DETECTION AND LOCALIZATION OF SYNTROPHIC PROPIONATE-OXIDIZING BACTERIA IN GRANULAR SLUDGE BY IN-SITU HYBRIDIZATION USING 16S RIBOSOMAL-RNA-BASED OLIGONUCLEOTIDE PROBES

In situ hybridization with fluorescent oligonucleotides was used to de tect and localize microorganisms in the grannies of two lab-scale upfl ow anaerobic sludge blanket reactors that had been fed for several mon ths with either sucrose or a mixture of volatile fatty acids, Sections of the granules were hybridized with 16S rRNA-targeted oligonucleotid e probes for Bacteria, Archaea, specific phylogenetic groups of methan ogens, and two syntrophic propionate-oxidizing strains, MPOB and KOPRO P1. Cells of the syntrophic strain KOPROP1 were not detected in either type of sludge granules. Hybridizations of the sucrose-fed granules s howed an outer layer of mainly bacterial microcolonies with different morphologies, More inwards of these granules, a layer of different met hanogenic microcolonies mixed with large colonies of the syntrophic st rain MPOB could be detected. The MPOB colonies were interwined with hy drogen- or formate-consuming methanogens, indicating their syntrophic growth, The granules fed with volatile fatty acids showed an outer lay er of mainly bacteria acid then a thick layer of Methanosaeta-like met hanogens mixed with a few bacteria and a layer of methanogens mixed wi th syntrophic MPOB microcolonies. The centers of both sludge types con sisted of large cavities and methanogenic microcolonies. These results indicate a juxtapositioning of syntrophic bacteria acid methanogens a nd provide additional evidence for a layered microbial architecture of anaerobic granular sludge.