Fig. 5.
Conceptual model of Ca. Scalindua thriving in the NATZ and their dependencies on other microbial guilds and processes. Metabolism of Ca. Scalindua depends on both reduced nitrogen (ammonium) and oxidized nitrogen (nitrite). The ammonium source of Ca. Scalindua in the NATZ is mainly from the upward diffusive flux of NH4+ from the anoxic zone, while local organic matter degradation by denitrifying bacteria and urea and cyanate degradation of Ca. Scalindua can also release NH4+. For the nitrite source, Ca. Scalindua probably rely on the activity of nitrate-reducing bacteria, which generates nitrite by reducing nitrate, mainly produced by nitrifiers in the overlying oxic zone and diffusing downward into the NATZ. In addition to the anammox reaction, nitrite can be consumed by denitrifying bacteria and ammonium can be assimilated to generate new biomass by local organisms such as Ca. S. sediminis. OM, organic matter.