A MOLECULAR ANALYSIS OF A BROAD-HOST-RANGE PLASMID ISOLATED FROM THIOBACILLUS-FERROOXIDANS

A 12.4-kb plasmid, pTF-FC2, that was isolated from Thiobacillus ferrooxidans and which is capable of replication in a wide range of Gram-negative bacteria, has been sequenced. The extent of the regions involved in both replication and mobilization have been delineated. The site of initiation of replication (oriV) has been localized on a 185-bp fragment and the origin of transfer (oriT) on a 138-bp fragment. Three proteins that were essential for replication and four that were essential for mobilization have been identified. The origin of replication was clearly similar to that of the IncQ plasmids although no complementation or incompatibility between pTF-FC2 and the IncQ plasmid, R300B, was detected. There was a clear similarity in the size, location and amino acid sequence of the proteins of the pTF-FC2 mobilization region with those of the Tral region of the IncP plasmids, RP4 and R751. Two inverted repeated sequences which had 37/38-bp and 38/38-bp sequence identity with the Tn21 transposon were identified. The C-terminal part of a transposase and the N-terminal portion of a resolvase were located between the inverted repeats. These open reading frames are most likely the remnants of a defective transposon. A protein with homology to a mercury-resistance regulator was also present within the transposon-like element although no gene encoding for mercury reductase could be indentified.