Formation of Hydrogen and Formate by Ruminococcus albus

Abstract

Radioisotopic growth studies with specifically labeled 14 C-glucose confirmed that Ruminococcus albus , strain 7, ferments glucose mainly by the Embden-Myerhof-Parnas pathway to acetate, ethanol, formate, CO 2 , H 2 , and an unidentified product. Cell suspensions and extracts converted pyruvate to acetate, H 2 , CO 2 , and a small amount of ethanol. Formate was not produced from pyruvate and was not degraded to H 2 and CO 2 , indicating that formate was not an intermediate in the production of H 2 and CO 2 from pyruvate. Cell extract and 14 C-glucose growth studies showed that the H 2 -producing pyruvate lyase reaction is the major route of H 2 and CO 2 production. An active pyruvate- 14 CO 2 exchange reaction was demonstrable with cell extracts. The 14 C-glucose growth studies indicated that formate, as well as CO 2 , arises from the 3 and 4 carbon positions of glucose. A formate-producing pyruvate lyase system was not demonstrable either by pyruvate- 14 C-formate exchange or by net formate formation from pyruvate. Growth studies with unlabeled glucose and labeled 14 CO 2 or 14 C-formate suggest that formate arises from the 3 and 4 carbon positions of glucose by an irreversible reduction of CO 2 . The results of the studies on the time course of formate production showed that formate production is a late function of growth, and the rate of production, as well as the total amount produced, increases as the glucose concentration available to the organism increases.