TABLE 5.

Effect of DNase I treatment on the frequency of recombinants in which either H. pylori cells or culture supernatants were used as exogenous DNA source

HPK1 (Specr Rifr)	HPK5 (Strepr pHP1 Kanr)	Treatment with DNase I (285 μg/ml)	Specr/Strepr CFU/107 bacterial pairsa	Relative %b
Cellsc	—e	−	0	0
Supernatantd	—	−	0	0
—	Cells	−	0	0
—	Supernatant	−	0	0
Cells	Cells	−	112 ± 22	100
Cells	Cells	+	12 ± 5	11f
Supernatant	Cells	−	67 ± 24	60g
Supernatant	Cells	+	0	0
Cells	Supernatant	−	10 ± 2	9f
Cells	Supernatant	+	0	0

^aMean ± SEM of three replicate experiments. 

^bIn comparison to cell-cell mating in the absence of DNase I. 

^cH. pylori cells from 48-h cultures on two TSA plates were resuspended in 250 μl of 0.9% saline, and 25 μl of the suspension was used as the source of cells. 

^dH. pylori cells from 48-h cultures on two TSA plates were suspended in 1 ml of 0.9% saline. The suspension was centrifuged at 8,500 × g for 5 min. The supernatant was saved and either passed through a 0.2-μm-pore-size filter or treated with 5% CHCl₃. 

^e—, no exogenous DNA source. 

^fP < 0.01 compared to cell-cell mating in the absence of DNase (Mann-Whitney test). 

^gP > 0.05 compared to cell-cell mating in the absence of DNase (Mann-Whitney test).