmC was a thiol-dependent OHP reductase and played important role of protection against OHPs together with Ohr.

Utility of OhrR-Ohr system for the expression of recombinant proteins in mycobacteria and for the delivery of M. tuberculosis antigens to the phagosomal compartment

We have recently reported that in vitro and intracellular organic peroxide stress oxidizes OhrR of Mycobacterium smegmatis and that the oxidized OhrR consequently derepresses the expression of Ohr. Here we demonstrate that the OhrR-Ohr system is highly useful for the expression of recombinant mycobacterial proteins and also for the delivery of Mycobacterium tuberculosis (Mtb) antigens to the phagosomal compartments. Recombinant M. smegmatis strains, which bear plasmid constructs to express Ohr₂-T85BCFP and Ohr₂-MtrA, showed expression of fusion proteins upon induction with t-butyl hydroperoxide (t-BHP) in a dose dependent manner. The M. smegmatis expressed Ohr₂-T85BCFP fusion could be affinity purified by adding a 9x histidine tag to the C-terminal end of the fusion protein. Further, mouse bone marrow derived macrophages (BMDMs) infected with either recombinant M. smegmatis or BCG strains with ohr₂-T85BCFP construct showed expression of T85BCFP protein without any exogenously added inducer. In addition, BMDMs infected with either recombinant BCG or Mtb with ohr₂-T85BCFP construct could effectively deliver the antigens to T-cells at higher levels than strains bearing the control plasmid alone. Altogether, these results suggest that the OhrR-Ohr system is a novel inducible system to study the biology and pathogenesis of mycobacteria.

SodA Contributes to the Virulence of Avian Pathogenic Escherichia coli O2 Strain E058 in Experimentally Infected Chickens

Strains of avian pathogenic Escherichia coli (APEC), the common pathogen of avian colibacillosis, encounter reactive oxygen species (ROS) during the infection process. Superoxide dismutases (SODs), acting as antioxidant factors, can protect against ROS-mediated host defenses. Our previous reports showed that the sodA gene (encoding a Mn-cofactor-containing SOD [MnSOD]) is highly expressed during the septicemic infection process of APEC. sodA has been proven to be a virulence factor of certain pathogens, but its role in the pathogenicity of APEC has not been fully identified. In this study, we deleted the sodA gene from the virulent APEC O2 strain E058 and examined the in vitro and in vivo phenotypes of the mutant. The sodA mutant was more sensitive to hydrogen peroxide in terms of both its growth and viability than was the wild type. The ability to form a biofilm was weakened in the sodA mutant. The sodA mutant was significantly more easily phagocytosed by chicken macrophages than was the wild-type strain. Chicken infection assays revealed significantly attenuated virulence of the sodA mutant compared with the wild type at 24 h postinfection. The virulence phenotype was restored by complementation of the sodA gene. Quantitative real-time reverse transcription-PCR revealed that the inactivation of sodA reduced the expression of oxidative stress response genes katE, perR, and osmC but did not affect the expression of sodB and sodC Taken together, our studies indicate that SodA is important for oxidative resistance and virulence of APEC E058.IMPORTANCE Avian colibacillosis, caused by strains of avian pathogenic Escherichia coli, is a major bacterial disease of severe economic significance to the poultry industry worldwide. The virulence mechanisms of APEC are not completely understood. This study investigated the influence of an antioxidant protein, SodA, on the phenotype and pathogenicity of APEC O2 strain E058. This is the first report demonstrating that SodA plays an important role in protecting a specific APEC strain against hydrogen peroxide-induced oxidative stress and contributes to the virulence of this pathotype strain. Identification of this virulence factor will enhance our knowledge of APEC pathogenic mechanisms, which is crucial for designing successful strategies against associated infections and transmission.

Comparative Transcriptomics of Cold Growth and Adaptive Features of a Eury- and Steno-Psychrophile

Permafrost subzero environments harbor diverse, active communities of microorganisms. However, our understanding of the subzero growth, metabolisms, and adaptive properties of these microbes remains very limited. We performed transcriptomic analyses on two subzero-growing permafrost isolates with different growth profiles in order to characterize and compare their cold temperature growth and cold-adaptive strategies. The two organisms, Rhodococcus sp. JG3 (-5 to 30°C) and Polaromonas sp. Eur3 1.2.1 (-5 to 22°C), shared several common responses during low temperature growth, including induction of translation and ribosomal processes, upregulation of nutrient transport, increased oxidative and osmotic stress responses, and stimulation of polysaccharide capsule synthesis. Recombination appeared to be an important adaptive strategy for both isolates at low temperatures, likely as a mechanism to increase genetic diversity and the potential for survival in cold systems. While Rhodococcus sp. JG3 favored upregulating iron and amino acid transport, sustaining redox potential, and modulating fatty acid synthesis and composition during growth at -5°C compared to 25°C, Polaromonas sp. Eur3 1.2.1 increased the relative abundance of transcripts involved in primary energy metabolism and the electron transport chain, in addition to signal transduction and peptidoglycan synthesis at 0°C compared to 20°C. The increase in energy metabolism may explain why Polaromonas sp. Eur3 1.2.1 is able to sustain growth rates at 0°C comparable to those at higher temperatures. For Rhodococcus sp. JG3, flexibility in use of carbon sources, iron acquisition, control of membrane fatty acid composition, and modulating redox and co-factor potential may be ways in which this organism is able to sustain growth over a wider range of temperatures. Increasing our understanding of the microbes in these habitats helps us better understand active pathways and metabolisms in extreme environments. Identifying novel, thermolabile, and cold-active enzymes from studies such as this is also of great interest to the biotechnology and food industries.

Roles of three FurA paralogs in the regulation of genes pertaining to peroxide defense in Mycobacterium smegmatis mc2 155

Mycobacterium smegmatis mc² 155 has three genes (MSMEG_6383, furA1; MSMEG_3460, furA2; MSMEG_6253, furA3) encoding FurA (ferric-uptake regulator A) paralogs. Three FurA paralogs in M. smegmatis are functionally redundant and negatively regulate expression of a subset of genes involved in peroxide detoxification such as ahpC, katG1 and katG2, as well as their own genes. The FurA paralogs sense H₂ O₂ via metal-catalyzed His oxidation (MCHO) in the same way as PerR. The propensity of FurA2 and FurA3 for MCHO is greater than that of FurA1. The three furA genes are transcribed into leaderless mRNAs lacking the Shine-Dalgarno (SD) sequence. FurA1 and FurA3 have the quaternary structure of homodimers like most Fur homologs, whereas FurA2 occurs as a monomer. The monomeric structure of FurA2 is determined by the C-terminal region of its dimerization domain. FurA2 monomers appear to cooperatively bind to the FurA-binding site with an inverted repeat configuration and have a broader binding specificity for the target DNA than dimeric FurA1 and FurA3. Comparative transcriptomic analysis revealed that the FurA paralogs do not regulate genes related to iron homeostasis in M. smegmatis, and that expression of SigF-regulated genes is significantly decreased in a furA triple mutant relative to the wild-type strain of M. smegmatis.

Synergistic Response of Rifampicin with Hydroperoxides on Mycobacterium: A Mechanistic Study

Prolonged chemotherapy as well as rapid development of antimicrobial resistance are two of the major concerns for treatment of mycobacterial infections. To enhance the effectiveness of current drug regimens, search for compounds having synergistic interaction with anti-mycobacterial drugs has become indispensable. Here, we have investigated the intervention by oxidative stress, a major factor in mycobacterial pathogenesis, in combination with rifampicin (RIF), a first-line drug used against Mycobacterium tuberculosis. We have observed that a sub-inhibitory concentration of cumene hydroperoxide (CHP), a hydrophobic oxidant, synergistically reduced the minimum inhibitory concentration of RIF by fourfold, with a Fractional Inhibitory Concentration Index (FICI) of 0.45. Also, this interaction was found to be robust and synergistic against different strains of M. smegmatis as well as on M. bovis BCG, with FICI ranging from 0.3 to 0.6. Various physiological, biochemical and molecular parameters were explored to understand the mechanism of synergy. It was observed that increased membrane permeability owing to the presence of the oxidant, led to higher uptake of the drug. Moreover, downregulation of the hydroperoxide reductases by RIF, a transcriptional inhibitor, prevented quenching of the reactive oxygen species produced in the presence of CHP. The lipid soluble reactive species triggered autocatalytic lipid peroxidation (LPO), observed here as extensive membrane damage eventually leading to growth inhibition. Furthermore, it was seen that in combination with hydrogen peroxide (H2O2), the effect was only additive, establishing LPO as a key aspect leading toward synergism. To conclude, this work suggests that targeting the bacterial membrane by a radical species can have a significant impact on the treatment of tuberculosis.

Cupriavidus pinatubonensis AEO106 deals with copper-induced oxidative stress before engaging in biodegradation of the herbicide 4-chloro-2-methylphenoxyacetic acid

BACKGROUND

Microbial degradation of phenoxy acid (PA) herbicides in agricultural soils is important to minimize herbicide leaching to groundwater reservoirs. Degradation may, however, be hampered by exposure of the degrader bacteria to toxic metals as copper (Cu) in the soil environment. Exposure to Cu leads to accumulation of intracellular reactive oxygen species (ROS) in some bacteria, but it is not known how Cu-derived ROS and an ensuing oxidative stress affect the degradation of PA herbicides. Based on the previously proposed paradigm that bacteria deal with environmental stress before they engage in biodegradation, we studied how the degradation of the PA herbicide 2-methyl-4-chlorophenoxyacetic acid (MCPA) by the model PA degrader Cupriavidus pinatubonensis AEO106 was affected by Cu exposure.

RESULTS

Exposure of C. pinatubonensis in batch culture to sublethal concentrations of Cu increased accumulation of ROS measured by the oxidant sensing probe 2,7-dichlorodihydrofluorescein diacetate and flow cytometry, and resulted in upregulation of a gene encoding a protein belong to the Ohr/OsmC protein family. The ohr/osmC gene was also highly induced by H₂O₂ exposure suggesting that it is involved in the oxidative stress response in C. pinatubonensis. The increased ROS accumulation and increased expression of the oxidative stress defense coincided with a delay in the catabolic performance, since both expression of the catabolic tfdA gene and MCPA mineralization were delayed compared to unexposed control cells.

CONCLUSIONS

The current study suggests that Cu-induced ROS accumulation in C. pinatubonensis activates a stress response involving the product of the ohr/osmC gene. Further, the stress response is launched before induction of the catabolic tfdA gene and mineralization occurs.

Home Alone: Elimination of All but One Alternative Sigma Factor in Listeria monocytogenes Allows Prediction of New Roles for σB

Among Listeria monocytogenes' four alternative σ factors, σ^B controls the largest regulon. As σ^B-dependent transcription of some genes may be masked by overlaps among regulons, and as some σ^B-dependent genes are expressed only under very specific conditions, we hypothesized that the σ^B regulon is not yet fully defined. To further extend our understanding of the σ^B regulon, we used RNA-seq to identify σ^B-dependent genes in an L. monocytogenes strain that expresses σ^B following rhamnose induction, and in which genes encoding the other alternative sigma factors have been deleted. Analysis of RNA-seq data with multiple bioinformatics approaches, including a sliding window method that detects differentially transcribed 5' untranslated regions (UTRs), identified 105 σ^B-dependent transcription units (TUs) comprising 201 genes preceded by σ^B-dependent promoters. Of these 105 TUs, 7 TUs comprising 15 genes had not been identified previously as σ^B-dependent. An additional 23 genes not reported previously as σ^B-dependent were identified in 9 previously recognized σ^B-dependent TUs. Overall, 38 of these 201 genes had not been identified previously as members of the L. monocytogenes σ^B regulon. These newly identified σ^B-dependent genes encode proteins annotated as being involved in transcriptional regulation, oxidative and osmotic stress response, and in metabolism of energy, carbon and nucleotides. In total, 18 putative σ^B-dependent promoters were newly identified. Interestingly, a number of genes previously identified as σ^B-dependent did not show significant evidence for σ^B-dependent transcription in our experiments. Based on promoter analyses, a number of these genes showed evidence for co-regulation by σ^B and other transcriptional factors, suggesting that some σ^B-dependent genes require additional transcriptional regulators along with σ^B for transcription. Over-expression of a single alternative sigma factor in the absence of all other alternative sigma factors allowed us to: (i) identify new σ^B-dependent functions in L. monocytogenes, such as regulation of genes involved in 1,2-propanediol utilization (LMRG_00594-LMRG_00611) and biosynthesis of pyrimidine nucleotides (LMRG_00978-LMRG_00985); and (ii) identify new σ^B-dependent genes involved in stress response and pathogenesis functions. These data further support that σ^B not only regulates stress response functions, but also plays a broad role in L. monocytogenes homeostasis and resilience.

Multidomain truncated hemoglobins: New members of the globin family exhibiting tandem repeats of globin units and domain fusion

Truncated hemoglobins (trHbs) are considered the most primitive members of globin superfamily and traditionally exist as a single domain heme protein in three distinct structural organizations, type I (trHb1_N), type II (trHb2_O) and type III (trHb3_P). Our search of microbial and lower eukaryotic genomes revealed a broad array of multidomain organization, representing multiunit and chimeric forms of trHbs, where multiple units of trHbs are joined together and/or integrated with distinct functional domains. Globin motifs of these multidomain trHbs were from all three groups of trHbs and unambiguously assigned to trHb1_N, trHb2_O and trHb3_P. Multiunit and chimeric forms of trHb1_N were identified exclusively in ciliated protozoan parasites, where multiple units of trHb are integrated in tandem and/or fused with another redox active or signalling domain, presenting an interesting example of gene duplication and fusion in lower eukaryotes. In contrast, trHb2_O and trHb3_P trHbs were found only in bacteria in two or multidomain organization, where amino or carboxy terminus of trHb unit is integrated with different redox-active or oxidoreductase domains. The identification of these new multiunit and chimeric trHbs and their specific phyletic distribution presents an interesting and challenging finding to explore and understand complex functionalities of these novel multidomain trHbs. © 2017 IUBMB Life, 69(7):479-488, 2017.

Functional and evolutionary characterization of Ohr proteins in eukaryotes reveals many active homologs among pathogenic fungi

Ohr and OsmC proteins comprise two subfamilies within a large group of proteins that display Cys-based, thiol dependent peroxidase activity. These proteins were previously thought to be restricted to prokaryotes, but we show here, using iterated sequence searches, that Ohr/OsmC homologs are also present in 217 species of eukaryotes with a massive presence in Fungi (186 species). Many of these eukaryotic Ohr proteins possess an N-terminal extension that is predicted to target them to mitochondria. We obtained recombinant proteins for four eukaryotic members of the Ohr/OsmC family and three of them displayed lipoyl peroxidase activity. Further functional and biochemical characterization of the Ohr homologs from the ascomycete fungus Mycosphaerella fijiensis Mf_1 (MfOhr), the causative agent of Black Sigatoka disease in banana plants, was pursued. Similarly to what has been observed for the bacterial proteins, we found that: (i) the peroxidase activity of MfOhr was supported by DTT or dihydrolipoamide (dithiols), but not by β-mercaptoethanol or GSH (monothiols), even in large excess; (ii) MfOhr displayed preference for organic hydroperoxides (CuOOH and tBOOH) over hydrogen peroxide; (iii) MfOhr presented extraordinary reactivity towards linoleic acid hydroperoxides (k=3.18 (±2.13)×10⁸ M⁻¹ s⁻¹). Both Cys⁸⁷ and Cys¹⁵⁴ were essential to the peroxidase activity, since single mutants for each Cys residue presented no activity and no formation of intramolecular disulfide bond upon treatment with hydroperoxides. The pK_a value of the Cys_p residue was determined as 5.7±0.1 by a monobromobimane alkylation method. Therefore, eukaryotic Ohr peroxidases share several biochemical features with prokaryotic orthologues and are preferentially located in mitochondria.

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Ohr/OsmC proteins are also present in lower eukaryotic organisms.

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While Ohr proteins are massively present among Fungi, OsmC proteins are restricted to the cellular slime molds.

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Eukaryotic Ohr and OsmC present a thiol dependent peroxidase activity similar to the bacterial counterparts.

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Most of these eukaryotic enzymes are predominantly present in mitochondria.

Characterisation of a New Family of Carboxyl Esterases with an OsmC Domain

Proteins in the serine esterase family are widely distributed in bacterial phyla and display activity against a range of biologically produced and chemically synthesized esters. A serine esterase from the psychrophilic bacterium Pseudoalteromonas arctica with a C-terminal OsmC-like domain was recently characterized; here we report on the identification and characterization of further putative esterases with OsmC-like domains constituting a new esterase family that is found in a variety of bacterial species from different environmental niches. All of these proteins contained the Ser-Asp-His motif common to serine esterases and a highly conserved pentapeptide nucleophilic elbow motif. We produced these proteins heterologously in Escherichia coli and demonstrated their activity against a range of esterase substrates. Two of the esterases characterized have activity of over two orders of magnitude higher than other members of the family, and are active over a wide temperature range. We determined the crystal structure of the esterase domain of the protein from Rhodothermus marinus and show that it conforms to the classical α/β hydrolase fold with an extended ‘lid’ region, which occludes the active site of the protein in the crystal. The expansion of characterized members of the esterase family and demonstration of activity over a wide-range of temperatures could be of use in biotechnological applications such as the pharmaceutical, detergent, bioremediation and dairy industries.

Recombinant Bacillus subtilis spores for the delivery of Mycobacterium tuberculosis Ag85B-CFP10 secretory antigens

Tuberculosis continues to be a great cause of morbidity and mortality in different parts of the world. Unfortunately, the current BCG vaccine being administered is not fully protective against tuberculosis; therefore, there is a great need for alternate vaccines. With an aim to develop such vaccines, we have analyzed the utility of Bacillus subtilis spores for the expression of two major immunodominant antigens of Mycobacterium tuberculosis, Ag85B and CFP10. We created three recombinant B. subtilis strains to express a truncated fusion of Ag85B_191-325 and CFP10_1-70 antigens (T85BCFP), either on the spore coat (MTAG1 strain) or in the cytosol of B. subtilis (MTAG 2 and MTAG 3 strains). Examination of spores isolated from these strains revealed successful expression of T85BCFP antigens on the spore coat of MTAG1 as well as in the cytosol of vegetatively grown cells of MTAG2 and MTAG3, indicating that spores can indeed express M. tuberculosis antigens. In vitro antigen presentation assays with spore-infected mouse bone marrow derived macrophages (BMDM) showed that all three recombinant spores could deliver these antigens to antigen presenting cells (APCs). Mice immunized with recombinant spores displayed significantly higher levels of Ag85B specific IFN-γ producing cells in the spleen than in mice immunized with wild-type (non-recombinant) spores. In addition, these mice showed relatively higher levels of Ag85B specific IgG antibodies in the serum in comparison to mice immunized with non-recombinant spores, thus providing additional evidence that recombinant spores can deliver these antigens in vivo. These results suggest that B. subtilis spores are ideal vehicles for antigen delivery and have great potential in the development of primary and booster vaccines against tuberculosis.

Lack of mycothiol and ergothioneine induces different protective mechanisms in Mycobacterium smegmatis

Mycobacterium smegmatis contains the low molecular weight thiols, mycothiol (MSH) and ergothioneine (ESH). Examination of transposon mutants disrupted in mshC and egtA, involved in the biosynthesis of MSH and ESH respectively, demonstrated that both mutants were sensitive to oxidative, alkylating, and metal stress. However, the mshC mutant exhibited significantly more protein carbonylation and lipid peroxidation than wildtype, while the egtA mutant had less protein and lipid damage than wildtype. We further show that Ohr, KatN, and AhpC, involved in protection against oxidative stress, are upregulated in the egtA mutant. In the mshC mutant, an Usp and a putative thiol peroxidase are upregulated. In addition, mutants lacking MSH also contained higher levels of Coenzyme F420 as compared to wildtype and two Coenzyme F420 dependent enzymes were found to be upregulated. These results indicate that lack of MSH and ESH result in induction of different mechanisms for protecting against oxidative stress.

Proteomic response of β-lactamases-producing Enterobacter cloacae complex strain to cefotaxime-induced stress

Bacteria of the Enterobacter cloacae complex are among the ten most common pathogens causing nosocomial infections in the USA. Consequently, increased resistance to β-lactam antibiotics, particularly expanded-spectrum cephalosporins like cefotaxime (CTX), poses a serious threat. Differential In-Gel Electrophoresis (DIGE), followed by LC-MS/MS analysis and bioinformatics tools, was employed to investigate the survival mechanisms of a multidrug-resistant E. hormaechei subsp. steigerwaltii 51 carrying several β-lactamase-encoding genes, including the 'pandemic' blaCTX-M-15 After exposing the strain with sub-minimal inhibitory concentration (MIC) of CTX, a total of 1072 spots from the whole-cell proteome were detected, out of which 35 were differentially expressed (P ≤ 0.05, fold change ≥1.5). Almost 50% of these proteins were involved in cell metabolism and energy production, and then cell wall organization/virulence, stress response and transport. This is the first study investigating the whole-cell proteomic response related to the survival of β-lactamases-producing strain, belonging to the E. cloacae complex when exposed to β-lactam antibiotic. Our data support the theory of a multifactorial synergistic effect of diverse proteomic changes occurring in bacterial cells during antibiotic exposure, depicting the complexity of β-lactam resistance and giving us an insight in the key pathways mediating the antibiotic resistance in this emerging opportunistic pathogen.

OsmC and incomplete glycine decarboxylase complex mediate reductive detoxification of peroxides in hydrogenosomes of Trichomonas vaginalis

Osmotically inducible protein (OsmC) and organic hydroperoxide resistance protein (Ohr) are small, thiol-dependent peroxidases that comprise a family of prokaryotic protective proteins central to the defense against deleterious effects of organic hydroperoxides, which are reactive molecules that are formed during interactions between the host immune system and pathogens. Trichomonas vaginalis, a sexually transmitted parasite of humans, possesses OsmC homologues in its hydrogenosomes, anaerobic mitochondrial organelles that harbor enzymes and pathways that are sensitive to oxidative damage. The glycine decarboxylase complex (GDC), which consists of four proteins (i.e., L, H, P and T), is in eukaryotes exclusively mitochondrial enzymatic system that catalyzes oxidative decarboxylation and deamination of glycine. However, trichomonad hydrogenosomes contain only the L and H proteins, whose physiological functions are unknown. Here, we found that the hydrogenosomal L and H proteins constitute a lipoate-dependent redox system that delivers electrons from reduced nicotinamide adenine dinucleotide (NADH) to OsmC for the reductive detoxification of peroxides. Our searches of genome databases revealed that, in addition to prokaryotes, homologues of OsmC/Ohr family proteins with predicted mitochondrial localization are present in various eukaryotic lineages. Therefore, we propose that the novel OsmC-GDC-based redox system may not be limited to T. vaginalis.

Elucidating the molecular physiology of lantibiotic NAI-107 production in Microbispora ATCC-PTA-5024

Background

The filamentous actinomycete Microbispora ATCC-PTA-5024 produces the lantibiotic NAI-107, which is an antibiotic peptide effective against multidrug-resistant Gram-positive bacteria. In actinomycetes, antibiotic production is often associated with a physiological differentiation program controlled by a complex regulatory and metabolic network that may be elucidated by the integration of genomic, proteomic and bioinformatic tools. Accordingly, an extensive evaluation of the proteomic changes associated with NAI-107 production was performed on Microbispora ATCC-PTA-5024 by combining two-dimensional difference in gel electrophoresis, mass spectrometry and gene ontology approaches.

Results

Microbispora ATCC-PTA-5024 cultivations in a complex medium were characterized by stages of biomass accumulation (A) followed by biomass yield decline (D). NAI-107 production started at 90 h (A stage), reached a maximum at 140 h (D stage) and decreased thereafter. To reveal patterns of differentially represented proteins associated with NAI-107 production onset and maintenance, differential proteomic analyses were carried-out on biomass samples collected: i) before (66 h) and during (90 h) NAI-107 production at A stage; ii) during three time-points (117, 140, and 162 h) at D stage characterized by different profiles of NAI-107 yield accumulation (117 and 140 h) and decrement (162 h). Regulatory, metabolic and unknown-function proteins, were identified and functionally clustered, revealing that nutritional signals, regulatory cascades and primary metabolism shift-down trigger the accumulation of protein components involved in nitrogen and phosphate metabolism, cell wall biosynthesis/maturation, lipid metabolism, osmotic stress response, multi-drug resistance, and NAI-107 transport. The stimulating role on physiological differentiation of a TetR-like regulator, originally identified in this study, was confirmed by the construction of an over-expressing strain. Finally, the possible role of cellular response to membrane stability alterations and of multi-drug resistance ABC transporters as additional self-resistance mechanisms toward the lantibiotic was confirmed by proteomic and confocal microscopy experiments on a Microbispora ATCC-PTA-5024 lantibiotic-null producer strain which was exposed to an externally-added amount of NAI-107 during growth.

Conclusion

This study provides a net contribution to the elucidation of the regulatory, metabolic and molecular patterns controlling physiological differentiation in Microbispora ATCC-PTA-5024, supporting the relevance of proteomics in revealing protein players of antibiotic biosynthesis in actinomycetes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2369-z) contains supplementary material, which is available to authorized users.

Interplay between calcineurin and the Slt2 MAP-kinase in mediating cell wall integrity, conidiation and virulence in the insect fungal pathogen Beauveria bassiana

The entomopathogenic fungus, Beauveria bassiana, is of environmental and economic importance as an insect pathogen, currently used for the biological control of a number of pests. Cell wall integrity and conidiation are critical parameters for the ability of the fungus to infect insects and for production of the infectious propagules. The contribution of calcineurin and the Slt2 MAP kinase to cell wall integrity and development in B. bassiana was investigated. Gene knockouts of either the calcineurin CNA1 subunit or the Slt2 MAP kinase resulted in decreased tolerance to calcofluor white and high temperature. In contrast, the Δcna1 strain was more tolerant to Congo red but more sensitive to osmotic stress (NaCl, sorbitol) than the wild type, whereas the Δslt2 strain had the opposite phenotype. Changes in cell wall structure and composition were seen in the Δslt2 and Δcna1 strains during growth under cell wall stress as compared to the wild type. Both Δslt2 and Δcna1 strains showed significant alterations in growth, conidiation, and viability. Elevation of intracellular ROS levels, and decreased conidial hydrophobicity and adhesion to hydrophobic surfaces, were also seen for both mutants, as well as decreased virulence. Under cell wall stress conditions, inactivation of Slt2 significantly repressed CN-mediated phosphatase activity suggesting some level of cross talk between the two pathways. Comparative transcriptome profiling of the Δslt2 and Δcna1 strains revealed alterations in the expression of distinct gene sets, with overlap in transcripts involved in cell wall integrity, stress response, conidiation and virulence. These data illustrate convergent and divergent phenotypes and targets of the calcineurin and Slt2 pathways in B. bassiana.

Inactivation of the organic hydroperoxide stress resistance regulator OhrR enhances resistance to oxidative stress and isoniazid in Mycobacterium smegmatis

The organic hydroperoxide stress resistance regulator (OhrR) is a MarR type of transcriptional regulator that primarily regulates the expression of organic hydroperoxide reductase (Ohr) in bacteria. In mycobacteria, the genes encoding these proteins exist in only a few species, which include the fast-growing organism Mycobacterium smegmatis. To delineate the roles of Ohr and OhrR in defense against oxidative stress in M. smegmatis, strains lacking the expression of these proteins were constructed by deleting the ohrR and ohr genes, independently and together, through homologous recombination. The OhrR mutant strain (MSΔohrR) showed severalfold upregulation of Ohr expression, which could be observed at both the transcript and protein levels. Similar upregulation of Ohr expression was also noticed in an M. smegmatis wild-type strain (MSWt) induced with cumene hydroperoxide (CHP) and t-butyl hydroperoxide (t-BHP). The elevated Ohr expression in MSΔohrR correlated with heightened resistance to oxidative stress due to CHP and t-BHP and to inhibitory effects due to the antituberculosis drug isoniazid (INH). Further, this mutant strain exhibited significantly enhanced survival in the intracellular compartments of macrophages. In contrast, the strains lacking either Ohr alone (MSΔohr) or both Ohr and OhrR (MSΔohr-ohrR) displayed limited or no resistance to hydroperoxides and INH. Additionally, these strains showed no significant differences in intracellular survival from the wild type. Electrophoretic mobility shift assays (EMSAs) revealed that the overexpressed and purified OhrR interacts with the ohr-ohrR intergenic region with a greater affinity and this interaction is contingent upon the redox state of the OhrR. These findings suggest that Ohr-OhrR is an important peroxide stress response system in M. smegmatis.

Functional characterization of osmotically inducible protein C (MG_427) from Mycoplasma genitalium

Mycoplasma genitalium is the smallest self-replicating bacterium and an important human pathogen responsible for a range of urogenital infections and pathologies. Due to its limited genome size, many genes conserved in other bacteria are missing in M. genitalium. Genes encoding catalase and superoxide dismutase are absent, and how this pathogen overcomes oxidative stress remains poorly understood. In this study, we characterized MG_427, a homolog of the conserved osmC, which encodes hydroperoxide peroxidase, shown to protect bacteria against oxidative stress. We found that recombinant MG_427 protein reduced organic and inorganic peroxide substrates. Also, we showed that a deletion mutant of MG_427 was highly sensitive to killing by tert-butyl hydroperoxide and H2O2 compared to the sensitivity of the wild type. Further, the fully complemented mutant strain reversed its oxidative sensitivity. Examination of the expression pattern of MG_427 during osmotic shock, oxidative stress, and other stress conditions revealed its lack of induction, distinguishing MG_427 from other previously characterized osmC genes.

Impact of Hfq on global gene expression and intracellular survival in Brucella melitensis

Brucella melitensis is a facultative intracellular bacterium that replicates within macrophages. The ability of brucellae to survive and multiply in the hostile environment of host macrophages is essential to its virulence. The RNA-binding protein Hfq is a global regulator that is involved in stress resistance and pathogenicity. Here we demonstrate that Hfq is essential for stress adaptation and intracellular survival in B. melitensis. A B. melitensis hfq deletion mutant exhibits reduced survival under environmental stresses and is attenuated in cultured macrophages and mice. Microarray-based transcriptome analyses revealed that 359 genes involved in numerous cellular processes were dysregulated in the hfq mutant. From these same samples the proteins were also prepared for proteomic analysis to directly identify Hfq-regulated proteins. Fifty-five proteins with significantly affected expression were identified in the hfq mutant. Our results demonstrate that Hfq regulates many genes and/or proteins involved in metabolism, virulence, and stress responses, including those potentially involved in the adaptation of Brucella to the oxidative, acid, heat stress, and antibacterial peptides encountered within the host. The dysregulation of such genes and/or proteins could contribute to the attenuated hfq mutant phenotype. These findings highlight the involvement of Hfq as a key regulator of Brucella gene expression and facilitate our understanding of the role of Hfq in environmental stress adaptation and intracellular survival of B. melitensis.

A serine/threonine phosphatase encoded by MG_207 of Mycoplasma genitalium is critical for its virulence

BACKGROUND

Bacterial signal transduction systems like two component system (TCS) and Serine/Threonine kinase (STK) and Serine/Threonine phosphatase (STP) play important roles in the virulence and pathogenesis of bacterial pathogens. Mycoplasma genitalium, a mollicute that causes the urogenital diseases urethritis and cervicitis in men and women, respectively, is a pathogen which lacks TCS but possesses STK/STP. In this study, we investigated the biochemical and virulence properties of an STP protein encoded by the gene MG_207 of this species.

RESULTS

We overexpressed MG207 in Escherichia coli overexpression system as a recombinant His10MG207 protein and purified it with affinity chromatography. This recombinant protein readily hydrolyzed the substrate p-nitrophenyl phosphate (pNPP) in a dose-dependent manner. Additional studies using synthetic peptides as substrates revealed that the recombinant protein was able to hydrolyze the threonine phosphate. Further, a transposon insertion mutant strain of M. genitalium (TIM207) that lacks the protein MG207 showed differentially phosphorylated proteins when compared to the wild type G37 strain. Mass spectrometry revealed that some of the key proteins differentially phosphorylated in TIM207 strain were putative cytoskeletal protein encoded by the gene MG_328 and pyruvate dehydrogenase E1 α chain encoded by the gene MG_274. In addition, TIM207 was noticed to be less cytotoxic to HeLa cells and this correlated with the production of less hydrogen peroxide by this strain. This strain was also less efficient in inducing the differentiation of THP-1 cell line as compared to wild type M. genitalium.

CONCLUSIONS

The results of the study suggest that MG207 is an important signaling protein of M. genitalium and its presence may be crucial for the virulence of this species.

Identification of disulphide stress-responsive extracytoplasmic function sigma factors in Rothia mucilaginosa

Rothia mucilaginosa is known as a member of commensal bacterial flora in the oral cavity and has received attention as a potential opportunistic pathogen. We previously determined the genomic sequence of R. mucilaginosa DY-18, a clinical strain with biofilm-like structures isolated from an infected root canal of a tooth with persistent apical periodontitis. We found that the DY-18 genome had only two sigma factor genes that encoded the primary and extracytoplasmic function (ECF) sigma factors. Genomic analysis on the available database of R. mucilaginosa ATCC 25296 (a type strain for R. mucilaginosa) revealed that ATCC 25296 has three sigma factors: one primary sigma factor and two ECF sigma factors, one of which was highly homologous to that of DY-18. ECF sigma factors play an important role in the response to environmental stress and to the production of virulence factors. Therefore, we first examined gene-encoding sigma factors on R. mucilaginosa genome in silico. The homologous ECF sigma factors found in strains DY-18 and ATCC 25296 formed a distinct SigH (SigR) clade in a phylogenetic tree and their cognate anti-sigma factor has a HXXXCXXC motif known to respond against disulphide stress. Quantitative reverse transcription polymerase chain reaction (PCR) and microarray analysis showed that the transcriptional levels of sigH were markedly up-regulated under disulphide stress in both strains. Microarray data also demonstrated that several oxidative-stress-related genes (thioredoxin, mycothione reductase, reductase and oxidoreductase) were significantly up-regulated under the diamide stress. On the basis of these results, we conclude that the alternative sigma factor SigH of R. mucilaginosa is a candidate regulator in the redox state.

The mechanism of redox sensing in Mycobacterium tuberculosis

Tuberculosis epidemics have defied constraint despite the availability of effective treatment for the past half-century. Mycobacterium tuberculosis, the causative agent of TB, is continually exposed to a number of redox stressors during its pathogenic cycle. The mechanisms used by Mtb to sense redox stress and to maintain redox homeostasis are central to the success of Mtb as a pathogen. Careful analysis of the Mtb genome has revealed that Mtb lacks classical redox sensors such as FNR, FixL, and OxyR. Recent studies, however, have established that Mtb is equipped with various sophisticated redox sensors that can detect diverse types of redox stress, including hypoxia, nitric oxide, carbon monoxide, and the intracellular redox environment. Some of these sensors, such as heme-based DosS and DosT, are unique to mycobacteria, whereas others, such as the WhiB proteins and anti-σ factor RsrA, are unique to actinobacteria. This article provides a comprehensive review of the literature on these redox-sensory modules in the context of TB pathogenesis.