Evidence that nano-TiO2 induces acute cytotoxicity to the agronomically beneficial nitrogen-fixing bacteria Sinorhizobium meliloti

Jieping Wang; Yu Jia; Joann K Whalen; Heather McShane; Brian T Driscoll; Geoffrey I Sunahara

doi:10.1139/cjm-2021-0124

Evidence that nano-TiO₂ induces acute cytotoxicity to the agronomically beneficial nitrogen-fixing bacteria Sinorhizobium meliloti

Can J Microbiol. 2021 Sep 13:1-6. doi: 10.1139/cjm-2021-0124. Online ahead of print.

Authors

Jieping Wang¹, Yu Jia^{1

2}, Joann K Whalen¹, Heather McShane¹, Brian T Driscoll¹, Geoffrey I Sunahara¹

Affiliations

¹ Department of Natural Resource Sciences, McGill University, 21111 Lakeshore Road, Ste-Anne-de-Bellevue, QC H9X 3V9, Canada.
² Harrow Research and Development Centre, Agriculture and Agri-Food Canada, 2585 Essex County Rd 20, Harrow, ON N0R 1G0, Canada.

PMID: 34516930
DOI: 10.1139/cjm-2021-0124

Abstract

When nano-sized titanium dioxide (nano-TiO₂) absorbs ultra-violet (UV-A) radiation, it produces reactive oxygen species that can be toxic to bacteria. We used the agronomically beneficial nitrogen-fixing bacterium Sinorhizobium meliloti strain 1021 as a model microorganism to detect nano-TiO₂ toxicity. Sinorhizobium meliloti was exposed to aqueous dispersions of micrometer-sized TiO₂ (micron-TiO₂, 44 μm) or nanometer-sized TiO₂ (nano-TiO₂, 21 nm) at nominal concentrations of 0, 100, 300, 600, 900, and 1800 mg TiO₂/L. There were fewer viable S. meliloti cells after exposure to nano-TiO₂ under dark and UV-A light conditions. Nano-TiO₂ was more toxic to S. meliloti with UV-A irradiation (100% mortality at 100 mg TiO₂/L) than under dark conditions (100% mortality at 900 mg TiO₂/L). Micron-TiO₂ concentrations less than 300 mg TiO₂/L had no effect on S. meliloti viability under dark or UV-A light conditions. Exposure to 600 mg/L or more of micron-TiO₂ under UV-A light could also photo-kill S. meliloti cells (100% mortality). Further studies are needed to ascertain whether nano-TiO₂ interferes with the growth of N₂-fixing microorganisms in realistic agricultural environments.

Keywords: Medicago truncatula; Sinorhizobium meliloti; TiO2 nanoparticle; dérivés réactifs de l’oxygène; fixation d’azote; nanoparticule de TiO2; nitrogen fixation; phototoxicity; phototoxicité; reactive oxygen species.