Our new study, now published in the Journal of Hazardous Materials, reveals promising insights into using microalgae to tackle one of agriculture’s most pressing environmental challenges: the spread of antibiotic resistance genes (ARGs) in livestock wastewater.
The Challenge
Nearly 55% of antibiotics used in China are applied in livestock farming, creating a major pathway for antibiotic resistance genes to enter the environment through farm wastewater. These genes pose serious risks to ecosystems and human health, making their removal from wastewater a critical priority. Similar risks are emerging in aquaculture, where high-nutrient effluents containing antibiotic residues and resistance genes threaten surrounding waters, highlighting the need for robust, nature-based treatment solutions across both terrestrial and aquatic production systems.
An Innovative Approach
Our international research team, including collaborators from RISE Research Institutes of Sweden and China’s Agro-Environmental Protection Institute (AEPI) under China´s Ministry of Agriculture and Rural Affairs (MARA), investigated how the microalga Chlorella pyrenoidosa responds to environmental stressors while treating dairy farm wastewater. Specifically, we examined the combined effects of lead stress and gibberellin (a plant hormone) stimulation on microalgal performance, bacterial communities, and ARG removal.
Key Findings
The “lead paradox” emerged clearly: low lead concentrations (1 mg/L) stimulated microalgal growth, while higher concentrations (5 mg/L) inhibited it. Lead stress significantly altered bacterial community structures in the wastewater, notably increasing the abundance of Pseudomonadota and promoting ARG proliferation.
Gibberellin played a protective role by helping microalgae cope with lead stress. It increased chlorophyll content (by 0.384 mg/L), boosted polysaccharide production in both cells and extracellular polymeric substances (EPS), enhanced nitrogen removal efficiency, and, crucially, contributed to mitigating the spread of antibiotic resistance genes.
EPS, the protective matrix surrounding microalgal cells, proved central to ARG distribution patterns. Lead stress had the strongest impact on tightly bound EPS (TB-EPS), driving bacterial redistribution from TB-EPS to more soluble fractions and reshaping the niches where ARGs are hosted and transferred.
A persistent concern was the resistance gene Ecol_fabG_TRC, associated with disinfectants and preservatives, which remained at high abundance under all treatment conditions. Its stability underlines the complexity of fully eliminating specific resistance determinants, even in optimized microalgae-based systems.
Beyond Dairy Farms: Aquaculture Applications
Although this study focused on dairy farm wastewater, the mechanisms observed are directly relevant to aquaculture operations. Fish farms face comparable challenges with antibiotic use and nutrient-rich effluents that can foster resistance development. Microalgae–bacteria treatment systems informed by our results could therefore support both livestock and aquaculture sectors, especially within integrated agri-aquaculture systems. In such settings, treated water and harvested microalgal biomass can help create circular nutrient flows between land and sea, aligning water quality improvements with resource recovery and low-carbon food production.
Environmental Implications
This research demonstrates that microalgae-based wastewater treatment systems can be fine-tuned through strategic use of plant hormones to enhance pollutant removal while controlling ARG dissemination. Future treatment strategies should consider heavy metal concentrations, microalgal species selection, EPS dynamics, and the targeted application of exogenous additives such as gibberellins to balance system resilience with treatment efficiency.
As we work toward more sustainable agricultural and aquaculture practices, understanding the intricate interactions between microalgae, bacterial communities, environmental stressors, and resistance genes provides a strong foundation for advancing effective, nature-based solutions to emerging pollutants.
Read the full open-access study:
Journal of Hazardous Materials
Xu, X., Cao, Y., Zhi, S., Cordeiro, C. M., Sindhöj, E., Phyu, K., Wang, H., Liu, J., Zhang, K., & Zhao, R. (2025). Exploration of extracellular polymeric substances changes and related antibiotic resistance gene migration and transformation patterns in microalgae under lead stress and gibberellin stimulation. Journal of Hazardous Materials, 499, 140275. https://doi.org/10.1016/j.jhazmat.2025.140275