Summary Inefficient syntrophic propionate degradation causes severe operating disturbances and reduces biogas productivity in many high‐ammonia anaerobic digesters, but propionate‐degrading microorganisms in these systems remain unknown. Here, we identified candidate ammonia‐tolerant syntrophic propionate‐oxidising bacteria using propionate enrichment at high ammonia levels (0.7–0.8 g NH 3 L −1 ) in continuously‐fed reactors....