Mutants of Pseudomonas aeruginosa male strains with altered mating properties have been obtained through treatment with nitrogen half mustards. The response varied with the type of male strain. A mutant of the infectious male PTO 13 was obtained which acts as a female strain and has apparently lost the FP sex factor. A mutant of the non-infectious strain 2 male mates not only with strain 1 females, but shows a thousand-fold increase in its ability to mate with strain 2 males, when it can act as either donor or recipient in conjugation. Derivatives of strain 1 males were obtained which had reduced recombinant forming ability.
While acriflavine is ineffective in producing such mutants, and has not been shown to cure male strains of their sex factor in P. aeruginosa, it is very effective in inhibiting infectious transfer of FP from FP+ to FP− strains. Furthermore, it markedly inhibits recombinant formation in 1 FP− × 1 FP+ crosses, and this latter effect is thought to be due to the inhibition of chromosome transfer by the male parent. In view of the almost complete lack of effect of AF on the normal growth of P. aeruginosa it is likely that the control of chromosome replication during vegetative cell division is different from the occurring during conjugation and that the FP factor is involved in this control during conjugation.