Diversity and potential environmental risks of DNA viruses on international ships' ballast water at Shanghai port, China.

Over 10 billion tons of ballast water is transferred annually globally, transporting many microorganisms such as bacteria and viruses into new environments and harming local ecology, economy and human health. Numerous studies on bacteria in ballast water have shown its remarkable bacterial diversity and potential risks in recent years. However, the diversity of viruses present in ballast water and their potential environmental implications remain extremely limited in our understanding. In this investigation, we utilized viral metagenomic sequencing to evaluate the viral diversity and distribution in ballast water sourced from five distinct shipping routes that docked at Shanghai Port. Additionally, we compared the distribution of antibiotic resistance genes (ARGs) and virulence factors (VFs) harbored by viruses in ballast water from different routes. The viral diversity and community composition exhibited significant differences in the ballast water samples collected along distinct shipping routes. The virus diversity index varies across different routes, and notably, for the Shannon and Pielou indices, the DJ and GG routes were significantly lower than other routes. Although Caudoviricetes was the dominant viral group, the abundances of Megaviricetes and Faserviricetes were also relatively high, albeit showing variations among different routes. 224 ARGs were identified, including 143 single resistance genes (SARGs) and 81 multiple resistance genes (MARGs), and their distribution varied across different shipping routes. Similarly, certain types of VFs also exhibit differences across various routes, including nutritional/metabolic processes, biofilm formation, and exotoxins. Moreover, the comparison of viral environmental risks showed that ballast water from routes through the Indian Ocean and the South China Sea posed a greater environmental risk. In summary, the results of our research have uncovered the virus diversity and potential risks associated with different routes. This underscores the imperative of implementing targeted management strategies for each individual route.