Nitrifying biofilm development with time: activity versus phylogenetic composition.

The development of nitrifying biofilms collected from a full-scale nitrifying trickling filter was evaluated through the application of fluorescent in situ hybridization (FISH) and by quantification of nitrification rates in bench-scale reactors. Two sampling campaigns were conducted to evaluate the structure and function of biofilms between 14 and 70 days old. The structure, or number of ammonia-oxidizing bacteria, was quantified with Nso190. The function was quantified with bench-scale nitrification rates. The two assays were compared by calculating correlation coefficients by simple linear regression of the two data sets. The number of ammonia-oxidizing bacteria closely tracked activity data (linear correlation, r2 > 0.500). Changes in ammonia-oxidation capacity with time (7-day intervals) were mirrored by shifts in the percent of ammonia-oxidizing bacteria present. Nitrification rates did not correlate to the EUB338-probe stained area (r2 < 0.500), suggesting that nonnitrifying bacteria play a larger role in nitrifying biofilm ecology than previously thought. Dry-weight biomass accumulations did not correlate to either the EUB338-probe stained area or the bench-scale nitrification rates. This suggests that inert materials accumulate in the biofilms over time.