CELL GROWTH AND ELECTRON TRANSPORT IN FUMARATE REDUCTION OF BACTEROIDES UREOLYTICUS

Abstract

The growth of the strictly anaerobic bacterium Bacteroides ureolyticus was supported by energy production coupled to an anaerobic electron transport from formate or hydrogen to fumarate. There was no growth in a medium containing peptone, yeast extract, and glucose. The growth yield was about 7g dry cells per mol of succinate produced. The electron transport pathway of fumarate reduction was investigated with extracts from cells grown on fumarate plus formate and on fumarate plus hydrogen. Reduction of fumarate to succinate occurred with formate and hydrogen as electron donors, but not with NAD(P)H, lactate, malate, or pyruvate in crude extracts. Activities of formate dehydrogenase, hydrogenase, and fumarate reductase and cytochrome b occurred mainly in a membrane fraction of the cell, c-Type cytochrome was present in both soluble and membrane fractions. All cytochromes were reduced by formate. In the membrane fraction the reduced form of the cytochrome b was immediately oxidized by adding fumarate, and oxidation of the cytochrome c also proceeded, but rather slowly. Apparently the membrane-bound cytochrome b is linked to the reduction of fumarate in B. ureolyticus.