Growth conditions influence UVB sensitivity and oxidative damage in an estuarine bacterial isolate

Abstract

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.