Figure 2. Effect of mutations in the leucine zipper of ArcB on the expressions of λΦ(cydA’-lacZ) and λΦ(lldP’- lacZ) operon fusions.

A) Strains ECL5012 [λΦ(lldP’- lacZ)] and ECL5004 [λΦ(cydA’-lacZ)] carrying low copy plasmids that harbor the arcB mutant variants were grown aerobically (solid bars) or anaerobically (empty bars) in Luria-Bertani broth containing 0.1 M MOPS (morpholinepropanesulfonic acid; pH 7.4) and 20 mM D-xylose. In the case of the λΦ(lldP’- lacZ)-bearing strains the growth medium was supplemented with 20 mM L-lactate as an inducer. At mid-exponential growth phase (OD₆₀₀ ∼ 0.5) the cells were harvested and the ß-Galactosidase activity was assayed and expressed in Miller units. The data are averages from three independent experiments and the standard deviations are indicated. (B) Equal number of bacteria of the above aerobic cultures were analyzed by Western blot analysis, using ArcB polyclonal antibodies as previously described [34].