Research On The Temporal And Spatial Changes Of The Biological Community And Quorum Sensing Bacteria In The Microplastic Biofilm Under The Exposed Environment Of The Coastal Waters Of China

Marine microplastics pollution has been a global marine environmental problem.Due to its' small particle size,relatively large specific surface area and stable properties,microplastics are easily attached by marine organisms to form biofilms in seawater.Biofilms not only change the surface property,affecting the vertical migration of microplastics in the ocean,thus affecting the fate of microplastics,but also bring complex ecological significance to the surrounding marine environment.However,the current research on microplastic epiphytic biofilms is still very limited.As a result,two materials of microplastics(PP,PVC)were selected in this study to conduct a one-year exposure experiments in the northern and southern coastal seawater of China.Aiming to fingure out the long-term succession process of microplastic biofilms and the impact of various factors such as sea area,time,plastic materials and environmental factors on the biofilm community structure in the natural marine environment.This research provides support for the study of the behavior and ecological effects of microplastics in the ocean,and provides a scientific basis for migration and management of microplastics pollution.The main conclusion of this study are as follows:(1)This study applied high-throughput sequencing to investigate the successional stages of microbial communities attached to polypropylene and polyvinyl chloride microplastics exposed for one year in the coastal seawater of China.The composition of plastisphere microbial communities varied remarkably across geographical locations and exposure times.The dominant bacteria in the plastisphere were affiliated with the Alphaproteobacteria class,particularly Rhodobacteraceae,followed by the Gammaproteobacteria class.Scanning electron microscopy analysis revealed that the microplastics showed signs of degradation.Microbial communities showed adaptations to plastisphere including more diverse microbial community and greater “xenobiotics biodegradation and metabolism” in metabolic pathway analysis.The findings elucidate the long-term changes in the community composition of microbes that colonize microplastics and expand the understanding of plastisphere microbial communities present in the marine environment.(2)The Miseq high-throughput sequencing was used to analyze and compare the eukaryotic biodiversity and community composition.Overall 1299 OTUs were obtained based on high-throughput sequencing of the V4 region of the 18 S r RNA gene.Eukaryotic species detected in these samples covered 66 phyla,126 classes,196 orders,222 families and 294 genera.The dominant species of eukaryotic communities are phytoplankton,fungi,protozoa,metazoans and vertebrates in the plastisphere.The composition of plastisphere eukaryotic communities varied remarkably across geographical locations and exposure times.Meanwhile,the proportion of eukaryotic organisms with higher evolutionary level increases with the prolongation of exposure time.Different microplastic types showed no selectivity for the attachment of eukaryotes.Mircoplastics have become new habitats for eukaryotic organisms in marine environments.These findings illustrate the biodiversity of eukaryotes assemblages that occur on microplastic and increase our understanding of plastisphere ecology.(3)Based on the research results of the community structure of microplastic epiphytic bacteria,the special population in the biofilm,quorum-sensing bacteria,was focused and isolated,identified and analyzed.Our results demonstrated that detection of AHLs in nine microplastic-associated strains was performed using the biosensor strains Agrobacterium tumefaciens KYC55 for AHLs with long and short acyl chains.The dominant bacteria in AHLs production were affiliated with the Alphaproteobacteria class,particularly Rhodobacterales.RP-TLC and GC-MS analyses revealed that five AHLs,i.e.,C6-HSL,C8-HSL,3-oxo-C6-HSL,3-oxo-C8-HSL and 3-oxo-C10-HSL were produced by microplastic-associated QS bacteria.QS bacteria in biofilms are equipped with many biological function including biofilm formation,antimicrobial activity,algicidal activity and DMSP degradation,some of which are enhanced by AHLs.