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 C2H2, the fermentation products, acetate and butyrate, were produced in nearly equimolar quantities along with copious quantities of CO2 and H-2. In the presence of 10 kPa of C2H2, there was significant inhibition of acetate, butyrate, CO2 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 C2H2 was reduced to C2H4, indicating the activity of the saccharolytic N2-fixing clostridia. In the presence of NH4+ (nitrogenase repressed), the inhibition of fermentation due to C2H2 appeared to be alleviated. The decrease in butyrate formation is suggested to result from reoxidation of NADH through the reduction of C2H, to C2H4 by nitrogenase, rather than by acetyl CoA reduction to butyrate. The potential implications of the use of C2H2 in conjunction with N transformations by heterotrophic organisms, in light of these data, are discussed.