Hydrogen peroxide-inducible proteins in Salmonella typhimurium overlap with heat shock and other stress proteins

NF-kappa B mediates the adaptation of human U937 cells to hydrogen peroxide

Low doses of oxidative stress can induce cellular resistance to subsequent higher doses of the same stress. By using human U937 leukemia cells, we previously demonstrated that H(2)O(2) can induce such an adaptive response without elevating the cellular capacity to degrade H(2)O(2), and were able to confer the cells a cross-resistance to an H(2)O(2)-independent lethal stimulus, C(2)-ceramide. In this study, it was found that the adaptation is accompanied by the translocation of cytoplasmic NF-kappa B to the nuclei. This event was promoted or abolished when either IKK alpha or a dominant negative mutant of I kappa B, respectively, was overexpressed. The overexpression of IKK alpha also resulted in the suppression of H(2)O(2)-induced cell death and DNA fragmentation, whereas these events were accelerated by the expression of the I kappa B mutant. The protective effect of IKK alpha was accompanied neither by an elevation of protein levels of various antioxidant enzymes such as catalase, superoxide dismutase, and glutathione peroxidase, nor by an increase in the cellular capacity to consume H(2)O(2). Moreover, the overexpression of IKK alpha resulted in an enhancement of H(2)O(2)-induced resistance to C(2)-ceramide. The overall data suggest that NF-kappa B mediates the H(2)O(2) adaptation induced in a manner independent of H(2)O(2)-degrading activity.

Heat shock-mediated APX gene expression and protection against chilling injury in rice seedlings

Rice (Oryza sativa L.) seedlings, when kept at 42 degrees C for 24 h before being kept at 5 degrees C for 7 d, did not develop chilling injury. Chilling resistance was enhanced in parallel with the period of heat-treatment. The level of APX activity was higher in heated seedlings whereas CAT activity was decreased by heat stress. There was no significant difference in SOD activity between heated and unheated seedlings. The elevated activity of APX was sustained after 7 d of chilling. The cytosolic APX gene expression in response to high and low temperature was analysed with an APXa gene probe. APXa mRNA levels increased within 1 h after seedlings were exposed to 42 degrees C. Elevated APXa mRNA levels could also be detected after 24 h of heating. The APXa mRNA level in preheated seedlings was still higher than unheated seedlings under cold stress. The promoter of the APXa gene was cloned from rice genomic DNA by TAIL-PCR, and characterized by DNA sequencing. The promoter had a minimal heat shock factor-binding motif, 5'-nGAAnnTTCn-3', located in the 81 bp upstream of the TATA box. Heat shock induction of the APXa gene could be a possible cause of reduced chilling injury in rice seedlings.

Cell death after exposure to subarachnoid hemolysate correlates inversely with expression of CuZn-superoxide dismutase

BACKGROUND AND PURPOSE

Subarachnoid hemolysate (SAH) has been associated with oxidative brain injury, cell death, and apoptosis. We hypothesized that over-expression of CuZn-superoxide dismutase (CuZn-SOD) would protect against injury after SAH, whereas reduction of its expression would exacerbate injury.

METHODS

Saline (n=16) or hemolysate (n=50) was injected into transgenic mice overexpressing CuZn-SOD (SOD1-Tg), CuZn-SOD heterozygous knockout mutants (SOD1+/-), and wild-type littermates (Wt). Mice were killed at 24 hours. Stress gene induction was evaluated by immunocytochemistry and Western blotting for hemeoxygenase-1 and heat shock protein 70. Apoptosis was evaluated by 3'-OH nick end-labeling and DNA gel electrophoresis. Cell death was quantified through histological assessment after cresyl violet staining.

RESULTS

Histological assessment demonstrated neocortical cell death in regions adjacent to the blood injection. Overall cell death was reduced 43% in SOD1-Tg mutants (n=6) compared with Wt littermates (n=6; P<0.02). In contrast, cell death was increased >40% in SOD1+/- mutants (n=6; P<0.05). Both hemeoxygenase-1 and heat shock protein 70 were induced after SAH. Apoptosis was also present after SAH, as evidenced by 3'-OH end-labeling and DNA laddering. However, the degree of stress gene induction and apoptosis did not vary between Wt, SOD1-Tg, and SOD1+/- mice.

CONCLUSIONS

The extent of CuZn-SOD expression in the cytosol correlates with cell death after exposure to SAH in a manner separate from apoptosis. Overexpression of CuZn-SOD may potentially be an avenue for therapeutic intervention.

Multiprobe RNase protection assay analysis of mRNA levels for the Escherichia coli oxidative DNA glycosylase genes under conditions of oxidative stress

Escherichia coli formamidopyrimidine DNA glycosylase (Fpg), MutY DNA glycosylase, endonuclease VIII, and endonuclease III are oxidative base excision repair DNA glycosylases that remove oxidized bases from DNA, or an incorrect base paired with an oxidized base in the case of MutY. Since genes encoding other base excision repair proteins have been shown to be part of adaptive responses in E. coli, we wanted to determine whether the oxidative DNA glycosylase genes are induced in response to conditions that cause the type of damage their encoded proteins remove. The genes fpg, mutY, nei, and nth encode Fpg, MutY, endonuclease VIII, and endonuclease III, respectively. Multiprobe RNase protection assays were used to examine the transcript levels of these genes under conditions that induce the SoxRS, OxyR, and SOS regulons after a shift from anaerobic to aerobic growth and at different stages along the growth curve. Transcript levels for all four genes decreased as cells progressed from log-phase growth to stationary phase and increased after cells were shifted from anaerobic to aerobic growth. None of the genes were induced by hydrogen peroxide, paraquat, X rays, or conditions that induce the SOS response.

Participation of stress-inducible systems and enzymes involved in BER and NER in the protection of Escherichia coli against cumene hydroperoxide

We studied the participation of the stress-inducible systems, as the OxyR, SoxRS and SOS regulons in the protection of Escherichia coli cells against lethal effects of cumene hydroperoxide (CHP). Moreover, we evaluated the participation of BER and NER in the repair of the DNA damage produced by CHP. Our results suggest that the hypersensitivity observed in the oxyR mutants to the lethal effect of CHP does not appear to be due to SOS inducing DNA lesions, but rather to cell membrane damage. On the other hand, DNA damage induced by CHP appears to be repaired by enzymes involved in BER and NER pathways. In this case, Fpg protein and UvrABC complex could be involved cooperatively in the elimination of a specific DNA lesion. Finally, we have detected the requirement for the uvrA gene function in SOS induction by CHP treatment.

Stress proteins as biomarkers of oxidative stress: effects of antioxidant supplements

The potential benefits to health of the supply of antioxidants, either through dietary intake or as supplements, is equivocal. There is a need to develop biomarkers that may act as monitors of cellular defense as influenced by antioxidant status. Thirty-two individuals participated in the project and 19 received supplements for 5 weeks in the form of a capsule containing a defined mixture of antioxidants. No change was noted in levels of superoxide dismutase and glutathione peroxidase following antioxidant supplementation. On the other hand, increase in total antioxidant status and decrease in malondialdehyde, protein carbonyl formation, and erythrocyte hemolysis were noted. In lymphocytes isolated from individuals receiving antioxidant supplements and subjected to a heat shock in the presence of the free radical generator 2, 2'-azobis-(2-amidinopropane)-dihydrochloride, enhanced synthesis of heat shock proteins hsp 105, hsp 90, hsp 70, and hsp 40 by contrast with decreased synthesis of heme oxygenase HO-1 (hsp 32) were noted. We conclude that antioxidant status modulates the synthesis of stress proteins.

Evidence against a direct antimicrobial role of H2O2 in the infection of plants by Erwinia chrysanthemi

We have investigated the role of bacterial resistance to oxidative stress in pathogenesis. The oxyR gene from the pathogenic bacterium Erwinia chrysanthemi has been characterized. It is closely related to that found in Escherichia coli (88% overall amino acid identity). An E. chrysanthemi oxyR mutant strain was constructed by marker exchange. After induction with a sublethal dose of H2O2, this mutant was more sensitive to H2O2 and showed reduced levels of catalase and glutathione reductase activities, compared with the wild type. The oxyR mutant was unable to form individual colonies on agar plates unless catalase was added exogenously. However, it retained full virulence in potato tubers and tobacco leaves. These results suggest that the host-produced H2O2 has no direct antimicrobial effect on the interaction of E. chrysanthemi with the two plant species.

Possible role of the superoxide anion in the development of neuronal tolerance following ischaemic preconditioning in rats

There is a large body of evidence that reactive oxygen species play a major role in the pathogenesis of ischaemic brain damage. On the other hand, it has recently been suggested that superoxide anions participate in the development of neuronal tolerance against lethal ischaemia following ischaemic preconditioning (PC). The present study aimed to examine whether or not the intravenous administration of human recombinant Cu/Zn superoxide dismutase (hr SOD) prior to PC would affect the subsequent development of neuronal tolerance. Animals were randomly assigned to the following three groups: group 1, sham PC treated with vehicle; group 2, PC treated with hr SOD and group 3, PC treated with vehicle. For PC, 10 min occlusion of the middle cerebral artery (MCA) by a modified intraluminal suture method was followed by 60 min recirculation and this procedure was successively repeated three times. The procedures were similar for sham PC except that the MCA was kept unoccluded. Just prior to PC or sham PC, a bolus of hr SOD (6 x 103 IU/2 ml/kg) was administered intravenously. Seventy-two hours thereafter, rats were subjected to lethal ischaemia, i.e. MCA occlusion for 100 min followed by recirculation for 48 h. The infarct area and volume were assessed with the 2,3,5-triphenyltetrazolium stain. A significant difference in the infarct volume was revealed between the sham PC/vehicle and the PC/vehicle groups (total and cortex P < 0.01; striatum P < 0.05), showing that PC induced a marked neuronal tolerance against lethal ischaemia. The infarct volume in the PC/SOD group was close to that in the sham PC/vehicle group, being significantly greater than that in the PC/vehicle group (total and cortex P < 0.01) and showing that the administration of hr SOD suppressed the development of neuronal tolerance induced by PC. In a parallel experiment, expression of 72-kDa heat-shock protein (hsp 72) at 72 h after PC was considerably reduced in rats treated with hr SOD compared with those treated with vehicle. These results suggest that superoxide anions intraluminally generated within cerebral microvessels participate in the development of neuronal tolerance as well as the induction of hsp 72 following PC.

Increased sensitivity to oxidative challenges associated with topA deletion in Escherichia coli

Deletion of topA in Escherichia coli was found to result in a higher level of killing after treatment with either hydrogen peroxide or N-ethylmaleimide. This effect on oxidative challenge response represents a new role for E. coli DNA topoisomerase I in addition to prevention of excessive negative supercoiling of DNA.

Bactericidal activities of essential oils of basil and sage against a range of bacteria and the effect of these essential oils on Vibrio parahaemolyticus

Basil and sage essential oils were examined for bactericidal activity against a range of Gram-positive and Gram-negative bacteria by viable count determinations. Generally, Gram-positive bacteria showed higher resistance to basil and sage essential oils than Gram-negative bacteria. Vibrio species showed a high sensitivity to both essential oils. Stationary growth phase cells of selected bacteria showed higher resistance to these essential oils than exponential growth phase cells. Basil-resistant (b21) and sage-resistant (s20) strains of Vibrio parahaemolyticus were isolated. Both strains showed higher resistance to heat and H2O2 than parent strain. Conversely, heat-adapted V. parahaemolyticus also showed a higher resistance to these essential oils than nonadapted cells.

Mechanisms for redox control of gene expression

This review discusses various mechanisms that regulatory proteins use to control gene expression in response to alterations in redox. The transcription factor SoxR contains stable [2Fe-2S] centers that promote transcription activation when oxidized. FNR contains [4Fe-4S] centers that disassemble under oxidizing conditions, which affects DNA-binding activity. FixL is a histidine sensor kinase that utilizes heme as a cofactor to bind oxygen, which affects its autophosphorylation activity. NifL is a flavoprotein that contains FAD as a redox responsive cofactor. Under oxidizing conditions, NifL binds and inactivates NifA, the transcriptional activator of the nitrogen fixation genes. OxyR is a transcription factor that responds to redox by breaking or forming disulfide bonds that affect its DNA-binding activity. The ability of the histidine sensor kinase ArcB to promote phosphorylation of the response regulator ArcA is affected by multiple factors such as anaerobic metabolites and the redox state of the membrane. The global regulator of anaerobic gene expression in alpha-purple proteobacteria, RegB, appears to directly monitor respiratory activity of cytochrome oxidase. The aerobic repressor of photopigment synthesis, CrtJ, seems to contain a redox responsive cysteine. Finally, oxygen-sensitive rhizobial NifA proteins presumably bind a metal cofactor that senses redox. The functional variability of these regulatory proteins demonstrates that prokaryotes apply many different mechanisms to sense and respond to alterations in redox.

Catalase activity is necessary for heat-shock recovery in Aspergillus nidulans germlings

To understand the molecular mechanisms induced by stress that contribute to the development of tolerance in eukaryotic cells, the filamentous fungus Aspergillus nidulans has been chosen as a model system. Here, the response of A. nidulans germlings to heat shock is reported. The heat treatment dramatically increased the concentration of trehalose and induced the accumulation of mannitol and mRNA from the catalase gene catA. Both mannitol and catalase function to protect cells from different reactive oxygen species. Treatment with hydrogen peroxide increased A. nidulans germling viability after heat shock whilst mutants deficient in catalase were more sensitive to a 50 degrees C heat exposure. It is concluded that the defence against the lethal effects of heat exposure can be correlated with the activity of the defence system against oxidative stress.

Use of in vivo-regulated promoters to deliver antigens from attenuated Salmonella enterica var. Typhimurium

This study describes the construction and analysis of three in vivo-inducible promoter expression plasmids, containing pnirB, ppagC, and pkatG, for the delivery of foreign antigens in the DeltaaroAD mutant of Salmonella enterica var. Typhimurium (hereafter referred to as S. typhimurium). The reporter genes encoding beta-galactosidase and firefly luciferase were used to assess the comparative levels of promoter activity in S. typhimurium in vitro in response to different induction stimuli and in vivo in immunized mice. It was determined that the ppagC construct directed the expression of more beta-galactosidase and luciferase in S. typhimurium than the pnirB and pkatG constructs, both in vitro and in vivo. The gene encoding the C fragment of tetanus toxin was expressed in the aroAD mutant of S. typhimurium (BRD509) under the control of the three promoters. Mice orally immunized with attenuated S. typhimurium expressing C fragment under control of the pagC promoter [BRD509(pKK/ppagC/C frag)] mounted the highest tetanus toxoid-specific serum antibody response. Levels of luciferase expression in vivo and C-fragment expression in vitro from the pagC promoter appeared to be equivalent to if not lower than the levels of expression detected with the constitutive trc promoter. However, mice immunized with BRD509(pKK/ppagC/C frag) induced significantly higher levels of tetanus toxoid-specific antibody than BRD509(pKK/C frag)-immunized mice, suggesting that the specific location of foreign antigen expression may be important for immunogenicity. Mutagenesis of the ribosome binding sites (RBS) in the three promoter/C fragment expression plasmids was also performed. Despite optimization of the RBS in the three different promoter elements, the expression levels in vivo and overall immunogenicity of C fragment when delivered to mice by attenuated S. typhimurium were not affected. These studies suggest that in vivo-inducible promoters may give rise to enhanced immunogenicity and increase the efficacy of S. typhimurium as a vaccine vector.

The Mycobacterium tuberculosis katG promoter region contains a novel upstream activator

An Escherichia coli-mycobacterial shuttle vector, pJCluc, containing a luciferase reporter gene, was constructed and used to analyse the Mycobacterium tuberculosis katG promoter. A 1.9 kb region immediately upstream of katG promoted expression of the luciferase gene in E. coli and Mycobacterium smegmatis. A smaller promoter fragment (559 bp) promoted expression with equal efficiency, and was used in all further studies. Two transcription start sites were mapped by primer extension analysis to 47 and 56 bp upstream of the GTG initiation codon. Putative promoters associated with these show similarity to previously identified mycobacterial promoters. Deletions in the promoter fragment, introduced with BAL-31 nuclease and restriction endonucleases, revealed that a region between 559 and 448 bp upstream of the translation initiation codon, designated the upstream activator region (UAR), is essential for promoter activity in E. coli, and is required for optimal activity in M. smegmatis. The katG UAR was also able to increase expression from the Mycobacterium paratuberculosis P(AN) promoter 15-fold in E. coli and 12-fold in M. smegmatis. An alternative promoter is active in deletion constructs in which either the UAR or the katG promoters identified here are absent. Expression from the katG promoter peaks during late exponential phase, and declines during stationary phase. The promoter is induced by ascorbic acid, and is repressed by oxygen limitation and growth at elevated temperatures. The promoter constructs exhibited similar activities in Mycobacterium bovis BCG as they did in M. smegmatis.

Role for the oxyS gene in regulation of intracellular hydrogen peroxide in Escherichia coli

Intracellular hydrogen peroxide is regulated in Escherichia coli by OxyR in response to the metabolic production of H2O2. Here, we show that the untranslated oxyS RNA controlled by OxyR has a role in this regulation. The oxyS transcript appears to affect the metabolic output of H2O2 rather than the removal of H2O2 by catalases-hydroperoxidases.

Oxidative stress pretreatment increases the X-radiation resistance of the nematode Caenorhabditis elegans

Pre-exposure of wild-type Caenorhabditis elegans to oxygen conferred a protective effect against the lethality imposed by subsequent X-irradiation. In contrast, two mutants (rad-1 and rad-2) that are UV and ionizing radiation hypersensitive but not oxygen sensitive, did not exhibit this adaptive response. To explore the molecular basis of protection, the expression of several key genes was examined using Northern blot analyses to measure mRNA levels. In the wild-type, expression of the heat shock protein genes, hsp16-1 and hsp16-48, increased dramatically after incubation under high oxygen. Expression of two superoxide dismutase genes (sod-1 and sod-3) was relatively unaffected. Unlike the wild-type, the basal levels of these four genes were significantly lower in the rad-1 and rad-2 mutants under atmospheric conditions. These genes were partially induced in response to oxidative stress. These data suggest that at least a portion of the hypersensitive phenotype of rad-1 and rad-2 may be attributed to inappropriate gene expression.

Clusterin gene expression mediates resistance to apoptotic cell death induced by heat shock and oxidative stress

Clusterin is a widely expressed, well conserved, secreted glycoprotein, which is highly induced in tissues regressing as a consequence of apoptotic cell death in vivo. It has recently been shown that clusterin expression is only confined to surviving cells following the induction of apoptosis in vitro, suggesting that it is involved in cell survival rather than death. In the hypothesis that clusterin may be implicated in cellular responses to stress, clusterin gene expression was analyzed in the A431 human epidermoid cancer cell line following heat shock and oxidative stress. Our results show that both a transient heat shock (20 min at 42 degrees C) and various oxidative stresses, including hydrogen peroxide, superoxide anion, hyperoxia and UVA exposure, induce a strong increase in clusterin mRNA levels as assessed by northern blot. Nuclear run-on analysis suggests that transcriptional activation is involved in inducing clusterin mRNA in response to heat shock. Using pulse-chase analysis of control and heat shocked cells, it is shown that clusterin mRNA is translated and secreted, thus resulting in increased extracellular levels of the protein following heat shock. To investigate the function of clusterin in response to these stresses, clusterin anti-sense transfectants that stably express virtually no clusterin at the mRNA and protein level were generated in A431 cells. These anti-sense transfectants are shown to be highly sensitive to apoptotic cell death induced by heat shock or oxidative stress compared with wild-type A431 cells or control transfectants. Taken together, our results show that clusterin gene expression is induced in response to heat shock and oxidative stress in human A431 cells, and confers cellular protection against heat shock and oxidative stress.

Effect of growth temperature on the biosynthesis of cell wall proteins from Bifidobacterium globosum

Seventy strains of Bifidobacterium globosum isolated from gastrointestinal tracts of different animals were studied. Strains were grown at temperatures ranging from 25 to 46.5 degrees C in order to examine changes both in the expression of bifidobacterial outer proteins (BIFOPs) and in their hydrophobic properties. It was observed that the expression of BIFOPs found on the cell-surface changes according to growth temperature, with quantitative and/or qualitative variations. Generally speaking, it was observed that BIFOP expression at low-growth temperature was considerably attenuated, while at medium- and high-growth temperature it increased. Furthermore, at high-growth temperatures, the presence of a new common protein was detected in all the strains studied. Cells from B. globosum strains grown under different temperature conditions were studied in terms of their cellular hydrophobicity properties. At medium-growth temperature, the cell hydrophobicity was strictly correlated with BIFOP expression, while at low and high-growth temperatures, the presence of BIFOP only partially influenced the hydrophobic features.

Role of DnaK in in vitro and in vivo expression of virulence factors of Vibrio cholerae

The dnaK gene of Vibrio cholerae was cloned, sequenced, and used to construct a dnaK insertion mutant which was then used to examine the role of DnaK in expression of the major virulence factors of this important human pathogen. The central regulator of several virulence genes of V. cholerae is ToxR, a transmembrane DNA binding protein. The V. cholerae dnaK mutant grown in standard laboratory medium exhibited phenotypes characteristic of cells deficient in ToxR activity. Using Northern blot analysis and toxR transcriptional fusions, we demonstrated a reduction in expression of the toxR gene in the dnaK mutant strain together with a concomitant increase in expression of a htpG-like heat shock gene that is located immediately upstream and is divergently transcribed from toxR. This may be due to increased heat shock induction in the dnaK mutant. In vivo, however, although expression from heat shock promoters in the dnaK mutant was similar to that observed in vitro, expression of both toxR and htpG was comparable to that by the parental strain. In both strains, in vivo expression of toxR was significantly higher than that observed in vitro, but no reciprocal decrease in htpG expression was observed. These results suggest that the modulation of toxR expression in vivo may be different from that observed in vitro.

Antiseptics and disinfectants: activity, action, and resistance

Antiseptics and disinfectants are extensively used in hospitals and other health care settings for a variety of topical and hard-surface applications. A wide variety of active chemical agents (biocides) are found in these products, many of which have been used for hundreds of years, including alcohols, phenols, iodine, and chlorine. Most of these active agents demonstrate broad-spectrum antimicrobial activity; however, little is known about the mode of action of these agents in comparison to antibiotics. This review considers what is known about the mode of action and spectrum of activity of antiseptics and disinfectants. The widespread use of these products has prompted some speculation on the development of microbial resistance, in particular whether antibiotic resistance is induced by antiseptics or disinfectants. Known mechanisms of microbial resistance (both intrinsic and acquired) to biocides are reviewed, with emphasis on the clinical implications of these reports.

Acquired resistance to acoustic trauma by sound conditioning is primarily mediated by changes restricted to the cochlea, not by systemic responses

Hearing loss caused by intense sound exposure can be significantly reduced by pre-exposing subjects to moderate-level acoustic stimuli. This phenomenon occurs in a variety of mammals. We investigated whether sound conditioning provides acquired resistance to acoustic trauma through local mechanisms selectively in the conditioned ears or if systemic mechanisms are involved that would yield contralateral protection in unconditioned ears. Guinea pigs (group I) in which one external ear canal was occluded were exposed to conditioning sound (2-20 kHz, 85 dB SPL, 5 h/day, 10 days). After removing the occlusion, the animals were then subjected bilaterally to intense noise (2-20 kHz, 110 dB SPL, 5 h) 5 days after the last conditioning exposure. Animals without ear canal occlusion were also exposed to the intense sound without conditioning (group II) or following the same conditioning exposure (group III). Intense sound exposure caused significantly greater permanent ABR threshold shifts at all frequencies tested (4, 8, 12, 16 and 20 kHz) in group II than in group III. In group I, the occluded ears showed significantly greater threshold shifts at all frequencies compared to the unoccluded ears. The threshold shifts in the occluded ears in group I were identical to those observed in group II; and the shifts in unoccluded ears in group I were identical to those in group III. Protective effects provided by sound conditioning were almost the same in group III and in the unoccluded ears in group I. The extent of hair cell damage supported the physiological findings. These results indicate that acquired resistance to acoustic trauma provided by sound conditioning is restricted to the cochlea exposed to conditioning sound, suggesting that conditioning protection is mediated primarily by the changes that occur locally within the conditioned cochlea. This animal model, with unilateral external ear canal occlusion during sound conditioning, is useful for studies of the mechanisms of conditioning protection.

Identification of a gene for a rubrerythrin/nigerythrin-like protein in Spirillum volutans by using amino acid sequence data from mass spectrometry and NH2-terminal sequencing

A hydrogen peroxide-resistant mutant of the catalase-negative microaerophile, Spirillum volutans, constitutively expresses a 21.5 kDa protein that is undetectable and non-inducible in the wild-type cells. Part of the gene that encodes the protein was cloned using amino acid sequence data obtained by both mass spectrometry and NH2-terminal sequencing. The deduced 158 amino acid polypeptide shows high relatedness to rubrerythrin and nigerythrin previously described in the anaerobes Clostridium perfringens and Desulfovibrio vulgaris. The protein also shows high similarity to putative rubrerythrin proteins found in the anaerobic archeons Archaeoglobus fulgidus, Methanococcus jannaschii and Methanobacterium thermoautotrophicum. This is the first report of this type of protein in an organism that must respire with oxygen. It seems likely that the novel combination of methodologies used in this study could be applied to the rapid cloning of other genes in bacteria for which no genomic library yet exists.

The heat-shock element is a functional component of the Arabidopsis APX1 gene promoter

Ascorbate peroxidases are important enzymes that detoxify hydrogen peroxide within the cytosol and chloroplasts of plant cells. To better understand their role in oxidative stress tolerance, the transcriptional regulation of the apx1 gene from Arabidopsis was studied. The apx1 gene was expressed in all tested organs of Arabidopsis; mRNA levels were low in roots, leaves, and stems and high in flowers. Steady-state mRNA levels in leaves or cell suspensions increased after treatment with methyl viologen, ethephon, high temperature, and illumination of etiolated seedlings. A putative heat-shock cis element found in the apx1 promoter was shown to be recognized by the tomato (Lycopersicon esculentum) heat-shock factor in vitro and to be responsible for the in vivo heat-shock induction of the gene. The heat-shock cis element also contributed partially to the induction of the gene by oxidative stress. By using in vivo dimethyl sulfate footprinting, we showed that proteins interacted with a G/C-rich element found in the apx1 promoter.

Hydrogen peroxide induces protection against lethal effects of cumene hydroperoxide in Escherichia coli cells: an Ahp dependent and OxyR independent system?

Pretreatment with 2.5 mM H2O2 protects bacterial cells against cumene hydroperoxide killing. This response is independent of the OxyR system, but possibly involves the participation of Ahp protein, since ahp mutants are not protected. Treatment of bacterial cells with high H2O2 concentrations caused an alteration on the electrophoretic profile of the smaller subunit (22-kDa) of Ahp. This alteration does not require novel gene products and is not dependent on the OxyR protein. In this way, we propose that the modification of the 22-kDa subunit of Ahp by high H2O2 concentration may be responsible for the protection against the lethal effects of cumene hydroperoxide.

Immune responses to stress proteins: applications to infectious disease and cancer

Heat shock proteins, or stress proteins have been identified as part of a highly conserved cellular defence mechanism mediated by multiple, distinct gene families and corresponding gene products. As intracellular chaperones, stress proteins participate in many essential biochemical pathways of protein maturation and function active during times of stress and during normal cellular homeostasis. In addition to their well-characterized role as protein chaperones, stress proteins are now realized to possess another important biological property: immunogenicity. Stress proteins are now understood to play a fundamental role in immune surveillance of infection and malignancy and this body of basic research has provided a framework for their clinical application. As key targets of both humoral and cellular immunity during infection, stress proteins have accordingly received considerable research interest as prophylactic vaccines for infectious disease applications. The unique and potent immunostimulatory properties of stress proteins have similarly been applied to the development of new approaches to cancer therapy, including both protein and gene-based modalities.

Regulation of Bacteriodes fragilis katB mRNA by oxidative stress and carbon limitation

Regulation of the katB catalase gene in the anaerobic bacterium Bacteroides fragilis was studied. Northern blot hybridization analyses revealed that katB was transcribed as an approximately 1.6-kb monocistronic mRNA. The levels of katB mRNA increased > 15-fold when anaerobic, mid-logarithmic-phase cultures were exposed to O2, O2 with paraquat, or hydrogen peroxide. Under anaerobic conditions, the low levels of katB mRNA increased in a growth-dependent manner, reaching maximum expression at late logarithmic or early stationary phase, followed by a decrease in stationary phase. Under anaerobic conditions, the expression of katB mRNA was strongly repressed by glucose and to a lesser extent by xylose. However, glucose repression was completely abolished upon exposure to oxygen. The nonfermentable carbon sources fumarate, succinate, acetate, and pyruvate did not significantly affect expression. Phosphate, nitrogen, and hemin limitation did not affect the expression of katB mRNA, suggesting that the nutritional control of katB expression is restricted to carbon and energy sources and not other forms of nutrient limitation. Primer extension analysis revealed that during both oxidative stress and carbon or energy limitation, katB utilized the same promoter region but transcription initiation occurred at two different nucleotides separated by 3 or 4 bases. Interestingly, a 6-bp inverted repeat sequence present in the katB regulatory region was also observed upstream of the B. fragilis superoxide dismutase gene sod. It is possible that this is a recognition site for a DNA binding protein involved in the regulation of oxidative stress genes in this organism.

Transcriptional regulation of the Escherichia coli oxyR gene as a function of cell growth

The oxyR regulon plays a central role in the defense of Escherichia coli against the endogenous oxidative damage associated with active aerobic growth. Here we have studied the transcriptional regulation of oxyR in E. coli growing aerobically in rich medium. Expression of a single-copy oxyR'::lacZ reporter construct varied sixfold along the growth curve, with the highest value at 4 to 6 h of growth (approximately 14 x 10(8) cells x ml(-1)). Direct measurements of oxyR mRNA by primer extension showed the same biphasic expression but with a peak somewhat earlier in cell growth (2 to 3 h; approximately 3.5 x 10(8) cells x ml(-1)). The results of immunoblotting experiments demonstrated that the level of OxyR protein exhibits the same biphasic expression. Mutant strains lacking adenylate cyclase (cya) or Crp protein (crp) failed to increase oxyR expression during exponential growth. On the other hand, an rpoS mutation allowed oxyR expression to continue increasing as the cells entered stationary phase. Consistent with a biological role for increased levels of OxyR during exponential growth, the crp cya strain had lower activities of catalase hydroperoxidase I and glutathione reductase and an increased sensitivity to exogenously added hydrogen peroxide. These results suggest that the Crp-dependent upregulation of oxyR in exponential phase is a component of a multistep strategy to counteract endogenous oxidative stress in actively growing E. coli cells.

Oxidants differentially regulate the heat shock response

Cells, animals, and humans respond to hyperthermia through the synthesis of a family of proteins termed heat shock proteins (HSPs). Because hyperthermic stress may also result in mitochondrial uncoupling and the generation of reactive oxygen species, we wondered whether oxidant stress was sufficient to increase cellular levels of HSP70. HSP70 was detected in cells heated or treated with menadione but not in those treated with hydrogen peroxide or xanthine/xanthine oxidase. We speculate that oxidant stress from menadione exposure is qualitatively different from exposure from hydrogen peroxide or xanthine/xanthine oxidase.

oxyR-dependent induction of Escherichia coli grx gene expression by peroxide stress

The Escherichia coli OxyR protein is a transcriptional activator for a number of genes induced in response to low concentrations of hydrogen peroxide. To identify additional OxyR-regulated genes, I cloned a DNA fragment that shows promoter activity regulated by OxyR by direct selection of OxyR-binding DNA fragments. Analyses of the cloned fragment indicate that the grx gene, encoding glutaredoxin 1, is inducible by hydrogen peroxide in an oxyR-dependent fashion.

Induction and characterization of heat shock proteins of Salmonella typhi and their reactivity with sera from patients with typhoid fever

The heat shock protein (HSP) response of Salmonella typhi following exposure to elevated growth temperatures was studied. Three major proteins with molecular sizes of 58, 68, and 88 kDa were abundantly expressed when S. typhi cells were shifted from 37 to 45 degrees C and to 55 degrees C. These proteins were also constitutively expressed at 37 degrees C. Western blotting and immunoprecipitation studies with anti-HSP monoclonal antibodies revealed that the 58- and 68-kDa proteins were analogous to the GroEL and DnaK proteins, respectively, of Escherichia coli. These HSPs are also abundantly present in the outer membrane fraction of disrupted cells and, to a lesser extent, in the cytosol. Immunoblotting experiments with sera from patients with a culture-positive diagnosis of typhoid fever showed the presence of antibodies to these HSPs. Nine of twelve sera reacted with the 58-, 68-, and 88-kDa proteins, while three sera reacted only with the 68- and 88-kDa proteins. All 10 sera from healthy individuals showed no binding to these HSPs. In light of the well-documented roles of HSPs in the pathogenesis of microbial infections and as immunodominant antigens, these findings may be relevant for a better understanding of disease processes and for the future development of diagnostic and preventive strategies.

Identification of the ahp operon of Salmonella typhimurium as a macrophage-induced locus

Previously, we tagged a macrophage-induced Salmonella typhimurium locus with Mudlux (K. P. Francis and M. P. Gallagher, Infect. Immun. 61:640-649, 1993). The insertion lies within the OxyR-regulated ahpC locus and conveys alkyl peroxide sensitivity. Plasmid-encoded ahp reverses sensitivity but reduces luminescence. This suggests that OxyR is titrated by the multicopy ahp promoter.

Identification of proteins of Francisella tularensis induced during growth in macrophages and cloning of the gene encoding a prominently induced 23-kilodalton protein

The adaptation of facultative intracellular bacteria to host macrophages involves regulation of the synthesis of bacterial proteins. We analyzed the protein synthesis of Francisella tularensis LVS growing intracellularly in the macrophage-like murine cell line J774 and extracellularly in culture medium. After pulse-labeling with [35S] methionine and separation by one- and two-dimensional polyacrylamide gel electrophoresis, induction of a few proteins during intracellular growth was demonstrated. One of them, a 23-kDa protein, was prominently induced in the macrophages and also when extracellularly growing F. tularensis was exposed to hydrogen peroxide. After isolation of the 23-kDa protein from a preparative two-dimensional gel, a 22-amino-acid N-terminal peptide and two peptides obtained by trypsin digestion were sequenced. Based on the sequences, degenerate oligonucleotides were constructed for use as primers in a PCR. Hybridization of amplified DNA to XbaI-digested LVS DNA identified the gene of the 23-kDa protein in a 1.3-kb DNA fragment. Nucleotide sequence analysis revealed an open reading frame encoding a putative protein of a calculated molecular mass of 22.2 kDa. The open reading frame was preceded by a sequence typical of ribosome-binding sites in Escherichia coli. The amplified gene was successfully expressed by the pTrc99A vector in E. coli under control of the trc promoter. The gene product showed the same mobility and immunoreactivity as the 23-kDa protein of F. tularensis. The deduced amino acid sequence showed no significant homology with protein sequences in current data banks. Thus, intracellular growth of F. tularensis in macrophages was associated with prominent upregulation of a novel 23-kDa protein.

Toluene Elicits a Carbon Starvation Response in Pseudomonas putida mt-2 Containing the TOL Plasmid pWW0

Pseudomonas putida mt-2(pWWO) exhibited a carbon starvation response in the presence of toluene, a utilizable carbon source. When growth-supporting (4-mg/liter), inhibitory (130-mg/liter), and lethal (267-mg/ liter) levels of toluene were provided as the sole carbon source, P. putida responded by rapidly inhibiting protein synthesis and by producing 26 new proteins, 22 of which overlapped with those induced by carbon starvation. P. putida produced the same proteins when cultures were starved by depleting their carbon source or were downshifted into a carbon-free medium. Carbon supplementation of toluene-exposed cells suppressed the production of the toluene-induced proteins. The level of toluene provided as the sole carbon source influenced the length of time that this response was observed. Following 1.5 to 3 h in a basal salts medium with 4 mg of toluene per liter, protein synthesis increased, the production of the majority of the toluene-induced proteins ceased, and the cells began to grow. In cells provided with 130 mg of toluene per liter, protein synthesis remained inhibited over a 6.5-h experimental period. At this concentration, the production of 15 toluene-induced proteins was prolonged, with nine still detectable in the profiles at 6.5 h. In cells provided with 267 mg of toluene per liter, there was a rapid loss of viability and the toluene-induced proteins were detected prior to death. In cells provided with 4 mg of toluene per liter, the carbon starvation response is transient and likely reflects a period of induction and/or adaptation prior to growth on toluene. At the toluene concentrations which inhibit growth, P. putida exhibits a prolonged starvation response despite the presence of an excess of a utilizable carbon source.

Hydrogen peroxide induces protection against N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) effects in Escherichia coli

Cross-adaptive response is defined as the capacity of cells to become resistant to a lethal agent when pretreated with a different lethal substance. In the present paper, the cross-adaptive response between hydrogen peroxide and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was studied in Escherichia coli repair mutants. Our results suggest that high doses of H2O2 induces protection against the lethal effects of MNNG in wild-type strain, ada, ogt, ada-ogt, aidB and alkA mutants. On the other hand, the MNNG induced mutagenesis is reduced by H2O2 pretreatment in wild-type and ogt mutant strains, but not in ada mutant. Furthermore, the protecting effect induced by H2O2 is time dependent: it decreases 15 min after the pretreatment and, after 30 min, is almost abolished. This reduction in the protecting effect is followed by an augmentation in the mutation frequency when MNNG is added 30 min after H2O2 pretreatment. This cross-adaptive response may be due to a modification of the MNNG alkylation pattern in the oxidized DNA.

A possibility for new evaluating method of cytotoxicity by using heat shock protein assay

To determine whether heat shock proteins can be utilized as a biomarker for cytotoxicity of dental materials the induction of synthesis of heat shock proteins by mercuric chloride was examined. To analyse the synthesis of heat shock proteins, HeLa cells were labelled with [35S] methionine, and the labelled proteins were separated by SDS-PAGE and autoradiographed. Incubation of the cells in a medium containing 1.25 to 40 microM mercuric chloride markedly increased the synthesis of HSP70. At 20 or 40 microM mercuric chloride in medium, HeLa cells synthesized HSP70 at 2 h after exposure, maximally at 4-7 h, and gradually diminished thereafter. Examination of the cytotoxicity of mercuric chloride by the conventional neutral red uptake assay revealed a reduction of uptake of the dye in the presence of mercuric chloride at 40 microM and above. These findings suggest that the induction of synthesis of HSP70 is one of the most sensitive cellular responses caused by mercury ion, and the heat shock protein assay can be utilized for evaluation of the cytotoxicity of dental materials.

Study of redox-regulated transcription factors in prokaryotes

Several prokaryotic regulatory proteins that respond to changes in oxygen tension or the presence of oxidative agents have now been identified. The Fnr protein governs the expression of numerous genes during anaerobic growth, both as a transcriptional activator and as a repressor. OxyR protein responds to cellular exposure to H2O2 to stimulate transcription of several defense proteins. SoxR protein is triggered by superoxide or nitric oxide to activate a multigene regulon for antioxidant defense and antibiotic resistance. Each of these proteins has been purified and characterized for DNA binding and transcriptional activity in vitro. Fnr, OxyR, and SoxR all seem to respond directly to redox signals generated in the cell, and their in vitro properties support this view: Fnr has an oxygen-sensitive [4Fe-4S] center essential for DNA binding; OxyR may be activated via oxidation of a key cysteine residue; and SoxR activation depends on redox-sensitive [2Fe-2S] centers. Basic methods for genetic and biochemical analysis in these systems are presented, with emphasis on detailed methods for SoxR that illustrate general approaches for all the systems.

Differential transcript induction of parsley pathogenesis-related proteins and of a small heat shock protein by ozone and heat shock

Parsley (Petroselinum (crispum L.) is known to respond to pathogen attack by the synthesis of furanocoumarins and to UV irradiation by the synthesis of flavone glycosides whereas ozone treatment results in the induction of both pathways. A cDNA library from parsley plants was differentially screened using labelled reverse-transcribed poly(A)+ RNA isolated from ozone-treated parsley plants. This resulted in the isolation of 13 independent cDNA clones representing ozone-induced genes and of 11 cDNA clones representing ozone-repressed genes. DNA sequencing of several clones resulted in the identification of pathogenesis-related protein 1-3 (PR1-3), of a new member of PR1 cDNAs (PRI-4) and of a small heat shock protein (sHSP). Northern blot analyses showed a transient induction of the three mRNA species after ozone fumigation. In contrast, heat shock treatment of parsley plants resulted in an increase of sHSP mRNA whereas no increase for transcripts of PR1-3 and PR1-4 could be observed. This is the first characterized sHSP cDNA clone for plants induced by heat shock, as well as by oxidative stress caused by ozone.

Identification and characterization of hydrogen peroxide-sensitive mutants of Escherichia coli: genes that require OxyR for expression

Escherichia coli produces an inducible set of proteins that protect the cell from exogenous peroxide stress. A subset of these genes is induced by hydrogen peroxide and is controlled at the transcriptional level by the OxyR protein. To identify additional genes involved in protection from hydrogen peroxide, a library of random transcriptional fusions of lambda(plac)Mu53 was screened for hydrogen peroxide sensitivity and 27 such mutants were identified. These fusions were transduced into nonlysogenic strains to ensure that the phenotypes observed were the result of a single mutation. The mutants were grouped into three classes based on the expression of the lacZ fusion during growth in oxyR+ and deltaoxyR backgrounds. The expression of the lacZ fusion in 8 mutants was independent of OxyR, 10 mutants required OxyR for expression, and 6 mutants showed reduced levels of expression in the presence of OxyR. OxyR dependence varied from 2- to 50-fold in these mutants. The OxyR-dependent phenotype was complemented by a plasmid-borne copy of oxyR gene in all mutants. Three mutants exhibited dual regulation by OxyR and RpoS. We sequenced the fusion junctions of several of these mutants and identified the genetic loci responsible for the hydrogen peroxide-sensitive (hps) phenotype. In this study, we report the identification of several genes that require OxyR for expression, including hemF (encoding coproporphyrinogen III oxidase), rcsC (encoding a sensor-regulator protein of capsular polysaccharide synthesis genes), and an open reading frame, f497, that is similar to arylsulfatase-encoding genes.

Oxidative stress response in an anaerobe, Bacteroides fragilis: a role for catalase in protection against hydrogen peroxide

Survival of Bacteroides fragilis in the presence of oxygen was dependent on the ability of bacteria to synthesize new proteins, as determined by the inhibition of protein synthesis after oxygen exposure. The B. fragilis protein profile was significantly altered after either a shift from anaerobic to aerobic conditions with or without paraquat or the addition of exogenous hydrogen peroxide. As determined by autoradiography after two-dimensional gel electrophoresis, approximately 28 newly synthesized proteins were detected in response to oxidative conditions. These proteins were found to have a broad range of pI values (from 5.1 to 7.2) and molecular weights (from 12,000 to 79,000). The hydrogen peroxide- and paraquat-inducible responses were similar but not identical to that induced by oxygen as seen by two-dimensional gel protein profile. Eleven of the oxidative response proteins were closely related, with pI values and molecular weights from 5.1 to 5.8 and from 17,000 to 23,000, respectively. As a first step to understanding the resistance to oxygen, a catalase-deficient mutant was constructed by allelic gene exchange. The katB mutant was found to be more sensitive to the lethal effects of hydrogen peroxide than was the parent strain when the ferrous iron chelator bipyridyl was added to culture media. This suggests that the presence of ferrous iron in anaerobic culture media exacerbates the toxicity of hydrogen peroxide and that the presence of a functional catalase is important for survival in the presence of hydrogen peroxide. Further, the treatment of cultures with a sublethal concentration of hydrogen peroxide was necessary to induce resistance to higher concentrations of hydrogen peroxide in the parent strain, suggesting that this was an inducible response. This was confirmed when the bacterial culture, treated with chloramphenicol before the cells were exposed to a sublethal concentration of peroxide, completely lost viability. In contrast, cell viability was greatly preserved when protein synthesis inhibition occurred after peroxide induction. Complementation of catalase activity in the mutant restored the ability of the mutant strain to survive in the presence of hydrogen peroxide, showing that the catalase (KatB) may play a role in oxidative stress resistance in aerotolerant anaerobic bacteria.

Lack of expression of the global regulator OxyR in Haemophilus influenzae has a profound effect on growth phenotype

A pBR322-based library of chromosomal DNA from the nontypeable Haemophilus influenzae TN106 was screened for the expression of transferrin-binding activity in Escherichia coli. A recombinant clone expressing transferrin-binding activity contained a 3.7-kb fragment of nontypeable H. influenzae DNA. Nucleotide sequence analysis of this insert revealed the presence of two complete open reading frames encoding proteins of approximately 26 and 34 kDa. Mini-Tn10kan transposon mutagenesis at different sites within the open reading frame encoding the 34-kDa protein resulted in the abolition of transferrin-binding activity in the recombinant E. coli clone. The deduced amino acid sequence of the 34-kDa protein had 70% identity with the OxyR protein of E. coli; this latter macromolecule is a member of the LysR family of transcriptional activators. When a mutated H. influenzae oxyR gene was introduced into the chromosome of the wild-type H. influenzae strain by allelic exchange, the resulting oxyR mutant still exhibited wild-type levels of transferrin-binding activity but was unable to grow on media containing the heme precursor protoporphyrin IX (PPIX) in place of heme. This mutant also exhibited reduced growth around disks impregnated with heme sources. Supplementation of the PPIX-based growth media with catalase or sodium pyruvate resulted in normal growth of the H. influenzae oxyR mutant. Provision of the wild-type H. influenzae oxyR gene in trans also permitted the growth of this mutant on a PPIX-based medium. Exogenously supplied catalase restored the growth of this mutant with heme sources to nearly wild-type levels. These results indicate that expression of a wild-type OxyR protein by H. influenzae is essential to allow this organism to protect itself against oxidative stresses in vitro.

Hypochlorous acid activates the heat shock and soxRS systems of Escherichia coli

A series of plasmids, containing fusions of different stress promoters to lux reporter genes, was used in an attempt to monitor the defense circuits activated upon exposure of Escherichia coli to sublethal doses of free chlorine. A significant level of activation was exhibited by promoters of three heat shock genes (grpE, dnaK, and lon), in an rpoH-dependent manner. The promoter of micF, a gene under the control of the soxRS regulon, was also strongly induced, but not in a soxR mutant. This induction was not affected by sodA and sodB mutations, implying that it did not involve oxygen radical activity. Free-chlorine activation of both heat shock and soxRS regulons required an exposure of less then I s in duration. The oxyR or the SOS regulons were apparently not induced by free chlorine (as judged by lack of activation of katG and recA, respectively), and neither was the universal stress (uspA) protein.

Expression of hsp70 mRNA is induced in the brain of transgenic mice overexpressing human CuZn-superoxide dismutase following transient global cerebral ischemia

We examined hsp70 mRNA expression in the brains of transgenic (Tg) mice overexpressing CuZn-superoxide dismutase and in wild-type (Wt) littermates after 3 min of bilateral common carotid artery occlusion. Significant induction of hsp70 mRNA occurred in the hippocampus, the cortex, and other brain regions of the Tg mice 4 h after ischemia compared to the Wt mice. However, there was no histological damage in the brains of Tg and Wt mice as assessed by both Cresyl violet staining and by TUNEL staining for DNA fragmentation. These data suggest that high levels of CuZn-superoxide dismutase activity increase hsp70 mRNA expression and that intense hsp70 mRNA expression does not predict neuronal damage, even in vulnerable hippocampal CA1 neurons.

Identification and characterization of the Yersinia enterocolitica gsrA gene, which protectively responds to intracellular stress induced by macrophage phagocytosis and to extracellular environmental stress

Yersinia enterocolitica is able to resist the microbicidal mechanisms of macrophages and to grow within phagocytic cells. Some bacteria including Y. enterocolitica have been shown to respond to the hostile environment in macrophages by producing a set of stress proteins which are also induced by environmental stresses. To understand the role of stress proteins in intracellular survival of bacteria, we identified and cloned a Y. enterocolitica gene, called gsrA (global stress requirement). The gsrA gene was identified because its insertional inactivation by a transposon resulted in the inability of the organism to grow at an elevated temperature and to survive within macrophages after phagocytosis. The gsrA gene was sequenced and shown to encode a basic, 49,500-Da protein. The GsrA protein shows significant amino acid sequence homology to the HtrA stress protein which was originally identified in Escherichia coli. Furthermore, the genetically defined Y. enterocolitica gsrA mutant was constructed and characterized. The insertional mutation of gsrA resulted in inhibition of growth at temperatures above 39 degrees C and greatly increased susceptibility to oxidative and osmotic stresses. The mutant additionally lost the ability to survive and replicate within macrophages. These results, taken together, indicate that the gsrA gene is an essential component of the protection mechanism employed by Y. enterocolitica, allowing it to respond to the intracellular stress in macrophages as well as extracellular environmental stress.

Oxidative stress is involved in heat-induced cell death in Saccharomyces cerevisiae

The cause for death after lethal heat shock is not well understood. A shift from low to intermediate temperature causes the induction of heat-shock proteins in most organisms. However, except for HSP104, a convincing involvement of heat-shock proteins in the development of stress resistance has not been established in Saccharomyces cerevisiae. This paper shows that oxidative stress and antioxidant enzymes play a major role in heat-induced cell death in yeast. Mutants deleted for the antioxidant genes catalase, superoxide dismutase, and cytochrome c peroxidase were more sensitive to the lethal effect of heat than isogenic wild-type cells. Overexpression of catalase and superoxide dismutase genes caused an increase in thermotolerance. Anaerobic conditions caused a 500- to 20,000-fold increase in thermotolerance. The thermotolerance of cells in anaerobic conditions was immediately abolished upon oxygen exposure. HSP104 is not responsible for the increased resistance of anaerobically grown cells. The thermotolerance of anaerobically grown cells is not due to expression of heat-shock proteins. By using an oxidation-dependent fluorescent molecular probe a 2- to 3-fold increase in fluorescence was found upon heating. Thus, we conclude that oxidative stress is involved in heat-induced cell death.

Participation of the molecular chaperone DnaK in intracellular growth of Brucella suis within U937-derived phagocytes

In the intracellular bacterium Brucella suis, the molecular chaperone DnaK was induced under heat-shock conditions and at low pH. Insertional inactivation of dnaK and dnaJ within the dnaK/J locus led to the conclusion that DnaK, but not DnaJ, was required for growth at 37 degrees C in vitro. Viability of the dnaK null mutant was also greatly affected at low pH. Under conditions allowing intracellular multiplication, the infection of U937-derived phagocytes resulted in long-lasting DnaK induction in the wild-type bacteria. In infection experiments performed with both mutants at the reduced temperature of 30 degrees C, the dnaK mutant of B. suis survived but failed to multiply within U937 cells, whereas the wild-type strain and the dnaJ mutant multiplied normally. Complementation of the dnaK mutant with the cloned dnaK gene restored growth at 37 degrees C, increased resistance to acid pH, and increased intracellular multiplication. This is the first report of the effects of dnaK inactivation in a pathogenic species, and of the temperature-independent contribution of DnaK to intracellular multiplication of the pathogen B. suis.

Antioxidant defense mechanisms in parasitic protozoa

Many of the parasitic protozoa, such as Entamoeba histolytica, Giardia, Trypanosoma, Leishmania, and Plasmodium, are considered to be anaerobes because they can be grown in vitro only under conditions of reduced oxygen tension. However, these parasitic protozoa have been found to be aerotolerant or microaerophilic, and also to consume oxygen to a certain extent. Furthermore, these organisms are highly susceptible to exogenous reactive oxygen species, such as hydrogen peroxide. They must, therefore, detoxify both oxygen and free radical products of enzymatic reactions. However, they lack some or all of the usual antioxidant defense mechanisms present in aerobic or other aerotolerant cells, such as catalase, superoxide dismutase, reduced glutathione, and the glutathione-recycling enzymes glutathione peroxidase and glutathione reductase. Instead, they possess alternative mechanisms for detoxification similar to those known to exist in certain prokaryotes. Although the functional aspects of these alternative mechanisms are yet to be understood completely, they could provide new insights into the biochemical peculiarities of these enigmatic pathogens.