Disruption-induced changes in syntrophic propionate and acetate oxidation: flocculation, cell proximity, and microbial activity.

backgroundSyntrophic propionate- and acetate-oxidising bacteria (SPOB and SAOB) play a crucial role in biogas production, particularly under high ammonia conditions that are common in anaerobic degradation of protein-rich waste streams. These bacteria rely on close interactions with hydrogenotrophic methanogens to facilitate interspecies electron transfer and maintain thermodynamic feasibility. However, the impact of mixing-induced disruption of these essential syntrophic interactions in biogas systems remains largely unexplored. This study investigates how magnetic stirring and orbital shaking influence degradation dynamics, microbial community composition, and gene expression in syntrophic enrichment communities under high-ammonia conditions.

resultsStirring significantly delayed the initiation of propionate degradation in one culture and completely inhibited it in the other two parallel cultures, whereas acetate degradation was less affected. Computational fluid dynamics modelling revealed that stirring generated higher shear rates (~ 20 s

conclusionsThis study highlights that stirring critically disrupts the initial syntrophic connection between SPOB and methanogens, whereas SAOB communities exhibit greater tolerance to shear stress and disruptive conditions that inhibits aggregate formation. These findings emphasize the importance of carefully managing mixing regimes, especially when attempting to reactivate ammonia-tolerant syntrophic propionate degraders in biogas systems experiencing rapid propionate accumulation under high-ammonia conditions.