Potential sources, intermediate steps of formation, genetic structure, and site of acquisition of the Ab-ST3-aadB element. (A) Partial diagrams of plasmids pTB11 (GB accession number AJ744860) and pSN254b (GB accession number KJ909290), representing potential sources for the two segments of a prospective Ab-ST3-aadB element. Black lines, the segments involved in the construction of Ab-ST3-aadB. The coding regions of these segments were labeled according to GenBank records. (B) Circular intermediate forms of Ab-ST3-aadB. The acquisition of IS26 was associated with a target site duplication, indicated by vertical lines. (C) Comparative analysis between Ab-ST3-aadB-negative Acinetobacter baumannii strain TCDC-AB0715 (GB accession number CP002522) and Ab-ST3-aadB-positive A. baumannii strains A085 (this study) and AB4857 (GB accession number AHAG01000030). The acquisition of Ab-ST3-aadB in A085 and AB4857 was not associated with a target site duplication. (D) Comparative sequence analysis between Ab-ST3-aadB-negative Acinetobacter baylyi strain ADP1 (GB accession number CR543861) and Ab-ST3-aadB-positive A. baylyi transformant Ab(II)3 (GB accession number JX041889). A. baylyi ADP1 was used as a recipient to detect the natural transformation of Ab-ST3-aadB from A. baumannii A064. The acquisition of Ab-ST3-aadB in A. baylyi Ab(II)3 was associated with a target site duplication, indicated by vertical lines. Arrows, coding regions oriented according to the direction of transcription.