Experimental design and DNA damage. (a) Illustration of the experiment design. After growth to early log phase, cells were placed in Petri dishes and exposed to 200 J/m2 UV irradiation, then allowed to recover in the dark at 80°C. Arrows indicate sampling time points. (b) Optical density measurement of S. solfataricus UV-treated (red) and control (blue) cultures. Cells were exposed to UV at time zero. (c) Generation and removal of CPDs in chromosomal DNA. DNA damage was measured by ELISA using a primary antibody specific for CPDs. Data were normalized so that the signal at time zero (immediately after UV irradiation) represented 100% unrepaired CPDs. Each data point represents the mean from six experimental replicates and error bars show the standard deviation of each data set.