FISH法を用いた都市下水生物膜内におけるアンモニア酸化細菌の空間分布の解析

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In situ spatial organization of ammonia-oxidizing bacteria in wastewater biofilms was investigated using fluorescent in situ hybridization (FISH) with 16S rRNA-targeted oligonucleotide probes in combination with confocal scanning laser microscopy (CSLM) and digital image analysis. In situ hybridization of steady-state biofilm samples indicated more than 65% of ammonia-oxidizing bacteria present in the biofilm formed dense spherical clusters with the diameter of less than 10 μm and 10∼20% formed clusters with the diameter of more than 10 μm. Most of ammonia-oxidizing bacteria were present in states of small clusters (d<5 μm) in the surface biofilm, because the bigger clusters were imposed on the higher shear stress and consequently sloughed off.On the other hand, about 4∼10 times higher bacterial population were found as the bigger clusters (d=5∼20 μm) in the bottom biofilm than in the surface, creating a spatial gradient of ammonia-oxidizing bacteria throughout the biofilm. Furthermore, evaluation of series of optical sections through the clusters taken by the CSLM showed that a cluster with the diameter of approximately 25 μm consisted of up to 9,000 rod-shaped cells. Areal cell density within the clusters was found to be in the range of 0.9∼1.1 cells·μm-2 with areal fraction of cells of 51 ± 6%, indicating that these clusters have relatively large openings. These experimental results suggested that the interior biofilm structure was porous and heterogeneous, the spatial distribution of ammonia-oxidizing bacteria was strongly influenced by the hydraulic shear stress and substrate concentration profiles within the biofilm.
社団法人　日本水環境学会の論文

FISH法を用いた都市下水生物膜内におけるアンモニア酸化細菌の空間分布の解析

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