Sodium acetate has been most commonly used as the external carbon source to achieve successful performance of full-scale enhanced biological phosphorus removal (EBPR) processes, but its microbial mechanism for the improvement of phosphorus removal performance was still unclear. DNA based stable-isotope probing (DNA-SIP) is able to discriminate the metabolic activity of different microbes for specific substrates, thus it was applied to explore the different effects of sodium acetate on the community structure of Candidatus Accumulibacter (hereafter called Accumulibacter) and Candidatus Competibacter (hereafter called Competibacter) in a modified University of Cape Town (MUCT) process treating the real domestic sewage. Results showed that acetate addition significantly improved the abundance of Accumulibacter and Competibacter in MUCT. Accumulibacter Glade IID exhibited the highest proportion in all clades before and after acetate supplementation but the proportion decreased from 95.4 % on day 23-66.3% on day 95. Contrarily, the proportion of Glade IIF increased from 0.9% to 24%. DNA-SIP incubation found that the ratio of Accumulibacter in the heavy fractions to the total quantities increased faster than that of Competthacter, which successfully revealed the acetate assimilating precedence of Accumulibacter over Competibacter. Besides, the ratios of Accumulibacter Glade IIF in heavy fraction increased by 22.3 %, exhibited a higher metabolic activity than other clades. Adequate acetate accomplied with high temperature possibly promoted the preferential proliferation of Glade IIF, which provided a way to enrich Glade IIF. This is the first study that successfully applied DNA-SIP to discriminate the acetate metabolic activity of Accumulibacter and Competibacter, and Accumulibacter clades.
