FUMARATE REDUCTION AND ITS ROLE IN THE DIVERSION OF GLUCOSE FERMENTATION BY STREPTOCOCCUS FAECALIS

Abstract

the normal fermentation of glucose by Streptococcus faecalis FB82, as shown by the production of increased amounts of CO2 , formate, acetate, and acetoin, and decreased formation of lactate and ethanol. Experiments with D-glucose-l-C'4, in which low levels of labeled CO2 were recovered, indicated that C-1 cleavage of the glucose molecule was not involved. The presence of fumarate afforded consistently larger cell crops in growth studies with glucose and other energy sources. On a molar growth-yield basis, anaerobically grown, glucose-fumarate cultures were equivalent to aerobically grown, glucose cultures. The reduction of fumarate by cell suspensions indicated that glucose, gluconate, and, to a lesser extent, glycerol and mannitol could serve as hydrogen donors. Several common metabolic inhibitors had no effect upon the fumarate reductase system in cell suspensions, although some sensitivity to acidic pH was noted. Significant levels of succinate oxidation activity were not detected. Fumarate reductase activity was demonstrated in all five S. faecalis strains tested. Distribution of this ability in S. faecium strains was variable, ranging from activity comparable with that of S. faecalis to total inactivity. The observations support the conclusion that fumarate functions as an alternate hydrogen acceptor, thus allowing pyruvate to participate in the energy-yielding phosphoroclastic and dismutation pathways. In a previous communication (Deibel, 1964b), 1 Journal paper no. 277, American Meat Institute Foundation.

Fumarate Reductase Activity ofStreptococcus faecalis

“…Some sensitivity of the fumarate reductase to acidity was observed with cell suspensions. However, common metabolic inhibitors such as azide, cyanide, arsenite, atabrin, and malonate did not effect an inhibition of activity (3). At the cellular level, no significant oxidation of succinate was demonstrable, and definitive evidence regarding the inducible or constitutive nature of the enzyme was not obtained.…”

“…Evidence for the oxidation of reduced nicotinamide adenine dinucleotide (NADH2) by fumarate in this organism, which probably occurs via a flavin intermediate, was observed subsequently (8). When S. faecalis is grown with substrate quantities of fumarate, a radical alteration of the normal homofermentative end products is effected (3). The end products of this diverted fermentation suggest the reduction of fumarate to succinate and an altered metabolism of pyruvate to yield volatile acids and carbon dioxide instead of lactate.…”

Molar Growth Yields as Evidence for Oxidative Phosphorylation in Streptococcus faecalis Strain 10C1

“…Radioactivity measuirements. For studies of glucose incorporation during growth, solutions containing 5 ,4C of D-'4C-glucose per ml were sterilized by filtration and added aseptically to the basal medium. Normal growth yields were determined on this medium as described above.…”

Production of N2O and CO2 during the reduction of NO2- by Lactobacillus lactis TS4

“…The subsequent catabolism of pyruvate via the dismutation and phosphoroclastic pathways would account for the alteration of products. These changes in pyruvate catabolism would yield additional energy, and small, but reproducible, increases in cell yields have been observed in the presence of fumarate (5).…”

“…Changes in the metabolism of various lactic acid bacteria under different circumstances have been noted. In the presence of fumarate, significant increases in the production of acetate and CO2 by Streptococcus faecalis occur (5). Fumarate can act as an alternate hydrogen acceptor, regenerating oxidized NAD+ and averting the reduction of pyruvate to lactate.…”