Azaserine: further evidence for DNA damage in Escherichia coli

Panel of Bacillus subtilis reporter strains indicative of various modes of action

In a recent project, we collected the transcriptional profiles of Bacillus subtilis 168 after treatment with a large set of diverse antibacterial agents. One result of the data analysis was the identification of marker genes that are indicative of certain compounds or compound classes. We cloned these promoter regions in front of a luciferase reporter gene and reintroduced the constructs individually into the B. subtilis chromosome. Strains were analyzed for their responsiveness after treatment with a set of 37 antibacterials. Twelve functional reporter strains were generated that were selectively and significantly upregulated by the compounds. The selectivity of the reporter strains ranged from generic pathways like protein biosynthesis, cell wall biosynthesis, and fatty acid biosynthesis to compound classes (quinolones and glycopeptides) and individual compounds (rifampin, cycloserine, and clindamycin). Five of the strains are amenable for high-throughput applications, e.g., pathway-specific screening. In summary, we successfully generated B. subtilis reporter strains that are indicative of the mechanisms of action of various classes of antibacterials. The set of reporter strains presented herein can be used for mode-of-action analyses and for whole-cell screening of compound libraries in a mode-of-action-specific manner.

Visual quantification of DNA double-strand breaks in bacteria

In this paper, we describe a method for the visualization of double-strand breaks in a single electrostretched Escherichia coli DNA molecule. We also provide evidence that electrostretched or migrated DNA under neutral microgel electrophoresis conditions is made up of individual chromosomes. Using the neutral microgel electrophoresis technique, DNA migration (stretching) was measured and the number of DNA double-strand breaks were counted following exposure of E. coli cells to 0, 12.5, 25, 50, or 100 rad of X-rays. The use of an intense fluorescent dye, YOYO and custom-made slides have helped us in visualizing individual bacterial DNA molecules. Bacterial DNA appears similar in structure compared to electrostretched DNA from human lymphocytes. We were able to detect changes in DNA migration (stretching) induced by an X-ray dose as low as 12.5 rad and an increase in the number of DNA breaks induced by a dose as low as 25 rad. The extent of DNA migration and number of breaks were directly correlated to X-ray dosage.