Filamentous Microorganisms Affiliated with Uncultured Bacterial Group at Phylum Level: Microbes as Causative Agent for Filamentous Bulking of Methanogenic Sludge Granules

Abstract

Filamentous anaerobic sludge bulking was observed in an upflow anaerobic sludge blanket (UASB) reactor treating high-strength wastewater discharged from a sugar-manufacturing factory. In the bulking sludge, a number of thick filamentous cells were found, which were considered to be the causative agent for the bulking. To identify these filamentous cells, we applied an rRNA-based approach to the filamentous microbes. 16S rRNA gene analysis revealed that the filaments are uncultivated microbes affiliated with a clone cluster at the phylum level. In situ hybridization using a 16S rRNA-targeted oligonucleotide probe specific for the phylum KSB3 showed that the microbes were abundantly present in the bulking sludge. In addition, in situ hybridization analysis of normal granules (before bulking) indicated that the microbes are also abundant in healthy sludge granules ; the microbes are the major population on the surface of healthy sludge granules. This finding indicates that these filamentous microbes normally reside on the surface of granules, and that they outgrow the granules due to certain environmental changes, resulting in the filamentous bulking of sludge granules.