Heterospecific transcription of theEscherichia coli rpoB-3 allele in Gram-negative bacteria

Abstract

SummaryrpoB is the structural gene for the β-subunit ofE. coliRNA polymerase. TherpoB-3 allele confers resistance to the antibiotic rifampicin and is unusual in being dominant to the wild-type allele. We used the plasmid pZD23, a derivative of the broad host range conjugative plasmid RP4, to introduce therpoB-3 allele into a range of bacterial species. Species belonging to the same family asE. coli(Enterobacter aerogenes, Citrobacter freundii, Hafnia alvei møller, Klebsiella pneumoniae, Salmonella typhimurium) expressedrpoB-3 to give a rifampicin resistant phenotype; this demonstrated heterospecific transcription. The transfer of pZD23 to the non-Enterobacteriaceae speciesAzotobacter vinelandiiandRhizobium leguminosarumdid not result in rifampicin resistance. In the former case this was due to non-expression of therpoB-3 resistance phenotype, in the latter case the dominant resistance phenotype had been lost from pZD23. Heterospecific transcription can be used as a criterion for the investigation of genetic relatedness between bacterial species.