The plasticity of indigenous microbial community in a full-scale heavy oil-produced water treatment plant.

•Regulating indigenous microbial community is an effective strategy for treatment of heavy oil-produced water.•Community structures significantly altered with change of dissolved oxygen concentration.•The communities of anaerobic stages play major roles for enhancing the heavy oil-produced water biodegradability.•The communities of aerobic stages may mineralize biological oxygen demand.•The plasticity is the common innate characteristics of microbial communities.