Compositional alterations in soil bacterial communities exposed to TiO2 nanoparticles are not reflected in functional impacts

Titanium dioxide nanoparticles (TiO2NP) are increasingly released in soil ecosystems, while there is limited understanding of the impacts of TiO2NP on soil bacterial communities. Here we investigated the effects of TiO2NP on the taxonomic composition and functional profile of a soil bacterial community over a 60-day exposure period. In short-term exposure (1-day), contradictory effects on the taxonomic composition of soil bacterial communities were found after exposure to a low realistic environmental concentration of TiO2NP at 1 mg/kg as compared to the effects induced by medium and high concentrations of TiO2NP at 500 and 2000 mg/kg. After long-term exposure (60-day), the negative effects of TiO2NP at the low concentration disappeared, and the inhibition by TiO2NP of the abundance of core taxa was enhanced along with increasing exposure concentrations. However, although significant alterations were observed in the taxonomic composition over time and exposure concentrations, no significant change was observed in the community functional profile as well as enzyme activity after 60-day exposure, indicating that functional redundancy likely contributed to the bacterial community tolerance after the exposure to TiO2NP. Our study highlighted the importance of assessing bacterial community compositional and functional responses in assessing the environmental risk of nanoparticles on soil ecosystems.