Undisclosed contribution of microbial assemblages selectively enriched by microplastics to the sulfur cycle in the large deep-water reservoir

The accumulation of microplastics in reservoirs due to river damming has drawn considerable attention due to their potential impacts on elemental biogeochemical cycling at the watershed scale. However, the effects of plastisphere communities on the sulfur cycle in the large deep-water reservoir remain poorly understood. Here, we collected microplastics and their surrounding environmental samples in the water and sediment ecosystems of Xiaowan Reservoir and found a significant spatiotemporal pattern of microplastics and sulfur distribution in this Reservoir. Based on the microbial analysis, plastic-degrading taxa (e.g., Ralstonia, Rhodococcus) involved in the sulfur cycle were enriched in the plastisphere of water and sediment, respectively. Typical thiosulfate oxidizing bacteria Limnobacter acted as keystone species in the plastisphere microbial network. Sulfate, oxidation reduction potential and organic matter drove the variations of the plastisphere. Environmental filtration significantly affected the plastisphere communities, and the deterministic process dominated the community assembly. Furthermore, predicted functional profiles related to sulfur cycling, compound degradation and membrane transport were significantly enriched in the plastisphere. Overall, our results suggest microplastics as a new microbial niche exert different effects in water and sediment environments, and provide insights into the potential impacts of the plastisphere on the sulfur biogeochemical cycle in the reservoir ecosystem. Microplastic pollution in freshwater ecosystems is increasing around the world. Considering the accumulation of microplastics in reservoirs due to damming and the importance of sulfur biogeochemical cycling in ecosystems, the effects of the plastisphere on sulfur biogeochemical cycling in reservoirs merit in-depth exploration. This study compares the diversity, environmental drivers, co-occurrence patterns, assembly processes and functions of sulfur-transforming microorganisms between the plastisphere and the surrounding environment. Our findings provide useful information about the effects of microplastics on sulfur cycles in both water and sediment media, which is important for the ecological risk assessment and management of microplastic polluted reservoirs.