Isolation and analysis of a circular form of the IncJ conjugative transposon-like elements, R391 and R997: implications for IncJ incompatibility

The incompatibility between the chromosomally integrating, conjugative tran sposon-like, IncJ elements R997 (ampicillin resistant) and R391 (kanamycin resistant) was examined by constructing strains harbouring both elements. U nusually, recA(+) strains harbouring the resistance determinants of both el ements could be isolated but all strains lacked detectable extrachromosomal DNA. The phenotypic characteristics and transfer patterns observed suggest ed the formation;of recombinant hybrids lather than strains harbouring both elements independently. formation of strains harbouring two IncJ elements in a recA background was thus examined and resulted in the visualisation of extrachromosomal DNA. When R391 was transferred to a recA strain containin g integrated R997, both elements co-existed stably and resulted in the isol ation of a plasmid of 93.9 kb. When R997 was transferred to a recA strain h arbouring an integrated R391, a plasmid of 85 kb was isolated. Comparison o f restriction patterns For both elements revealed many common and several d istinct fragments indicating a close physical relationship. These data sugg est that although IncJ elements normally integrate at a unique site in the Escherichia coil chromosome, they possess the ability for autonomous replic ation which becomes manifest in a recA background when this site is occupie d. This observation has implications For the nature of the incompatibility associated with IncJ elements and also provides a reliable method for isola ting IncJ elements for molecular characterisation. (C) 2000 Federation of E uropean Microbiological Societies. Published by Elsevier Science B.V, All r ights reserved.