Figure 2. The HK022 prophage increases torS transcription and has no effect on torT transcription.

Aerobic and anaerobic transcription of torS (A) and torT (B) was measured by β-galactosidase assays in strains carrying torS-lacZ or torT-lacZ operon fusions, with or without the HK022 prophage (strains JNC166, JNC169, JNC163, and JNC168). Each circle represents a measurement obtained from an independent experiment, and the horizontal lines indicate average values. (C) Overexpression of torT restores aerobic torCAD expression in an HK022 lysogen. The distributions of single-cell fluorescence are shown for strains carrying a fluorescent reporter of torCAD transcription. The strains are an HK022 lysogen (DFE12) and a non-lysogen (MMR8) containing a plasmid for torT overexpression (pMR26) or an empty vector control (pDSW206), grown in the presence or absence of oxygen. Expression of torT from the plasmid is driven by a weakened trc promoter without added inducer. Each circle represents a fluorescence measurement made in an individual cell. To facilitate qualitative comparisons between distributions, density curves (shown in gray) were generated from single-cell measurements (see Materials and methods). Data are pooled from three independent experiments, with the vertical red lines indicating the population mean fluorescence for each experiment. a.u., arbitrary units.