科研之友
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摘要
The fate of nitrogen in natural environments is controlled by anaerobic nitrate-reducing processes by which nitrogen is removed as N-2 or retained as NH4+. These processes can potentially be driven by oxidation of reduced inorganic compounds at oxic-anoxic interfaces. Several studies have investigated the use of Fe2+ as an electron donor in nitrate reduction in bacterial cultures, however current information on this process in the environment is sparse. We aimed to determine whether nitrate-reducing processes in the freshwater Lake Almind (Silkeborg, Denmark) were linked to Fe2+ oxidation. Anaerobic sediment slurries were supplemented with 15 N-substrates and electron donors Fe2+ and/or acetate) to characterize nitratereducing processes under environmentally relevant substrate concentrations and at higher concentrations traditionally used in microbial enrichment studies. Dissimilatory nitrate reduction to ammonium, DNRA, was stimulated by Fe2+ addition in 7 of 10 slurry experiments and in some cases, denitrification was concomitantly reduced. The determined kinetic parameters (V-max and K-m) for Fe2+- driven DNRA were 4.7 mmol N L-1 d(-1) and 33.8 mu mol Fe2+ L-1, respectively and reaction stoichiometry for Fe2+: NH4+ (8.2:1) was consistent with that of predicted stoichiometry (8: 1). Conversely, under enrichment conditions, denitrification was greatly increased while DNRA rates remained unchanged. Increased Fe2+ concentrations may be exploited by DNRA organisms and have an inhibitory effect on denitrification, thus Fe2+ may play a role in regulating N transformations in Lake Almind. Furthermore, we suggest enrichment conditions may promote the adaptation or change of microbial communities to optimally utilize the available high substrate concentrations; misrepresenting metabolisms occurring in situ.
- 出版日期2017-5-15
