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Independent Regulation of Two Genes in Escherichia coli by Tetracyclines and Tet Repressor Variants. Annette Kamionka, 2004.We report a regulation system in Escherichia coli for independent regulation of two distinct reporter genes by application of Tet repressors with different specificities . One Tet repressor variant comprises wild-type tet operator (tetO) recognition and exclusive induction with the novel inducer 4-dedimethylamino-anhydrotetracycline . The other Tet repressor variant shows tetO-4C recognition and induction with tetracycline . We demonstrate that both variants are independently active in vivo and allow selective regulation of two genes in the same cell without any cross talk . Effects of Tylosin Use on Erythromycin Resistance in Enterococci Isolated from Swine. Charlene R. Jackson, 2004.The effect of tylosin on erythromycin-resistant enterococci was examined on three farms; farm A used tylosin for growth promotion, farm B used tylosin for treatment of disease, and farm C did not use tylosin for either growth promotion or disease treatment . A total of 1,187 enterococci were isolated from gestation, farrowing, suckling, nursery, and finishing swine from the farms . From a subset of those isolates (n = 662), 59% (124 out of 208), 28% (80 out of 281), and 2% (4 out of 170) were resistant to erythromycin (MIC  8 µg/ml) from farms A, B, and C, respectively . PCR analysis and Southern blotting revealed that 95% (65 out of 68) of isolates chosen from all three farms for further study were positive for ermB, but all were negative for ermA and ermC . By using Southern blotting, ermB was localized to the chromosome in 56 of the isolates while 9 isolates from farms A and B contained ermB on two similar-sized plasmid bands (12 to 16 kb) . Pulsed-field gel electrophoresis revealed that the isolates were genetically diverse and represented a heterogeneous population of enterococci . This study suggests that although there was resistance to a greater number of enterococcal isolates on a farm where tylosin was used as a growth promotant, resistant enterococci also existed on a farm where no antimicrobial agents were used .
HPr Kinase/Phosphorylase, the Sensor Enzyme of Catabolite Repression in Gram-Positive Bacteria: Structural Aspects of the Enzyme and the Complex with Its Protein Substrate. Sylvie Nessler, 2003. Slipped-Strand Mispairing Can Function as a Phase Variation Mechanism in Escherichia coli. Joshua Torres-Cruz, 2003.Slipped-strand mispairing (SSM) has not been identified as a mechanism of phase variation in Escherichia coli . Using a reporter gene, we show that sequences that cause phase variation by SSM in Haemophilus influenzae also lead to phase variation when introduced onto the chromosome of E . coli, and the frequencies of switching are in the biologically relevant range . Thus, the absence of SSM-mediated phase variation in E . coli does not appear to be due to a mechanistic constraint . Degradation of Anthracene by Mycobacterium sp . Strain LB501T Proceeds via a Novel Pathway, through o-Phthalic Acid. René van Herwijnen, 2003.Mycobacterium sp . strain LB501T utilizes anthracene as a sole carbon and energy source . We analyzed cultures of the wild-type strain and of UV-generated mutants impaired in anthracene utilization for metabolites to determine the anthracene degradation pathway . Identification of metabolites by comparison with authentic standards and transient accumulation of o-phthalic acid by the wild-type strain during growth on anthracene suggest a pathway through o-phthalic acid and protocatechuic acid . As the only productive degradation pathway known so far for anthracene proceeds through 2,3-dihydroxynaphthalene and the naphthalene degradation pathway to form salicylate, this indicates the existence of a novel anthracene catabolic pathway in Mycobacterium sp . LB501T . Establishment of an Arbitrary PCR for Rapid Identification of Tn917 Insertion Sites in Staphylococcus epidermidis: Characterization of Biofilm-Negative and Nonmucoid Mutants. Johannes K.-M. Knobloch, 2003.Transposon mutagenesis with the Enterococcus faecalis transposon Tn917 is a genetic approach frequently used to identify genes related with specific phenotypes in gram-positive bacteria . We established an arbitrary PCR for the rapid and easy identification of Tn917 insertion sites in Staphylococcus epidermidis with six independent, well-characterized biofilm-negative Tn917 transposon mutants, which were clustered in the icaADBC gene locus or harbor Tn917 in the regulatory gene rsbU . For all six of these mutants, short chromosomal DNA fragments flanking both transposon ends could be amplified . All fragments were sufficient to correctly identify the Tn917 insertion sites in the published S . epidermidis genomes . By using this technique, the Tn917 insertion sites of three not-yet-characterized biofilm-negative or nonmucoid mutants were identified . In the biofilm-negative and nonmucoid mutant M12, Tn917 is inserted into a gene homologous to the regulatory gene purR of Bacillus subtilis and Staphylococcus aureus . The Tn917 insertions of the nonmucoid but biofilm-positive mutants M16 and M20 are located in genes homologous to components of the phosphoenolpyruvate-sugar phosphotransferase system (PTS) of B . subtilis, S . aureus, and Staphylococcus carnosus, indicating an influence of the PTS on the mucoid phenotype in S . epidermidis .
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