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. 2018 Oct 3;8:14759. doi: 10.1038/s41598-018-33089-4

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© The Author(s) 2018

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Strong inhibition of the supercoiling-sensitive P_gyrA by TCDS on the chromosome. (A,B) TCDS assays for P_gyrA on the chromosome. E. coli strains FL1181 (MG1655(DE3)ΔlacZ attTn7::P_T7A1/O4lacZ-P_gyrAluc; black squares and lines) and FL1182 (VS111(DE3)ΔlacZ attTn7::P_T7A1/O4lacZ-P_gyrAluc; red circles and lines) were used. The activities of β-galactosidase and firefly luciferase were determined as described under Methods and plotted versus the IPTG concentration. (C,D) Effects of novobiocin (C) and ciprofloxacin (D) on P_gyrA of FL1181 (black squares and lines) and FL1182 (red circles and lines) in the absence of IPTG. (E,F) DNA gyrase inhibitors significantly enhanced the expression of firefly luciferase for FL1181 and FL1182 in the presence of IPTG. Overnight cell cultures were diluted 100-fold and grown until OD600 reached ~0.2. Then 0.5 mM of IPTG and various concentrations of ciprofloxacin or other antibiotics were added to the cell cultures. After 30 min incubation, the activities of β-galactosidase and firefly luciferase were determined described under Methods. (C) Ciprofloxacin (CIXP) inhibited the expression of β-galactosidase. (D) CIXP greatly enhanced the expression of firefly luciferase. The standard deviation (SD) was determined according to results from three independent experiments.