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Microbial community of a non-phosphate removing anaerobic-aerobic activated sludge system fed with fermented products was characterized. Predominant microbial populations were initially identified using 16S rDNA cloning analysis, and 34 different sequences were found among 161 clones screened. These sequences were mostly affiliated with the divisions Proteobacteria (57.2 % of total clones) and Cytophagales (25.5%). Particularly, the genus Hydrogenophaga and its related novel bacterial group in the β-I subdivision (49.7%), and the genus Flavobacterium (17.4%) were the predominant ones. The abundance of major phylogenetic groups was further evaluated using fluorescent in-situ hybridization (FISH) with group-specific rRNA probes. Like the clone library results, bacteria of the β subdivision of the division Proteobacteria was the most dominate one and possibly responsible for the substrate metabolism in the process. FISH analysis further detected bacteria from α- and γ-subdivisions, but not from the divisions Cytophagales and actinobacteria. [ABSTRACT FROM AUTHOR]

The present paper focuses on possible strategies to highlight bacterial populations playing key roles in EBPR processes. Three experimental approaches are presented. First, measurement of acetoacetyl-CoA reductase activity implies that the amount of the enzyme actually present is much higher than the amount that is needed to ensure the observed PHB synthesis rate. It is likely that acetoacetyl-CoA reductatse is an intrinsic (not necessarily a rate-limiting) enzyme in the PHA production, thus a key enzyme for EBPR. It is also indicated that the source of reducing power for this enzyme can be different among sludges. Acetoacetyl-CoA reductase should be metabolically (and thus genotypically) diverse. Second, fluorescence in situ hybridization is applied to characterize bacterial community of activated sludge. There is no significant difference in the bacterial structure between the non- EBPR activated sludge and the EBPR activated sludge. It is likely that possible differences, if any, are not reflected on the subgroup level bacterial structures. Third, very diverse nature of the EBPR community is demonstrated by the polymerase chain reaction- denaturing gradient gel electrophoresis. In summary, the assumption that PAOs are phylogenetically diverse must be verified by evidence. It is important to develop as many probes for PAOs and to apply them to as many EBPR sludges as possible together with metabolic characterization of the EBPR sludges. [ABSTRACT FROM AUTHOR]