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Worldwide Genetic Relationships among Francisella tularensis Isolates Determined by Multiple-Locus Variable-Number Tandem Repeat Analysis. Anders Johansson, 2004.The intracellular bacterium Francisella tularensis is the causative agent of tularemia and poses a serious threat as an agent of bioterrorism . We have developed a highly effective molecular subtyping system from 25 variable-number tandem repeat (VNTR) loci . In our study, multiple-locus VNTR analysis (MLVA) was used to analyze genetic relationships and potential population structure within a global collection of 192 F . tularensis isolates, including representatives from each of the four subspecies . The VNTR loci displayed between 2 and 31 alleles with Nei's diversity values between 0.05 and 0.95 . Neighbor-joining cluster analysis of VNTR data revealed 120 genotypes among the 192 F . tularensis isolates, including accurate subspecies identification . F . tularensis subsp . tularensis (type A) isolates showed great diversity at VNTR loci, while F . tularensis subsp . holarctica (type B) isolates showed much lower levels despite a much broader geographical prevalence . The resolution of two distinct clades within F . tularensis subsp . tularensis (designated A.I and A.II) revealed a previously unrecognized genetic division within this highly virulent subspecies . F . tularensis subsp . holarctica appears to have recently spread globally across continents from a single origin, while F . tularensis subsp . tularensis has a long and complex evolutionary history almost exclusively in North America . The sole non-North American type A isolates (Slovakian) were closely related to the SCHU S4 strain . Significant linkage disequilibrium was detected among VNTR loci of F . tularensis consistent with a clonal population structure . Overall, this work greatly augments the study of tularemia ecology and epidemiology, while providing a framework for future forensic analysis of F . tularensis isolates . Genome-Wide Transposon Mutagenesis of Borrelia burgdorferi for Identification of Phenotypic Mutants. Philip E. Stewart, 2004.The spirochete Borrelia burgdorferi is the causative agent of Lyme disease, the leading vector-borne illness in the United States . Many of the genetic factors affecting spirochete morphology and physiology are unknown due to the limited genetic tools available and the large number of open reading frames with unknown functions . By adapting a mariner transposon to function in B . burgdorferi, we have developed a random mutagenesis system that tags the mutated locus for rapid identification . Transposition occurs at saturating levels in B . burgdorferi and appears to be random, targeting both linear and circular replicons . By combining the transposon system with a screen for factors affecting growth rate, mutations were readily identified in genes putatively involved in cell division and chemotaxis and a hypothetical open reading frame involved in outer membrane integrity . The successful adaptation of a mariner transposon to function in B . burgdorferi should aid in identifying virulence factors and novel gene products related to spirochete physiology . Microorganisms Associated with Uranium Bioremediation in a High-Salinity Subsurface Sediment. Kelly P. Nevin, 2003.Although stimulation of dissimilatory metal reduction to promote the reductive precipitation of uranium has been shown to successfully remove uranium from some aquifer sediments, the organisms in the family Geobacteraceae that have been found to be associated with metal reduction in previous studies are not known to grow at the high salinities found in some uranium-contaminated groundwaters . Studies with a highly saline uranium-contaminated aquifer sediment demonstrated that the addition of acetate could stimulate the removal of U(VI) from the groundwater . This removal was associated with an enrichment in microorganisms most closely related to Pseudomonas and Desulfosporosinus species .
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