Metagenomics-based interpretation of the impacts of silica nanoparticles exposure on phenol treatment performance in sequencing batch reactor system

Abstract The specific objective of this study was to investigate the effects of long-term exposure to silica nanoparticles (SiNP) on sequencing batch reactors (SBRs). The results showed that exposure to 400–600 mg/L SiNP induced an increase of phenol degradation rate (86.29%–100%), which was consistent with the enhancement of enzymatic activities. Meanwhile, protein (PN) and polysaccharide (PS) content in extracellular polymeric substances (EPS) exhibited a notably decreased trend within this range of SiNP. However, reactors presented an entirely opposite result when facing higher SiNP concentration (800–1000 mg/L). Moreover, oxidative stress occurred when exceeding 600 mg/L, accompanied by the increased intracellular reactive oxygen species (ROS) and lactic dehydrogenase (LDH). 2D-FTIR-COS of EPS indicated that C = O associated with PN changed the most significant in the presence of SiNP suggesting that PN might be the main components responsible for binding SiNP to reduce its toxicity to microorganisms. Metagenomic analysis demonstrated that genes responsible for phenol metabolism in SBR up- and downregulated when exposed to 400–600 mg/L and 800–1000 mg/L SiNP, respectively, which accounted for the changes of phenol degradation rate from the perspective of gene regulation. PN and PS biosynthesis genes down- and upregulated at 400–600 mg/L and 800–1000 mg/L SiNP, respectively, which might be attributed to the changes of the percentage of PN and PS biosynthesis in each relevant genus, as well as the contribution of oxidative stress-resistant bacteria at high SiNP concentrations. This approach will prove useful in expanding our understanding of potential applications and environmental risks of SiNP on wastewater treatment processes.