Experimental evidence for the role of phages in mitigating antibiotic resistance genes in mangrove sediments

The ecological role of bacteriophages (phages) in mitigating or proliferating antibiotic resistance genes (ARGs) in mangroves remains elusive due to the lack of direct experimental validation. Climate change-driven seawater encroachment introduces non-native phages into mangrove ecosystems, yet the potential impacts of this process on ARG spread have not been elucidated. Here, we established flooded microcosms inoculated with phage suspensions derived from native and non-native mangrove sediments, thus simulating phage input disturbance caused by climate change. Our results revealed distinct phage-host interaction patterns: non-native phages exerted short-term disturbances on bacterial communities, but neither phage source altered the bacterial or resistome structure. Nevertheless, phages specifically influenced the composition and dynamics of ARGs, with non-native phages showing stronger regulatory effects. Furthermore, 77 ± 2.1% of viral operational taxonomic units (vOTUs) were lytic, and 154 out of 185 phage-antibiotic-resistant bacteria (ARB) links were lytic, indicating that lytic phages played a dominant role in controlling ARB abundance and promoting ARG mitigation, whereas 0.68 ± 0.46% of host-infecting lysogenic phages carried ARGs, contributing little to ARG proliferation. Moreover, only 3.2 ± 0.56% vOTUs carried ARGs, resulting in negligible phage-mediated transduction for ARG dissemination. This study provides the first direct experimental evidence for the impacts of phages from different sources on the fate of ARGs in mangrove ecosystems, and offers novel insights into the ecological mechanisms underlying the spread of ARGs in the context of global climate change.