Effect of 1,10-phenanthroline on bacterial conjugation in Escherichia coli K-12: inhibition of maturation from preliminary mates into effective mates

The addition of 1 mM orthophenanthroline (OP) into a mating mixture drastically reduced the production of recombinants. Examination of the effect of OP on each step of conjugation showed that the effect on the following steps could not account for the up to 500-fold reduction of recombinant formation: (i) preliminary mate formation and (ii) deoxyribonucleic acid transfer and integration. Taking these results and additional experiments together, we conclude that OP inhibits the maturation of preliminary mates into effective mates. Kinetic experiments showed that there were two phases in the maturation of preliminary (OP-sensitive) mates into effective (OP-resistant) mates. The half-time (the time required to reach 50% OP-resistant mates) was 2.5 min for the first phase and 4 min for the second phase, with an overall half-time of 7.5 min. In contrast, only 3 min was required to reach 50% Zn2+-resistant mates. The difference in half-time suggests that there is an intermediate step involved to form an effective mate from a preliminary mate.