The Research On The Diversity Of Bacterial Communities And Antibiotic Resistance Genes In Different Media From The Ganjiang River At The Watershed Level

This paper took the entire Ganjiang River basin as the research area,and the emerging water pollutant-microplastics as the main research object.The pollution characteristics of microplastics in the Ganjiang River basin were determined through comprehensive research methods such as sampling investigation,experimental testing,and data analysis.From a qualitative and quantitative point of view,the adsorption characteristics and behaviors of microplastics and other environmental media(surface water,sediments and woods)on microorganisms,antibiotic resistance genes(ARGs)and human pathogenic bacteria(HPB)were comprehensively compared with a scientific and systematic method.The main results of this paper were as follows:(1)The Ganjiang River was found to be polluted with microplastics at the whole watershed level.Microplastics in the surface water of the Ganjiang River was in the range 160-720 particles m^-3with an average value of 407 particles m^-3,which was at a relatively low pollution level.Particles,fibers,films and fragments(69.6%)were the main forms of microplastics in the surface water of the Ganjiang River.In addition,color and miniaturization were also the primary morphological characteristics of the tested microplastics.The main compositions of microplastics were polyethylene(PE)and polypropylene(PP),accounting for 40.0%and 52.5%,respectively.It showed that the water quality of the Ganjiang River was at a relatively good level with the results of p H,NH₃-N,TP,heavy metals(Cr,Pb,Cd,Cu,Zn,and Hg).The result of pearson correlation analysis showed that there was a significant correlation between microplastics and total organic carbon(TOC)(r=0.75,P?0.01).(2)The diversity of bacterial communities in the sediments of the Ganjiang River was the highest,and significantly higher than that on microplastics,surface water and woods(based on the Alpha diversity index,P<0.01).In addition,the diversity of bacterial communities on microplastics was the second highest,and significantly higher than that in surface water(based on the chao1 index and the number of observed species,P<0.05).The structure of bacterial community on microplastics was similar to that on woods,and it was confirmed that the change of environmental media had a higher impact on the bacterial community structure than the difference of sampling points.Compared with surface water,sediments and woods,microflora on microplastics had high aromatic compounds degradation and photoautotrophic function.Its unique composition and function indicated that microplastics biofilm provided a new microbial niche.(3)In the Ganjiang River,the total of 73 HPB were identified in the four environmental media,including 58,60,61,and 55 on microplastics,woods,water,and sediments,respectively.There were 46 species of HPB shared by the four types of environmental media,and the number of unique HPB to microplastics,woods,surface water,and sediments were 2,1,6,and 3,respectively.The statistical results showed that the number of HPB did not have significant differences in different environmental media(T-test,P>0.05),and there was also no significant feature in the spatial distribution(one-way analysis of variance,?=0.05).Principal component analysis(PCA)showed that microplastics had a significantly different profile of HPB compared with surface water,but were partly similar to sediments and woods.The relative abundance of HPB on woods was the highest,followed by microplastics.Aeromonas hydrophila was the most abundant pathogenic bacteria colonizing on microplastics,woods and sediments.However,the most abundant in surface water was Streptococcus mitis.The results of turkey test showed that Pseudomonas protegens and Pseudomonas stutzeri were significantly enriched on microplastics compared with surface water and sediments.The results of the one-way analysis of variance(One way ANOVA,?=0.05)showed that there was no significant difference for the distribution of the top 10 HPB in the upper,middle and lower reaches of the Ganjiang River.(4)In various environmental media,sulfa ARGs sul1 and sul2 were dominant genes,accounting for 55%-77%of the total ARGs.Among the 10 resistance genes studied,the relative abundance of only 2 ARGs showed significant differences in different environmental media.The relative abundance of tet B in surface water was significantly higher than that on microplastics and woods,besides,the relative abundance of erm B on woods was significantly lower than that in surface water and sediments.Correlation analysis showed that there was a significant positive correlation between relative abundance of Int I1 and total ARGs on microplastics(r=0.97),woods(r=0.82),surface water(r=0.82)and sediments(r=0.73),indicating that the mobile genetic element Int I1 played an important role in horizontal transfer of ARGs in Ganjiang River basin.(5)The network of antibiotic resistance genes,mobile genetic elements,and human pathogenic bacteria in different environmental media from the Ganjiang River was visualized by Gephi software based on the strong spearman correlation(r>0.70,P<0.05).It could be found that in all the four media,int I1 was positively correlated with the sul1 and sul2,indicating int I1 played a vital role in the horizontal transfer of sulfonamide antibiotic resistance genes among different media.On microplastics,only Streptococcus mitis was found to be the potential host of erm F and erm B.On woods,Pseudomonas protegens was found to be the potential host of sul2 and qnr S.Pseudomonas fluorescens was found to be a potential host of tet A and qnr S.qnr S was also found to be positively correlated with Acinetobacter oleivorans.In surface water,Bordetella avium,and Bordetella paraertussis were positively correlated with the erm B and sul2,respectively.In sediments,Bacteroides vulgatus had a strong positive correlation with sul1.