HIGH-FREQUENCY TRANSFER OF A NATURALLY-OCCURRING CHROMOSOMAL TETRACYCLINE RESISTANCE ELEMENT IN THE RUMINAL ANAEROBE BUTYRIVIBRIO-FIBRISOLVENS

Butyrivibrio fibrisolvens strains resistant to tetracycline were isola ted from the bovine rumen. Two of three Tc-r B. fibrisolvens tested we re able to donate tetracycline resistance at frequencies ranging from 10(-7) to 10(-1) per donor cell in anaerobic filter matings to a rifam pin-resistant mutant of the type strain of B. fibrisolvens, 2221(R). T he recipient strain 2221(R) exhibited rapid autoaggregation, which mig ht be a factor in the high transfer rates observed. Tc-r transconjugan ts of B. fibrisolvens 2221(R) were also capable of further transferrin g tetracycline resistance to a fusidic acid-resistant mutant, 2221(F). Comparison of genomic DNAs by pulsed-field gel electrophoresis demons trated altered band profiles in transconjugants, consistent with the a cquisition of a large mobile chromosomal element. The transferable ele ments from the two B. fibrisolvens donors 1.23 and 1.230 (TnB123 and T nB1230, respectively) showed the same preferred insertion site in the B. fibrisolvens 2221(R) chromosome and are likely to be similar, or id entical, elements. Hybridization experiments showed no close relations hip between TnB1230 and int-xis regions from Tn916 of Tn5253. Although DNA from the B. fibrisolvens donor stains hybridized with probes carr ying tet(M) of tet(O) sequences, transconjugants were found to have ac quired a distinct band that hybridized only weakly with these probes, suggesting that a second, distantly related Tc-r determinant had been transferred.