TABLE 4.

Transfer of plasmid pBF1::gfp from P. putida KT2442 to indigenous marine bacteria detected by GFP fluorescence of transconjugants after 3 days of incubation^a

Expt	Incubationb	No. of transconjugants per recipient cell with addition of HgCl2 (μg/ml)c			No. of replicates	No. of recipientsd	Donor/recipient ratio
		0	0.1	1.0
1	Filter	1.15 × 10−5 (5.12 × 10−6)	5.56 × 10−5 (4.09 × 10−5)	2.56 × 10−5 (1.28 × 10−5)	2	5.8 × 107	8:1
	Bulk	3.95 × 10−6	3.00 × 10−6	4.00 × 10−6	1	2.2 × 106	8:1
2	Filter	3.08 × 10−5 (1.98 × 10−5)	6.27 × 10−5 (2.44 × 10−5)	2.32 × 10−5 (1.44 × 10−5)	3	4.1 × 107	1:1
	Bulk	NDe	8.97 × 10−6	2.30 × 10−6	1	1.6 × 106	1:1
3	Filter	1.42 × 10−4	1.01 × 10−4	2.24 × 10−4	5	5.5 × 107	1:5
	Bulk	5.57 × 10−5	1.16 × 10−5	4.87 × 10−6	3	2.1 × 106	1:5

^aResults of experiments with seawater from three different samplings are shown. 

^bDonor cells were added to seawater samples and incubated on filters floating on sterile seawater (filter) or incubated in flasks (bulk). 

^cIncubations were made in the presence of different additions of HgCl₂ as indicated. Values in parentheses are numbers of aggregates with two or more fluorescent cells on the filters per recipient cell. 

^dNumbers of marine recipients added to the mating mixtures were determined by acridine orange direct counting. Counts are numbers of cells/milliliter (bulk) or numbers of cells/cm² (filter). 

^eND, not determined.