Scientists have discovered that cyanobacteria, microscopic organisms best known for driving harmful algal blooms, may play a major role in spreading antibiotic resistance genes in coastal environments. The findings highlight a previously overlooked link between natural nutrient cycling and the global challenge of antibiotic resistance.
Antibiotic resistance genes enable bacteria to survive exposure to antibiotics, posing serious risks to public health, agriculture, and ecosystem stability. While these genes are widely detected in aquatic environments, their biological drivers and ecological roles have remained poorly understood.
In a new study examining biofilms, sediments, and water samples from the Yangtze River estuary, researchers found that cyanobacteria serve as dominant hosts for antibiotic resistance genes. The team combined advanced metagenomic sequencing with DNA-based stable isotope probing to trace how microbial metabolism influences the distribution of resistance genes across different environmental compartments.
The researchers discovered that biofilms, thin microbial layers that grow on submerged surfaces, contained far higher concentrations of antibiotic resistance genes than surrounding water or sediment. Within these biofilms, cyanobacteria accounted for approximately 39 percent of the identified resistance genes, making them the primary carriers.
"Our results show that cyanobacteria are not just participants in nutrient cycling but also important reservoirs of antibiotic resistance genes," said the study's corresponding author. "This dual role reveals an unexpected ecological connection between natural biogeochemical processes and antibiotic resistance."
The study also uncovered strong connections between microbial carbon and nitrogen cycling and the presence of resistance genes. The researchers found that genes associated with carbon fixation, particularly the Calvin cycle, and nitrogen fixation were strongly correlated with antibiotic resistance gene abundance. Nitrogen fixation alone explained more than half of the variation in resistance gene distribution across samples.
To confirm these relationships, the scientists used isotope labeling techniques to track how microorganisms involved in carbon and nitrogen fixation incorporate nutrients. The experiments demonstrated that cyanobacteria actively performing these metabolic processes were also major carriers of resistance genes. Several cyanobacterial genomes were identified as simultaneously involved in nutrient metabolism and antibiotic resistance, further supporting the biological link.
The findings suggest that natural ecological processes, such as nutrient cycling in estuarine biofilms, may unintentionally support the persistence and spread of antibiotic resistance. Estuaries are highly dynamic environments where rivers meet the ocean, often receiving pollutants, nutrients, and antibiotics from human activities. These conditions can stimulate microbial growth and create favorable habitats for resistance gene transfer.
The study also highlights the complex environmental role of cyanobacteria. On one hand, cyanobacteria contribute to carbon sequestration and nitrogen fixation, both essential for ecosystem productivity and global climate regulation. On the other hand, their ability to host and potentially disseminate resistance genes raises new environmental and public health concerns.
The researchers note that nutrient pollution, which promotes cyanobacterial blooms, may amplify the spread of antibiotic resistance in aquatic ecosystems. Monitoring nutrient inputs and microbial community dynamics may therefore be critical for managing resistance risks in coastal regions.
"This work improves our understanding of how environmental microorganisms influence antibiotic resistance in nature," the researchers said. "By identifying key microbial hosts and metabolic pathways, we can better predict how resistance genes spread and develop more effective environmental management strategies."
The authors emphasize that further research using multi-omics approaches and ecological monitoring will be needed to fully understand how microbial metabolism, pollution, and environmental change interact to influence antibiotic resistance globally.
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Journal reference: Guo XP, Tang XF, Sidikjan N, Zhao XY, Wang LL, et al. 2026. Cyanobacteria-mediated carbon-nitrogen coupling promotes the enrichment of antibiotic resistance genes in the Yangtze estuarine biofilms. Environmental and Biogeochemical Processes 2: e004 doi: 10.48130/ebp-0025-0021
https://www.maxapress.com/article/doi/10.48130/ebp-0025-0021
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About the Journal:
Environmental and Biogeochemical Processes (e-ISSN 3070-1708) is a multidisciplinary platform for communicating advances in fundamental and applied research on the interactions and processes involving the cycling of elements and compounds between the biological, geological, and chemical components of the environment.
