Interspecific variability in sensitivity to UV radiation and subsequent recovery in selected isolates of marine bacteria

The interspecific variability in the sensitivity of marine bacterial isolat es to UV-B (295- to 320-nm) radiation and their ability to recover from pre vious UV-B stress were examined, Isolates originating from different microe nvironments of the northern Adriatic Sea were transferred to aged seawater and exposed to artificial UV-B radiation for 4 h and subsequently to differ ent radiation regimens excluding UV-B to determine the recovery from UV-B s tress. Bacterial activity was assessed by thymidine and leucine incorporati on measurements prior to and immediately after the exposure to UV-B and aft er the subsequent exposure to the different radiation regimens. Large inter specific differences among the 11 bacterial isolates,were found in the sens itivity to UV-g, ranging from 21 to 92% inhibition of leucine incorporation compared to the bacterial activity measured in dark controls and from 11 t o 84% for thymidine incorporation. Interspecific differences in the recover y from the UV stress were also large.,in inverse relation was detectable be tween the ability to recover under dark conditions and the recovery under p hotosynthetic active radiation (400 to 700 nm). The observed large interspe cific differences in the sensitivity to UV-B radiation and even more so in the subsequent recovery from UV-B stress are not related to the prevailing radiation conditions of the microhabitats from which the bacterial isolates originate. Based on our investigations on the II marine isolates, we concl ude that there are large interspecific differences in the sensitivity to UV -B radiation and even larger differences in the mechanisms of recovery from previous UV stress. This might lead to UV-mediatad shifts in the bacteriop lankton community composition in marine surface waters.