Abstract
Anaerobic ammonium oxidizing (anammox) bacteria oxidize ammonium to dinitrogen gas with nitrite as the electron acceptor. These bacteria are the key players in the global nitrogen cycle, responsible for the most of nitrogen production in natural ecosystems. The anammox process is also a cost-effective and environment-friendly alternative to conventional ammonium removal from wastewater streams. Still, little is known about the metabolism and niche differentiation of anammox bacteria. The intermediates of anammox metabolism were investigated with an array of complementary methods. Experiments with 15N isotopes showed that hydrazine, a rocket fuel, was turned over. Inhibition studies, batch incubations, fluorescence imaging showed that nitric oxide was an intermediate. For a better understanding of the niche differentiation of anammox bacteria, different anammox cultures were grown under varying conditions. A co-culture of Kuenenia stuttgartiensis (freshwater species) and Scalindua wagneri (marine species) was subjected to gradually increasing salinity. Ultimately, Kuenenia stuttgartiensis was the dominant species indicating that gradual adaptation could be used as a strategy for the application of the anammox bacteria to different types of wastewater. When acetate or propionate was introduced during different anammox enrichments, Brocadia fulgida or Anammoxoglobus propionicus became the dominant species, respectively. These species could out-compete other bacteria in the presence of ammonium, nitrate, nitrite and the corresponding organic acid. It was shown that all investigated anammox species could use nitrate as an electron acceptor for organic acid reduction. This metabolism of the anammox bacteria was investigated with 15N isotopes. It was shown that unlike conventional denitrifiers, the anammox bacteria reduce nitrate to ammonium via nitrite, and subsequently combine the formed nitrite and ammonium through the usual anammox pathway. An enzyme capable of nitrite reduction to ammonium was partially purified. Taken together, these results show that the anammox bacteria are versatile, and can be applied in different nitrogen removal systems.
