Tilton
Research
Group

Research
Carnegie Mellon University
Department of Chemical Engineering
Department of Biomedical Engineering
Center for Complex Fluids Engineering
Center for Environmental Implications of Nanotechnology
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Environmental Implications of Nanotechnologies: Engineered Nanoparticle Effects on Bacterial Communities

Engineered nanomaterials offer unique physical and chemical properties that promise breakthrough technologies across a spectrum of industries, especially in advanced materials, energy conversion, data storage, medical therapies and medical diagnostics. These unique physical and chemical properties might lead to undesirable impacts on ecosystems in the event that engineered nanoparticles enter the environment.  Because of their fundamental significance in ecological element recycling and food webs, we have begun studies of the interactions between engineered nanoparticles and microbial communities.  Of particular interest are bacterial biofilms, since these are the most abundant form of life on earth. While several types of engineered nanoparticles are proven to be highly toxic to bacteria in planktonic (freely suspended) cultures, bacterial biofilms appear to be significantly less vulnerable to some of these nanoparticles.  For example, we have found nanoscale zero valent iron (NZVI) to have no overall biocidal effect on the total abundance of bacteria in microcosms prepared from contaminated aquifer solids where these nanoparticles would be deployed, although NZVI does alter the relevant species abundance in favor of sulfate reducers and methanogens. See Kirschling et al. “Impact of nanoscale zero valent iron on geochemistry and microbial populations in trichloroethylene contaminated aquifer materials,” Environmental Science and Technology 44, 3474–3480 (2010).

  NZVI gradient gel electrophoresis

In addition to these NZVI studies, which were motivated by our related work on NZVI engineering for in situ groundwater remediation, we have also investigated impacts of silver nanoparticles (AgNPs) on laboratory grown Pseudomonas fluorescens biofilms. AgNPs are commonly deployed in consumer products because of their broad-spectrum antimicrobial effects and could therefore be suspected as a problematic emerging pollutant. AgNPs are highly lethal to planktonic P. fluorescens suspensions, causing six orders of magnitude reduction in colony forming units at AgNP concentrations of 100 ppm, but they have far less effect on viability in P. fluorescens biofilms. When established biofilms are exposed to 100 ppm AgNP suspensions, they retain approximately 10% of their viability – though this is a significant loss of viability, the biofilm growth mode clearly provides a very strong protective effect compared to planktonic culture.  Most of the toxicity is due to dissolved silver ions, and this can be greatly attenuated by the presence of natural organic matter at environmentally relevant concentrations.  See Wirth et al. “Natural organic matter alters biofilm tolerance to silver nanoparticles and dissolved silver,” Environmental Science and Technology 46, 12687-12696 (2012).


Left: Denaturing Gradient Gel Electrophoresis of PCR-amplified DNA extracts from aquifer solids show changes in community structure relative to NZVI-free control.



Representative Publications

T.L. Kirschling, K.B. Gregory, E.G. Minkley, Jr, G.V. Lowry, R.D. Tilton, “Impact of nanoscale zero valent iron on geochemistry and microbial populations in trichloroethylene contaminated aquifer materials,” Environmental Science and Technology 44, 3474–3480 (2010). DOI: 10.1021/es903744f

T.L. Kirschling, P.L. Golas, J.M. Unrine, K. Matyjaszewski, K.B. Gregory, G.V. Lowry, R.D. Tilton, “Microbial bioavailability of covalently bound polymer coatings on model engineered nanomaterials,” Environmental Science and Technology  45, 5253-5259 (2011). dx.doi.org/10.1021/es200770z

S. M. Wirth, G.V. Lowry, R.D. Tilton “Natural organic matter alters biofilm tolerance to silver nanoparticles and dissolved silver,” Environmental Science and Technology 46, 12687-12696 (2012). DOI 10.1021/es301521p