TABLE 1.

Effects of pH and salt on fimB-lacZ and fimE-lacZ fusions in WT E. coli compared to effects on isogenic rcsB and rcsC mutants

Fusion and strain	Expression level (Miller units) under indicated growth conditiona
	pH 7.0	pH 7.0 (+)	pH 5.5	pH 5.5 (+)
fimB-lacZ fusion
WT	345 ± 30	259 ± 36	271 ± 20	219 ± 23
rcsB	201 ± 19b	229 ± 27	274 ± 62	182 ± 48
rcsB/pRcsBc	329 ± 21	315 ± 13	297 ± 11	231 ± 11
rcsC	305 ± 34	235 ± 36	284 ± 51	238 ± 57
fimE-lacZ fusion
WT	335 ± 26	318 ± 54	252 ± 35	237 ± 26
rcsB	332 ± 34	463 ± 68	260 ± 54	221 ± 60
rcsB/pRcsB	339 ± 32	377 ± 70	231 ± 55	245 ± 13
rcsC	365 ± 21	437 ± 53	260 ± 32	253 ± 48

^aValues indicate fimB and fimE promoter expression in terms of β-galactosidase activity and are means ± standard deviations from at least three independent experiments. Cells were grown in LB at pH 7.0 or pH 5.5 with the low or high (+) salt and harvested during mid-exponential phase.

^bBold denotes that the differential expression is significant (P < 0.05) as determined by Student's t test.

^crcsB/pRcsB is the rcsB mutant transformed with pHRcsB, which encodes a His-tagged WT rcsB allele under the control of the lac promoter. Induction, however, was unnecessary.