Activity of Various Catabolic Functions inUV-C-Irradiated Escherichia coli

摘要

It is generally accepted that microorganisms are inactivated by UV light between 240 and 300 nm due to the formation of DNA damages. The accumulation of DNA lesions leads to an inhibition of transcription and replication and thus prevents the cells from multiplying. However, little is known on additional effects of UV-C irradiation on cellular functions. Therefore, we studied the impact of UV-C irradiation on the metabolic activity of E. coli cells that had been grown on a complex medium (LB) either in batch culture into stationary phase or in chemostat culture. Activity of catabolic functions in non-irradiated control cells as well as in UV-C-irradiated bacteria was analysed with a respiration assay based on BIOLOG AN MicroPlates. The BIOLOG AN MicroPlate performs 95 discrete substrate utilisation tests simultaneously. In the test wells, oxidation of an organic substrate results in colour formation due to the reduction of a tetrazolium salt. Monitoring the color formation as a function of time enables quantification of the activity level for individual substrates. In addition, total ATP (being the primary energy source in cellular metabolism) in non-irradiated and irradiated cells were compared directly after irradiation. Moreover, ATP formation upon addition of carbon substrates to UV-C-treated and control cell suspensions was monitored for a time period of 20 min. Eventually, both BIOLOG analysis and ATP measurements were performed in cells that were hold in liquid in the dark for 24 and 48 hours to study metabolic responsiveness after storage.UV-C irradiation reduced activities of catabolic functions in the BIOLOG assay. This reduction was significantly higher in growing than in stationary phase cells The fact, that reduction was observed for all substrates, hints at a general UV-C induced damage at the level the respiratory chain. In contrast, total ATP was not significantly affected by UV-C irradiation up to fluences of 800 J m~(-2). However, after liquid holding, ATP formation upon substrate addition was lowered in cells exposed to low or high fluences when compared to the unirradiated control.