Estimates of potential nitrate reductase activity in sediments: comparisons of two incubation methods and four inhibitors

Sediment samples, collected from a large shallow lake, Taihu, China, were incubated in two conditions (with and without air extraction) with regard to four soil enzyme’s inhibitors (dry and moist heat sterilizations, chloramphenicol and toluene) to estimate the potential nitrate reductase (Nar) activities. The objectives of paper were to define (1) whether to exclude air from the mixture of sediment and substrate solution prior to incubation was necessary, and (2) the efficacy of four inhibitors when assaying the enzyme. No significant difference between two incubation methods was found (P < 0.05), indicating that it is not necessary for estimating the potential Nar activity in the sediment to construct an initial anaerobic condition by air extractions prior to incubation. Toluene (1.0 mL/g sediment) and dry heat sterilization effectively and persistently inhibit the reduction of nitrate to nitrite during the incubation of 42 h. The authors concluded that both should be used as preferred inhibitors. In contrast, chloramphenicol (30 μg/g sediment) and moist heat sterilization inhibitors restrained nitrate reduction for <24 h only. In addition, it was found that no nitrite produced was substantially reduced in 24 h. Therefore, it should be needless for potential Nar activity estimation in the sediment to add 2,4-dinitrophenol to inhibit nitrite reductase.