Effect and Mechanism of Titanium Nanomaterials on Microbial Community Structure and Function in Sequencing Batch Reactor

A series doses (0–1.0 g/L) of titanium dioxide (TiO2) and titanate nanotubes (TNTs) were added into the sequencing batch reactor (SBR) to investigate the biological effect of titanium nanomaterials. TNTs and TiO2 showed a moderate suppressing effect on SBR performance, while TiO2 seemed to be more toxic. Further, 0.04 g/L TiO2 resulted in significant inhibition on the removal of methylene blue (p < 0.05, n = 30). Illumina high-throughput sequencing revealed that the two titanium nanomaterials changed the composition of the microbial community in SBR, and LEfSe (linear discriminant analysis effect size) and Random forests analyses identified genus Hylemonella as the biomarker with the highest contribution to community response. Metagenomic analysis indicated that the presence of nanomaterials downregulated the community metabolic pathways related to metabolism and led to degradation of xenobiotics and pollutants, agreeing with the decrease of treatment performance of SBR. The exposure test with pure Escherichia coli and isolated Pseudomonas taiwanensis demonstrated the nanotoxic mechanisms of TiO2 and TNTs in interaction with the microbial cell surface and elevation of the cellular reactive oxygen species (ROS) level. These nanotoxic effects could also be due to the enhanced community functions, such as membrane-associated proteins, respiratory chain complexes I/III, NADPH oxidase complexes, and the pathway of endocytosis.