Evidence for cytochrome involvement in fumarate reduction and adenosine 5'-triphosphate synthesis by Bacteroides fragilis grown in the presence of hemin

Abstract

Growth of Bacteroides fragilis subsp. fragilis on glucose was very much stimulated by the addition of hemin (2 mg/liter) to the medium. The generation time decreased from 8 to 2 h, and the molar growth yield increased from YM = 17.9 to YM = 47 g (dry weight) of cells per mol of glucose. In the absence of hemin, glucose was fermented to fumarate, lactate, and acetate. The cells did not contain detectable amounts of cytochromes or fumarate reductase. In the presence of hemin, the major products of fermentation were succinate, propionate, and acetate. A b-type cytochrome, possibly a c-type cytochrome, and a very active fumarate reductase were present in the cells. It is concluded from these results that hemin is required by B. fragilis to synthesize a functional fumarate reductase and that the hemin-dependent, enormous increase of the growth yield may be due to adenosine 5'-triphosphate production during reduction of fumarate to succinate.