In order to determine the conditions for the maximum performance of a fed-batch composting (FBC) reactor, polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) was used to analyze the microbial communities established under the confined conditions of moisture content and environmental temperature. To evaluate the effects of microbial community structures on the performance of FBC reactors, degradation experiments using small-scale reactors and model waste were conducted under confined environmental conditions. A high degradation rate was observed under a wide range of MC conditions (30-60%) and at higher than usual temperatures (30-50 degrees C). The microbial communities that formed in the experimental FBC reactors were analyzed by DGGE of PCR-amplified 16S rRNA genes. The DGGE banding patterns at the same level as the degradation rates were similar even if the environmental conditions were different. Sequence analysis of the DGGE bands revealed the primary microbes which act in the reactor. (c) 2007 Elsevier Ltd. All rights reserved.