TABLE 1.

Alkaline phosphatase activities of various E. coli strains^a

Strainb	Relevant characteristics	Plasmidc	PhoA activityd
K10	pitA10 relA1 spoT1		16 ± 3
CE1485	K10 pstS::kan		2,180 ± 45
CE1491	CE1485 pitB::gm		2,070 ± 300
CE1493	CE1491 PitA+		40 ± 4
CE1494	CE1491 PitA+		25 ± 3
CE1495	CE1493 pitB+metC::Tn10		40 ± 3
CE1496	CE1494 pitB+metC::Tn10		23 ± 2
CE1497	CE1495 pitA::gm		1,570 ± 140
CE1498	CE1496 pitA::gm		1,300 ± 125
CE1491	CE1485 pitB::gm	pJF118EH	1,885 ± 280
CE1491	CE1485 pitB::gm	pSL41 (pitB)	42 ± 15
CE1491	CE1485 pitB::gm	pSL42 (pitA)	100 ± 10
CE1487	CE1485 PitB+		80 ± 10
CE1492	CE1487 Δ(pstSCAB-phoU)::cam		2,940 ± 170
MG1655			15 ± 2
CE1500	MG1655 pitA::gm pstS::kan	pJF118EH	1,690 ± 110
CE1501	MG1655 pitA::gm Δ(pstSCAB- phoU)::cam	pJF118EH	2,080 ± 150
CE1500	MG1655 pitA::gm pstS::kan	pSL41 (pitB)	48 ± 5
CE1501	MG1655 pitA::gm Δ(pstSCAB- phoU)::cam	pSL41 (pitB)	1,645 ± 230

^aStrains were grown overnight at 37°C in L broth supplemented with 1 mM glucose-3-phosphate. Addition of glucose-3-phosphate resulted in equal growth of all strains and did not influence alkaline phosphatase activities (data not shown). 

^bStrains K10 and MG1655 were obtained from the E. coli Genetic Stock Center, Department of Biology, Yale University, Conn. Strains CE1485, CE1491, and CE1487 were described previously (9), and all other strains were constructed in the present work. The pstS::kan mutation is an insertion of a kanamycin resistance cassette in the PvuI site approximately in the middle of the pstS gene. Strains carrying this mutation do not produce the P_i-binding protein, as was verified by Western blotting (9). 

^cVector plasmid pJF118EH (7) and plasmids pSL41 and pSL42 (9) have been described previously. 

^dThe alkaline phosphatase activities were determined with para-nitrophenyl phosphate as a substrate (17). Alkaline phosphatase activity is expressed in units, which are defined as nanomoles of para-nitrophenol released per minute per optical density at 660 nm of cell culture. Values represent the averaged results of three or four independent experiments, and standard deviations are given.