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Oxidative Stress in Synechococcus sp. Strain PCC 7942: Various Mechanisms for H2O2 Detoxification with Different Physiological Roles. Alexander Perelman, 2003.This study focuses on the mechanisms for hydrogen peroxide detoxification in Synechococcus sp . strain PCC 7942 . To gain better understanding of the role of different routes of hydrogen peroxide detoxification, we inactivated tplA (thioredoxin-peroxidase-like), which we recently identified . In addition, we inactivated the gene encoding catalase-peroxidase and examined the ability to detoxify H2O2 and to survive oxidative stress in both of the single mutants and in the double mutant . Surprisingly, we observed that the double mutant survived H2O2 concentrations that the single catalase-peroxidase mutant could not tolerate . This phenotype correlated with an increased ability of the double mutant to detoxify externally added H2O2 compared to the catalase-peroxidase mutant . Therefore, our studies suggested the existence of a hydrogen peroxide detoxification activity in addition to catalase-peroxidase and thioredoxin-peroxidase . The rate of detoxification of externally added H2O2 was similar in the wild-type and the TplA mutant cells, suggesting that, under these conditions, catalase-peroxidase activity was essential for this process and TplA was dispensable . However, during excessive radiation, conditions under which the cell might experience oxidative stress, TplA appears to be essential for growth, and cells lacking it cannot compete with the wild-type strain . Overall, these studies suggested different physiological roles for various cellular hydrogen peroxide detoxification mechanisms in Synechococcus sp . strain PCC 7942 . Omiganan Pentahydrochloride (MBI 226), a Topical 12-Amino-Acid Cationic Peptide: Spectrum of Antimicrobial Activity and Measurements of Bactericidal Activity. Helio S. Sader, 2004.The activity of omiganan pentahydrochloride (formerly MBI 226; a synthetic cationic peptide) was assessed against 1,437 recent clinical bacterial isolates and 214 recent clinical yeast isolates . The omiganan was highly active, and minimal bactericidal concentrations or minimal fungicidal concentrations were either equal to or two- to fourfold higher than MICs . Kill curve experiments showed a clear pattern of bactericidal activity . Temporal and Spatial Profiles of Chitinase Expression by Norway Spruce in Response to Bark Colonization by Heterobasidion annosum. Ari M. Hietala, 2004.Pathogen colonization and transcript levels of three host chitinases, putatively representing classes I, II, and IV, were monitored with real-time PCR after wounding and bark infection by Heterobasidion annosum in 32-year-old trees of Norway spruce (Picea abies) with low (clone 409) or high (clone 589) resistance to this pathogen . Three days after inoculation, comparable colonization levels were observed in both clones in the area immediately adjacent to inoculation . At 14 days after infection, pathogen colonization was restricted to the area immediately adjacent to the site of inoculation for clone 589 but had progressed further into the host tissue in clone 409 . Transcript levels of the class II and IV chitinases increased after wounding or inoculation, but the transcript level of the class I chitinase declined after these treatments . Transcript levels of the class II and class IV chitinases were higher in areas immediately adjacent to the inoculation site in clone 589 than in similar sites in clone 409 3 days after inoculation . This difference was even more pronounced 2 to 6 mm away from the inoculation point, where no infection was yet established, and suggests that the clones differ in the rate of chitinase-related signal perception or transduction . At 14 days after inoculation, these transcript levels were higher in clone 409 than in clone 589, suggesting that the massive upregulation of class II and IV chitinases after the establishment of infection comes too late to reduce or prevent pathogen colonization . Bacillus subtilis YhaM, a Member of a New Family of 3'-to-5' Exonucleases in Gram-Positive Bacteria. Irina A. Oussenko, 2002.A strain of Bacillus subtilis lacking two 3'-to-5' exoribonucleases, polynucleotide phosphorylase (PNPase) and RNase R, was used to purify another 3'-to-5' exoribonuclease, which is encoded by the yhaM gene . YhaM was active in the presence of Mn2+ (or Co2+), was inactive in the presence of Mg2+, and could also degrade single-stranded DNA . The half-life of bulk mRNA in a mutant lacking PNPase, RNase R, and YhaM was not significantly different from that of the wild type, suggesting the existence of additional activities that can participate in mRNA turnover . Sequence homologues of YhaM were found only in gram-positive organisms . The Staphylococcus aureus homologue, CBF1, which had been characterized as a double-stranded DNA binding protein involved in plasmid replication, was also shown to be an Mn2+-dependent exoribonuclease . YhaM protein has a C-terminal "HD domain," found in metal-dependent phosphohydrolases . By structure modeling, it was shown that YhaM also contains an N-terminal "OB-fold," present in many oligosaccharide- and oligonucleotide-binding proteins . The combination of these two domains is unique . Thus, YhaM and 10 related proteins from gram-positive organisms constitute a new exonuclease family . Characterization of Fe(III) Reduction by Chlororespiring Anaeromxyobacter dehalogenans. Qiang He, 2003.Anaeromyxobacter dehalogenans strain 2CP-C has been shown to grow by coupling the oxidation of acetate to the reduction of ortho-substituted halophenols, oxygen, nitrate, nitrite, or fumarate . In this study, strain 2CP-C was also found to grow by coupling Fe(III) reduction to the oxidation of acetate, making it one of the few isolates capable of growth by both metal reduction and chlororespiration . Doubling times for growth of 9.2 and 10.2 h were determined for Fe(III) and 2-chlorophenol reduction, respectively . These were determined by using the rate of [14C]acetate uptake into biomass . Fe(III) compounds used by strain 2CP-C include ferric citrate, ferric pyrophosphate, and amorphous ferric oxyhydroxide . The addition of the humic acid analog anthraquinone 2,6-disulfonate (AQDS) increased the reduction rate of amorphous ferric iron oxide, suggesting AQDS was used as an electron shuttle by strain 2CP-C . The addition of chloramphenicol to fumarate-grown cells did not inhibit Fe(III) reduction, indicating that the latter activity is constitutive . In contrast, the addition of chloramphenicol inhibited dechlorination activity, indicating that chlororespiration is inducible . The presence of insoluble Fe(III) oxyhydroxide did not significantly affect dechlorination, whereas the presence of soluble ferric pyrophosphate inhibited dechlorination . With its ability to respire chlorinated organic compounds and metals such as Fe(III), strain 2CP-C is a promising model organism for the study of the interaction of these potentially competing processes in contaminated environments .
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