FIG 4.

SatA detoxifies streptothricin over a range of concentrations. Soft agar (0.5%, wt/vol) seeded with a satA⁺ strain was layered on rich medium agar plates. Various concentrations of streptothricin were spotted. In the top row, in each area, 5-μl volumes of streptothricin at (from left to right) 25 μM, 50 μM, 100 μM, 150 μM, and 200 μM were spotted. In the bottom row, the same concentration of streptothricin with 3 μM H₆-BsSatA was spotted. Zones of inhibition were not observed when H₆-BsSatA was added to reaction mixtures containing 25 μM, 50 μM, or 100 μM streptothricin. However, heat-inactivated enzyme (HIE) did not detoxify streptothricin (50 μM, white circle on right). A sample from a reaction mixture containing H₆-BsSatA and AcCoA but devoid of streptothricin was spotted as a negative control and no zone of inhibition was observed (white circle on left).