Extrachromosomal genetic elements detected in Escherichia coli treated with the antibacterial agents kanamycin and benzenetriol

Abstract

Resistance to kanamycin was induced in Escherichia coli cells subjected to gradually increasing concentrations of the amino glycoside antibiotic kanamycin. The frequency of the appearance of resistance is not in agreement with a spontaneously generated genetic alteration, but rather to an inducible phenomenon. PCR, with forward primer corresponding to the A-box of DNA polymerase III-recognizable promoters, and in conjunction with two types of primers for the end of SI-NE-like retrons was applied to the plasmid extracts, RNA extracts and genomic DNA extracts. Amplification products were obtained with the plasmid extracts and the RNA extracts of the treated cells but not from the untreated controls. PCR using genomic DNA extracts verified the preexistence of the amplified sequences in the bacterial chromosome. PCR amplification products were also obtained from extrachromosomal nucleic acid extracts of cells exposed to the bacteriostatic agent 1,3,5-benzenetriol, but the pattern was different from that obtained with genomic DNA. SINE-like element-related PCR products were also obtained from the extrachromosomal nucleic acids, using a different primer pair. It is concluded that genetic elements possessing retrons with tRNA-like promoters are mobilized during stress conditions imposed by the kanamycin or benzene triol. The excision/mobilization might be associated with the mechanism generating resistance to the chemical agent.