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  • 1
    Electronic Resource
    Electronic Resource
    The Burkholderia pseudomallei RpoE (AlgU) operon is involved in environmental stress tolerance and biofilm formation (2005)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 252 (2005), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Burkholderia pseudomallei, the causative agent of melioidosis, can be isolated from soil and water. To persist, adapt and survive within and outside their human host, bacteria rely on regulatory mechanisms that allow them to respond rapidly to stressful situations. We have examined the possible role of B. pseudomallei alternative sigma factor σE (RpoE) in the stress response and found that rpoE and its putative regulators (bprE-rseB-mucD) are transcribed in a single transcriptional unit. Inactivation of the rpoE operon changed the B. pseudomallei phenotype. Changes included increased susceptibility to killing by menadione and H2O2, susceptibility to high osmolarity, reduced ability to form biofilms, and reduced survival in macrophage J774A.1. Therefore, we conclude that rpoE controls gene expression that contributes, at least in part, to B. pseudomallei adaptation to adverse environmental conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/j.femsle.2005.09.002
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  • 2
    Electronic Resource
    Electronic Resource
    Analysis of growth phase regulated KatA and CatE and their physiological roles in determining hydrogen peroxide resistance in Agrobacterium tumefaciens (2004)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 237 (2004), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Agrobacterium tumefaciens possesses two catalases, a bifunctional catalase-peroxidase, KatA and a homologue of a growth phase regulated monofunctional catalase, CatE. In stationary phase cultures and in cultures entering stationary phase, total catalase activity increased 2-fold while peroxidase activity declined. katA and catE were found to be independently regulated in a growth phase dependent manner. KatA levels were highest during exponential phase and declined as cells entered stationary phase, while CatE was detectable at early exponential phase and increased during stationary phase. Only small increases in H2O2 resistance levels were detected as cells entering stationary phase. The katA mutant was more sensitive to H2O2 than the parental strain during both exponential and stationary phase. Inactivation of catE alone did not significantly change the level of H2O2 resistance. However, the katA catE double mutant was more sensitive to H2O2 during both exponential and stationary phase than either of the single catalase mutants. The data indicated that KatA plays the primary role and CatE acts synergistically in protecting A. tumefaciens from H2O2 toxicity during all phases of growth. Catalase-peroxidase activity (KatA) was required for full H2O2 resistance. The expression patterns of the two catalases in A. tumefaciens reflect their physiological roles in the protection against H2O2 toxicity, which are different from other bacteria.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.2004.tb09699.x
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  • 3
    Electronic Resource
    Electronic Resource
    Induction of peroxide and superoxide protective enzymes and physiological cross-protection against peroxide killing by a superoxide generator in Vibrio harveyi (2003)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 221 (2003), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Vibrio harveyi is a causative agent of destructive luminous vibriosis in farmed black tiger prawn (Penaeus monodon). V. harveyi peroxide and superoxide stress responses toward elevated levels of a superoxide generated by menadione were investigated. Exposure of V. harveyi to sub-lethal concentrations of menadione induced high expression of genes in both the OxyR regulon (e.g., a monofunctional catalase or KatA and an alkyl hydroperoxide reductase subunit C or AhpC), and the SoxRS regulon (e.g., a superoxide dismutase (SOD) and a glucose-6-phosphate dehydrogenase). V. harveyi expressed two detectable, differentially regulated SOD isozymes, [Mn]-SOD and [Fe]-SOD. [Fe]-SOD was expressed constitutively throughout the growth phase while [Mn]-SOD was expressed at the stationary phase and could be induced by a superoxide generator. Physiologically, pre-treatment of V. harveyi with menadione induced cross-protection against subsequent exposure to killing concentrations of H2O2. This induced cross-protection required newly synthesized proteins. However, the treatment did not induce significant protection against exposures to killing concentrations of menadione itself or cross-protect against an organic hydroperoxide (tert-butyl hydroperoxide). Unexpectedly, growing V. harveyi in high-salinity media induced protection against menadione killing. This protection was independent of SOD induction. Stationary-phase cells were more resistant to menadione killing than exponential-phase cells. The induction of oxidative stress protective enzymes and stress-altered physiological responses could play a role in the survival of this bacterium in the host marine crustaceans.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/S0378-1097(03)00172-1
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  • 4
    Electronic Resource
    Electronic Resource
    OxyR mediated compensatory expression between ahpC and katA and the significance of ahpC in protection from hydrogen peroxide in Xanthomonas campestris (2005)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 249 (2005), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: katA and ahpC, encoding monofunctional catalase and alkyl hydroperoxide reductase, respectively, play important protective roles against peroxide toxicity in Xanthomonas campestris pv. phaseoli (Xp). The expression of both katA and ahpC is controlled by the global peroxide sensor and transcriptional activator, OxyR. In Xp, these two genes have compensatory expression patterns. Inactivation of katA leads to an increase in the level of AhpC and a concomitant increase in resistance to tert-butyl hydroperoxide (tBOOH). High-level expression of katA from an expression vector in Xp also lowered the level of ahpC expression. The compensatory regulation of katA and ahpC was mediated by OxyR, since the compensatory response was not observed in an oxyR mutant background. ahpC and katA play important but unequal roles in protecting Xp from H2O2 toxicity. These observations, taken together with a previous observation that an ahpC mutant expresses high levels of KatA and is hyper-resistant to H2O2, suggest the possibility that inactivation of either gene leads to accumulation of intracellular H2O2. This in turn oxidizes reduced OxyR and converts the regulator to the oxidized form that then activates expression of genes in the OxyR regulon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/j.femsle.2005.06.002
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  • 5
    Electronic Resource
    Electronic Resource
    Characterization of Xanthomonas oryzae pv. oryzae recX, a gene that is required for high-level expression of recA (2001)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 205 (2001), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Analysis of the nucleotide sequence downstream from the Xanthomonas oryzae pv. oryzae recA gene reveals two orfs designated orfX and recX. The former has the potential to code for a 5.6 kDa protein of unknown function while the latter encodes for a putative 14.6 kDa protein with homology to RecX from various bacteria. Northern blot analysis and RT-PCR results show that recA-orfX-recX are co-regulated and arranged in an operon. A recX mutant was constructed. The mutant has no obvious growth defects or stress response defects, except that it cannot support high-level expression of recA from an expression vector. Introduction of the plasmid containing recA into the recX mutant resulted in reduced transformation efficiency and all transformants tested had mutations with reduced RecA levels. Moreover, the recX mutant has reduced basal levels of RecA. This has not been observed in other bacteria. When inactivated recX was complemented in trans, both changes were reversed. recX mutation has no effect on the regulation of the recA promoter, suggesting that its effect on the RecA level could be post-transcriptional.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.2001.tb10929.x
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  • 6
    Electronic Resource
    Electronic Resource
    Construction and characterization of regulated L-arabinose-inducible broad host range expression vectors in Xanthomonas (1999)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 181 (1999), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Several versions of broad host range (BHR), L-arabinose-inducible expression vectors were constructed. These expression vectors were based on a high copy number BHR pBBR1MCS-4 replicon that could replicate in both enteric and non-enteric Gram-negative bacteria. Two versions of expression cassettes containing multiple cloning sites either with or without a ribosome binding site were placed under transcriptional control of the Escherichia coli BAD promoter and araC gene. Three versions of vectors containing ampicillin or kanamycin or tetracycline resistance genes as selectable markers were constructed. In all six new L-arabinose-inducible BHR expression vectors containing many unique cloning sites, selectable markers were made to facilitate cloning and expression of genes in various Gram-negative bacteria. A Tn9 chloramphenicol acetyl transferase (cat) gene was cloned into an expression vector, resulting in pBBad18Acat that was used to establish optimal expression conditions (addition of 0.02%L-arabinose to mid-exponential phase cells for at least 1 h) in a Xanthomonas campestris pv. phaseoli. Comparison of the Cat enzyme activities between uninduced and a 180-min L-arabinose-induced culture showed a greater than 150-fold increased Cat specific activity. In addition, L-arabinose induction of exponential phase cells harboring pBBad18Acat gave a higher amount of Cat than similarly treated stationary phase cells. The usefulness of the expression vector was also demonstrated in both enteric and non-enteric Gram-negative bacteria.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1999.tb08847.x
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  • 7
    Electronic Resource
    Electronic Resource
    Modulation of peroxide stress response by thiol reagents and the role of a redox sensor-transcription regulator, OxyR in mediating the response in Xanthomonas (1999)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 176 (1999), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Pretreatment of Xanthomonas campestris pv. phaseoli with low inducing concentrations of thiol reagents such as N-ethylmaleimide (NEM) and diamide induced resistance to H2O2 killing. In addition, these compounds were moderate inducers of peroxide detoxification enzymes such as catalase and alkyl hydroperoxide reductase. For both cases, thiol reagent induced responses required a functional redox sensor/transcription activator oxyR and were absent in an oxyR mutant. By contrast, NEM pretreatment enhanced the killing effects of organic peroxide. The observed Xanthomonas physiological responses to thiol reagent pretreatment, and subsequent challenge with peroxide stress, differed from other bacteria.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1999.tb13699.x
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  • 8
    Electronic Resource
    Electronic Resource
    Evaluation of the role hydroxyl radicals and iron play in hydrogen peroxide killing of Xanthomonas campestris pv. phaseoli (1998)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 169 (1998), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Hydroxyl radical, a product of H2O2 metabolism in the Fenton reaction, is a major reactive oxygen species involved in H2O2 killing of Xanthomonas campestris pv. phaseoli (Xp). Compounds which absorbed hydroxyl radicals protected Xanthomonas from H2O2 killing, but not from killing by a superoxide generator or an organic peroxide. Addition of iron potentiated H2O2 killing. On the other hand, pre-treatment of Xp with an iron chelator showed no protective effects and H2O2 killing was actually enhanced. Unexpectedly, resuspension of Xp in either water or phosphate buffer induced high-level resistance to H2O2 killing. The unknown protection mechanism was independent of new protein synthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1998.tb13326.x
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  • 9
    Electronic Resource
    Electronic Resource
    Oxidant-inducible resistance to hydrogen peroxide killing in Agrobacterium tumefaciens requires the global peroxide sensor-regulator OxyR and KatA (2003)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 225 (2003), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Induced adaptive and cross-protective responses to peroxide stress are important strategies used by bacteria to survive stressful environments. We have shown that exposure to low levels of peroxide (adaptive) and superoxide anions (cross-protection) induced high levels of resistance to peroxide killing in Agrobacterium tumefaciens. The mechanisms and genes involved in these processes have not been identified. Here, the roles played by peroxide (oxyR) and superoxide (soxR) global regulators and a catalase gene (katA) during these responses were investigated. H2O2-induced adaptive protection was completely abolished in both the oxyR and katA mutants. Superoxide generator (menadione)-induced cross-protection to H2O2 killing was observed in a soxR mutant, but not in either an oxyR or a katA mutant. In vivo analysis of the katA promoter, using a katA::lacZ transcriptional fusion, revealed that it could be induced by menadione in an oxyR-dependent manner. These results lead us to conclude that H2O2 and superoxide anions directly or indirectly oxidize OxyR and it is the resulting activation of katA expression that is responsible for the induced protection against lethal concentrations of H2O2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/S0378-1097(03)00511-1
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  • 10
    Electronic Resource
    Electronic Resource
    Induced adaptive and cross-protection responses against oxidative stress killing in a bacterial phytopathogen, Xanthomonas oryzae pv. oryzae (1997)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 146 (1997), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: In Xanthomonas oryzae pv. oryzae, exposure to a sub-lethal concentration of H2O2 conferred protection to subsequent challenges with a killing concentration of H2O2 (30 mM, adaptive response). No adaptive response to tert-butylhydroperoxides (tBOOH) or the superoxide generator menadione was observed. However, exposure to sub-lethal concentrations of tBOOH or N-ethylmaleimide (a thiol reagent) induced cross-protection to low 30 mM lethal levels of H2O2 but not to organic peroxides. Pre-treatment with a superoxide generator conferred cross-protection against a high lethal concentration (150 mM) of H2O2 and an organic hydroperoxide (tBOOH). The levels of protection against H2O2 killing caused by various inducers were correlated with their ability to induce catalase. There was no cross-regulation between oxidative stress and heat shock. Both adaptive and cross-protection responses required de novo protein synthesis. Many aspects of these responses in X. oryzae pv. oryzae are unlike responses previously observed in other microbes and they may have important physiological roles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1997.tb10196.x
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