All data suggest that microbial community structures or samples of sludge with a content of phosphate between 8 and 12% were very similar but distinct from those containing phosphate at 1.8%. In all samples analyzed, ubiquinones, menaquinone and fatty acids were the main components. Dominance and E5 suggested that a large number of organisms belonging to the b and subclasses Proteobacteria and Actinobacteria from higher GMC Gram-positive bacteria, respectively, were present. Denaturing gradient gel electrophoresis analysis revealed at least 6-10 predominant DNA bands and numerous other fragments in each sample. Five major denaturing gradient gel electrophoresis fragments from each of 1.8% and 11.8% phosphate containing sludge samples, respectively, were successfully isolated and sequenced. Phylogenetic analysis of the sequences revealed that both 3% and 15% phosphate -containing sludge samples shared three common phylotypes which are separately associated with new bacterial groups of subclass C Proteobacteria, two E5 containing Actinobacteria, and Caulobacter spp. The subclass Proteobacteria. Phylogenetic analysis revealed useful phylotypes unique for both samples sludge. Therefore, changes in the phosphate content did not affect the composition and quantity prevailing microbial population, although specific phylotypes could not be unambiguously associated with EBPR.