Evidence that nano-Ti[O.sub.2] induces acute cytotoxicity to the agronomically beneficial nitrogen-fixing bacteria Sinorhizobium meliloti.

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From: Canadian Journal of Microbiology(Vol. 68, Issue 1)
Publisher: NRC Research Press
Document Type: Report
Length: 4,014 words
Lexile Measure: 1660L

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Abstract :

When nano-sized titanium dioxide (nano-Ti[O.sub.2]) 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-Ti[O.sub.2] toxicity. Sinorhizobium meliloti was exposed to aqueous dispersions of micrometer-sized Ti[O.sub.2] (micron-Ti[O.sub.2], 44 im) or nanometer-sized Ti[O.sub.2] (nano-Ti[O.sub.2], 21 nm) at nominal concentrations of 0,100, 300, 600, 900, and 1800 mg Ti[O.sub.2]/L. There were fewer viable S. meliloti cells after exposure to nano-Ti[O.sub.2] under dark and UV-A light conditions. Nano-Ti[O.sub.2] was more toxic to S. meliloti with UV-A irradiation (100% mortality at 100 mg Ti[O.sub.2]/L) than under dark conditions (100% mortality at 900 mg Ti[O.sub.2]/L). Micron-Ti[O.sub.2] concentrations less than 300 mg Ti[O.sub.2]/L had no effect on S. meliloti viability under dark or UV-A light conditions. Exposure to 600 mg/L or more of micron-Ti[O.sub.2] under UV-A light could also photo-kill S. meliloti cells (100% mortality). Further studies are needed to ascertain whether nano-Ti[O.sub.2] interferes with the growth of [N.sub.2]-fixing microorganisms in realistic agricultural environments. Key words: Sinorhizobium meliloti, Ti[O.sub.2] nanoparticle, phototoxicity, reactive oxygen species, nitrogen fixation, Medicago truncatula. Lorsque le dioxyde de titane de taille nanometrique (nano-Ti[O.sub.2]) absorbe le rayonnement ultraviolet (UV-A), il produit des derives reactifs de l'oxygene qui peuvent etre toxiques pour les bacteries. Les auteurs ont utilise la souche 1021 de la bacterie fixatrice d'azote Sinorhizobium meliloti, benefique en agronomie, comme microorganisme modele pour detecter la toxicite du nano-Ti[O.sub.2]. S. meliloti a ete expose a des dispersions aqueuses de Ti[O.sub.2] de taille micrometrique (micron-Ti[O.sub.2], 44 im) ou de taille nanometrique (nano-Ti[O.sub.2], 21 nm) a des concentrations nominales de 0,100, 300, 600, 900 et 1800 mg de Ti[O.sub.2]/L. Il y avait moins de S. meliloti viable apres l'exposition au nano-Ti[O.sub.2] dans des conditions d'obscurite et de lumiere UV-A. Le nano-Ti[O.sub.2] etait plus efficace que le Ti[O.sub.2]. Le nano-Ti[O.sub.2] etait plus toxique pour S. meliloti sous irradiation UV-A (100% de mortalite a 100 mg Ti[O.sub.2]/L) que dans des conditions d'obscurite (100 % de mortalite a 900 mg Ti[O.sub.2]/L). Des concentrations de Ti[O.sub.2] inferieures a 300 mg Ti[O.sub.2]/L n'avaient aucun effet sur la viabilite de S. meliloti dans des conditions d'obscurite ou de lumiere UV-A. L'exposition a 600 mg/L ou plus de micron-Ti[O.sub.2] sous lumiere UV-A pouvait egalement detruire les cellules de S. meliloti (100% de mortalite). Des etudes supplementaires sont necessaires pour determiner si le nano-Ti[O.sub.2] interfere avec la croissance des microorganismes fixateurs de [N.sub.2] dans des environnements agricoles realistes. [Traduit par la Redaction] Mots-cles : Sinorhizobium meliloti, nanoparticule de Ti[O.sub.2], phototoxicite, derives reactifs de l'oxygene, fixation d'azote, Medicago truncatula.

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Gale Document Number: GALE|A690284824