FIG 4.

Hydrogen sulfide production in strain 630Δerm. (A) Detection of H₂S production using lead-acetate paper. H₂S production was evaluated in the media PY, PY plus cysteine (PYC), and PY plus homocysteine (PYHC). The production of H₂S yielded a black color due to the formation of PbS. (B) Detection of the homocysteine γ-lyase activity on a zymogram. Crude extracts of strain 630Δerm grown in PY, PYC, or PYHC were loaded on a native polyacrylamide gel (12%) and incubated with 10 mM homocysteine. Homocysteine γ-lyase was detected by the formation of insoluble PbS via the release of H₂S. Lanes of the zymogram have been reorganized from the same image to present data chronologically. (C) Quantitative detection of H₂S after 6 or 10 h of growth of strain 630Δerm in PY (white boxes) or PYC (black boxes). H₂S production was measured using the quantitative methylene blue method, as described in Materials and Methods. The statistical analysis was performed by using the Mann-Whitney test for all genes. (D) Detection of cysteine desulfhydrase activities on a zymogram. Crude extracts of strain 630Δerm (lanes 1 and 2), 630Δerm::cysK (lane 3), 630Δerm::sigL (lane 4), 630Δerm(pRPF185) (lane 5), and 630Δerm(pDIA6456-ASmalY) (lane 6). The strains were grown in PY (lane 1) or PYC (lanes 2 to 6). Samples were charged on a native polyacrylamide gel (12%) and incubated with 10 mM cysteine. The cysteine desulfhydrases were detected by the formation of insoluble PbS formed by the release of H₂S. The results presented are representative of at least three independent experiments. Lanes of the zymogram have been reorganized from the same image to present data chronologically.