Organic loading rate disturbances were introduced into a mesophilic anaerobic digester treating food waste to induce stable and deteriorative phases,respectively.The microbial community of each phase was investigated using pyrosequencing.Results show that the relative abundance of acid-producing bacteria and syntrophic volatile fatty acid oxidizers increased dramatically at deteriorative phase,while the dominant methanogens did not shift from acetoclastic to hydrogenotrophic groups.The mismatching between bacteria and methanogens may partially be responsible for the process deterioration.