TABLE 3.

Effects of phoPQ, medium composition, and iron on expression of a iviXVII::lac (pdu) fusion

iviXVII::lac derivative	β-Galactosidase activity (U)a
	pH 5.5, 0.05 mM Mg2+		pH 7.0, 0.05 mM Mg2+		pH 7.6, 10 mM Mg2+
	−Iron	+Iron	−Iron	+Iron	−Iron	+Iron
phoP+	22	25	27	288	27	322
phoP102::Tn10d-Cm	13	216	15	361	13	344
phoQ24	11	10	12	15	13	247

^aDetermined in cultures grown for 16 h in MOPS minimal medium at the given pH and Mg²⁺ concentration in the presence or absence of 50 μM iron. Medium without iron added also contained the iron-chelating agent 2,2′-dipyridyl (0.03 mM). Data represent averages of three independent cultures with a standard deviation of <10% of the mean.