Inhibition of the fermentation process in soil by acetylene

The effect of acetylene on the fermentation of added carbon in anaerobic soil was examined. With glucose as the C source and in the absence of C 2H 2, the fermentation products, acetate and butyrate, were produced in nearly equimolar quantities along with copious quantities of CO 2 and H 2. In the presence of 10 kPa of C 2H 2, there was significant inhibition of acetate, butyrate, CO 2 and H 2 production. The inhibitory effect was significantly greater on butyrate production than acetate production. In the absence of an inorganic N source, added C 2H 2 was reduced to C 2H 4, indicating the activity of the saccharolytic N 2-fixing clostridia. In the presence of NH + 4 (nitrogenase repressed), the inhibition of fermentation due to C 2H 2 appeared to be alleviated. The decrease in butyrate formation is suggested to result from reoxidation of NADH through the reduction of C 2H 2 to C 2H 4 by nitrogenase, rather than by acetyl CoA reduction to butyrate. The potential implications of the use of C 2H 2 in conjunction with N transformations by heterotrophic organisms, in light of these data, are discussed.