DNA Inversion Regulates Outer Membrane Vesicle Production in Bacteroides fragilis
A 4.2-kilobase cryptic Bacteroides plasmid, pB8-51, is found in several colonic Bacteroides species. To determine whether pB8-51 is mobilized by any of the known Bacteroides conjugal elements, we constructed an Escherichia coli-Bacteroides shuttle vector, pVAL-1, which contains pB8-51. We constructed Bacteroides uniformis 0061 derivatives which carry pVAL-1 and various Bacteroides conjugal elements. The Bacteroides conjugal elements tested were six conjugal tetracycline resistance (Tcr) elements (which appear to be chromosomal), i.e., Tcr ERL, Tcr V479, Tcr Emr ERL, Tcr Emr 12256, Tcr Emr DOT, and Tcr Emr CEST, and the conjugal erythromycin resistance (Emr) plasmid pBF4. These Tcr conjugal elements have not been extensively characterized, except for Tcr ERL. All six Tcr elements tested mobilized pVAL-1 at high frequency (10(-3) to 10(-5)) from one Bacteroides strain to another or from a Bacteroides strain to E. coli. Pregrowth of the donors (containing one of the Tcr elements and pVAL-1) in 1 microgram of tetracycline per ml enhanced the transfer of pVAL-1 by 20- to 10,000-fold, depending on which Tcr element was present in the donor. An Ems derivative of pBF4 (pBF4 delta E2) mobilized pVAL-1 from one Bacteroides strain to another at a frequency of 10(-4) but did not mobilize pVAL-1 from a Bacteroides strain to E. coli as efficiently. Thus the Tcr conjugal elements and pBF4 recognize a mobilization region on pB8-51.