Compared with CBS-derived H₂S, exogenous H₂S was less effective in protecting V. cholerae cells from H₂O₂.

(A). Survival of Δcbs in M9 minimal medium (M9 salts plus 2 mM MgSO₄, 0.1 mM CaCl₂) plus 0.2% casein acid hydrolysate, when NaHS, the rapid donor of H₂S, was supplied 1hr before under H₂O₂ challenge. 1 mM of H₂O₂ treatment was performed on log-phase bacteria for 30 min. (B). Semi-quantification of CBS-derived H₂S production in M9 minimal medium with 0.2% casein acid hydrolysate as the sole carbon source. H₂S production within 6 hrs was examined with Pb(Ac)₂ paper strips, and compared with NaHS standards (0, 10 μM, 100 μM, 1 mM). cbs expression was induced by 200 μM IPTG.

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