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Molecular Identification of the Catabolic Vinyl Chloride Reductase from Dehalococcoides sp . Strain VS and Its Environmental Distribution. Jochen A. Müller, 2004.Reductive dehalogenation of vinyl chloride (VC) to ethene is the key step in complete anaerobic degradation of chlorinated ethenes . VC-reductive dehalogenase was partially purified from a highly enriched culture of the VC-respiring Dehalococcoides sp . strain VS . The enzyme reduced VC and all dichloroethene (DCE) isomers, but not tetrachloroethene (PCE) or trichloroethene (TCE), at high rates . By using reversed genetics, the corresponding gene (vcrA) was isolated and characterized . Based on the predicted amino acid sequence, VC reductase is a novel member of the family of corrinoid/iron-sulfur cluster containing reductive dehalogenases . The vcrA gene was found to be cotranscribed with vcrB, encoding a small hydrophobic protein presumably acting as membrane anchor for VC reductase, and vcrC, encoding a protein with similarity to transcriptional regulators of the NosR/NirI family . The vcrAB genes were subsequently found to be present and expressed in other cultures containing VC-respiring Dehalococcoides organisms and could be detected in water samples from a field site contaminated with chlorinated ethenes . Therefore, the vcrA gene identified here may be a useful molecular target for evaluating, predicting, and monitoring in situ reductive VC dehalogenation . Short-Sequence Tandem and Nontandem DNA Repeats and Endogenous Hydrogen Peroxide Production Contribute to Genetic Instability of Streptococcus pneumoniae. Christopher D. Pericone, 2002.Loss-of-function mutations in the following seven pneumococcal genes were detected and analyzed: pspA, spxB, xba, licD2, lytA, nanA, and atpC . Factors associated with these mutations included (i) frameshifts caused by reversible gain and loss of single bases within homopolymeric repeats as short as 6 bases, (ii) deletions caused by recombinational events between nontandem direct repeats as short as 8 bases, and (iii) substitutions of guanine residues caused at an increased frequency by the high levels of hydrogen peroxide (>2 mM) typically generated by this species under aerobic growth conditions . The latter accounted for a frequency as high as 2.8 x 10-6 for spontaneous mutation to resistance to optochin and was 10- to 200-fold lower in the absence of detectable levels of H2O2 . Some of these mutations appear to have been selected for in vivo during pneumococcal infection, perhaps as a consequence of immune pressure or oxidative stress . Molecular and Physical Characterization of Burkholderia mallei O Antigens. Mary N. Burtnick, 2002.Burkholderia mallei lipopolysaccharide (LPS) has been previously shown to cross-react with polyclonal antibodies raised against B . pseudomallei LPS; however, we observed that B . mallei LPS does not react with a monoclonal antibody (Pp-PS-W) specific for B . pseudomallei O polysaccharide (O-PS) . In this study, we identified the O-PS biosynthetic gene cluster from B . mallei ATCC 23344 and subsequently characterized the molecular structure of the O-PS produced by this organism . Low-Temperature Isolation of Disease-Suppressive Bacteria and Characterization of a Distinctive Group of Pseudomonads. P. Maria Johansson, 2003.The influence of environmental factors during isolation on the composition of potential biocontrol isolates is largely unknown . Bacterial isolates that efficiently suppressed wheat seedling blight caused by Fusarium culmorum were found by isolating psychrotrophic, root-associated bacteria and by screening them in a bioassay that mimicked field conditions . The impact of individual isolation factors on the disease-suppressive index (DSI) of almost 600 isolates was analyzed . The bacteria originated from 135 samples from 62 sites in Sweden and Switzerland . The isolation factors that increased the probability of finding isolates with high DSIs were sampling from arable land, Swiss origin of samples, and origination of isolates from plants belonging to the family Brassicaceae . The colony morphology of the isolates was characterized and compared to DSIs, which led to identification of a uniform morphological group containing 57 highly disease-suppressive isolates . Isolates in this group were identified as Pseudomonas sp.; they were fluorescent on King's medium B and had characteristic crystalline structures in their colonies . These isolates were morphologically similar to seven strains that had previously been selected for suppression of barley net blotch caused by Drechslera teres . Members of this morphological group grow at 1.5°C and produce an antifungal polyketide (2,3-deepoxy-2,3-didehydrorhizoxin [DDR]) . They have similar two-dimensional polyacrylamide gel electrophoresis protein profiles, phenotypic characteristics, and in vitro inhibition spectra of pathogens . In summary, in this paper we describe some isolation factors that are important for obtaining disease-suppressive bacteria in our system, and we describe a novel group of biocontrol pseudomonads .
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