Identification of the plasmid-mobilization potential of the strain Klebsiella pneumoniae ozenae KIIIA isolated from a polluted aquatic environment

The Klebsiella pneumoniae ozenae KIIIA strain was isolated from the River R hine soon after a serious mercury pollution episode and was selected for me rcury resistance as well as for intergeneric DNA mobilization helper potent ial. This transfer helper capacity was shown to be related to the presence of a Tn3-like transposable element. Tn5403. Because transposon-mediated fus ion was found to be involved in the mobilization potential of KIIIA, the vi sualization and the identification of the conjugative element, responsible for the transfer, were necessary. Our results show that, in addition to the four nonconjugative plasmids visualized in a previous study, K. pneumoniae ozenae KIIIA harbors two other plasmids, pK130 and pK45, of respective siz es of 130 and 45 kb, but none of these plasmids is involved in the mobiliza tion mechanism. The presence of yet another extrachromosomal element pK225, with a size of 225 kb, was established by indirect methods, since yields o f pK225 isolated from KIIIA were low and the plasmid was difficult to visua lize directly. However, the integration of this plasmid into the chromosome was not detected. The present paper highlights the problem of detecting so me plasmids in bacteria which have been isolated from the environment. For these plasmids, indirect approaches, that detect conjugative functions, con stitute a feasible alternative for the investigation of the plasmid content of bacteria, if the direct approach fails. An analysis of the different ty pes of transconjugants indicated that the mercury-resistance marker as well as the mobilization potentials, expressed by KIIIA, are linked to pK225. T his plasmid could not be assigned to a described Inc group either by DNA hy bridization or by PCR amplification. (C) 1999 Academic Press.