Isolation and Characterization of BTF-37: Chromosomal DNA Captured from Bacteroides fragilis That Confers Self-Transferability and Expresses a Pilus-Like Structure in Bacteroides spp. and Escherichia coli

Abstract

ABSTRACT We report the isolation and preliminary characterization of BTF-37, a new 52-kb transfer factor isolated from Bacteroides fragilis clinical isolate LV23. BTF-37 was obtained by the capture of new DNA in the nonmobilizable Bacteroides-Escherichia coli shuttle vector pGAT400ΔBglII using a functional assay. BTF-37 is self-transferable within and from Bacteroides and also self-transfers in E. coli . Partial DNA sequencing, colony hybridization, and PCR revealed the presence of Tet element-specific sequences in BTF-37. In addition, Tn 5520 , a small mobilizable transposon that we described previously (G. Vedantam, T. J. Novicki, and D. W. Hecht, J. Bacteriol. 181:2564–2571, 1999), was also coisolated within BTF-37. Scanning and transmission electron microscopy of Tet element-containing Bacteroides spp. and BTF-37-harboring Bacteroides and E. coli strains revealed the presence of pilus-like cell surface structures. These structures were visualized in Bacteroides spp. only when BTF-37 and Tet element strains were induced with subinhibitory concentrations of tetracycline and resembled those encoded by E. coli broad-host-range plasmids. We conclude that we have captured a new, self-transferable transfer factor from B. fragilis LV23 and that this new factor encodes a tetracycline-inducible Bacteroides sp. conjugation apparatus.