Phycosphere as a hotspot of antibiotic resistomes in aquatic environments

Algal-bacterial interactions represent fundamental ecological processes in aquatic environments, crucially governing nutrient cycling and energy flow within food webs. Beyond their ecological roles, the algal phycosphere has recently been identified as a critical hotspot for the proliferation and enrichment of antibiotic resistance genes (ARGs). It's reported that the total abundance of ARGs in the phycosphere of microalgae is up to 47-fold higher than in the surrounding water. However, a systematic understanding of how the phycosphere drives ARG dynamics in aquatic ecosystems remains limited. This review synthesizes current evidence to evaluate the mechanisms by which algae influence ARG proliferation within aquatic ecosystems. Findings indicate that in the phycosphere, algal-bacterial interactions shape ARG fate by modulating bacterial community composition. The symbiotic bacteria are specifically enriched in the phycosphere and play important roles in the proliferation of ARGs. Furthermore, exogenous factors (e.g., nutrients, antibiotics, microplastics, and warming) alter these interactions, thereby changing the phycospheric bacterial community and further affecting ARG evolution. Algal blooms typically enhance the dominance of key ARG hosts, promoting aquatic ARG proliferation. The review concludes by outlining research priorities essential for advancing mechanistic insights into algal-associated ARG dynamics.