The Occurrence And Source Of Antibiotic Resistance Genes In Typical Semi-enclosed Bays

The potential risks to ecotoxicology and threat to public health of antibiotic resistance genes(ARGs)have attracted widespread attention.As a special marine environment with weak water exchange capacity,human activities strongly influence semi-enclosed bays and have been important reservoirs of ARGs.In addition,their significant gradient of environmental conditions and sedimentary characteristics make them become ideal areas to study the occurrence and influencing factors of ARGs.51target ARGs,2 integron genes and 16S r RNA in water and sediments of Jiaozhou Bay and Zhelin Bay were quantitatively detected by high throughput quantitative detection.The occurrence,distribution and source of ARGs in two typical semi-closed bays were analyzed respectively.Furthermore,the influencing factors affecting the distribution of ARGs in the two typical semi-closed bays were analyzed by mathematical statistics.The main results are as follows:(1)A total of 43 target genes were detected in the water bodies of Jiaozhou Bay and21 in sediments;39 target genes were detected in the water of Zhelin Bay and 31 in sediments.Antibiotic inactivation and antibiotic efflux were the main resistance mechanisms of ARGs in the water and sediment of Jiaozhou Bay and Zhelin Bay.Aminoglycoside,β-lactam,macrolide and tetracycline resistant genes were dominant in water and sediment of Jiaozhou Bay,while aminoglycoside,chloramphenicol,macrolide and sulfonamide resistant genes were dominant in water and sediment of Zhelin Bay.The absolute abundance of ARGs in the water of Jiaozhou Bay was in the range of 9.06-4.44×10~4 copies/L,and that in Zhelin Bay was in the range of 2.53-1.21×10~8 copies/L.The absolute abundance of ARGs in sediments of Jiaozhou Bay was in the range of1.17×10~1-2.5×10~3 copies/g,and that in Zhelin Bay was between 6.01×10~2-2.8×10~7copies/g.In total,the absolute abundance of ARGs in water and sediments of Zhelin Bay was higher than that of Jiaozhou Bay.(2)The detection and composition of ARGs in coastal and bay waters of Jiaozhou Bay and Zhelin Bay were consistent,but there were significant spatial distribution variations in the richness and abundance of ARGs between the coastal and bay water in both bays.The ARGs in the sediments and corresponding water samples of Jiaozhou Bay and Zhelin Bay were consistent in terms of detection and composition,and gene migration between the sediments and corresponding water samples was observed in both bays,but there were also significant media distribution variations of ARGs between the water and sediments in the two bays.The richness of ARGs in the water was higher than that of sediments in both Jiaozhou Bay and Zhelin Bay.The abundance of ARGs in the sediments of Jiaozhou Bay was significantly higher than that of the corresponding water samples,while it was opposite was in Zhelin Bay.There were significant regional variations of ARGs in the two typical semi-enclosed bays,no matter for the water or the sediment.In terms of composition,the correlations and core genes among ARGs differed in the two regions.In terms of abundance and richness,the abundance and richness of ARGs in the water and sediments of Zhelin Bay were higher than those in Jiaozhou Bay.The results of principal component analysis-multiple linear regression indicated that ARGs in Jiaozhou Bay mainly originated from river inputs,while those in Zhelin Bay mainly originated from aquaculture activities in the bay.(3)As for the factors influencing the spatial distribution of ARGs,the ARGs in the coastal waters were mainly influenced by anthropogenic activities both in Jiaozhou Bay and Zhelin Bay.The ARGs in the bay water of Jiaozhou Bay were mainly influenced by environmental physicochemical factors,while the ARGs in Zhelin Bay were influenced by multiple environmental factors,and salinity and p H were important environmental factors affecting the spatial distribution of ARGs in Zhelin Bay.In terms of the factors influencing the media distribution variation of ARGs,the different ways of assembly were a vital intrinsic reason for the significant distribution variation of ARGs in the sediments and corresponding water samples in Jiaozhou Bay.However,the assembly of ARGs in Zhelin Bay was not the main reason for the media distribution variation of ARGs.The results of variation partitioning analysis indicated that ARGs in water were mainly influenced by environmental physicochemical factors,while that in sediments were mainly influenced by heavy metals both in Jiaozhou Bay and Zhelin Bay,and such difference was an important external reason for the media distribution variation.The redundancy analysis and aggregated boosted tree model quantified the influence of each environmental factor on ARGs,and the results showed that salinity had the greatest influence on ARGs in water of Jiaozhou Bay and Cu exerted the greatest influence on ARGs in sediments.ARGs in the water of Zhelin Bay was mainly affected by eutrophication,while Zn had the greatest influence on ARGs in the sediments of Zhelin Bay.There were obvious differences in the co-occurrence network models between water and sediments in Jiaozhou Bay and Zhelin Bay,and environmental media had an important influence on the occurrence of ARGs.The partial least squares path modeling proved the way of environmental factors influencing ARGs.The results show that class I integron gene int1 played an important indirect role in the process of environmental factors affecting ARGs in Jiaozhou Bay.