The dose-dependent variation of oxidative cellular damage imposed by UVB exposure in a representative estuarine bacterial strain, Pseudomonas sp. NT5I1.2B, was studied at different growth phases (mid-exponential, late-exponential, and stationary), growth temperatures (15 °C and 25 °C) and growth media (nutrient-rich Tryptic Soy Broth [TSB] and nutrient-poor M9). Survival and markers of oxidative damage (lipid peroxidation, protein carbonylation, DNA strand breakage, and DNA–protein cross-links) were monitored during exposure to increasing UVB doses (0–60 kJ m−2).
Oxidative damage did not follow a clear linear dose-dependent pattern, particularly at high UVB doses (>10 kJ m−2), suggesting a dynamic interaction between damage induction and repair during irradiation and/or saturation of oxidative damage. Survival of stationary phase cells generally exceeded that of exponential phase cells by up to 33.5 times; the latter displayed enhanced levels of DNA–protein cross-links (up to 15.6-fold) and protein carbonylation (up to 6.0-fold). Survival of mid-exponential phase cells was generally higher at 15 °C than at 25 °C (up to 6.6-fold), which was accompanied by lower levels of DNA strand breaks (up to 4000-fold), suggesting a temperature effect on reactive oxygen species (ROS) generation and/or ROS interaction with cellular targets. Survival under medium–high UVB doses (>10 kJ m−2) was generally higher (up to 5.4-fold) in cells grown in TSB than in M9. These results highlight the influence of growth conditions preceding irradiation on the extent of oxidative damage induced by UVB exposure in bacteria.
Santos, A.L., Gomes, N.C., Henriques, I., Almeida, A., Correia, A. and Cunha, Â., 2013. Growth conditions influence UVB sensitivity and oxidative damage in an estuarine bacterial isolate. Photochemical & Photobiological Sciences, 12(6), pp.974-986.
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