Impairment of Biofilm Formation by TiO₂ Photocatalysis through Quorum Quenching

Abstract

The release of nanomaterials into the environment, due to their massive production and application today, has caused ecological and health safety concerns. Semiconductor photocatalysts like TiO 2 exhibit cytotoxicity to bacterial cells when exposed to UV irradiation. However, information about their impacts on individual or group bacterial behaviors is limited. In this work, the biofilm formation of Escherichia coli K12 in the presence of TiO 2 with and without UV irradiation was investigated and biofilm formation was found not to be affected under the sole application of TiO 2 or UV irradiation. However, biofilm development was substantially delayed by TiO 2 under UV irradiation, although no obvious cytotoxicity to cell growth was observed. The reactive oxygen species photogenerated by TiO 2 were found to quench the autoinducer 2 (AI-2) signals secreted by E. coli K12. As a result, the initiation of quorum sensing for biofilm formation activated by AI-2 was restrained. The expressions of two biofilm-formation-related genes, motA and rcsB, were also suppressed. A dose of an AI-2 precursor, 4,5-dihydroxy-2,3-pentanedione, effectively restored the biofilm development. These results show that the photoexcited TiO 2 could suppress biofilm formation through quenching AI-2 signals. This work may facilitate a better understanding about the ecological effects of increasingly released nanomaterials and provide implications for development of antifouling membranes.