Polyhydroxybutyrate (PHB) production directly by waste activated sludge (WAS) was investigated in aerobic fed-batch conditions using acetic acid as substrate. PHB production was induced by phosphorus limitation. WAS of different origin were tested with various degrees of phosphorus limitation and PHB contents of up to 70% (gCOD(PHB)/gCOD(particulate)) were obtained. This strategy showed the importance of maintaining cell growth for PHB production in order to increase PHB concentration and that the degree of phosphorus limitation has a direct impact on the quantity of PHB produced. Pyrosequencing of 165 rRNA transcripts showed changes in the active bacteria of the WAS microbial community as well as the acclimation of populations depending on sludge origin. The monitoring of the process appeared as the key factor for optimal PHB production by WAS. Different strategies are discussed and compared in terms of carbon yield and PHB content with the feast and famine selection process. (C) 2013 Elsevier Ltd. All rights reserved.