Deciphering the role of extracellular polymeric substances in the regulation of microbial extracellular electron transfer under low concentrations of tetracycline exposure: Insights from transcriptomic analysis

Low concentrations of antibiotics can regulate the formation of electroactive biofilms, however, the underlying mechanisms, especially the composition and spatial distribution of extracellular polymeric substances (EPS) and their effects on extracellular electron transfer (EET) process, have not been fully deciphered. Here, the response of EPS of Geobacter sulfurreducens biofilm to low concentrations of tetracycline (μg L−1 to mg L−1) was explored, and the impact of such EPS variations on EET efficiency was further elucidated by transcriptomic analysis. Results showed that 0.05 mg L−1 of tetracycline achieved both beneficial quantitative and spatial regulation of redox-active proteins and non-conducting exopolysaccharides in EPS, while higher concentrations induced negative effects. Moreover, 1 mg L−1 of tetracycline upregulated multiple exopolysaccharide biosynthesis-related genes, indicating a stress response for cell-protection, while 0.05 mg L−1 of tetracycline upregulated most direct EET-related gene expressions, resulting in the promoted EET efficiency. Furthermore, 0.05 mg L−1 of tetracycline selectively enriched Geobacter (45.55% vs 19.55% in control, respectively) from mixed inoculum. This research provides a new insight of how antibiotics at low concentrations regulated EET process through modulation of EPS.