Overlooked role of extracellular polymeric substances in antibiotic-resistance gene transfer within microalgae-bacteria system

Controlling the spread of antibiotic-resistance genes (ARGs) under antibiotic stress has become an increasingly urgent issue. Microalgae possess the capability to remove antibiotics while concurrently inhibiting ARGs. Microalgae-bacteria systems can produce significant quantities of extracellular polymeric substances (EPS). However, the roles of EPS in the spread of ARGs have not been sufficiently explored, resulting in an insufficient understanding of the contribution of each EPS component and a lack of analysis on the complex interactions between EPS and ARGs. This study systematically explored the overlooked role of EPS in the transmission of ARGs within microalgae-bacteria systems. The current results showed that the potential of the microalgae-bacteria system for treating antibiotic wastewater. The tightly bound-EPS (TB-EPS) can acquire the higher absolute abundances of ARGs compared with the loosely bound-EPS (LB-EPS). The correlation coefficient between polysaccharides and TB-EPS ARGs was higher than that between polysaccharides and LB-EPS ARGs. The gene patterns of LB-EPS closely clustered with those of TB-EPS, while intracellular ARG gene patterns differed from both TB-EPS and LB-EPS. Metagenomic analyses indicated that the relative abundances of sul1 and sul2 were considerably higher at the beginning stage compared to the end stage. The abundance of Achromobacter, increased by the end stage, aligning with its potential to produce exopolysaccharide. Additionally, the absolute abundance of genes encoding exopolysaccharides (nagB and galE) and conjugative transfer transcription regulator (traF), increased over time. These findings enhanced our comprehension of the significance of EPS on the fate of ARGs in microalgae-bacteria systems during the treatment of antibiotic-contaminated wastewater.