TABLE 3.

Comparison of β-galactosidase activities and stabilities of the heterologous genes from the cascade and single expression systems in different configurations

Strain	Plasmid	β-Galactosidase activity (Miller units)a		β-Galactosidase/total proteins (%)b		% of Lac+ coloniesc
		−2OHB	+2OHB	−2OHB	+2OHB	−2OHB	+2OHB
CC118λpir	pTPm-lacZ	1,211	1,358	NDd	ND	100	100
CC118λpir	pCNB2-lacZ	10,917	67,002	3.6	13	98, 81	20, 1.5
CC118λpir	pCNB4-lacZ	510	17,952	ND	3.9	100, 97	96, 85
CC4S2PT32		171	30,383	ND	8.8	100	100
CC4S2PT97		408	39,143	ND	11	100	100
CC1184S2λpir	pTPm-lacZ	1,487	78,257	ND	20	100, 99	5, 0

^aβ-Galactosidase activity was assayed after 5 h of incubation without salicylate (−2OHB) or with 2 mM salicylate (+2OHB). The data are means from three independent experiments.

^bThe relative amounts of β-galactosidase in cells were measured by densitometry of Coomassie blue-stained SDS-8% PAGE gels.

^cThe stability assay was performed as described in Materials and Methods. Three independent experiments were performed for each strain and type of conditions. As expected, the values varied considerably for the experiments with the plasmid-containing strains, probably due to the stochastic appearance of the cured strains during culture. The maximum and minimum values are shown except for cases when identical results were obtained.

^dND, not determined (0.5%).