“…Studies on nitrifying microbes in wastewater treatment systems and the natural environment using molecular methods have indicated that Nitrosomonas species are the main AOB populations in wastewater treatment bioreactors (Tsuneda et al, 2003; Chen and Wong, 2004; Mota et al, 2005; Wells et al, 2009), as well as in diverse natural environments including freshwater, coastal and brackish water regions (Stehr et al, 1995; Zhang et al, 2015). Among Nitrosomonas species, Nitrosomonas europaea / Nitrosomonas mobilis cluster 7 was dominant in wastewater treatment bioreactors loaded with high concentrations of ammonia and nitrite, whereas Nitrosomonas oligotropha cluster 6a was dominant in systems with a lower ammonia environment (Suwa et al, 1994, 1997; Bollmann and Laanbroek, 2001; Limpiyakorn et al, 2005, 2007; Tan et al, 2008).…”