Energy requirements for specific pair formation during conjugation in Escherichia coli K-12.

are pre-endowed with appendages, called donor pili, which are responsible for specific pair formation (C. C. Brinton, Trans. N.Y. Acad. Sci. 27:1003, 1965); this led us to believe that specific pair formation might occur in the absence of energy metabolism. However, K. W. Fisher (J. Gen. Microbiol. 16:136, 1957), in showing that zygote formation was dependent on active energy metabolism, concluded that ". . . energy is utilized by the donor cell in the establishment of effective contacts. . ." , and C. C. Brinton (Trans. N.Y. Acad. Sci. 27:1003, 1965) also concluded that specific pair formation was an endergonic process. We feel that Fisher's conclusion might be in error since he did not experimentally separate specific pair formation from later events during bacterial conjugation. We cannot evaluate Brinton's conclusion, because in stating that ". . . no pairs are formed at 0 C or in the presence of 10-3 M dinitrophenol . . . " he did not provide data or specify whether these treatments, which resulted in no recombinant formation, were for the entire mating period or for just the short period of time needed for specific pair formation at the commencement of mating. Thus, we were prompted to determine experimentally the energy requirements, if any, during specific pair formation. The de Haan and Gross definition (Genet. Res. 3:251, 1962) for specific pair formation was used. Experimentally, pair formation was allowed to occur at high bacterial density for