title: Tactic response of bacteria to zero-valent iron nanoparticles.
abstract: The microbial assessment of pollutant toxicity rarely includes behavioral responses. In this study, we investigated the tactic response of Pseudomonas putida G7, a representative of soil bacterium, towards engineered zero-valent iron nanoparticles (nZVIs), as a new end-point assessment of toxicity. The study integrated the characterization of size distribution and charge of nZVIs and tactic reaction response by means of inverted capillary assay and computer-assisted motion analysis of motility behavior. Iron nanoparticles (diameter ≤ 100 nm) were prepared in the absence of oxygen to prevent aggregation, and then exposed in aerobic conditions. We first demonstrate that iron nanoparticles can elicit a negative tactic response in bacteria at low but environmentally-relevant, sub-lethal concentrations (1-10 μg/L). Cells were repelled by nZVIs in the concentration gradients created inside the capillaries, and a significant increase in turning events, characteristic of negative taxis, was detected under exposure to nZVIs. These tactic responses were not detectable after sustained exposure of the nanoparticles to oxygen. This new behavioral assessment may be prospected for the design of sensitive bioassays for nanomaterial toxicity.
authors.affiliation: Department of Engineering Science, University of Oxford, Parks Road OX1 3PJ, United Kingdom; Instituto de Recursos Naturales y Agrobiología, C.S.I.C., Apartado 1052, E-41080-Seville, Spain.
authors.forename: José-Julio
authors.initials: JJ
authors.lastname: Ortega-Calvo
authors.affiliation: Instituto de Recursos Naturales y Agrobiología, C.S.I.C., Apartado 1052, E-41080-Seville, Spain.
authors.forename: Celia
authors.initials: C
authors.lastname: Jimenez-Sanchez
authors.affiliation: Instituto de Recursos Naturales y Agrobiología, C.S.I.C., Apartado 1052, E-41080-Seville, Spain.
authors.forename: Paolo
authors.initials: P
authors.lastname: Pratarolo
authors.affiliation: Interface Analysis Centre, University of Bristol, United Kingdom.
authors.forename: Huw
authors.initials: H
authors.lastname: Pullin
authors.affiliation: Interface Analysis Centre, University of Bristol, United Kingdom.
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Scott
authors.affiliation: Department of Engineering Science, University of Oxford, Parks Road OX1 3PJ, United Kingdom. Electronic address: ian.thompson@eng.ox.ac.uk.
authors.forename: Ian P
authors.initials: IP
authors.lastname: Thompson
mesh_terms: D007501:Iron / Q000633:toxicity*; D053768:Metal Nanoparticles / Q000633:toxicity*; D016958:Pseudomonas putida / Q000187:drug effects* / Q000502:physiology*; D012987:Soil / Q000737:chemistry; D012988:Soil Microbiology
chemical_list: D012987:Soil; D007501:Iron
keywords: Iron; Nanomaterial; Taxis; Toxicity