High-throughput absolute quantification sequencing reveals the adaptive succession and assembly pattern of plastisphere communities in municipal sewer systems: Influence of environmental factors and microplastic polymer types

Municipal sewer systems have received increasing attention due to the magnitude of the microplastic stock and its potential ecological impacts. However, as a critical aspect of the adverse impacts, little is known about the plastisphere that forms in these engineered environments. Using high-throughput absolute quantification sequencing, we conducted a systemic study combining field survey and laboratory batch test to explain the general plastisphere pattern and the role of environmental and polymeric factors in driving plastisphere succession and assembly there. We demonstrated the capacity of microplastics to support high levels of microbial colonization, increasing by 8.7-56.0 and 1.26-5.62 times at field and laboratory scales, respectively, despite the less diverse communities hosted in the resulting plastisphere. Sediment communities exhibited higher diversity but greater loss of specific operational taxonomic units in their plastisphere than in the wastewater. The former plastisphere had primarily an enhanced methanogenesis-oriented metabolic network linked to hydrolysis fermentation, hydrogen-producing acetogenesis, and denitrification, while the latter had a pronounced niche partitioning and competitive interaction network. Exogenous substrate flux and composition were key in stimulating plastisphere community growth and succession. Furthermore, the high nitrogen baseline facilitated alternative niche formation for plastisphere nitrifiers and denitrifiers, and the plastisphere pathogens associated with denitrification and plastic biodegradation functions increased significantly. The aerobic state also promoted a 1.71 times higher colonizer load and a denser interaction pattern than the anaerobic state. Selective filtering by polymers was evident: polyethylene supported higher plastisphere diversity than polypropylene. This study provides new insights into the mechanisms driving colonizer loads and the adaptive succession and assembly of the plastisphere in such a typically hydrodynamic and highly contaminated environment. The results help to fill the knowledge gap in understanding the potential role of microplastics in shaping the microecology of sewers and increasing health risks and substrate loss during sewer transfer.