Human colonic Bacteroides species harbor a family of large conjugative transposons, called tetracycline resistance (Tcr) elements. Activities of these elements are enhanced by pregrowth of bacteria in medium containing tetracycline, indicating that at least some Tcr element genes are regulated by tetracycline. An insertional disruption in the rteC gene abolished self-transfer of the Tcr element to Bacteroides recipients, indicating that the gene was essential for self-transfer [1].

1: Tetracycline regulation of genes on Bacteroides conjugative transposons. Stevens AM, Shoemaker NB, Li LY, Salyers AA; J Bacteriol. 1993;175:6134-6141. PMID:8407786