Dispersion of TiO ₂ 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 TiO 2 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 TiO 2 suspensions in the absence of cells, 81% by mass was retained on a 5-m-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 m to 1.9 m because of nano-TiO 2 biosorption. High-magnification scanning electron micrographs showed that P. aeruginosa dispersed TiO 2 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 TiO 2 nanoparticle agglomerates.

Heteroaggregation of nanoparticles with biocolloids and geocolloids

“…Heteroaggregation of NPs with microbial cells such as bacteria and algae is important for fate, transport, transformation, and toxicity of NPs in both aquatic and terrestrial environments [106][107][108][109][110][111][112][113]. Heteroaggregation could occur between a single particle and a cell, or via particle aggregate-cell interactions [114] -with important implications in the natural environment.…”

Analysis of engineered nanomaterials in complex matrices (environment and biota): General considerations and conceptual case studies

“…The aggregation state of nanomaterials in association with cells is, for example, resolved by ESEM but also by cryogenic SEM [41]. Environmental scanning electron microscopy, EDS, and fluorescence microscopy have been used together to resolve CdSe QDs and their integrity, in part from Cd and Se atomic ratios by EDS but also by QD fluorescence [42].…”

“…Cryogenic SEM allows for imaging surface associations of nanoparticles with cells without sample embedding or other damaging preparation [41]. Imaging internal associations is accomplished by creating a random fracture plane using a coarse fracture knife.…”

“…1, pp. [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49]2012 # 2011 SETAC Printed in the USA DOI: 10.1002/etc.723 This paper evolved from discussions held at a SETAC-endorsed Technical Workshop held at Clemson University in August, 2010. The workshop was sponsored by the United States Environmental Protection Agency (U.S. EPA), Arcadis-US, and the Clemson University Institute of Environmental Toxicology.…”

Gravity-driven transport of three engineered nanomaterials in unsaturated soils and their effects on soil pH and nutrient release

“…Sorption can occur via electrostatic attraction between charged clay surfaces and oppositely-charged ENMs (Zhou et al, 2012) or chemically (for metal oxides or metals with an outer oxide layer) through a dehydration reaction similar to the binding of phosphate or iron oxides to clays (Horst et al, 2010;Hofstetter et al, 2003). Sorption to organic matter (Duester et al, 2011) and organisms (Mudunkotuwa and Grassian, 2010) in soil may take place through similar mechanisms.…”