| The widespread usage and inefficient disposal of plastic products has put enormous pressure on the environment,and the resulting problem of Microplastics(MPs,plastic particles less than5 mm in diameter)is currently considered as the second largest scientific problem in the field of ecology and environment.Urban surface water environment is affected by human activities and material transport,which is a hotspot area and an important way of migration and transformation of MPs.As an emerging pollutant of global concern,MPs not only adsorbs other pollutants,but also forms biofilms on the surfaces,which are colonized by specific types of microorganisms,forming a unique niche called "plastisphere".Antibiotics resistance genes(ARGs)and metal resistance genes(MRGs)are carried by the microbial communities on the biofilm of MPs,and these pollutants will spread into the environment with MPs.In addition,MPs are closely related to microbial metabolism and widely participate in the biogeochemical cycle of carbon,nitrogen,phosphorus,sulfur and other elements.Therefore,this study took the surface water of Huangpu River and Taihu Lake in the Yangtze River Delta as the research object.All the samples were collected in situ,and MPs were analyzed under a stereomicroscope followed by Micro-Fourier Transform Infrared(FTIR)spectroscopy.The bioinformatics indexes on MPs and in water samples were determined by metagenomic method.The results revealed the composition of microbial communities and the construction mechanism of resistance genes in the "plastisphere",clarified the role of MPs of carrying and spreading resistance genes,elaborated the process of MPs participating in the regulation of microbial carbohydrate metabolism and element cycle,provided scientific reference for understanding the evolution and spread of resistance genes on MPs,and assessed the ecological risk of MPs in aquatic environment.Specific research results are as follows:(1)MPs were 100% detected in 10 sampling sites in Huangpu River,and the abundance ranged from 0.400-3.20 n/L,with an average abundance of(1.78±0.840)n/L.The particle size ranged from 43.5-5765μm,of which small-sized MPs(<500μm)accounted for 40.3%.Fibers were the most common shape of MPs(93.2%),followed by fragments(5.70%),films(0.70%),and spheres(0.40%).Polyethylene terephthalate(PET)was the dominant polymer type,accounting for 62.5% of total.MPs were also 100% detected in 15 sampling sites in Taihu Lake,and the abundance range was 5.60-10.4 n/L,with an average of(7.33±1.70)n/L.The particle size ranged from 23.0-4238μm,and 61.5% of total were small-sized.Fiber was the most common shape(92.9%).PET remained the main contributor,accounting for 53.4% of the total.There was no significant correlation between the abundance of MPs and water quality indexes.The MPs pollution in the Huangpu River was significantly influenced by human activities,and the abundance was significantly higher in densely populated downtown areas than in other areas.The MPs pollution in Taihu Lake was greatly affected by industry,and the abundance of MPs near the electronics industrial park and dyeing and textile factory was significantly higher than other sampling sites.(2)There were significant differences in bacterial community composition between surface water and MPs in Huangpu River.The Chao1 index of MPs and waters were 3967 and 5264 respectively.The nodes and diameter of MPs network(137 and 11,respectively)were significantly smaller than those of water samples(208 and 12,respectively),indicating that the bacterial community composition on MPs was simpler,but the correlation between bacteria was stronger.At phylum level,Proteobacteria was the dominant bacteria on MPs(52.1%)and in water(76.5%),but Bacteroidetes were significantly enriched on MPs,which was related to the structure and habit of the bacteria.According to the results of metagenomics,a total of 19 species of ARGs were detected,and the average relative abundance of ARGs on MPs was 0.06±0.04,which was significantly lower than that in waters(0.170±0.032).The ARG-Multi＿drug accounted for the highest proportion in both matrixes.ARGs of Rifamycin and Vancomycin were selectively enriched on MPs.The random rate of null model and the result of neutral community models indicated that the assembly of ARG profile on MPs was mainly driven by random processes.Microbial communities and mobile genetic elements(MGEs)played important roles in the formation and dynamic changes of ARG profiles on MPs.Afipia was significantly enriched on MPs,which was a genus of bacteria associated with multiple ARGs.Thus,the surface of MPs can be a unique niche for horizontal gene transfer of some plasmid-mediated ARGs.Besides,a total of 18 MRGs were detected,and the relative abundance of MRGs in waters was 1.68±0.210,in which the MRG-Multi＿metals was the dominant type(32.8%).The relative abundance of MRGs on MPs was 1.63±0.530,and MRG-Hg dominated(45.8%),followed by MRGMulti＿metals(32.3%).and The MRGs subtypes of mer T-P,cop B,zia A,sod A,dme F were significantly enriched on MPs,mainly subtypes of MRGs resistant to mercury,copper and Multi＿metals.Meanwhile,they were significantly positively correlated with Inc FIC(FII),Rep7,rep7,and rep13,which were the subtypes of the MGE of plasmid,so the presence of MPs may have a significant effect on the horizontal gene transfer of specific MRGs mediated by plasmids.(3)The Chao1 index of microbial diversity in surface water and MPs of Taihu Lake was37213 and 8064,respectively,similar to that of Huangpu River.Proteobacteria was the dominant bacteria on MPs(41.6%)and water samples(48.6%),but Bacteroidetes was significantly enriched on MPs(48.9%).According to the results of microbial metabolic pathway analysis,the abundances of metabolic pathways of metabolism of other amino acids,Biosynthesis of other secondary metabolite and glycan biosynthesis and metabolism on the surfaces of MPs were too high.Carbohydrate enzyme analysis showed that the specific glycoside hydrolase was dominant on MPs and in waters,accounting for(43.3±9.83%)and(30.5±1.42%),respectively.Rhamnosidase degradation genes(GH78,GH106),chitosanase degradation genes(GH46),fucosidase degradation(GH1,GH29,GH95),amylosucrase degradation genes(GH13)and multi-pathway related genes were expressed higher on MPs.The presence of MPs in water has significant effects on the metabolism and carbohydrate enzymes of the microbial community.And for the element cycle of nitrogen,phosphorus,and sulfur,the abundances of organic synthesis genes(ans B,ure B)related to nitrogen cycle,two-component system genes(Reg X3,pho B,pho P),oxidative phosphorylation genes(ppk),pentose phosphate pathway genes(gcd)related to phosphorus cycle,assimilatory sulfate reduction genes(cys C,cys H,cys),organic sulfur transformation genes(com B,dms A,isf D,mdh,slc C)and linkages between inorganic and organic sulfur transformation genes(mcc B,met A,suy A,suy B)related to sulfur cycle on MPs were significantly higher than those in waters.Microplastic pollution has a significant effect on element cycling in aquatic environment. |
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