FIG. 5.

Streptonigrin tolerance. The tolerance of S. thermophilus strains to streptonigrin was assessed by measuring the OD₆₀₀ (OD600) after growth in TPPYC medium containing various concentrations of streptonigrin unsupplemented (A) or supplemented with 1 mM of 2,2′-dipyridyl (B) (see Material and Methods for details). The relative OD₆₀₀ was determined by comparing the OD₆₀₀s obtained with and without streptonigrin. ○ and •, wild-type strain; □ and ▪, iscU₉₇ mutant; ▵ and ▴, ΔsufD mutant.