Inhibition of growth of Clostridium pasteurianum by acetylene: implication for nitrogen fixation assay

Abstract

Acetylene (0.1 atm) prevented rapid increase of CO₂ evolution in glucose-amended anaerobically incubated sandy loam soil. This effect was explainable in terms of an effect of C₂H₂ on nitrogen-fixing Clostridia.In a N₂ase-repressed Clostridium pasteurianum culture growing on a medium supplemented with 339 μg NH₄-N/ml, C₂H₂ caused 60 to 100% inhibition of cell proliferation and of cell-nitrogen accumulation, and prevented the increase in rate of CO₂ evolution normally associated with growth. In N₂ase-containing cultures the competitive inhibition of nitrogen fixation by C₂H₂ was relieved when C₂H₂ reduction brought the pC₂H₂ to near 0.025 atm. The C₂H₂ inhibition of the NH₄-grown culture, however, was not reversed by removal of the C₂H₂ after 11 h of exposure. Ethylene showed no inhibitory effect.Variation of NH₄-N concentration and addition, to the medium, of casein hydrolysate and of pyruvate separately and in combination had no marked effect on the inhibition pattern.The effect of C₂H₂ reported here suggests that, until more information is available, the results of long-term C₂H₂ assays of low-activity materials such as soils should be interpreted with some caution.