title: SOS gene induction and possible mutagenic effects of freeze-drying in Escherichia coli and Salmonella typhimurium.
abstract: We report the results of a study of the potential negative effects of the freeze-drying process, normally considered a benign means for long-term conservation of living cells and the golden standard in bacterial preservation. By monitoring gene induction using a whole-cell Escherichia coli bioreporter panel, in which diverse stress-responsive gene promoters are fused to luminescent or fluorescent reporting systems, we have demonstrated that DNA repair genes belonging to the SOS operon (recA, sulA, uvrA, umuD, and lexA) were induced upon resuscitation from the freeze-dried state, whereas other stress-responsive promoters such as grpE, katG, phoA, soxS, and sodA were not affected. This observation was confirmed by the UMU-chromotest (activation of the umuD gene promoter) in Salmonella typhimurium, as well as by real-time PCR analyses of selected E. coli SOS genes. We further show that a functional SOS operon is important in viability maintenance following resuscitation, but that at the same time, this repair system may introduce significantly higher mutation rates, comparable to those induced by high concentrations of a known mutagen. Our results also indicate that the entire freeze-drying process, rather than either freezing or drying separately, is instrumental in the induction of DNA damage.
authors: Department of Plant and Environmental Sciences, The Institute of Life Sciences, The Hebrew University of Jerusalem, 91904, Jerusalem, Israel.
authors: Rachel
authors: R
authors: Rosen
authors: Division of Qualitative Hydrology, German Federal Institute of Hydrology (BfG), Am Mainzer Tor 1, 56068, Koblenz, Germany.
authors: Sebastian
authors: S
authors: Buchinger
authors: Division of Qualitative Hydrology, German Federal Institute of Hydrology (BfG), Am Mainzer Tor 1, 56068, Koblenz, Germany.
authors: Ramona
authors: R
authors: Pfänder
authors: Department of Environmental Health, Hadassah Academic College, Jerusalem, Israel.
authors: Rami
authors: R
authors: Pedhazur
authors: Division of Qualitative Hydrology, German Federal Institute of Hydrology (BfG), Am Mainzer Tor 1, 56068, Koblenz, Germany.
authors: Georg
authors: G
authors: Reifferscheid
authors: Department of Plant and Environmental Sciences, The Institute of Life Sciences, The Hebrew University of Jerusalem, 91904, Jerusalem, Israel. shimshon.belkin@mail.huji.ac.il.
authors: Shimshon
authors: http://orcid.org/0000-0001-8283-1673
authors: S
authors: Belkin
mesh_terms: D004926:Escherichia coli / Q000502:physiology* / Q000528:radiation effects*; D005612:Freeze Drying; D020869:Gene Expression Profiling; D017930:Genes, Reporter; D050296:Microbial Viability; D013014:SOS Response, Genetics; D012486:Salmonella typhimurium / Q000502:physiology* / Q000528:radiation effects*; D013312:Stress, Physiological
keywords: Bioreporters; DNA damage; Freeze-drying; Lyophilization; Mutagenesis; SOS regulon