FIG. 1.

A shift to nonstimulating conditions leads to immediate release of the Arc-dependent transcriptional control. The ArcA/B two-component system responds very rapidly to changes in redox conditions of growth. Strain ECL5002 carrying the λΦ(lldP′-lacZ) reporter was grown anaerobically in LB containing 0.1 M MOPS (morpholinepropanesulfonic acid) (pH 7.4), 20 mM d-xylose, and 20 mM l-lactate as inducer. At an OD₆₀₀ of 0.2, one aliquot was withdrawn for measuring the β-galactosidase activity (depicted as −10 min). At time 0 min, the cultures were divided in two: one of the subcultures continued growth under anaerobiosis, serving as control, while the other was shifted to aerobiosis. The β-galactosidase activity was monitored for 1 h with 10-min intervals. Open squares, anaerobic growth; closed circles, shift to aerobiosis.