Distribution patterns and influencing factors of antibiotic resistance genes in sediments from representative wetlands in Hebei Province

Increasing research is currently focused on the ecological safety and health risks associated with the dissemination of antibiotic resistance genes (ARGs) in the environment. Wetland ecosystems possess significant ecological, social, and economic value as crucial ecological barriers that effectively separate anthropogenic activities from the natural environment. The propagation of ARGs in wetland ecosystems poses a significant threat to both ecosystem integrity and human well-being, and has thus garnered increasing attention. In this study, we analyzed the distribution characteristics of ARGs and their influencing factors in representative coastal wetlands (Caofeidian and Nandagang) as well as inland freshwater wetlands (Baiyangdian and Hengshui lakes) located in Hebei Province using quantitative PCR and high-throughput sequencing techniques. The presence and abundance of ten ARGs, including two sulphonamide resistance genes (sul1 and sul2), eight tetracycline resistance genes (tetA, tetC, tetG, tetL, tetM, tetQ, tetW, and tetX), and one integrase gene (intI1), were detected and quantified in wetland sediments. The average total absolute abundance of ARGs detected in sediments in Nandagang 4.14×10⁸ copies∙g⁻¹ (dry soil) was significantly higher than that in Caofeidian 1.21×10⁸ copies·g⁻¹ (dry soil), Baiyangdian Lake 1.11×10⁸ copies·g⁻¹ (dry soil) and Hengshui Lake 1.97×10⁸ copies·g⁻¹ (dry soil) (not including sampling site 1 in Hengshui Lake) (P<0.05). The absolute abundance of tetracycline resistance genes ranged from 8.91 ×10³ to 8.42 ×10⁷ copies∙g⁻¹ (dry soil), while the absolute abundance of sulfonamide resistance genes ranged from 9.63 ×10⁵ to 2.62 ×10⁷ copies∙g⁻¹ (dry soil). Notably, the distribution of ARGs in sediments varied even within the same lake. The absolute abundance of intI1 gene ranged from 3.26×10⁵ to 1.11×10⁸ copies·g⁻¹ (dry soil), and a significant positive correlation was observed between the intI1 gene with tetA, tetL, sul1 and sul2 genes (P<0.05 or P<0.01 or P<0.001). These findings suggest that intI1 plays a crucial role in facilitating the dissemination of sediment ARGs. In addition, high-throughput sequencing revealed that Proteobacteria, Chloroflexi, Bacteroidota, Actinobacteriota, Acidobacteriota, Firmicutes, Desulfobacterota, Gemmatimonadota, Planctomycetota, Verrucomicrobiota, Nitrospirota, and Myxococcota were the predominant bacterial phyla in the sediment samples. These phyla collectively accounted for 89.57%~96.05% of the total sediment bacterial community composition. Lower relative abundances of Proteobacteria and Firmicutes were observed in the coastal wetlands than that in the inland freshwater wetlands (P<0.05), whereas Planctomycetota exhibited the opposite trend. The Shannon and Simpson indices indicated a significantly higher alpha diversity of sediment bacterial communities in Caofeidian and Nandagang compared to Hengshui Lake. However, the NMDS analysis showed no significant differences in beta diversity among the Caofeidian, Nandagang, Baiyangdian Lake and Hengshui Lake sediments (Anosim: P>0.05). Variance partitioning analysis demonstrated that sediment physicochemical properties and bacterial community explained 60.78% of the ARGs distribution variance, with the bacterial community accounting for 37.42%, indicating its dominant role as a driving factor. The distribution of the bacterial community was also significantly influenced by the sediment physicochemical properties, including SOM, TN, and TP. The findings of our study offer valuable data and scientific insights for the assessment of ARGs pollution in typical wetland sediments as well as for the preservation of wetland ecosystem security.