Quantification of nitrifying bacterial populations in a full-scale nitrifying trickling filter using fluorescent in situ hybridization.

Fluorescent in situ hybridization (FISH) was used to quantify the ammonia-oxidizing populations within intact biofilm samples collected from a full-scale nitrifying trickling filter (NTF). Ammonia, nitrite, and nitrate concentrations were measured for aqueous samples taken in conjunction with biofilm samples at multiple filter depths. Correlation coefficients for individual sampling events, calculated by simple linear regression of FISH signal area and ammonia removal rates, ranged from 0.558 when using probe NEU23a to 0.982 when using probe Nso190. The improved correlations with Nso190 suggest that genera other than Nitrosomonas are present in this system. Percent biofilm coverage, as determined by 4',6-diamidino-2-phenylindole counterstaining and dry weight biomass measurements, did not change throughout the NTF. This indicates that biofilm growth is fairly uniform throughout the filter even if nitrifier growth is not.