Authors: EBRU ÇELEN, MEHMET AKİF KILIÇ
Abstract: Denitrification is generally considered an anaerobic process. However, in recent years it has been shown that bacteria can also reduce nitrate to nitrite under aerobic conditions. The characterization of biologically available nitrogen forms and their biological cycling mechanisms is important for ecological and agricultural implications. In this study, aerobic nitrate reducers were isolated from greenhouse soil. Using a nitrate reduction assay, it was found that 39 out of 60 isolates can reduce nitrate to nitrite under aerobic conditions. Five of those 39 isolates were selected for further characterization of their aerobic nitrate reduction activity. Four of those 5 isolates were found to have periplasmic nitrate reductase activity using MV^+ as a non-biological electron donor. Nitrite production of these isolates under aerobic conditions was determined using different nitrogen forms as sole nitrogen sources. It was found that nitrite accumulation in all isolates was higher when nitrate was the sole nitrogen source than when nitrate+ammonium was the sole nitrogen source. No nitrite accumulation was observed when ammonium was the sole nitrogen source. This study suggests that when ammonium exists together with nitrate, aerobic nitrate reduction does not lead to high nitrite accumulation.
Keywords: denitrification, aerobic denitrification, aerobic nitrate reduction, periplasmic nitrate reductase
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