Microcystin-LR (MC-LR), produced by cyanobacterial harmful algal blooms, poses a serious threat to aquatic ecosystems and human health. Biodegradation is an important method for MC-LR elimination. Aerobic biodegradation has been extensively studied and many bacteria were identified. However, few MC-degrading bacteria have been isolated from anaerobic environments, and these degradation mechanisms are poorly understood. The aim of this study was to collect anaerobic MC-degrading bacteria from lake sediments in Lake Taihu using acclimation culture to assess biodegradation. Five strains with MC-LR degradation ability were isolated, with strain A4 belonging to