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

Escalating research is currently focused on the ecological safety and health risks associated with the dissemination of antibiotic resistance genes (ARGs) in the environment. The wetland ecosystems possess significant ecological, social, and economic values as a crucial ecological barrier that effectively separates anthropogenic activities from the natural environment. The propagation of ARGs whithin wetland ecosystems poses a significantly threat to both ecosystem integrity and human well-being, thus garnering increasing attention. In this study, we conducted an analysis of the distribution characteristics of ARGs and their influencing factors in representative coastal wetlands (Caofeidian and Nandagang) as well as inland freshwater wetlands (Baiyangdian Lake and Hengshui Lake) located in Hebei Province, utilizing quantitative PCR and high-throughput sequencing techniques. The presence and abundance of ten ARGs, including two sulfonamide resistance genes (sul1 and sulII), eight tetracycline resistance genes (tetA, tetC, tetG, tetL, tetM, tetQ, tetW, tetX), as well as one integrase gene (intI1) were detected and quantified in wetland sediments. The total absolute abundance of ARGs in Nandagang sediments (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) sediments (P<0.05). The absolute abundance of tetracycline resistance genes ranged from 8.91 ×10³ (tetM) to 8.42 ×10⁷ (tetX) copies∙g⁻¹ dry soil, while the absolute abundance of sulfonamide resistance genes ranged from 9.63 ×10⁵ (sul2) to 2.62 ×10⁷ (sul1) copies∙g⁻¹ dry soil. Notably, the distribution of ARGs in sediments varied even in 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 and the tetA, tetL, sul1 and sul2 genes (P<0.05). These findings suggested that intI1 gene may play a crucial role in facilitating the dissemination of sediment ARGs. In addition, high-throughput sequencing results revealed that Proteobacteriota, Chloroflexi, Bacteroidota, Actinobacteriota, Acidobacteriota, Firmicutes, Desulfobacterota, Gemmatimonadota, Planctomycetota, Verrucomicrobiota, Nitrospirota, Myxococcota were the predominant bacterial phyla in the sediment samples. These phyla collectively accounted for 89.57% (NDG1)~96.05% (CFD1) of the total sediment bacterial community composition in the sediments. Lower relative abundances of Proteobacteriota and Firmicutes were observed in coastal wetlands compared to freshwater wetlands (P<0.05), while Planctomycetota exhibited an opposite trend. The Shannon and Simpson indices indicated significantly higher Alpha diversity of sediment bacteria communities in Caofeidian and Nandagang compared to Hengshui Lake. However, NMDS analysis showed no significant differences in Beta diversity among Caofeidian, Nandagang, Baiyangdian Lake, and Hengshui Lake sediments (P>0.05). Variation partitioning analysis demonstrated that sediment physicochemical properties and bacterial community explained a total of 60.78% of ARGs distribution variance, with bacterial community accounting for 37.42%, indicating its dominant role as a driving factor. The distribution of bacterial community was also significantly influenced by sediment physicochemical properties including SOM, TN, and TP. The findings of our study offer valuable data and scientific insights for the assessment of ARG pollution in typical wetland sediments, as well as for the preservation of wetland ecosystem security.