Table 5.

Effect of divalent cations on efficiency of natural transformation of SW810 (ΔepsA) by plasmid pZJY41^a

Transformation medium and bufferb		Mean transformation frequencyc	Range
MgSO4 (mM)	CaCl2 (mM)
0	0	—d	—
2	0	5,900	1,700–9,300
4	0	7,300	2,700–11,000
6	0	7,100	3,600–9,900
0	2	36	25–53
0	4	31	16–46
0	6	39	24–56
4	2	7,600	3,300–12,000

^aPlasmid was isolated from SW810-41 and used at 10 ng/μl in the transformation assay.

^bThe buffer was used to suspend cells, and the solid medium was used to incubate cells with DNA in the transformation assay (see Materials and Methods). Both contained 10 mM MOPS at pH 7.6.

^cAverage of three experiments (×10⁷).

^d—, not detected.