Fig. 1

Analysis of β-galactosidase reporter activity from different expression systems. a–c Schematic representation of expression systems. a The ATNT system, in which expression of the transcriptional regulator terR is controlled by Tet-on. The reverse transactivator is constitutively expressed from the fraA promoter and transcription is terminated by the ergA terminator (T). In the presence of doxycycline the reverse transactivator binds to the tet-on responsive element (1), which leads to transcription of terR from the minimal gpdA promoter (2). TerR specifically recognises its PterA target promoter, which results in transcription of the β-galactosidase gene lacZ. b Direct control of lacZ expression by the Tet-on promoter system. c The P2 expression system. The amyB promoter controls expression of terR and is activated in the presence of sugars. TerR controls expression of lacZ by binding to the PterA promoter. d β-Galactosidase activity from expression systems shown in a–c. ATNT and Tet-on lacZ strains were grown in the presence of different doxycycline concentrations, whereas the P2 lacZ strain was cultivated without doxycycline. The positions of activities derived from parental strains are highlighted by arrows. Three individual transformants from each expression system were measured in biological and technical duplicates. Bars represent mean values of all measurements and standard deviations are indicated by error bars. Multiple t-tests using the Holm-Sidak method were applied, which confirmed significantly different expression levels in all groups in dependence of the doxycycline concentration. (****p < 0.0001; n. d. not determined)