FIG. 4.

Growth of M. smegmatis mutants on various sulfur nutrients. (A) Growth of the ΔsirA mutant on minimal media containing cysteine (□), sulfide (♦), sulfite (○), or sulfate (•) as the sole sulfur source. Generation times for growth on cysteine and sulfide were 7.5 and 6.7 h, respectively; no growth was observed in media containing sulfite or sulfate. (B) Growth of the ΔRv2393 mutant on the same sulfur sources as those mentioned for panel A. The generation time for the mutant was 10 h when the medium contained cysteine or sulfide. Both cells fed sulfate and cells fed sulfite exhibited steady-state growth with a generation time of 19 h. (C) To demonstrate that the growth effects of the deletions were due solely to a lack of expression of the intended coding regions, the growth on sulfate of the deletion strains complemented with plasmids that express the wild-type gene was compared to that of the wild-type strain containing an empty vector. The doubling times of the three strains were extremely similar: for the wild type (○), 8.8 h; for the ΔsirA strain compared with the sirA strain (nirA:comp sirA) (□), 8.6 h; and for the ΔRv2393 strain compared with the Rv2393 strain (Δrv2939:comp rv2393) (♦), 8.5 h. Growth protocols are described in Materials and Methods. Each data point represents the average of results from three experiments; single standard deviation units (not shown) are comparable to the diameters of the symbols representing the averaged values. OD₆₀₀, optical density at 600 nm.