Antibiotic resistance genes (ARGs) pose significant threats to public health and ecosystem stability due to their widespread dissemination in natural environments. Phytoplankton, especially bloom-forming algae, have recently been recognized as key players in the proliferation of ARGs in aquatic systems. Furthermore, emerging contaminants-including antibiotics and microplastics enhance the spread of ARGs by altering phytoplankton-bacteria interactions and facilitating horizontal gene transfer. Climate change-induced water warming further amplifies these effects by influencing microbial community dynamics and pollutant behavior. Although laboratory studies have shed light on individual stressors, the combined impact of multiple environmental factors on the evolution and transmission of ARGs within the phycosphere in natural waters remains poorly understood. 

Recently, research teams led by Prof. WU Chenxi and Prof. XU Jun from the Institute of Hydrobiology (IHB) of the Chinese Academy of Sciences, have provided new insights into how multiple environmental stressors regulate the evolution of phytoplankton, phycospheric bacteria, and phycospheric resistome in the Microcystis dominance ecosystem. Their findings underscore the necessity of considering the combined warming-pollutant effects in ARG ecological risk assessment in natural waters, particularly under phytoplankton succession scenarios. The study was published in Journal of Hazardous Materials. 

In this study, the researchers conducted a long-term, large-scale mesocosm experiment to evaluate how warming, antibiotics, and microplastics influence phytoplankton dominance, phycospheric bacteria, and ARG evolution. They found that in the Microcystis dominant ecosystem, a single stressor strengthened Microcystis dominance (up to 82.37 % of total abundance), but only warming significantly enhanced phycospheric bacterial metabolic activity (e.g., quorum sensing and secondary metabolite biosynthesis) and promoted phycospheric ARG proliferation. These enhancements were primarily driven by the increased abundance of Microcystis symbiotic bacteria (e.g., Roseomonas and Methylobacterium) and microcystin-degraders (e.g., Pseudomonas and Sphingomonas). 

The researchers further investigated the combined effects of these stressors on the evolution of ARGs within the phycosphere. Results indicated that while antibiotics or microplastics alone reduced ARG abundance, their combination with warming counteracted this suppression. This reversal underscores the dominant influence of warming in promoting the proliferation of phycospheric ARGs in environments contaminated with antibiotics or microplastics, effectively overriding the inhibitory impact of environmental-level antibiotics and microplastics on aquatic organisms.

This study provides an integrated assessment of phycospheric ARG dynamics under concurrent climate warming and pollution stress from antibiotics and microplastics in a simulated natural aquatic environment. The findings demonstrate that overlooking the synergistic interactions between warming and pollutants may lead to a significant underestimation of environmental ARG risks. These results emphasize the urgent need for comprehensive management strategies for aquatic antimicrobial resistance within the context of global change.

The impacts of multiple stressors on the assembly of phytoplankton and phycospheric resistome in the Microcystis dominance ecosystem (Image by IHB)

(Editor: MA Yun)