Abstract
Filamentous cells belonging to the candidate bacterial phylum KSB3 were previously identified as the causative agent of fatal filament overgrowth (bulking) in a high-rate industrial anaerobic wastewater treatment bioreactor. Here, we obtained near complete genomes from two KSB3 populations in the bioreactor, including the dominant bulking filament, using differential coverage binning of metagenomic data. Fluorescence in situ hybridization with 16S rRNA-targeted probes specific for the two populations confirmed that both are filamentous organisms. Genome-based metabolic reconstruction and microscopic observation of the KSB3 filaments in the presence of sugar gradients indicate that both filament types are Gram-negative, strictly anaerobic fermenters capable of non-flagellar based gliding motility, and have a strikingly large number of sensory and response regulator genes. We propose that the KSB3 filaments are highly sensitive to their surroundings and that cellular processes, including those causing bulking, are controlled by external stimuli. The obtained genomes lay the foundation for a more detailed understanding of environmental cues used by KSB3 filaments, which may lead to more robust treatment options to prevent bulking.
Highlights
Anaerobic digestion is a major type of biological treatment extensively used around the world (Ahring, 2003a) that is cost effective for treating organic waste and wastewater, and can frequently produce energy in the form of methane (Angelidaki et al, 2011)
Bulking of anaerobic digestion systems can be caused by a variety of filamentous microorganisms (Hulshoff Pol et al, 2004; Li et al, 2008; Yamada & Sekiguchi, 2009) and a phylogenetically novel filament was previously reported to be the cause of bulking in an industrial upflow anaerobic sludge blanket (UASB) reactor treating sugar manufacturing wastewater (Yamada et al, 2007; Yamada et al, 2011)
Fluorescence in situ hybridization (FISH) with KSB3-specific 16S rRNA-directed probes revealed that the KSB3 filaments are localized at the outer layer of healthy granules (Yamada et al, 2007) which become substantially thicker during bulking
Summary
Anaerobic digestion is a major type of biological treatment extensively used around the world (Ahring, 2003a) that is cost effective for treating organic waste and wastewater, and can frequently produce energy in the form of methane (biogas) (Angelidaki et al, 2011). The study of filamentous KSB3 bacteria will undoubtedly contribute to our understanding of and ability to prevent bulking in anaerobic wastewater treatment systems, but has been hampered by an inability to obtain a pure culture despite repeated and long term isolation efforts (Yamada et al, 2011). Culture-independent molecular and imaging methods are beginning to provide clues regarding the ecophysiology of these organisms This includes their ability to uptake simple carbohydrates, maltose and glucose, under anaerobic conditions and from these observations it was proposed that high carbohydrate loading in the UASB reactor may trigger proliferation of KSB filament populations (Yamada et al, 2011)
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