A new extant respirometric assay to estimate intrinsic growth parameters applied to study plasmid metabolic burden

Start‐up phenomena in microbial biokinetic assays are not captured by the most commonly used growth‐related equations. In this study we propose a new respirometric experimental design to estimate intrinsic growth parameters that allow us to avoid these limitations without data omission, separate mathematical treatment, or wake‐up pulses prior to the analysis. Identifiability and sensitivity analysis were performed to confirm the robustness of the new approach for obtaining unique and accurate estimates of growth kinetic parameters. The new experimental design was applied to establish the metabolic burden caused by the carriage of a pWW0 TOL plasmid in the model organism Pseudomonas putida KT2440. The metabolic burden associated was manifested as a reduction in the yield and the specific growth rate of the host, with both plasmid maintenance and the over‐expression of recombinant proteins from the plasmid contributing equally to the overall effect. Biotechnol. Bioeng. 2010;105: 141–149. © 2009 Wiley Periodicals, Inc.     

Repair incorporation of pyrimidine deoxynucleosides into DNA of mammalian cells exposed to UV light

Summary Mammalian cells were exposed to ultraviolet light and the incorporation of labelled DNA precursors was studied. Irradiation caused stimulated incorporation of pyrimidine precursors in cells in which normal DNA synthesis was suppressed byhydroxyurea. This occurred also in non S-phase cells and has been ascribed to a repair process of photochemical damage in DNA. Substitution of thymine bases by bromouracil promoted repair incorporation of labelled thymidine as well as deoxycytidine. A modification of current theories on the sensitizing action of bromouracil in UV irradiated cells is discussed.

---

Zusammenfassung SÄugetierzellen in Gewebekultur wurden mit ultraviolettem Licht bestrahlt und der Einbau von markierten DNS-Bausteinen gemessen. Die Bestrahlung verursachte eine Hemmung der DNS-Synthese, dagegen eine Stimulierung des Einbaus von markierten Pyrimidin-Desoxyribonucleosiden in Zellen, die normalerweise keine Synthese von DNS aufweisen. Die teilweise Ersetzung von Thymin durch Bromuracil führte nach Bestrahlung zu einer verstÄrkten Stimulierung des Einbaus von Thymidin als auch von Desoxycytidin. Die Ergebnisse weisen auf eine Reparatur von UV-SchÄden in der DNS hin. Eine Erweiterung bestehender Auffassungen über die Strahlensensibilisierung durch Bromuracil wurde diskutiert.