Nucleotide sequence of a small cryptic plasmid from Acidithiobacillus ferrooxidans strain A-6

A 2.1 kb cryptic plasmid from Acidithiobacillus ferrooxidans strain A-6 was isolated and cloned into the Escherichia coli vector plasmid, pUC128. The cloned plasmid was mapped by restriction enzyme fragment analysis and subsequently sequenced. Much of the plasmid remains cryptic, but substantial nucleotide and protein sequence similarities have been observed to the putative replication protein, RepA, of the small cryptic plasmids pAYS and pAYL found in the ammonia-oxidizing Nitrosomonas sp. strain ENI-11. These results suggest that an entirely new class of plasmid is maintained in at least one strain of A. ferrooxidans and other acidophilic bacteria, and raises interesting questions about the origin of this plasmid in acidic environments.