In situ analysis of Nitrosomonas spp. in wastewater treatment wetland biofilms

The presence of the ammonia-oxidising group Nitrosomonas in developing biofilms from a subsurface flow dairy effluent treatment wetland was investigated using in situ hybridisation and a crude semi-quantitative PCR. Fluorescently labelled oligonucleotide probes, specific for the Nitrosomonas europaea and Nitrosomonas eutropha species, showed that nitrifying bacteria were present from the onset of biofilm development but that over a five month period the proportions remained low (averaging less than 1% of the total bacterial population). The greatest presence of these nitrifiers was found in the second trench of the subsurface flow wetland. Nitrosomonas were also found to be susceptible to environmental change; adverse environmental conditions, such as low temperatures, coincided with negligible Nitrosomonas presence throughout the wetland. However, during one period of elevated ammonium concentrations Nitrosomonas presence rapidly increased as high as 7% of the total bacterial population. Investigations of relative occurrence of effluent bacterial population of Nitrosomonas europaea and the biofilm populations showed that Nitrosomonas presence in the effluent coincided with significant presence in adjacent biofilms. This suggests seeding between both sessile and planktonic populations of this species. Nitrosomonas occurred as single cells in biofilms throughout the study and were never observed as dense clusters.