An in-vessel composting bioremediation of C-13(4)-4,5,9,10-pyrene and unlabeled pyrene spiked soil amended with fresh wastes was investigated by DNA-based stable isotope probing (SIP) of active bacteria involved. Highest dissipation of C-13(4)-pyrene was detected at 55 degrees C after 42 days composting. The active bacterial communities in the composting changed over time, showing a distinct difference among different stages. alpha-, beta-, gamma-Proteobacteria, and Actinobacteria were detected mainly involving in pyrene degradation at 38 degrees C over 14 days composting. Streptomyces appeared to dominate the pyrene degradation at 55 degrees C. beta- and gamma-Proteobacteria and Actinobacteria were the dominant pyrene degraders at 70 degrees C after 42 days composting and at 38 degrees C after 60 days composting. The results of this study suggest the pyrene degradation was performed by phylogenetically distinct bacterial guilds from the phyla Actinobacteria and Proteobacteria during in-vessel composition processes. (c) 2013 Elsevier Ltd. All rights reserved.