FIGURE 4.

The bigR operon is required for hydrogen sulfide detoxification. A, growth of A. tumefaciens wild type and bigR⁻ and blh⁻ insertion mutants in BiGGY agar medium, showing that the blh⁻ cells accumulate higher levels of hydrogen sulfide relative to wild type (wt) and bigR⁻ mutant. B and C, growth of the wild type, bigR⁻, and blh⁻ cells in thiosulfate (0–25 mm) or ammonium sulfide (0–1 mm) gradient plates, respectively. D, effect of pH on the toxicity of 1 mm ammonium sulfite relative to control (no ammonium sulfide). The growth of the blh⁻ cells is affected by the acidic pH only. Bacterial cells were plated as indicated in A. E, sulfite levels in the culture supernatants of wild type, bigR⁻, and blh⁻ cells estimated by the sulfite test strip, according to the scale. Culture medium without bacterial growth (control) is shown for comparison.