A wild-type donor strain (JD1545, cnp::mTnCm3 recA6) efficiently donates the chloramphenicol resistance marker to a wild-type recipient strain (MS11 Spc) when the two strains are grown together, yielding over 10,000 transformants per milliliter of log-phase culture (left plate). An atlA mutant (JD1543, cnp::mTnCm3 recA6 atlA::ermC) donates the chloramphenicol resistance marker very poorly in coculture with recipient strain MS11 Spc, yielding sometimes 10 or 100 transformants. No transformants were obtained in this experiment (right plate).