Effects Of Refractory Microplastics On Bacterial Community Succession In Marine Sediment

With the excessive use of plastics,a large amount of plastic is discarded and part of it enters the air and soil.Most of the plastic particles enter the ocean under the action of wind,etc.Under the action of wind and ultraviolet light,microplastics(MPs)are generated and enter the sediment,affecting the composition of microbial community and the process of nitrogen cycle.By using the enrichment culture system,the experiment added three different types of microplastics,namely Low density polyethylene,Polyethylene terephthalate and polypropylene.After 180 days of enrichment culture,combined with 16S rRNA gene amplicon sequencing technology,the effects of plastic addition on the plankton bacterial community and the rule of plastic surface colonization were investigated.Culturable analysis was performed on the samples at the late enrichment stage,and the surface of microplastics was characterized by infrared spectroscopy and scanning electron microscopy to screen potential degradation strains and perform comparative genome analysis.The main results are as follows:(1)The addition of microplastics affected the uniformity of bacterial community in sediments,and had a certain effect on the function of bacterial community in the early enrichment stage.The prediction results of community structure,species composition and function showed that the community had obvious succession rule,but the community reached a relatively stable state in the middle and late enrichment,indicating that the influence of microplastics on the sediment bacterial community may be the result of short-term action.(2)The bacterial community attached to the surface of microplastics had obvious differences,such as bacterial community richness,community structure,species abundance and network properties.At the family classification level,the relative abundance of Pseudomonadaceae was high on PET and LDPE.The surface attached bacteria were significantly different from the surrounding water environment,which was reflected in the differences in species composition and diversity,and the functional prediction results showed that the bacterial community colonized on the surface of microplastics was the potential source of plastic-degrading strains.(3)The number of culturable strains in the 180-day enrichment solution was significantly higher than that on the plastic surface.Obvious degradation occurred on the LDPE surface,and more bacteria related to degradation came from the surface attached groups of microplastics.Potential LDPE degrading strains were obtained by genome annotation of two of them.Genome analysis was performed on the two Bacilus strains screened,KEGG Ortholog database,CAZyme database and antiSMASH database 6.1.16 annotated genes and metabolic pathways related to plastic degradation,which may have potential plastic degradation ability.These results are important for understanding the environmental behavior and ecological effects of microplastics as well as the interactions between microorganisms and microplastics.Further studies can explore the metabolic function and ecological effects of microorganisms attached to the surface of microplastics,and provide scientific basis for environmental management and treatment of microplastics.