FIG. 3.

Growth and TDA synthesis are affected by mutations in cysI. TM1040 (inverted triangles) and a cysI mutant (HG1220; circles) were grown in minimal medium lacking sulfate and containing either methionine (closed symbols) or cysteine (open symbols), and growth was measured optically at 600 nm. Unlike the wild-type, the CysI⁻ mutant cannot grow on methionine, but does utilize cysteine. Measurement of antibiotic activity indicates that the cysI defect also affects TDA synthesis, which is corrected by the addition of cysteine to the medium but not by the addition of methionine, DMSP, sulfite, or sulfate.