Tn 5 to assess soil fate of genetically marked bacteria: screening for aminoglycoside-resistance advantage and labelling specificity

Abstract The reliability of Tn 5 as labelling tool was investigated in soil microcosm. The occurence of a selective in soil microcosm. The occurence of resistances encoded by Tn 5 nptII gene was assesed by kanamycin and neomycin amendment. The bioassay developed to monitor the persistence of the soil-added kanamycin did not detect the antibiotic activity in soil extract. A nptII -engineered Escherichia coli strain showed no enhanced survival in aminoglycoside amended soil. Tn 5-marker properties were investigated within indigenous bacteria to determine the specificity of labelling to follow the fate of recombinant DNA. Kanamycin and neomycin resistant population levels made Tn 5 aminoglycoside-resistance phenotype non-sensitive enough to select a soil dissemination of the labelled DNA. The unexpected occurrence of homologous sequences among soil organisms also prevented Tn 5 from being a specific DNA marker. By contrast, colony hybridization did not reveal homology to nptII suggesting its use as a reliable gene transfer indicator.