Fig. 1: Amt and Rh-type transporters encoded by ammonia oxidising microorganisms.
From: Nitrification and beyond: metabolic versatility of ammonia oxidising archaea
Amt transporters are energy-dependent and bind ammonium. Amt2 is a high-affinity Amt and can function at low pH and substrate concentration. Rh proteins facilitate the bidirectional flow of NH3 and therefore function at high pH and substrate concentration. NH3 can also cross the bilipid membrane by diffusion. NH4+ and NH3 exist in equilibrium based on pH. Membrane permeability between AOA and AOB may differ as their membrane compositions are different [60].
