Transcriptional regulator of oxidative stress-inducible genes: direct activation by oxidation

Regulation of minD by oxyR in Neisseria gonorrhoeae

In Neisseria gonorrhoeae, cytokinesis involves Escherichia coli homologues of minC, minD and minE which are encoded as part of a min operon. MinD, a 30 kD protein component of the MinC-MinD septum inhibitory complex, together with MinE, mediates cell division site selection. Gonococci mutated in minD display aberrant cytokinesis, abnormal morphology, defective microcolony formation and virulence. minD is 274 bp upstream of oxyR, another min operon gene in N. gonorrhoeae, which encodes a redox-responsive transcriptional regulator implicated in responses to oxidative stress. In this study, we aimed to examine the oxyR-mediated regulation of minD. We observed the cotranscription of oxyR with the minCDE gene cluster. The mutation of oxyR resulted in non-midline formation of the division septum, anomalous DNA segregation, and increased aggregation of bacterial cells. qRT-PCR and Western Blot analysis revealed upregulation of minD in an oxyR mutant as compared to its isogenic wild-type N. gonorrhoeae strain in stationary phase. Furthermore, the exposure to oxidative stress in the form of H2O2 increased MinD expression levels in wild-type N. gonorrhoeae. Using β-galactosidase activity-based promoter assays, we found that oxyR negatively regulates the promoter region (PminD) upstream of minD. Our results demonstrate the involvement of oxyR in cell division and minD expression in N. gonorrhoeae.

Metabolic Regulation of a Bacterial Cell System with Emphasis on Escherichia coli Metabolism

It is quite important to understand the overall metabolic regulation mechanism of bacterial cells such as Escherichia coli from both science (such as biochemistry) and engineering (such as metabolic engineering) points of view. Here, an attempt was made to clarify the overall metabolic regulation mechanism by focusing on the roles of global regulators which detect the culture or growth condition and manipulate a set of metabolic pathways by modulating the related gene expressions. For this, it was considered how the cell responds to a variety of culture environments such as carbon (catabolite regulation), nitrogen, and phosphate limitations, as well as the effects of oxygen level, pH (acid shock), temperature (heat shock), and nutrient starvation.

DsbM, a novel disulfide oxidoreductase affects aminoglycoside resistance in Pseudomonas aeruginosa by OxyR-regulated response

A Pseudomonas aeruginosa mutant strain M122 was isolated from a Mu transposon insertion mutant library. In our prophase research, we have found that PA0058, a novel gene encodes a 234-residue conserved protein, was disrupted in the M122 mutant. In this study, the bacteriostatic experiment in vitro indicates that M122 has abnormally high aminoglycoside resistance. We expressed PA0058 in E. coli and found that PA0058 oxidizes and reduces disulfide. This biochemical characterization suggests that PA0058 is a novel disulfide oxidoreductase. Hence, the protein was designated as DsbM. Microarray analysis of the M122 mutant showed its unusual phenotype might be related to the bacterial antioxidant defense system mediated by the oxyR regulon. Meanwhile, we detected -SH content in the periplasm of M122 and wild strain and found a lower -SH/S-S ratio in M122. Therefore, we consider that the loss of dsbM function decreased the -SH/S-S ratio, which then prolongs the OxyR-regulated response, thereby conferring high aminoglycoside resistance to the M122 mutant strain. Our findings have important implications for understanding the mechanisms underlying aminoglycoside resistance in P. aeruginosa.

A universally conserved ATPase regulates the oxidative stress response in Escherichia coli

YchF is an evolutionarily conserved ATPase of unknown function. In humans, the YchF homologue hOla1 appears to influence cell proliferation and was found to be up-regulated in many tumors. A possible involvement in regulating the oxidative stress response was also suggested, but details on the underlying mechanism are lacking. For gaining insight into YchF function, we used Escherichia coli as a model organism and found that YchF overexpression resulted in H(2)O(2) hypersensitivity. This was not caused by transcriptional or translational down-regulation of H(2)O(2)-scavenging enzymes. Instead, we observed YchF-dependent inhibition of catalase activity and a direct interaction with the major E. coli catalase KatG. KatG inhibition was dependent on the ATPase activity of YchF and was regulated by post-translational modifications, most likely including an H(2)O(2)-dependent dephosphorylation. We furthermore showed that YchF expression is repressed by the transcription factor OxyR and further post-translationally modified in response to H(2)O(2). In summary, our data show that YchF functions as a novel negative regulator of the oxidative stress response in E. coli. Considering the available data on hOla1, YchF/Ola1 most likely execute similar functions in bacteria and humans, and their up-regulation inhibits the ability of the cells to scavenge damaging reactive oxygen species.

Redox active thiol sensors of oxidative and nitrosative stress

SIGNIFICANCE

The reactivity of the thiol in the side chain of cysteines is exploited by bacterial regulatory proteins that sense and respond to reactive oxygen and nitrogen species.

RECENT ADVANCES

Charged residues and helix dipoles diminish the pKa of redox active cysteines, resulting in a thiolate that is stabilized by neighboring polar amino acids. The reaction of peroxides with thiolates generates a sulfenic acid (-SOH) intermediate that often gives rise to a reversible disulfide bond. Peroxide-induced intramolecular and intermolecular disulfides and intermolecular mixed disulfides modulate the signaling activity of members of the LysR/OxyR, MarR/OhrR, and RsrA family of transcriptional regulators. Thiol-dependent regulators also help bacteria resist the nitrosative and nitroxidative stress. -SOHs, mixed disulfides, and S-nitrosothiols are some of the post-translational modifications induced by nitrogen oxides in the thiol groups of OxyR and SsrB bacterial regulatory proteins. Sulfenylation, disulfide bond formation, S-thiolation, and S-nitrosylation are reversible modifications amenable to feedback regulation by antioxidant and antinitrosative repair systems. The structural and functional changes engaged in the thiol-dependent sensing of reactive species have been adopted by several regulators to foster bacterial virulence during exposure to products of NADPH phagocyte oxidase and inducible nitric oxide synthase.

CRITICAL ISSUES

Investigations with LysR/OxyR, MarR/OhrR, and RsrA family members have helped in an understanding of the mechanisms by which thiols in regulatory proteins react with reactive species, thereby activating antioxidant and antinitrosative gene expression.

FUTURE DIRECTIONS

To define the determinants that provide selectivity of redox active thiolates for some reactive species but not others is an important challenge for future investigations.

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.

EPA covalently bound to smooth titanium surfaces decreases viability and biofilm formation of Staphylococcus epidermidis in vitro

Colonization of implant surfaces with bacteria should ideally be prevented right from implantation, as bacteria attaching to the surface will form a biofilm, being then well protected against antibiotic treatment. Therefore, implant coatings should combine antibacterial properties with biocompatibility towards their host tissue. We tested a UV-induced covalent coating procedure with eicosapentaenoic acid (EPA) for smooth titanium (Ti) surfaces for its ability to prevent attachment and proliferation of Staphylococcus epidermidis and to allow mineralization of MC3T3-E1 osteoblasts. Bacterial initial attachment was highest for EPA-coated surfaces, but was reduced by vigorous washing, possibly due to low adhesive strength on those surfaces. We found an increase in the ratio of dead bacteria and in overall biofilm after 16 h on Ti surfaces with covalently bound EPA compared to Ti. The UV-induced EPA coating did not impair the ability of MC3T3-E1 preosteoblasts to mineralize, while a reduction in mineralization could be found for UV-irradiated Ti surfaces and UV-irradiated surfaces washed with ethanol compared to Ti. Although in vivo studies are needed to evaluate the clinical significance, our results indicate that covalent coating of Ti surfaces with EPA by UV irradiation decreases the survival of S. epidermidis and maintains the mineralization ability of osteoblasts.

Leptospira interrogans catalase is required for resistance to H2O2 and for virulence

Pathogenic Leptospira spp. are likely to encounter higher concentrations of reactive oxygen species induced by the host innate immune response. In this study, we characterized Leptospira interrogans catalase (KatE), the only annotated catalase found within pathogenic Leptospira species, by assessing its role in resistance to H(2)O(2)-induced oxidative stress and during infection in hamsters. Pathogenic L. interrogans bacteria had a 50-fold-higher survival rate under H(2)O(2)-induced oxidative stress than did saprophytic L. biflexa bacteria, and this was predominantly catalase dependent. We also characterized KatE, the only annotated catalase found within pathogenic Leptospira species. Catalase assays performed with recombinant KatE confirmed specific catalase activity, while protein fractionation experiments localized KatE to the bacterial periplasmic space. The insertional inactivation of katE in pathogenic Leptospira bacteria drastically diminished leptospiral viability in the presence of extracellular H(2)O(2) and reduced virulence in an acute-infection model. Combined, these results suggest that L. interrogans KatE confers in vivo resistance to reactive oxygen species induced by the host innate immune response.

MicroRNA-30b-mediated regulation of catalase expression in human ARPE-19 cells

BACKGROUND

Oxidative injury to retinal pigment epithelium (RPE) and retinal photoreceptors has been linked to a number of retinal diseases, including age-related macular degeneration (AMD). Reactive oxygen species (ROS)-mediated gene expression has been extensively studied at transcriptional levels. Also, the post-transcriptional control of gene expression at the level of translational regulation has been recently reported. However, the microRNA (miRNA/miR)-mediated post-transcriptional regulation in human RPE cells has not been thoroughly looked at. Increasing evidence points to a potential role of miRNAs in diverse physiological processes.

METHODOLOGY/PRINCIPAL FINDINGS

We demonstrated for the first time in a human retinal pigment epithelial cell line (ARPE-19) that the post-transcriptional control of gene expression via miRNA modulation regulates human catalase, an important and potent component of cell's antioxidant defensive network, which detoxifies hydrogen peroxide (H(2)O(2)) radicals. Exposure to several stress-inducing agents including H(2)O(2) has been reported to alter miRNA expression profile. Here, we demonstrated that a sublethal dose of H(2)O(2) (200 µM) up-regulated the expression of miR-30b, a member of the miR-30 family, which inhibited the expression of endogenous catalase both at the transcript and protein levels. However, antisense (antagomirs) of miR-30b was not only found to suppress the miR-30b mimics-mediated inhibitions, but also to dramatically increase the expression of catalase even under an oxidant environment.

CONCLUSIONS/SIGNIFICANCE

We propose that a microRNA antisense approach could enhance cytoprotective mechanisms against oxidative stress by increasing the antioxidant defense system.

The respiratory burst activity and expression of catalase in white shrimp, Litopenaeus vannamei, during long-term exposure to pH stress

In this study, changes of reactive oxygen species (ROS) and the mRNA expression of catalase of the Pacific white shrimp, Litopenaeus vannamei, exposed to pH (5.4, 6.7, 8.0, and 9.3) stress was investigated at different stress time (24, 48, 72, 96, and 120 h). Level of malondialdehyde (MDA) in shrimp also were assessed. The results revealed that acidic (pH 5.4 and 6.7) or alkaline exposure (pH 9.3) induced production of ROS hemocytes and increase of MDA level in shrimp. Moreover, the catalase mRNA expression in hepatopancreas of L. vannamei was up-regulated in 24 h at pH 5.4, in 72 h at pH 6.7 and in 48 h at pH 9.3, whereas was down-regulated significantly after 72 h acidic (pH 5.4 and 6.7) or alkaline (pH 9.4) exposure. In the present study, there was the relationship between ROS and catalase mRNA expression under normal acidic and alkaline conditions. At pH 8, the increase of catalase transcripts due to up-regulation by ROS, whereas MDA level did not significantly change, suggesting activation of corresponding protective mechanisms of detoxifying ROS is essential for the proper functioning of cells and the survival of shrimps.

Peroxide-sensing transcriptional regulators in bacteria

The ability to maintain intracellular concentrations of toxic reactive oxygen species (ROS) within safe limits is essential for all aerobic life forms. In bacteria, as well as other organisms, ROS are produced during the normal course of aerobic metabolism, necessitating the constitutive expression of ROS scavenging systems. However, bacteria can also experience transient high-level exposure to ROS derived either from external sources, such as the host defense response, or as a secondary effect of other seemingly unrelated environmental stresses. Consequently, transcriptional regulators have evolved to sense the levels of ROS and coordinate the appropriate oxidative stress response. Three well-studied examples of these are the peroxide responsive regulators OxyR, PerR, and OhrR. OxyR and PerR are sensors of primarily H(2)O(2), while OhrR senses organic peroxide (ROOH) and sodium hypochlorite (NaOCl). OxyR and OhrR sense oxidants by means of the reversible oxidation of specific cysteine residues. In contrast, PerR senses H(2)O(2) via the Fe-catalyzed oxidation of histidine residues. These transcription regulators also influence complex biological phenomena, such as biofilm formation, the evasion of host immune responses, and antibiotic resistance via the direct regulation of specific proteins.

Evidence for augmented oxidative stress in the subjects with type 1 diabetes and their siblings: a possible preventive role for antioxidants

BACKGROUND/OBJECTIVES

Oxidative stress (OS) is thought to be involved in both development of type 1 diabetes (T1D) and its further complications. In this study, certain biomarkers of OS were compared among the subjects with T1D, their non-diabetic siblings and unrelated healthy controls.

SUBJECTS/METHODS

Known cases of T1D from both sexes aged 5-25 years were enrolled in a case-control study (n(1)=60). There were two control groups; non-diabetic siblings (n(2)=60) and unrelated apparently healthy subjects (n(3)=60). Anthropometric, dietary and laboratory assessments were done.

RESULTS

There was no significant difference in dietary data among the groups. Total antioxidant capacity was significantly lower in T1D than both related and unrelated controls (1.6 ± 0.05, 1.7 ± 0.05 and 1.8 ± 0.06 mmol BSA equivalent/l, respectively, P=0.044). Both T1D subjects and their siblings showed lower glutathione peroxidase (GSH-px) levels (median (interquartile range): 22.2 (28.6), 29.9 (23) and 41.8 (73.6) U/ml, respectively, P=0.006). On the contrary, superoxide dismutase concentrations were significantly higher in T1D group and the siblings than unrelated healthy controls (243 (45.3), 157.8 (176.9) and 27.9 (8.7) U/l, respectively, P<0.001). Serum concentrations of GSH correlated with energy intake in the siblings (r=0.521, P<0.001) and unrelated controls (r=0.268, P=0.042) but not in T1D group. The associations remained significant after controlling for blood glucose (r=0.437, P=0.001 and r=0.420, P=0.011, respectively) in both the groups.

CONCLUSION

Augmented OS in the siblings may indicate an increased requirement for antioxidants in genetically diabetes-prone subjects.

The MerR-like transcriptional regulator BrlR contributes to Pseudomonas aeruginosa biofilm tolerance

Biofilms are composed of surface-attached microbial communities. A hallmark of biofilms is their profound tolerance of antimicrobial agents. While biofilm drug tolerance has been considered to be multifactorial, our findings indicate, instead, that bacteria within biofilms employ a classical regulatory mechanism to resist the action of antimicrobial agents. Here we report that the transcriptional regulator BrlR, a member of the MerR family of multidrug transport activators, plays a role in the high-level drug tolerance of biofilms formed by Pseudomonas aeruginosa. Expression of brlR was found to be biofilm specific, with brlR inactivation not affecting biofilm formation, motility, or pslA expression but increasing ndvB expression. Inactivation of brlR rendered biofilms but not planktonic cells grown to exponential or stationary phase significantly more susceptible to hydrogen peroxide and five different classes of antibiotics by affecting the MICs and the recalcitrance of biofilms to killing by microbicidal antimicrobial agents. In contrast, overexpression of brlR rendered both biofilms and planktonic cells more tolerant to the same compounds. brlR expression in three cystic fibrosis (CF) isolates was elevated regardless of the mode of growth, suggesting a selection for constitutive brlR expression upon in vivo biofilm formation associated with chronic infections. Despite increased brlR expression, however, isolate CF1-8 was as susceptible to tobramycin as was a ΔbrlR mutant because of a nonsense mutation in brlR. Our results indicate for the first time that biofilms employ a specific regulatory mechanism to resist the action of antimicrobial agents in a BrlR-dependent manner which affects MIC and recalcitrance to killing by microbicidal antimicrobial agents.

SHuffle, a novel Escherichia coli protein expression strain capable of correctly folding disulfide bonded proteins in its cytoplasm

BACKGROUND

Production of correctly disulfide bonded proteins to high yields remains a challenge. Recombinant protein expression in Escherichia coli is the popular choice, especially within the research community. While there is an ever growing demand for new expression strains, few strains are dedicated to post-translational modifications, such as disulfide bond formation. Thus, new protein expression strains must be engineered and the parameters involved in producing disulfide bonded proteins must be understood.

RESULTS

We have engineered a new E. coli protein expression strain named SHuffle, dedicated to producing correctly disulfide bonded active proteins to high yields within its cytoplasm. This strain is based on the trxB gor suppressor strain SMG96 where its cytoplasmic reductive pathways have been diminished, allowing for the formation of disulfide bonds in the cytoplasm. We have further engineered a major improvement by integrating into its chromosome a signal sequenceless disulfide bond isomerase, DsbC. We probed the redox state of DsbC in the oxidizing cytoplasm and evaluated its role in assisting the formation of correctly folded multi-disulfide bonded proteins. We optimized protein expression conditions, varying temperature, induction conditions, strain background and the co-expression of various helper proteins. We found that temperature has the biggest impact on improving yields and that the E. coli B strain background of this strain was superior to the K12 version. We also discovered that auto-expression of substrate target proteins using this strain resulted in higher yields of active pure protein. Finally, we found that co-expression of mutant thioredoxins and PDI homologs improved yields of various substrate proteins.

CONCLUSIONS

This work is the first extensive characterization of the trxB gor suppressor strain. The results presented should help researchers design the appropriate protein expression conditions using SHuffle strains.

Structural mechanism of disulphide bond-mediated redox switches

The oxidation of cysteine sulphydryl in proteins produces sulphenic acid that can form a reversible disulphide bond with another cysteine. The disulphide bond formation often triggers switches in protein structure and activity, especially when the distance between the two cysteine sulphur atoms is longer than the resulting disulphide bond distance. As an early example for the reversible disulphide bond-mediated functional switches, the reduced and oxidized forms of the bacterial transcription factor OxyR were characterized by X-ray crystallography. Recently, the Drosophila vision signalling protein, the association of inactivation-no-afterpotential D (INAD) was analysed by structural and functional methods. The two conserved cysteines of INAD were found to cycle between reduced and oxidized states during the light signal processing in Drosophila eyes, which was achieved by conformation dependent modulation of the disulphide bond redox potential. The production of the hypertension control peptide angiotensins was also shown to be controlled by the reversible disulphide bond in the precursor protein angiotensinogen. The crystal structure of the complex of angiotensiongen with its processing enzyme renin elucidated the role of the disulphide bond in stabilizing the precursor-enzyme complex facilitating the production of angiotensins. The increasing importance of the disulphide bond-mediated redox switches in normal and diseased states has implications in the development of novel antioxidant-based therapeutic approaches.

Regulators of oxidative stress response genes in Escherichia coli and their functional conservation in bacteria

Oxidative stress, through the production of reactive oxygen species, is a natural consequence of aerobic metabolism. Escherichia coli has several major regulators activated during oxidative stress, including OxyR, SoxRS, and RpoS. OxyR and SoxR undergo conformation changes when oxidized in the presence of hydrogen peroxide and superoxide radicals, respectively, and subsequently control the expression of cognate genes. In contrast, the RpoS regulon is induced by an increase in RpoS levels. Current knowledge regarding the activation and function of these regulators and their dependent genes in E. coli during oxidative stress forms the scope of this review. Despite the enormous genomic diversity of bacteria, oxidative stress response regulators in E. coli are functionally conserved in a wide range of bacterial groups, possibly reflecting positive selection of these regulators. SoxRS and RpoS homologs are present and respond to oxidative stress in Proteobacteria, and OxyR homologs are present and function in H(2)O(2) resistance in a range of bacteria, from gammaproteobacteria to Actinobacteria. Bacteria have developed complex, adapted gene regulatory responses to oxidative stress, perhaps due to the prevalence of reactive oxygen species produced endogenously through metabolism or due to the necessity of aerotolerance mechanisms in anaerobic bacteria exposed to oxygen.

Singlet oxygen stress in microorganisms

Singlet oxygen is the primary agent of photooxidative stress in microorganisms. In photosynthetic microorganisms, sensitized generation by pigments of the photosystems is the main source of singlet oxygen and, in nonphotosynthetic microorganisms, cellular cofactors such as flavins, rhodopsins, quinones, and porphyrins serve as photosensitizer. Singlet oxygen rapidly reacts with a wide range of cellular macromolecules including proteins, lipids, DNA, and RNA, and thereby further reactive substances including organic peroxides and sulfoxides are formed. Microorganisms that face high light intensities or exhibit potent photosensitizers have evolved specific mechanisms to prevent photooxidative stress. These mechanisms include the use of quenchers, such as carotenoids, which interact either with excited photosensitizer molecules or singlet oxygen itself to prevent damage of cellular molecules. Scavengers like glutathione react with singlet oxygen. Despite those protection mechanisms, damage by reactions with singlet oxygen on cellular macromolecules disturbs cellular functions. Microorganisms that regularly face photooxidative stress have evolved specific systems to sense singlet oxygen and tightly control the removal of singlet oxygen reaction products. Responses to photooxidative stress have been investigated in a range of photosynthetic and nonphotosynthetic microorganisms. However, detailed knowledge on the regulation of this response has only been obtained for the phototrophic alpha-proteobacterium Rhodobacter sphaeroides. In this organism and in related proteobacteria, the extracytoplasmic function (ECF) sigma factor RpoE is released from the cognate antisigma factor ChrR in the presence of singlet oxygen and triggers the expression of genes providing protection against photooxidative stress. Recent experiments show that singlet oxygen acts as a signal, which is sensed by yet unknown components and leads to proteolysis of ChrR. RpoE induces expression of a second alternative sigma factor, RpoH(II), which controls a large set of genes that partially overlaps with the heat-shock response controlled by RpoH(I). In addition to the transcriptional control of gene regulation by alternative sigma factors, a set of noncoding small RNAs (sRNAs) appear to affect the synthesis of several proteins involved in the response to photooxidative stress. The interaction of mRNA targets with those sRNAs is usually mediated by the RNA chaperone Hfq. Deletion of the gene encoding Hfq leads to a singlet oxygen-sensitive phenotype, which underlines the control of gene regulation on the posttranscriptional level by sRNAs in R. sphaeroides. Hence, a complex network of different regulatory components controls the defense against photooxidative stress in anoxygenic photosynthetic bacteria.

Re-examining the role of hydrogen peroxide in bacteriostatic and bactericidal activities of honey

The aim of this study was to critically analyze the effects of hydrogen peroxide on growth and survival of bacterial cells in order to prove or disprove its purported role as a main component responsible for the antibacterial activity of honey. Using the sensitive peroxide/peroxidase assay, broth microdilution assay and DNA degradation assays, the quantitative relationships between the content of H(2)O(2) and honey's antibacterial activity was established(.) The results showed that: (A) the average H(2)O(2) content in honey was over 900-fold lower than that observed in disinfectants that kills bacteria on contact. (B) A supplementation of bacterial cultures with H(2)O(2) inhibited E. coli and B. subtilis growth in a concentration-dependent manner, with minimal inhibitory concentrations (MIC(90)) values of 1.25 mM/10(7) cfu/ml and 2.5 mM/10(7) cfu/ml for E. coli and B. subtilis, respectively. In contrast, the MIC(90) of honey against E. coli correlated with honey H(2)O(2) content of 2.5 mM, and growth inhibition of B. subtilis by honey did not correlate with honey H(2)O(2) levels at all. (C) A supplementation of bacterial cultures with H(2)O(2) caused a concentration-dependent degradation of bacterial DNA, with the minimum DNA degrading concentration occurring at 2.5 mM H(2)O(2). DNA degradation by honey occurred at lower than ≤2.5 mM concentration of honey H(2)O(2) suggested an enhancing effect of other honey components. (D) Honeys with low H(2)O(2) content were unable to cleave DNA but the addition of H(2)O(2) restored this activity. The DNase-like activity was heat-resistant but catalase-sensitive indicating that H(2)O(2) participated in the oxidative DNA damage. We concluded that the honey H(2)O(2) was involved in oxidative damage causing bacterial growth inhibition and DNA degradation, but these effects were modulated by other honey components.

In vitro transcription profiling of the σS subunit of bacterial RNA polymerase: re-definition of the σS regulon and identification of σS-specific promoter sequence elements

Specific promoter recognition by bacterial RNA polymerase is mediated by σ subunits, which assemble with RNA polymerase core enzyme (E) during transcription initiation. However, σ⁷⁰ (the housekeeping σ subunit) and σ^S (an alternative σ subunit mostly active during slow growth) recognize almost identical promoter sequences, thus raising the question of how promoter selectivity is achieved in the bacterial cell. To identify novel sequence determinants for selective promoter recognition, we performed run-off/microarray (ROMA) experiments with RNA polymerase saturated either with σ⁷⁰ (Eσ⁷⁰) or with σ^S (Eσ^S) using the whole Escherichia coli genome as DNA template. We found that Eσ⁷⁰, in the absence of any additional transcription factor, preferentially transcribes genes associated with fast growth (e.g. ribosomal operons). In contrast, Eσ^S efficiently transcribes genes involved in stress responses, secondary metabolism as well as RNAs from intergenic regions with yet-unknown function. Promoter sequence comparison suggests that, in addition to different conservation of the −35 sequence and of the UP element, selective promoter recognition by either form of RNA polymerase can be affected by the A/T content in the −10/+1 region. Indeed, site-directed mutagenesis experiments confirmed that an A/T bias in the −10/+1 region could improve promoter recognition by Eσ^S.

Mitochondrial ROS generation and its regulation: mechanisms involved in H(2)O(2) signaling

Mitochondria are the main source of reactive oxygen species in the cell. These reactive oxygen species have long been known as being involved in oxidative stress. This is a review of the mechanisms involved in reactive oxygen species generation by the respiratory chain and some of the dehydrogenases and the control by thermodynamic and kinetic constraints. Mitochondrial ROS produced at the level of the bc1 complex as well at the level of complex I are discussed. It was recognized more than a decade ago that they can also function as signaling molecules. This signaling role will be developed both in terms of mechanism and in terms of mitochondrial ROS signaling. The notion that hydrogen peroxide acts not only as a damaging oxidant but also as a signaling molecule was proposed more than a decade ago. Hydrogen peroxide signaling can be either direct (oxidation of its target) or indirect (involving peroxiredoxins, for example). The consequences of ROS signaling on crucial biologic processes such as cell proliferation and differentiation are discussed.

Symbiotic association between soybean plants and Bradyrhizobium japonicum develops oxidative stress and heme oxygenase-1 induction at early stages

We have previously demonstrated that the induction of heme oxygenase-1 (HO-1) (EC 1.14.99.3) plays a protective role against oxidative stress in leaves and nodules of soybean plants subjected to cadmium, UV-B radiation, and salt stress. Here, we investigated HO-1, localization and their relationship with oxidative stress in different growth stages of soybean plants roots inoculated with Bradyrhizobium japonicum (3, 5, 7, 10, and 20 days post-inoculation) and nodules. After 7 days of inoculation, we observed a 70% increase in thiobarbituric acid-reactive substances that correlates with an enhancement in the gene expression of HO-1, catalase, and superoxide dismutase. Furthermore, the inhibition of HO-1 activity by Zn-protoporphyrin IX produced an increase in lipid peroxidation and a decrease in glutathione content suggesting that, in this symbiotic process, HO-1 may act as a signal molecule that protects the root against oxidative stress. We determined, for the first time, the tissular localization of HO-1 in nodules by electron-microscope examination. These results undoubtedly demonstrated that this enzyme is localized only in the plant tissue and its overexpression may play an important role as antioxidant defense in the plant. Moreover, we demonstrate that, in roots, HO-1 is induced by oxidative stress produced by inoculation of B. japonicum and exerts an antioxidant response against it.

Vibrio cholerae anaerobic induction of virulence gene expression is controlled by thiol-based switches of virulence regulator AphB

Bacterial pathogens have evolved sophisticated signal transduction systems to coordinately control the expression of virulence determinants. For example, the human pathogen Vibrio cholerae is able to respond to host environmental signals by activating transcriptional regulatory cascades. The host signals that stimulate V. cholerae virulence gene expression, however, are still poorly understood. Previous proteomic studies indicated that the ambient oxygen concentration plays a role in V. cholerae virulence gene expression. In this study, we found that under oxygen-limiting conditions, an environment similar to the intestines, V. cholerae virulence genes are highly expressed. We show that anaerobiosis enhances dimerization and activity of AphB, a transcriptional activator that is required for the expression of the key virulence regulator TcpP, which leads to the activation of virulence factor production. We further show that one of the three cysteine residues in AphB, C(235), is critical for oxygen responsiveness, as the AphB(C235S) mutant can activate virulence genes under aerobic conditions in vivo and can bind to tcpP promoters in the absence of reducing agents in vitro. Mass spectrometry analysis suggests that under aerobic conditions, AphB is modified at the C(235) residue. This modification is reversible between oxygen-rich aquatic environments and oxygen-limited human hosts, suggesting that V. cholerae may use a thiol-based switch mechanism to sense intestinal signals and activate virulence.

Transcriptome analysis of parallel-evolved Escherichia coli strains under ethanol stress

Background

Understanding ethanol tolerance in microorganisms is important for the improvement of bioethanol production. Hence, we performed parallel-evolution experiments using Escherichia coli cells under ethanol stress to determine the phenotypic changes necessary for ethanol tolerance.

Results

After cultivation of 1,000 generations under 5% ethanol stress, we obtained 6 ethanol-tolerant strains that showed an approximately 2-fold increase in their specific growth rate in comparison with their ancestor. Expression analysis using microarrays revealed that common expression changes occurred during the adaptive evolution to the ethanol stress environment. Biosynthetic pathways of amino acids, including tryptophan, histidine, and branched-chain amino acids, were commonly up-regulated in the tolerant strains, suggesting that activating these pathways is involved in the development of ethanol tolerance. In support of this hypothesis, supplementation of isoleucine, tryptophan, and histidine to the culture medium increased the specific growth rate under ethanol stress. Furthermore, genes related to iron ion metabolism were commonly up-regulated in the tolerant strains, which suggests the change in intracellular redox state during adaptive evolution.

Conclusions

The common phenotypic changes in the ethanol-tolerant strains we identified could provide a fundamental basis for designing ethanol-tolerant strains for industrial purposes.

The methanogen-specific transcription factor MsvR regulates the fpaA-rlp-rub oxidative stress operon adjacent to msvR in Methanothermobacter thermautotrophicus

Methanogens represent some of the most oxygen-sensitive organisms in laboratory culture. Recent studies indicate that they have developed mechanisms to deal with brief oxygen exposure. MsvR is a transcriptional regulator that has a domain architecture unique to a select group of methanogens. Here, runoff in vitro transcription assays were used to demonstrate that MsvR regulates transcription of the divergently transcribed fpaA-rlp-rub operon in Methanothermobacter thermautotrophicus in addition to transcription from its own promoter. The protein products of the fpaA-rlp-rub operon have previously been implicated in oxidative stress responses in M. thermautotrophicus. Additionally, electrophoretic mobility shift assays (EMSAs) and DNase I footprinting were used to confirm a binding site inferred by bioinformatic analysis. Sequence mutations within these binding sites did not significantly alter EMSA shifting patterns on longer templates but did on shorter 50-bp fragments encompassing only the region containing the binding sites. Footprinting confirmed that the regions protected for the longer mutant templates are at different positions within the intergenic region compared to those seen in the intact intergenic region. Oxidized and reduced preparations of MsvR demonstrated different EMSA binding patterns and regions of protection on the intergenic sequence, suggesting that MsvR may play a role in detecting the redox state of the cell.

SurR regulates hydrogen production in Pyrococcus furiosus by a sulfur-dependent redox switch

We present structural and biochemical evidence for a redox switch in the archaeal transcriptional regulator SurR of Pyrococcus furiosus, a hyperthermophilic anaerobe. P. furiosus produces H(2) during fermentation, but undergoes a metabolic shift to produce H(2) S when elemental sulfur (S(0) ) becomes available. Changes in gene expression occur within minutes of S(0) addition, and the majority of these S(0) -responsive genes are regulatory targets of SurR, a key regulator involved in primary S(0) response. SurR was shown in vitro to have dual functionality, activating transcription of some of these genes, notably the hydrogenase operons, and repressing others, including a gene-encoding sulfur reductase. This work demonstrates via biochemical and structural evidence that the activity of SurR is modulated by cysteine residues in a CxxC motif that constitutes a redox switch. Oxidation of the switch with S(0) inhibits sequence-specific DNA binding by SurR, leading to deactivation of genes related to H(2) production and derepression of genes involved in S(0) metabolism.

Oxidative stress drives disulfide bond formation between basic helix-loop-helix transcription factors

Basic helix-loop-helix (bHLH) transcription factors including Twist1 and E2a proteins regulate essential processes. These factors bind DNA as homo- or heterodimers and the choice of binding partners determines their functional output. To investigate potential regulators of bHLH dimerization, cells were exposed to the oxidative agent hydrogen peroxide (H(2)O(2)). Western blot analysis in the presence or absence of reducing agents, revealed that H(2)O(2) induces the rapid formation of an intermolecular disulfide bond between Twist1 homodimers and Twist/E2a proteins heterodimers. The disulfide bond is first observed between Twist1 homodimers at 25 mM H(2)O(2) and between Twist1 heterodimers at 75 mM H(2)O(2). This response is dependent upon cell density as H(2)O(2) did not induce disulfide bridge formation between bHLH proteins in cells seeded at high density. In the presence of E proteins, the formation of Twist1/E2a proteins heterodimers is favored over Twist1 homodimers, identifying an oxidative stimulus as an important factor in modulating binding partner specificity. We further demonstrated that a cysteine residue located at the C-terminus of Twist1 and E2a proteins is involved in this response. Disulfide bond formation between Twist1 homodimers significantly reduced its ability to interact with two of its binding partners, Runx2 and HDAC4, indicating that disulfide dimerization in response to H(2)O(2) has functional significance. These data support the conclusion that disulfide bond formation in response to an oxidative stimulus contributes to Twist1 homo- and heterodimerization and raises the possibility that the redox status of a cell may represent an important step in bHLH transcriptional regulation.

Phase variation controls expression of Salmonella lipopolysaccharide modification genes by a DNA methylation-dependent mechanism

The O-antigen of Salmonella lipopolysaccharide is a major antigenic determinant and its chemical composition forms the basis for Salmonella serotyping. Modifications of the O-antigen that can affect the serotype include those carried out by the products of glycosyltransferase operons (gtr), which are present on specific Salmonella and phage genomes. Here we show that expression of the gtr genes encoded by phage P22 that confers the O1 serotype is under the control of phase variation. This phase variation occurs by a novel epigenetic mechanism requiring OxyR in conjunction with the DNA methyltransferase Dam. OxyR is an activator or a repressor of the system depending on which of its two binding sites in the gtr regulatory region is occupied. Binding is decreased by methylation at Dam target sequences in either site, and this confers heritability of the expression state to the system. Most Salmonella gtr operons share the key regulatory elements that are identified here as essential for this epigenetic phase variation.

Contribution of rpoS and bolA genes in biofilm formation in Escherichia coli K-12 MG1655

Flexibility of gene expression in bacteria permits its survival in varied environments. The genetic adaptation of bacteria through systematized gene expression is not only important, but also clinically relevant in their ability to grow biofilms in stress environments. Stress responses enable their survival under more severe conditions, enhanced resistance and/or virulence. In Escherichia coli (E. coli), two of the possible important genes for biofilm growth are rpoS and bolA gene. RpoS is also called as a master regulator of general stress response. Even though many studies have revealed the importance of rpoS in planktonic cells, little is known about the functions of rpoS in biofilms. In contrast, bolA which is a morphogene in E. coli is overexpressed under stressed environments resulting in round morphology. The hypothesis is that bolA could be implicated in biofilm development. This study reviewed the literature with the aim of understanding the stress tolerance response of E. coli in relation with rpoS and bolA genes in different environmental conditions including heat shock, cold shock, and stress in response to oxidation, acidic condition and in presence of cadmium. Knowledge of the genetic regulation of biofilm formation may lead to the understanding of the factors that drive the bacteria to switch to the biofilm mode of growth.

Antioxidants and redox regulation: changing notions in a changing world

The concepts of antioxidants and redox regulation are reconsidered in the light of recent findings, and some new future challenges for redox biology are outlined. It is suggested that antioxidants, thioredoxin-mediated redox regulation, and signal transduction mediated by reactive oxygen and nitrogen species, are all part of the same broad mechanism. The integration of different redox inputs, by affecting reversible thiol-disulfide dynamics in a set of target proteins, could result in the regulation of key processes such as proteolysis, gene expression and the functioning of selected metabolic pathways. Most interestingly, redox regulation is not just based on a binary "yes or no" response, and is therefore a convenient way to achieve graded control over the continuum of environmental variables.

The L-cysteine/L-cystine shuttle system provides reducing equivalents to the periplasm in Escherichia coli

Intracellular thiols like L-cysteine and glutathione play a critical role in the regulation of cellular processes. Escherichia coli has multiple L-cysteine transporters, which export L-cysteine from the cytoplasm into the periplasm. However, the role of L-cysteine in the periplasm remains unknown. Here we show that an L-cysteine transporter, YdeD, is required for the tolerance of E. coli cells to hydrogen peroxide. We also present evidence that L-cystine, a product from the oxidation of L-cysteine by hydrogen peroxide, is imported back into the cytoplasm in a manner dependent on FliY, the periplasmic L-cystine-binding protein. Remarkably, this protein, which is involved in the recycling of the oxidized L-cysteine, is also found to be important for the hydrogen peroxide resistance of this organism. Furthermore, our analysis of the transcription of relevant genes revealed that the transcription of genes encoding FliY and YdeD is highly induced by hydrogen peroxide rather than by L-cysteine. These findings led us to propose that the inducible L-cysteine/L-cystine shuttle system plays an important role in oxidative stress tolerance through providing a reducing equivalent to the periplasm in E. coli.

Transcriptome analysis of Escherichia coli O157:H7 exposed to lysates of lettuce leaves

Harvesting and processing of leafy greens inherently cause plant tissue damage, creating niches on leaves that human pathogens can exploit. We previously demonstrated that Escherichia coli O157:H7 (EcO157) multiplies more rapidly on shredded leaves than on intact leaves (M. T. Brandl, Appl. Environ. Microbiol. 74:5285-5289, 2008). To investigate how EcO157 cells adapt to physicochemical conditions in injured lettuce tissue, we used microarray-based whole-genome transcriptional profiling to characterize gene expression patterns in EcO157 after 15- and 30-min exposures to romaine lettuce lysates. Multiple carbohydrate transport systems that have a role in the utilization of substrates known to be prevalent in plant cells were activated in EcO157. This indicates the availability to the human pathogen of a variety of carbohydrates released from injured plant cells that may promote its extensive growth in leaf lysates and, thus, in wounded leaf tissue. In addition, microarray analysis revealed the upregulation of numerous genes associated with EcO157 attachment and virulence, with oxidative stress and antimicrobial resistance (including the OxyR and Mar regulons), with detoxification of noxious compounds, and with DNA repair. Upregulation of oxidative stress and antimicrobial resistance genes in EcO157 was confirmed on shredded lettuce by quantitative reverse transcription-PCR. We further demonstrate that this adaptation to stress conditions imparts the pathogen with increased resistance to hydrogen peroxide and calcium hypochlorite. This enhanced resistance to chlorinated sanitizers combined with increased expression of virulence determinants and multiplication at sites of injury on the leaves may help explain the association of processed leafy greens with outbreaks of EcO157.

Redox-mediated interactions of VHb (Vitreoscilla haemoglobin) with OxyR: novel regulation of VHb biosynthesis under oxidative stress

The bacterial haemoglobin from Vitreoscilla, VHb, displays several unusual properties that are unique among the globin family. When the gene encoding VHb, vgb, is expressed from its natural promoter in either Vitreoscilla or Escherichia coli, the level of VHb increases more than 50-fold under hypoxic conditions and decreases significantly during oxidative stress, suggesting similar functioning of the vgb promoter in both organisms. In the present study we show that expression of VHb in E. coli induced the antioxidant genes katG (catalase–peroxidase G) and sodA (superoxide dismutase A) and conferred significant protection from oxidative stress. In contrast, when vgb was expressed in an oxyR mutant of E. coli, VHb levels increased and the strain showed high sensitivity to oxidative stress without induction of antioxidant genes; this indicates the involvement of the oxidative stress regulator OxyR in mediating the protective effect of VHb under oxidative stress. A putative OxyR-binding site was identified within the vgb promoter and a gel-shift assay confirmed its interaction with oxidized OxyR, an interaction which was disrupted by the reduced form of the transcriptional activator Fnr (fumurate and nitrate reductase). This suggested that the redox state of OxyR and Fnr modulates their interaction with the vgb promoter. VHb associated with reduced OxyR in two-hybrid screen experiments and in vitro, converting it into an oxidized state in the presence of NADH, a condition where VHb is known to generate H2O2. These observations unveil a novel mechanism by which VHb may transmit signals to OxyR to autoregulate its own biosynthesis, simultaneously activating oxidative stress functions. The activation of OxyR via VHb, reported in the present paper for the first time, suggests the involvement of VHb in transcriptional control of many other genes as well.

Establishing and maintaining sequestration of Dam target sites for phase variation of agn43 in Escherichia coli

Phase variation of the outer membrane protein Ag43 encoded by agn43 in Escherichia coli is controlled by an epigenetic mechanism. Sequestration of the regulatory region from Dam-dependent methylation has to be established and maintained throughout a generation to obtain and maintain the OFF phase. This work shows that hemimethylated DNA, which is formed by the passage of the DNA replication fork in an ON-phase cell, can be sequestered from methylation by OxyR binding, which is thus a key event for the switch from ON to OFF. No evidence was found that the protein SeqA, which also binds to the region, is involved in sequestration. To facilitate the dissection of this process further, a novel approach was introduced that does not alter the sequence of the regulatory region or the cellular concentration of Dam or OxyR, which consists of inserting auxiliary OxyR binding sites upstream of the regulatory region. Using this strategy, it was shown that the ON-to-OFF switch frequency can be modulated without changing the OFF-to-ON frequency. The data support a model in which in an ON-phase cell, the subcellular OxyR availability at the replication fork as it passes through the agn43 regulatory region is key for initiating an ON-to-OFF switch. In contrast, this availability is not a determining factor for the switch from OFF to ON. This finding shows that different variables affect these two stochastic events. This provides new insight into the events determining the stochastic nature of epigenetic phase variation.

DNA-mediated charge transport in redox sensing and signaling

The transport of charge through the DNA base-pair stack offers a route to carry out redox chemistry at a distance. Here we describe characteristics of this chemistry that have been elucidated and how this chemistry may be utilized within the cell. The shallow distance dependence associated with these redox reactions permits DNA-mediated signaling over long molecular distances in the genome and facilitates the activation of redox-sensitive transcription factors globally in response to oxidative stress. The long-range funneling of oxidative damage to sites of low oxidation potential in the genome also may provide a means of protection within the cell. Furthermore, the sensitivity of DNA charge transport to perturbations in base-pair stacking, as may arise with base lesions and mismatches, may be used as a route to scan the genome for damage as a first step in DNA repair. Thus, the ability of double-helical DNA in mediating redox chemistry at a distance provides a natural mechanism for redox sensing and signaling in the genome.

Orchestrating redox signaling networks through regulatory cysteine switches

Hydrogen peroxide (H(2)O(2)) acts as a second messenger that can mediate intracellular signal transduction via chemoselective oxidation of cysteine residues in signaling proteins. This Review presents current mechanistic insights into signal-mediated H(2)O(2) production and highlights recent advances in methods to detect reactive oxygen species (ROS) and cysteine oxidation both in vitro and in cells. Selected examples from the recent literature are used to illustrate the diverse mechanisms by which H(2)O(2) can regulate protein function. The continued development of methods to detect and quantify discrete cysteine oxoforms should further our mechanistic understanding of redox regulation of protein function and may lead to the development of new therapeutic strategies.

Effects of cigarette smoke on the activation of oxidative stress-related transcription factors in female A/J mouse lung

Cigarette smoke contains a high concentration of free radicals and induces oxidative stress in the lung and other tissues. Several transcription factors are known to be activated by oxidative stress, including nuclear factor-kappaB (NF-kappaB), activator protein-1 (AP-1), and hypoxia-inducible factor (HIF). Studies were therefore undertaken to examine whether cigarette smoke could activate these transcription factors, as well as other transcription factors that may be important in lung carcinogenesis. Female A/J mice were exposed to cigarette smoke for 2, 5, 10, 15, 20, 42, or 56 d (6 hr/d, 5 d/wk). Cigarette smoke did not increase NF-kappaB activation at any of these times, but NF-kappaB DNA binding activity was lower after 15 d and 56 d of smoke exposure. The DNA binding activity of AP-1 was lower after 10 d and 56 d but was not changed after 42 d of smoke exposure. The DNA binding activity of HIF was quantitatively increased after 42 d of smoke exposure but decreased after 56 d. Whether the activation of other transcription factors in the lung could be altered after exposure to cigarette smoke was subsequently examined. The DNA binding activities of FoxF2, myc-CF1, RORE, and p53 were examined after 10 d of smoke exposure. The DNA binding activities of FoxF2 and p53 were quantitatively increased, but those of myc-CF1 and RORE were unaffected. These studies show that cigarette smoke exposure leads to quantitative increases in DNA binding activities of FoxF2 and p53, while the activations of NF-kappaB, AP-1, and HIF are largely unaffected or reduced.

Heme Oxygenase Contributes to Alleviate Salinity Damage in Glycine max L. Leaves

Plants are frequently subjected to different kinds of stress, such as salinity and, like other organisms, they have evolved strategies for preventing and repairing cellular damage caused by salt stress. Glycine max L. plants were subjected to different NaCl concentrations (0–200 mM) for 10 days. Treatments with 100 and 200 mM NaCl induced ion leakage and lipid peroxidation augmentation, loss in chlorophyll content, and accumulation of O₂^•− and H₂O₂. However, 50 mM NaCl did not modify these parameters, which remains similar to control values. Catalase, superoxide dismutase, and heme oxygenase (HO-1) activities and gene expressions were increased under 100 mM NaCl, while no differences were observed with respect to controls under 50 mM salt. Treatment with 200 mM NaCl caused a diminution in the enzyme activities and gene expressions. Results here reported let us conclude that HO also plays a leading role in the defense mechanisms against salinity.

Suppression of MKK5 reduces ozone-induced signal transmission to both MPK3 and MPK6 and confers increased ozone sensitivity in Arabidopsis thaliana

In Arabidopsis thaliana, ozone-induced signaling has been shown to involve the mitogen-activated protein kinases (MAPKs) MPK3 and MPK6. To identify a possible ozone-induced mitogen-activated protein kinase kinase (MAPKK) involved in the activation of these specific MAPKs, we employed RNA interference-(RNAi)-based suppression of MKK5, a known cognate MAPKK to both MPK3 and MPK6. When exposed to ozone, activation of both MPK3 and MPK6 was markedly reduced in the MKK5-suppressed plants compared to WT. Additionally, the MKK5-suppressed plants were found to be highly sensitive to ozone as determined by visible leaf damage concomitant with elevated levels of leaf-localised H(2)O(2). Taken together, our data suggest MKK5 functions both in ozone-induced activation of MPK3 and MPK6 and in integrating ROS homeostasis during ozone stress.

Metabolic impact and potential exploitation of the stress reactions in lactobacilli

Lactic acid bacteria (LAB) are a functionally related group of organisms known primarily for their bioprocessing roles in food and beverages. The largest variety of metabolic properties is found in the group of lactobacilli the vast majority of which has been isolated in cereal environments, namely sourdoughs, in which their role ranges from sporadic contaminants to major fermentative flora. Growth or survival in each of these environmental niches depends on the ability of the organism to sense and respond to varying conditions such as temperature, pH, nutrients availability and cell population density. Fermentation process conditions, including temperature range, dough yield, oxygen, pH as well as the amount and composition of starter cultures, determine the cells' metabolic response. In fact, the exposure of microbial cells to stressful conditions during fermentation involves a broad transcriptional response with many induced or repressed genes. The complex network of such responses, involving several metabolic activities will reflect upon the metabolome of the fermentative flora, and thus on the composition and organoleptic properties of the final products. This review shall provide insight into stress response mechanisms and delineate the vast potential residing in the exploitation of the stress dependent metabolome of LAB focusing on bacteria of the sourdough environment as one of the richest sources of lactobacilli.

Chronic intermittent hypobaric hypoxia protects the heart against ischemia/reperfusion injury through upregulation of antioxidant enzymes in adult guinea pigs

AIM

To investigate the protection and the anti-oxidative mechanism afforded by chronic intermittent hypobaric hypoxia (CIHH) against ischemia/reperfusion (I/R) injury in guinea pig hearts.

METHODS

Adult male guinea pigs were exposed to CIHH by mimicking a 5000 m high altitude (p(B)=404 mmHg, p(O2)=84 mmHg) in a hypobaric chamber for 6 h/day for 28 days. Langendorff-perfused isolated guinea pig hearts were used to measure variables of left ventricular function during baseline perfusion, ischemia and the reperfusion period. The activity and protein expression of antioxidant enzymes in the left myocardium were evaluated using biochemical methods and Western blotting, respectively. Intracellular reactive oxygen species (ROS) were assessed using ROS-sensitive fluorescence.

RESULTS

After 30 min of global no-flow ischemia followed by 60 min of reperfusion, myocardial function had better recovery rates in CIHH guinea pig hearts than in control hearts. The activity and protein expression of superoxide dismutase (SOD) and catalase (CAT) were significantly increased in the myocardium of CIHH guinea pigs. Pretreatment of control hearts with an antioxidant mixture containing SOD and CAT exerted cardioprotective effects similar to CIHH. The irreversible CAT inhibitor aminotriazole (ATZ) abolished the cardioprotection of CIHH. Cardiac contractile dysfunction and oxidative stress induced by exogenous hydrogen peroxide (H(2)O(2)) were attenuated by CIHH and CAT.

CONCLUSIONS

These data suggest that CIHH protects the heart against I/R injury through upregulation of antioxidant enzymes in guinea pig.Acta Pharmacologica Sinica (2009) 30: 947-955; doi: 10.1038/aps.2009.57; published online 22 June 2009.

HIGH-LIGHT AND SODIUM CHLORIDE STRESS DIFFERENTIALLY REGULATE THE BIOSYNTHESIS OF ASTAXANTHIN IN CHLORELLA ZOFINGIENSIS (CHLOROPHYCEAE)(1)

Although light and salt stresses are known to enhance the biosynthesis of astaxanthin in certain green algae, the mechanism of their action remains largely unknown. Here we report the regulation of the genes encoding phytoene desaturase (PDS), carotenoid hydroxylase (CHYb), and carotenoid ketolase (BKT) in the green alga Chlorella zofingiensis Dönz under light or sodium chloride (NaCl) stress. High-light illumination (150 μmol photons · m(-2)  · s(-1) ) up-regulated the transcripts of PDS, CHYb, and BKT and greatly enhanced the biosynthesis of zeaxanthin, canthaxanthin, and astaxanthin. In contrast, sodium chloride stress only up-regulated the transcript of BKT and enhanced the biosynthesis of canthaxanthin and astaxanthin. High-light and NaCl stresses were revealed to result in an increase in the intracellular reactive oxygen species (ROS) level. By applying chemically generated ROS to the algal cells, we determined that (1) O2 specifically up-regulated the CHYb gene, whereas •OH up-regulated the PDS and BKT genes. We suggest that high-light and NaCl stresses may stimulate the generation of different ROS, which in turn trigger the up-regulation of specific carotenogenic genes and the enhanced biosynthesis of carotenoids in C. zofingiensis.