The microbial composition and spatial distribution in a terephthalate-degrading anaerobic granular sludge system were characterized using molecular techniques. 16S rDNA clone library and sequence analysis revealed that 78·5% of 106 bacterial clones belonged to the δ subclass of the class Proteobacteria; the remaining clones were assigned to the green non-sulfur bacteria (7·5%), Synergistes (0·9%) and unidentified divisions (13·1%). Most of the bacterial clones in the δ-Proteobacteria formed a novel group containing no known bacterial isolates. For the domain Archaea, 81·7% and 18·3% of 72 archaeal clones were affiliated with Methanosaeta and Methanospirillum, respectively. Spatial localization of microbial populations inside granules was determined by transmission electron microscopy and fluorescent in situ hybridization with oligonucleotide probes targeting the novel δ-proteo-bacterial group, the acetoclastic Methanosaeta, and the hydrogenotrophic Methanospirillum and members of Methanobacteriaceae. The novel group included at least two different populations with identical rod-shape morphology, which made up more than 87% of the total bacterial cells, and were closely associated with methanogenic populations to form a nonlayered granular structure. This novel group was presumed to be the primary bacterial population involved in the terephthalate degradation in the methanogenic granular consortium.
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