title: Molecular characterization of Rif(r) mutations in Pseudomonas aeruginosa and Pseudomonas putida.
abstract: The rpoB gene encoding for beta subunit of RNA polymerase is a target of mutations leading to rifampicin resistant (Rif(r)) phenotype of bacteria. Here we have characterized rpoB/Rif(r) system in Pseudomonas aeruginosa and Pseudomonas putida as a test system for studying mutational processes. We found that in addition to the appearance of large colonies which were clearly visible on Rif selective plates already after 24h of plating, small colonies grew up on these plates for 48 h. The time-dependent appearance of the mutant colonies onto selective plates was caused by different levels of Rif resistance of the mutants. The Rif(r) clusters of the rpoB gene were sequenced and analyzed for 360 mutants of P. aeruginosa and for 167 mutants of P. putida. The spectrum of Rif(r) mutations characterized for P. aeruginosa grown at 37 degrees C and that characterized for P. putida grown at 30 degrees C were dissimilar but the differences almost disappeared when the mutants of both strain were isolated at the same temperature, at 30 degrees C. The strong Rif(r) phenotype of P. aeruginosa and P. putida was accompanied only with substitutions of these residues which belong to the putative Rif-binding pocket. Approximately 70% of P. aeruginosa mutants, which were isolated at 37 degrees C and expressed weak Rif(r) phenotype, contained base substitutions in the N-terminal cluster of the rpoB gene. The differences in the spectra of mutations at 30 degrees C and 37 degrees C can be explained by temperature-sensitive growth of several mutants in the presence of rifampicin. Thus, our results imply that both the temperature for the growth of bacteria and the time for isolation of Rif(r) mutants from selective plates are critical when the rpoB/Rif(r) test system is employed for comparative studies of mutagenic processes in Pseudomonas species which are conventionally cultivated at different temperatures.
authors.affiliation: Department of Genetics, Institute of Molecular and Cell Biology, Tartu University, Tartu, Estonia.
authors.forename: Tatjana
authors.initials: T
authors.lastname: Jatsenko
authors.forename: Andres
authors.initials: A
authors.lastname: Tover
authors.forename: Radi
authors.initials: R
authors.lastname: Tegova
authors.forename: Maia
authors.initials: M
authors.lastname: Kivisaar
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D012321:DNA-Directed RNA Polymerases / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology*; D011550:Pseudomonas aeruginosa / Q000235:genetics* / Q000254:growth & development; D016958:Pseudomonas putida / Q000235:genetics* / Q000254:growth & development; D012293:Rifampin / Q000494:pharmacology*; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid
chemical_list: C492263:ARR-2 protein, Pseudomonas aeruginosa; D001426:Bacterial Proteins; D019384:Nucleic Acid Synthesis Inhibitors; D012321:DNA-Directed RNA Polymerases; C105078:RNA polymerase beta subunit; D012293:Rifampin