Dynamic responses of community structure and microbial functions of periphytic biofilms during chronic exposure to TiO2 NPs†
The widespread application of TiO2 NPs will lead to their increasing release into the aquatic environment and thus affects the ecosystem function of aquatic life. As a microbial community, responses of periphytic biofilm to toxicity of TiO2 NPs are largely unknown, in particular with respect to dynamic shifts of community structure and microbial functions of periphytic biofilms. Therefore, this study investigated the relationship between microbial functions and community composition of periphytic biofilms after chronic exposure (21 days) to 50 μg L−1 and 500 μg L−1 TiO2 NPs. The increase of DOC in surface water was inhibited during the first 11 days (49.55%) by 500 μg L−1 TiO2 NPs and then recovered. Distinct responses were observed between community structure and microbial functions of biofilms after exposure to TiO2 NPs. Specifically, both 50 μg L−1 and 500 μg L−1 TiO2 NPs promoted the growth of microalgae (78.85–134.86%) and altered the bacterial community composition at day 7, and these trends lasted at day 21. In terms of the microbial functions determined using Biolog™ ECO microplates, biofilms maintained their total carbon metabolic activities under the stress of 50 μg L−1 TiO2 NPs. However, the carbon metabolic activities were significantly inhibited (24.63%) by the exposure to 500 μg L−1 TiO2 NPs at day 7 and then recovered to the control level at day 21. Although inhibition still existed in the metabolic activity for carbohydrate (17.00%) after long-term exposure, periphytic biofilms exhibited resistance to TiO2 NPs and continuous decrease in nanotoxicity was observed.