title: Dispersion of TiO₂ nanoparticle agglomerates by Pseudomonas aeruginosa.
abstract: Engineered nanoparticles are increasingly incorporated into consumer products and are emerging as potential environmental contaminants. Upon environmental release, nanoparticles could inhibit bacterial processes, as evidenced by laboratory studies. Less is known regarding bacterial alteration of nanoparticles, including whether bacteria affect physical agglomeration states controlling nanoparticle settling and bioavailability. Here, the effects of an environmental strain of Pseudomonas aeruginosa on TiO₂ nanoparticle agglomerates formed in aqueous media are described. Environmental scanning electron microscopy and cryogenic scanning electron microscopy visually demonstrated bacterial dispersion of large agglomerates formed in cell culture medium and in marsh water. For experiments in cell culture medium, quantitative image analysis verified that the degrees of conversion of large agglomerates into small nanoparticle-cell combinations were similar for 12-h-growth and short-term cell contact experiments. Dispersion in cell growth medium was further characterized by size fractionation: for agglomerated TiO₂ suspensions in the absence of cells, 81% by mass was retained on a 5-μm-pore-size filter, compared to only 24% retained for biotic treatments. Filtrate cell and agglomerate sizes were characterized by dynamic light scattering, revealing that the average bacterial cell size increased from 1.4 μm to 1.9 μm because of nano-TiO₂ biosorption. High-magnification scanning electron micrographs showed that P. aeruginosa dispersed TiO₂ agglomerates by preferential biosorption of nanoparticles onto cell surfaces. These results suggest a novel role for bacteria in the environmental transport of engineered nanoparticles, i.e., growth-independent, bacterially mediated size and mass alterations of TiO₂ nanoparticle agglomerates.
authors.affiliation: Donald Bren School of Environmental Science and Management, 2308 Bren Hall, University of California at Santa Barbara, Santa Barbara, CA 93106-5131, USA. ahorst@umail.ucsb.edu
authors.forename: Allison M
authors.initials: AM
authors.lastname: Horst
authors.forename: Andrea C
authors.initials: AC
authors.lastname: Neal
authors.forename: Randall E
authors.initials: RE
authors.lastname: Mielke
authors.forename: Patrick R
authors.initials: PR
authors.lastname: Sislian
authors.forename: Won Hyuk
authors.initials: WH
authors.lastname: Suh
authors.forename: Lutz
authors.initials: L
authors.lastname: Mädler
authors.forename: Galen D
authors.initials: GD
authors.lastname: Stucky
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Holden
mesh_terms: D002462:Cell Membrane / Q000378:metabolism; D003470:Culture Media; D053768:Metal Nanoparticles / Q000382:microbiology*; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D011550:Pseudomonas aeruginosa / Q000254:growth & development / Q000378:metabolism*; D055672:Static Electricity; D014025:Titanium / Q000378:metabolism*
chemical_list: D003470:Culture Media; C009495:titanium dioxide; D014025:Titanium