On April 17, Associate Professor Liu Xiaohui from the College of Environmental Science and Engineering at Ocean University of China (OUC) published a research article entitled “Urban wetlands as hotspots of antibiotic resistomes and their potential viral transmission” in Nature Cities, a Nature portfolio journal.
Urban wetlands, often referred to as the “sponges” of cities, play an irreplaceable role in flood prevention and disaster mitigation, carbon sequestration, urban cooling, and providing leisure spaces for residents. However, urban wetlands often receive surface runoff, stormwater runoff, and treated tailwater effluent from populous surrounding areas, making them prone to becoming reservoirs of harmful contaminants. Under the “One Health” framework, the occurrence characteristics and health risks of antibiotic resistance genes (ARGs) in urban wetlands, especially whether viruses play a key role in promoting the accumulation and transmission of ARGs, remain unclear.
The research team conducted systematic sampling across 9 representative provinces and municipalities in China, covering 17 urban wetlands. By comparing them with global metagenomic datasets from natural lakes and urban raw sewage, they drew the following major conclusions:
1. Urban wetlands are hotspots for ARGs occurrence. Although the overall water quality of the wetlands studied was relatively good, the average abundances of ARGs were strikingly high: about nine times higher than in natural lakes and comparable to that in raw urban sewage. ARGs associated with high health risks were also significantly enriched.
2. The study reveals the co-occurrence risks of bacterial pathogens and resistance genes. The researchers identified 67 human bacterial pathogens in the wetlands, such as Pseudomonas aeruginosa, Salmonella, and Klebsiella pneumoniae. The abundance of these pathogens was highly positively correlated with the total abundance of ARGs, suggesting a serious risk of co-distribution between antibiotic resistance and pathogenicity.
3. Viruses act as “invisible super-vectors” for the transmission of ARGs. The study found a strong positive correlation between ARGs carried by bacteriophages and the total abundance of ARGs. In particular, analysis of the core host, the Pseudomonasgenus, showed that multiple bacteriophages could cross-infect different Pseudomonas strains and transfer multidrug resistance genes, such as MexB and OprM, between the strains. Because Pseudomonas and its associated bacteriophages have significantly larger genomes than other groups, they have a greater capacity to carry “genetic cargo”, thereby significantly promoting the horizontal transfer and vertical evolution of ARGs.
4. Socioeconomic factors shape the geographic patterns of resistant genes. The study found that the GDP per capita and ARGs abundance are significantly negatively correlated. This suggests that in more economically developed cities, more advanced “Sponge City” development and more effective green stormwater infrastructures may help reduce the risk for runoff-borne ARGs from entering urban wetlands.
This study, for the first time, quantified at the national scale and from the perspective of virus-mediated transfer mechanisms the ecological and health risks posed by urban wetlands as hotspots and dissemination sources of ARGs. It calls for microbial contamination, especially extracellular ARGs, to be incorporated into wetland water quality monitoring systems in future urban planning. It also recommends that effective collection, ecological interception, and treatment measures be adopted before runoff is discharged into wetlands.
