Cytochromes and Anaerobic Sulfide Oxidation in the Purple Sulfur Bacterium Chromatium warmingii

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Abstract
Two soluble acidic c-type cytochromes (c'' and c-552) were isolated by ion exchange chromatography, gel filtration and ammonium sulfate fractionation. Cytochrome c'' is a high-spin cytochrome with maxima at 399 nm, 490 nm and 634 nm in the oxidized form and at 550 nm, 425 nm and a characteristic shoulder at 434 nm in the reduced state. The best purity index obtained (A280/A399) was 0.35. Cytochrome c'' is autoxidizable, has a MW of 12,000 (estimated by sodium dodecylsulfate electrophoresis), a midpoint redoxpotential of +10 mV and an isoelectric point at pH 4.0). The reduced cytochrome c'' reacts with carbon monoxide. The reaction is reversible. Cytochrome c-552 shows maxima at 552 nm, 523 nm and 417 nm in the redued form and at 408 nm in the oxidized state. The best purity index obtained (A280/A408) was 0.94. Cytochrome c-552 has a MW of 30,000 and an isoelectric point between pH 4.3 and 5.0. C. warmingii also contains a membrane-bound cytochrome c-552. During anaerobic sulfide oxidation, elemental S and sulfate were formed at the same time. When all sulfide was consumed by the cells, the remaining intracellular elemental S was further oxidized to sulfate.