The present study was conducted to evaluate the specific acetate uptake rates of microorganisms with and without polyhydroxyalkanoates (PHA) accumulation. Activated sludge was aerobically incubated with 75 mgC L−1 radiolabeled or non-labeled acetate, and acetate consumption and PHA accumulation were monitored. Microorganisms were quantified as follows: all microbial cells by DAPI staining, whole acetate utilizing organisms by microautoradiography, and PHA-accumulating organisms by staining with Nile blue A. The abundance of acetate-utilizing organisms without PHA accumulation was also calculated from the outcomes. The estimate of acetate utilized by PHAAOs included both the acetate converted to PHA and that used to supply reducing power and ATP. Acetate utilized by PHAAOs and non-PHAAOs were divided by their respective abundances to obtain their respective specific acetate uptake rates: PHAAOs ranged between 5.3 and 8.0 × 10−10 mgC cell−1 h−1, and non-PHAAOs ranged between 2.8 and 4.2 × 10−10 mgC cell−1 h−1.

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