FIG. 6.
Growth of M. smegmatis mutants on nitrate. (A) Growth of the ΔsirA mutant on minimal medium containing nitrate as the sole nitrogen source and either cysteine (○) or sulfate (•) as the sole sulfur source. The generation time for growth on cysteine was 7.1 h, as no growth was observed in medium containing sulfate. (B) Growth of the Δche1 mutant on the same nitrogen and sulfur sources as described for panel A. Generation times for growth on cysteine or sulfate were virtually identical, 7.3 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.