Nitrous oxide (N2O) production by Alcaligenes faecalis during feast and famine regimes

The environmentally harmful compound. nitrous oxide (N2O), can accumulate a s an intermediate in the process of denitrification. One important paramete r, which can influence this accumulation, is the feeding regime sensed by t he bacteria involved, in which an unbalanced supply of electron donor and a cceptor may occur. When pulse additions of C-compounds (acetate, butyrate a nd malate) were given to denitrifying cultures of Alcaligenes faecalis stra in TUD, the production rate of N2O was reduced from 9.9-18.5% to 1.8-10.4% of the total nitrite converted, as long as the C-substrate was in excess. H owever, as soon as the availability of carbon compounds became exhausted an d the culture entered starvation. N2O was one of the main products of denit rification and production increased to 32-64% of the total N-feed. Under dy namic feeding conditions, the culture was able to adapt to the fluctuating conditions and the ratio of N2O to nitrite decreased. However, during starv ation the ratio of N2O to nitrite was still high (+/- 27%), indicating that with prolonged starvation, the overall N2O emission will increase. Competition between the enzymes of denitrification fur electrons from the c ytochrome c pool could explain the emission of N2O, if the enzyme N2O-reduc tase has a lower affinity for the electron-donor than the other reductases. (C) 2000 Elsevier Science Ltd. All rights reserved.