Cluster structure of anaerobic aggregates of an expanded granular sludge bed reactor.
The metabolic properties and ultrastructure of mesophilic aggregates from a full-scale expanded granular sludge bed reactor treating brewery wastewater are described. The aggregates had a very high methanogenic activity on acetate (17.19 mmol of CH(4)/g of volatile suspended solids [VSS].day or 1.1 g of CH(4) chemical oxygen demand/g of VSS.day). Fluorescent in situ hybridization using 16S rRNA probes of crushed granules showed that 70 and 30% of the cells belonged to the archaebacterial and eubacterial domains, respectively. The spherical aggregates were black but contained numerous whitish spots on their surfaces. Cross-sectioning these aggregates revealed that the white spots appeared to be white clusters embedded in a black matrix. The white clusters were found to develop simultaneously with the increase in diameter. Energy-dispersed X-ray analysis and back-scattered electron microscopy showed that the whitish clusters contained mainly organic matter and no inorganic calcium precipitates. The white clusters had a higher density than the black matrix, as evidenced by the denser cell arrangement observed by high-magnification electron microscopy and the significantly higher effective diffusion coefficient determined by nuclear magnetic resonance imaging. High-magnification electron microscopy indicated a segregation of acetate-utilizing methanogens (Methanosaeta spp.) in the white clusters from syntrophic species and hydrogenotrophic methanogens (Methanobacterium-like and Methanospirillum-like organisms) in the black matrix. A number of physical and microbial ecology reasons for the observed structure are proposed, including the advantage of segregation for high-rate degradation of syntrophic substrates.
Gonzalez-Gil
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Sub-department of Environmental Technology, University of Wageningen, 6700 EV Wageningen, The Netherlands. graciela.gonzalez@algemeen.mt.wau.nl
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Van Aelst
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D000085:Acetates / Q000378:metabolism; D001421:Bacteria, Anaerobic / Q000145:classification / Q000235:genetics / Q000502:physiology*; D001422:Bacterial Adhesion; D018533:Biomass; D019149:Bioreactors; D020564:Deltaproteobacteria / Q000145:classification / Q000235:genetics / Q000502:physiology; D019605:Euryarchaeota / Q000145:classification / Q000235:genetics / Q000502:physiology; D017404:In Situ Hybridization, Fluorescence; D009682:Magnetic Resonance Spectroscopy; D008697:Methane / Q000378:metabolism; D008855:Microscopy, Electron, Scanning; D012722:Sewage / Q000382:microbiology*; D014865:Waste Disposal, Fluid / Q000295:instrumentation / Q000379:methods
D000085:Acetates; D012722:Sewage; D008697:Methane