DISTRIBUTION OF CLASS-II TRANSPOSASE AND RESOLVASE GENES IN SOIL BACTERIA AND THEIR ASSOCIATION WITH MER GENES

Southern hybridization was performed on 30 gram-negative, mercury-resi stant soil bacteria isolated from three terrestrial sites in Great Bri tain; two of these sites were mercury polluted (SO and SE), and one wa s pristine (SE), Most of the isolates (20 of 30) hybridized to probes encoding regions of the transposase (tnpA) and resolvase (tnpR) genes from Tn501 and Tn21, Isolates SE9 and SB3 hybridized to the Tn21 but n ot the Tn501 tnpA probe; however, they differed in that SB3 hybridized to both Tn501 and Tn21 tnpR probes while SE9 did not hybridize to eit her tnpR probe, The remaining isolates (7 of 30) did not hybridize to any of the transposon gene probes under the conditions used, tnpA and tnpR regions were PCR amplified from most of the hybridizing isolates and from Tn501 and Tn21, and variation was assessed by restriction fra gment length polymorphism analysis, On the basis of these data, tnpA r egions were divided into eight restriction fragment length polymorphis m classes and tnpR regions were divided into five classes. Similarity coefficients were calculated between classes and used to construct den drograms showing percent similarity, A compilation of the data from th is study on tnpA and tnpR regions and a previous study on merRT Delta P regions (A, M. Osborn, K. D. Bruce, P. Strike, and D. A. Ritchie, Ap pl. Environ. Microbiol. 59:4024-4030, 1993) indicates the presence of hybrid transposons and provides evidence for extensive recombination, both between transposon genes and between transposon and mer genes, wi thin these natural populations of bacteria.