INFLUENCE OF VOLATILE FATTY-ACIDS ON NITRITE ACCUMULATION BY A PSEUDOMONAS-STUTZERI STRAIN ISOLATED FROM A DENITRIFYING FLUIDIZED-BED REACTOR

Intermediate nitrite accumulation during denitrification by Pseudomona s stutzeri isolated from a denitrifying fluidized bed reactor was exam ined in the presence of different volatile fatty acids. Nitrite accumu lated when acetate or propionate served as the carbon and electron sou rce but did not accumulate in the presence of butyrate, valerate, or c aproate. Nitrite accumulation in the presence of acetate was caused by differences in the rates of nitrate and nitrite reduction and, in add ition, by competition between nitrate and nitrite reduction pathways f or electrons. Incubation of the cells with butyrate resulted in a slow er nitrate reduction rate and a faster nitrite reduction rate than inc ubation with acetate, Whereas nitrate inhibited the nitrite reduction rate in the presence of acetate, no such inhibition was found in butyr ate-supplemented cells. Cytochromes b and c were found to mediate elec tron transport during nitrate reduction by the cells. Cytochrome c was reduced via a different pathway when nitrite-reducing cells were incu bated with acetate than, when they were incubated with butyrate. Furth ermore, addition of antimycin A to nitrite-reducing cells resulted in partial inhibition of electron transport to cytochrome c in acetate-su pplemented cells but not in butyrate-supplemented cells. On the basis of these findings, we propose that differences in intermediate nitrite accumulation are caused by differences in electron flow to nitrate an d nitrite reductases during oxidation of either acetate or butyrate.