TABLE 1.

Transfer of Tn4555 oriT derivatives

Expt	Plasmid(s)a	Selective mediumb	Transfer frequencyc
1	pFD576	Ap + Sm	1.2 × 10−1 ± 1.2
2	pFD601	Cm + Sm	<10−7
3	pFD576 + pFD601	Ap + Sm	2.3 × 10−2 ± 1
4	pFD576 + pFD601	Cm + Sm	3.3 × 10−3 ± 2.4
5	pFD576 + pFD601	Ap + Cm + Sm	2.9 × 10−3 ± 1.7
6	pFD576 + pSG335	Cm + Sm	<10−7 to 4.7 × 10−6d
7	pFD576ΔoriT1	Ap + Sm	5.1 × 10−4 ± 1
8	pFD576ΔoriT2	Ap + Sm	1.9 × 10−4 ± 1.5
9	pFD648	Ap + Sm	<10−7

^aAll matings were triparental matings with a strain containing the plasmids indicated, HB101 (1) as the recipient, and the RK231 conjugation helper strain (5). Matings were performed aerobically as described previously except that incubations were for only 4 h prior to plating on selective medium (28). 

^bSelective medium was L-agar (18) supplemented with the following antibiotics where indicated: streptomycin (Sm), 25 μg/ml; ampicillin (Ap), 50 μg/ml; and chloramphenicol (Cm) 25 μg/ml. 

^cTransfer frequency is the number of transconjugants per input donor cell ± the standard deviation. 

^dResults were variable with this set of plasmids ranging from undetectable to a transfer frequency near the lower end of detectable.