The microbial communities in activated sludge acclimated with either acetate or glucose as the major carbon source under phosphorus limited or rich conditions were investigated morphologically, phylogenetically and chemotaxonomically. The sludge with a minimized polyphosphate content was dominated by tetrad shaped bacteria, which were suspected to be ‘glycogen accumulating bacteria (GAOs) or G bacteria’ The sludge containing high polyphosphate was dominated by cluster forming coccus bacteria. Quinone analyses suggested that all the sludge tested contained various ubiquinones and menaquinones, of which the ubiquinones Q-8 and Q-10 were dominant. Analyses with rRNA targeted probes showed that beta sub class of Proteobacteria was most predominant in all sludges tested. Morphological, phylogenetic and chemotaxonomic investigation all indicated that both high and low P sludges are microbiologically diverse.

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