Sulfide oxidation by C. necator H16 and its mutants. Cells were suspended in 100 mM Tris buffer (pH 8.0) at an OD600 of 2, and NaHS (100 μM) was added to initiate the reaction. Controls used the same buffer without bacterial cells. ■, C. necator H16; ▲, C. necator H16 ΔfccAB; ●, C. necator H16 ΔfccAB/fccAB; □, buffer; △, heat-killed C. necator H16; ○, heat-killed C. necator H16 ΔfccAB/fccAB. All data are averages of three samples with standard deviations (error bars).