FIG. 1.

Induction kinetics of bchE expression from the bchE::lacZ transcriptional fusion plasmid pBCHE in the wild-type strain (●) and FNRL mutant strain (○) following a shift from 30 to 2% oxygen (indicated by the vertical arrow). Strains were grown under 30% O₂ to an optical density at 600 nm (OD₆₀₀) of 0.15 to 0.2, and the partial pressure of O₂ was reduced to 2%. Cultures were sampled at the times indicated, and crude extracts were assayed for β-galactosidase activity.