Abstract
Time dependent developments of in situ spatial distributions of NH4+- and NO2-- oxidizing bacterial populations in domestic wastewater biofilms and in synthetic nitrifying biofilms were investigated by fluorescent in situ hybridization (FISH) with a set of 16S rRNA-targeted oligonucleotide probes. NH4+-oxidizing bacterial populations were classified into three groups according to the probe specificity, and population dynamics of these groups was correlated with the biofilm performance. In situ hybridization indicated that Nitrosomonas spp. (excluding probe NEU stained NH4+-oxidizing bacteria : i.e., N. marina-lineage, N. europaea-lineage, N. eutropha, and N. halophila) and Nitrospira-like bacteria were the numerically dominant species in the domestic wastewater biofilms. However, probe NEU stained NH4+-oxidizing bacteria became dominant populations in the synthetic nitrifying biofilms (which were initially cultured with the primary settling tank effluent) after switching to the synthetic media. This population shift might be attributed to the accumulation of NO2--N and relatively higher loads of NH4+-N which accelerate the growth of N. europaea-lineage and N. eutropha. This evidence indirectly supported that N. europaea has been most commonly isolated and studied in most of the previous researches. These observations have considerable significance to our understanding of microbial nitrification process in wastewater treatment processes and in natural environment.
