Analysis of the Current Situation and Sources of ARG Pollution in the Seawater of Dapeng, Shenzhen

Antibiotics are the cornerstone of modern medicine and aquaculture, but their extensive use has triggered a global antibiotic resistance crisis. Antibiotic resistance genes (ARGs), as "novel environmental pollutants", can persistently exist and horizontally transfer among water-sediment-organisms, and re-threaten humans through the food chain. The ocean is the ultimate sink for land-based ARGs. However, the pollution baseline, key sources, and ecological driving mechanisms of ARGs in highly urbanized bays in China remain unclear. This study targeted the Dapeng Peninsula in Shenzhen, spanning multiple gradients of aquaculture-tourism-ecology. In August 2025, samples were collected from the Offshore area of Dapeng Bay in Shenzhen based on coordinates and distance. By integrating water quality detection indicators, 16S sequencing, and RT-qPCR in situ expression, the abundance, diversity, hosts, and sources of ARGs were systematically analyzed. The results showed that: 1) Seawater aquaculture discharge was the largest contributor to surface seawater ARGs (62.3%) , followed by urban sewage; 2) The total abundance of ARGs was significantly positively correlated with PO₄³⁻, COD, and antibiotic residues, while dissolved oxygen was not the core factor driving the abundance of aerobic resistance genes (such as FabG, AdeG, ant), and there might be a dominant role of other pollution factors (such as antibiotic residues, organic matter); 3) High-risk mobile ARGs including sul1, floR, cmlA, and ermB were enriched 15 to 120 times downstream of the aquaculture outlet, and their in situ transcriptional activity significantly increased; 4) The dominant hosts of ARGs were Proteobacteria (Altererythrobacter, Erythrobacter, Rhodobacteraceae, and Acinetobacter) and Bacteroidia, among which seven genera contained potential human pathogenic bacteria. This study finely resolves the ARG source contributions in Dapeng Bay for the first time and clearly traces the leading role of aquaculture discharge, providing a scientific basis for precise control of antibiotic resistance genes in the coastal zone of the Guangdong-Hong Kong-Macao Greater Bay Area.