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Detection and Characterization of Conjugative Degradative Plasmids in Xenobiotic-Degrading Sphingomonas Strains. Tamara Basta, 2004.A systematic survey for the presence of plasmids in 17 different xenobiotic-degrading Sphingomonas strains was performed . In almost all analyzed strains, two to five plasmids with sizes of about 50 to 500 kb were detected by using pulsed-field gel electrophoresis . A comparison of plasmid preparations untreated or treated with S1 nuclease suggested that, in general, Sphingomonas plasmids are circular . Hybridization experiments with labeled gene probes suggested that large plasmids are involved in the degradation of dibenzo-p-dioxin, dibenzofuran, and naphthalenesulfonates in S . wittichii RW1, Sphingomonas sp . HH69, and S . xenophaga BN6, respectively . The plasmids which are responsible for the degradation of naphthalene, biphenyl, and toluene by S . aromaticivorans F199 (pNL1) and of naphthalenesulfonates by S . xenophaga BN6 (pBN6) were site-specifically labeled with a kanamycin resistance cassette . The conjugative transfer of these labeled plasmids was attempted with various bacterial strains as putative recipient strains . Thus, a conjugative transfer of plasmid pBN6 from S . xenophaga BN6 to a cured mutant of strain BN6 and to Sphingomonas sp . SS3 was observed . The conjugation experiments with plasmid pNL1 suggested a broader host range of this plasmid, because it was transferred without any obvious structural changes to S . yanoikuyae B1, Sphingomonas sp . SS3, and S . herbicidovorans . In contrast, major plasmid rearrangements were observed in the transconjugants after the transfer of plasmid pNL1 to Sphingomonas sp . HH69 and of pBN6 to Sphingomonas sp . SS3 . No indications for the transfer of a Sphingomonas plasmid to bacteria outside of the Sphingomonadaceae were obtained . Use of Growth Indices from Radiometric Culture for Quantification of Sheep Strains of Mycobacterium avium subsp . paratuberculosis. Leslie A. Reddacliff, 2003.A simple method for using growth indices from radiometric BACTEC cultures was evaluated for the enumeration of Australian sheep strains of Mycobacterium avium subsp . paratuberculosis . The numbers of viable organisms in inocula were determined by end-point titration in BACTEC cultures . Growth indices were measured by using a BACTEC 460 machine . There was a linear relationship between the number of days taken for the cumulative growth index to reach 1,000 (dCGI1000) and log10 inoculum size . The use of dCGI1000 was shown to be as effective as the use of growth index data from the entire growth cycle for the estimation of inoculum size . For particular isolates characterized by end-point titration, the dCGI1000 of a single BACTEC vial provided estimates of viable numbers within narrow prediction limits . Predictive relationships were also established for the enumeration of M . avium subsp . paratuberculosis from field samples by using the dCGI1000 of a single BACTEC vial, with prediction limits of ±1 to 2 log units . Organisms from feces or contaminated soil grew more slowly than those from cultures or tissues, and separate equations were developed for enumeration from these sources .
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