Microplastics drive nitrification by enriching functional microorganisms in aquaculture pond waters

The plastisphere refers to biofilm formation on the microplastic (MP) surface, but its subsequent functions, especially driving the nitrogen biogeochemical cycle, are rarely studied. Here, MPs were incubated in the pelagic water and benthic water-sediment interface of an aquaculture pond, and the two corresponding microcosms amended with incubated plastisphere were simulated. The results showed decreased ammonia concentrations and increased nitrification rates in microcosms with either pelagic or benthic plastispheres. To uncover the possible mechanisms, the community structure and function of the plastisphere were investigated. As clarified by 16S rRNA, the community diversity of the pelagic plastisphere was significantly higher than that of the corre-sponding hydrosphere. Plastisphere communities, especially those incubated in pelagic water, were separated from the hydrosphere. Moreover, the abundance of Proteobacteria increased while the abundance of Cyano-bacteria decreased in both plastispheres. Metagenome further revealed that the abundance of amoA and anno-tated Nitrososphaeraceae_archaeon and hao and affiliated Nitrosomonas_europaea, which contributed to ammonia oxidation to nitrite, was higher in the benthic plastisphere. Comparing the pelagic plastisphere with the corre-sponding hydrosphere, however, the abundance of nxrA and annotated Nitrobacter hamburgensis and nxrB and the affiliated Nitrospira moscoviensis, which are involved in nitrite oxidation, was more abundant in the plastisphere. These findings suggest that the plastisphere might selectively enrich functional microorganisms and genes in a habitat-dependent manner to promote nitrification in aquaculture ponds.

Automated summary

The study explores the role of the plastisphere, biofilm formation on microplastics, in driving nitrogen biogeochemical cycle in aquaculture ponds. The results show that the presence of plastisphere leads to decreased ammonia concentrations and increased nitrification rates. The community structure and function of the plastisphere play a crucial role in promoting nitrification in a habitat-dependent manner.