Comparative Analysis of Vertical Heterogeneity of Microbial Community in Sulfur-Packed Reactor Used for Autotrophic Nitrate Removal

摘要

To better understand microbial community in sulfur-based nitrate removal process, comparative molecular analyses were performed with the biofilm formed on sulfur particles that were obtained from different bed-heights of a laboratory-scale reactor employed for the process. Microbial community in the reactor showed vertical heterogeneity in terms of total cell count and nitrate removal activity. DAPI (4,6-diamidino-2-phenylindole) staining revealed that total cell count (per g sulfur particle) gradually decreased as bed height increased until reaching approximately middle of the reactor bed, showing a nearly plateau afterward. This result partly supported ion chromatography result that most nitrate removal activity was found in the lower part of the reactor bed. Phylogenetic composition of bacterial community in the biofilm was almost similar regardless of bed height as determined by whole cell hybridization using group-specific probes. Cells affiliated with the β- and γ-Proteobacteria were the most abundant proteobacterial groups throughout the bed, although their fractions were fluctuating along the bed height. Total number of the two major groups decreased as bed height increased, showing similar trend to total cell count and nitrate removal activity. Denaturating gradient gel electrophoresis revealed similar profiles of nitrous oxide reductase gene (nosZ) fragments from denitrifying populations at the different bed-heights, suggesting similar diversity of the nosZ fragments regardless of bed height.