Biomass and Polysaccharides in Granule

The exopolysaccharide (EPS) matrix in the granule was detected with a FITC-labeled lectin (ConA-FITC) from Canavalia ensiformis. The LIVE/DEAD® BacLight Bacterial Viability Kit (Molecular Probes, OR, USA) was used to evaluate quantity of dead and viable biomass. Intensity of green fluorescence of biomass stained with SYTO™ from this kit correlated with the number of ribosomes in cells, which depends on specific growth rate. Therefore, staining with SYTO™ was used for the detection of the active biomass layer in the granule.

The anaerobic layer in the aerobically grown granule was detected by the presence of obligate anaerobic bacteria Bacteroides spp. This layer was situated at a depth of 800-900 |xm from the surface of the granule (Fig. 6.4c). The layer of anaerobic bacteria was followed by a layer of dead microbial cells at a depth of 800-1000 |xm from the surface of the granule (Fig. 6.4e). Anaerobiosis and cell death in the granule interior was probably promoted by the formation of polysaccharide plugs in the channels and pores. These plugs diminished the mass transfer rate of both nutrients and metabolites. Polysaccharide formation peaked at a depth of 400 |xm from the surface of the granule (Fig. 6.4f).

The core in some granules contains dead microbial cells and polysac-charides at a depth of 800-1000 |xm from the surface of the granule (Fig. 6.4e). Cell death in the core was probably promoted by the formation of polysaccharide plugs in the channels and pores.

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