Fig. 2

Optimizing the protein content in the S9 Mix. Based on the results of the preliminary investigation, the total protein contents in the S9 Mix were set at 0, 0.3, 0.6, 1.2, or 2.4 mg/plate. The pre-incubation time was set at 1 h. The plots indicate the ratio of the average number of revertant colonies observed (treated: solvent control) in two plates and the number of spontaneous revertants. The number of spontaneous colonies per plate ranged from 108 to 151, varying slightly in response to the different protein levels used