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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
    The role of a bifunctional catalase-peroxidase KatA in protection of Agrobacterium tumefaciens from menadione toxicity (2004)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 232 (2004), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Agrobacterium tumefaciens is an aerobic plant pathogenic bacterium that is exposed to reactive oxygen species produced either as by-products of aerobic metabolism or by the defense systems of host plants. The physiological function of the bifunctional catalase-peroxidase (KatA) in the protection of A. tumefaciens from reactive oxygen species other than H2O2 was evaluated in the katA mutant (PB102). Unexpectedly, PB102 was highly sensitive to the superoxide generator menadione. The expression of katA from a plasmid vector complemented the menadione-hypersensitive phenotype. A. tumefaciens possesses an additional catalase gene, a monofunctional catalase encoded by catE. Neither inactivation nor high-level expression of the catE gene altered the menadione resistance level. Moreover, heterologous expression of the catalase-peroxidase-encoding gene katG from Burkholderia pseudomallei, but not the monofunctional catalase gene katE from Xanthomonas campestris could restore normal levels of menadione resistance to PB102. A recent observation suggests that the menadione resistance phenotype involves increased activities of organic peroxide-metabolizing enzymes. Heterologous expression of X. campestris alkyl hydroperoxide reductase from a plasmid vector failed to complement the menadione-sensitive phenotype of PB102. The level of menadione resistance shows a direct correlation with the level of peroxidase activity of KatA. This is a novel role for KatA and suggests that resistance to menadione toxicity is mediated by a new, and as yet unknown, mechanism in A. tumefaciens.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/S0378-1097(04)00075-8
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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
    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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  • 5
    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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  • 6
    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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  • 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
    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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  • 9
    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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  • 10
    Electronic Resource
    Electronic Resource
    Unusual adaptive, cross protection responses and growth phase resistance against peroxide killing in a bacterial shrimp pathogen, Vibrio harveyi (2001)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 200 (2001), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Oxidant induced protection against peroxide killing was investigated in a prawn bacterial pathogen, Vibrio harveyi. Exposure to 250 μM H2O2 induced adaptive protection against subsequent exposure to killing concentrations of H2O2. In addition, 200 μM t-butyl hydroperoxide (tBOOH) induced cross protection to H2O2 killing. On the other hand, peroxide pretreatment did not induce protection against tBOOH killing. Peroxide induced adaptive and cross protection responses required new protein synthesis and were abolished by addition of a protein synthesis inhibitor. Pretreatments of V. harveyi with 250 μM H2O2 and 200 μM tBOOH induced an increase in peroxide scavenging enzymes, catalase and alkyl hydroperoxide reductase subunit C. In addition, stationary phase cells of V. harveyi were more resistant to H2O2 and iodoacetamide killing but highly susceptible to tBOOH killing compared to exponential phase cells. Many aspects of the oxidative stress response of V. harveyi are different from those of other bacteria and these factors may be important for bacterial survival in the environment and during interactions with host shrimp.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.2001.tb10701.x
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