Thiobacillus ferrooxidansATCC 23270 was grown with elemental sulfur as the energy source. Substrate oxidation was measured using a Clark#x2010;type oxygen electrode. Whole cells demonstrated a broad pH optimum for sulfur oxidation between pH 2.0 and 8.0. TheVmaxand Ksfor sulfur oxidation varied depending on pH. Sulfite was oxidized at 227 nmol O2/min/mg protein. Thiosulfate oxidation was slow, and tetrathionate oxidation was not detected. At a concentration of 2 mM, sodium azide completely inhibited sulfur, sulfite, and thiosulfate oxidation. Inhibition byN#x2010;ethylmaleimide, antimycin A, and 2#x2010;heptyl#x2010;4#x2010;hydroxyquinoline N#x2010;oxide varied with substrate.
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