Characterization of microbial community structures and their activities in single anaerobic granules by beta imaging, microsensors and fluorescence in situ hybridization.

ABSTRACT

The spatial distribution of microorganisms and their in situ activities in anaerobic granules were investigated by fluorescence in situ hybridization (FISH), beta imaging and microsensors. FISH results revealed a layered structure of microorganisms in the granule, where Chloroflexi was present in the outermost layer, Smithella spp. and Syntrophobacter spp. were found in a depth of ca. 100 µm, and Archaea was restricted to the inner layer (below ca. 300 µm from the surface). Substrate uptake patterns elucidated by beta imaging demonstrated that glucose uptake was highest at 50 µm depth, whereas propionate uptake had a peak at 200 µm depth. In addition, microsensor measurements revealed that acid was produced mainly at 100 µm depth and H(2) production was detected at a depth from 100 to 200 µm. H(2) consumption and corresponding CH(4) production were found below 200 µm from the surface. Direct comparison of these results implied sequential degradation of complex organic compounds in anaerobic granules; Chloroflexi contributed to fermentation of organic compounds and acid production in the outermost layer, volatile fatty acids were oxidized and H(2) was produced mainly by Smithella spp. and Syntrophobacter spp. at a depth from 100 to 200 µm, and Archaea produced CH(4) below ca. 300 µm from the surface.