The 640-bp minimal replication region derived from a plasmid DNA preparation from an Acidothiobacillus ferrooxidans strain capable of autonomous replication in a range of Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Acinetobacter calcoaceticus and Alcaligenes faecalis) was identified. This DNA fragment (named TFK replicon) does not encode Rep proteins and appears to be unrelated to other known replicons. ß 2002 Published by Elsevier Science B.V. on behalf of the Federation of European Microbiological Societies.