A TN7-LIKE TRANSPOSON IS PRESENT IN THE GLMUS REGION OF THE OBLIGATELY CHEMOAUTOLITHOTROPHIC BACTERIUM THIOBACILLUS-FERROOXIDANS

The region downstream of the Thiobacillus ferrooxidans ATCC 33020 atp operon was examined, and the genes encoding N-acetylglucosamine-1-urid yltransferase (glmU) and glucosamine synthetase (glmS) were found. Thi s atpEFHAGDC-glmUS gene order is identical to that of Escherichia coli , The T. ferrooxidans glmS gene was shown to complement E. coli glmS m utants for growth on minimal medium lacking glucosamine, A Tn7-like tr ansposon, Tn5468, was found inserted into the region immediately downs tream of the glmS gene in a manner similar to the site-specific insert ion of transposon Tn7 within the termination region of the E. coli glm S gene. Tn5468 was sequenced, and Tn7-like terminal repeat sequences a s well as several open reading frames which are related to the Tn7 tra nsposition genes tnsA, tnsB, tnsC, and tnsD were found. Tn5468 is the closest relative of Tn7 to have been characterized to date. Southern b lot hybridization indicated that a similar or identical transposon was present in three T. ferrooxidans strains isolated from different part s of the world but not in two Thiobacillus thiooxidans strains or a Le ptospirillum ferrooxidans strain. Since T. ferrooxidans is an obligate ly acidophilic autotroph and E. coli is a heterotroph, ancestors of th e Tn7-like transposons must have been active in a variety of physiolog ically different bacteria so that their descendants are now found in b acteria that occupy very different ecological niches.