Common freshwater bacteria vary in their responses to short-term exposure to nano-TiO₂

Nanostructured titania (nano-TiO₂) is an engineered nanomaterial that can be cytotoxic primarily as a result of its ability to generate reactive oxygen species when illuminated. Production of nano-TiO₂ has increased rapidly over the last decade, leading to concerns about its release into aquatic environments. To address the possible ecological impacts of nano-TiO₂, the authors used high-throughput screening to assess the responses of 4 bacteria representative of genera common in freshwater to short-term exposure (1-2h) in 2 natural aqueous media (stream water and lake water) to 2 widely used TiO₂ products, pigment white 6 (PW6) and P25. Under simulated solar illumination PW6 and P25 reduced the abundance of viable Bacillus subtilis and Aeromonas hydrophila, confirming the cytotoxicity of nano-TiO₂. In contrast, PW6 and P25 stimulated growth of Arthrobacter sp. and Klebsiella sp., which the authors hypothesize was driven by oxidation of organic matter in these natural waters into more labile compounds. This hypothesis is supported by data demonstrating PW6 photo-oxidation of organic matter in stream water, which subsequently supported enhanced bacterial growth. The results indicate that bacterial responses to nano-TiO₂ can be species-specific, suggesting that nano-TiO₂ may alter bacterial community composition and function. Finally, the results indicate that bacterial responses to nano-TiO₂ are influenced by the water matrix, emphasizing the importance of assessing bacterial responses to nanomaterials in natural environmental media.