Nanotoxicology, December 2011; 5(4): 730–742 Morphological responses of Legionella pneumophila biofilm to nanoparticle exposure AMBER R. STOJAK, TARA RAFTERY, STEPHEN J. KLAINE, & TAMARA L. MCNEALY Department of Biological Sciences, Institute of Environmental Toxicology, Clemson University, Pendleton, South Carolina, USA (Received 18 May 2010; accepted 9 December 2010) Abstract Legionella pneumophila is a pathogenic bacterium that forms biofilms in natural and anthropogenic habitats. This feature not only facilitates colonization but also limits the effectiveness of biocides. L. pneumophila was exposed to three sizes of citrate- capped gold nanospheres in both planktonic and biofilm stages. TEM micrographs indicated that gold nanoparticles (AuNPs) adsorbed to the bacterial cell surface, were absorbed into the cells, aggregated within the cells, and integrated into the extrapolymeric matrix of the biofilm. Both 4 and 18 nm, but not 50 nm AuNPs caused an alteration of biofilm morphology. Treatment with 20 nm polystyrene spheres did not induce these changes suggesting that the response was a result of the gold and not just the presence of the nanosphere. The morphological changes observed in the biofilm suggest that aquatic ecosystems may be affected by nanoparticle exposure. This may compromise ecosystem functions such as nutrient cycling facilitated by natural biofilms. Keywords: Nanoparticles, biofilms, ecotoxicity, microbiology Introduction The rapid evolution of nanotechnology has impacted practically every sector of our society. From drug delivery to cosmetics, from water purification to haz- ardous waste treatment, from car bumpers to tennis racquets, new uses and applications of nanotechnol- ogy emerge daily. Unfortunately, our knowledge of environmental, health, and safety (EHS) implications of nanotechnology has not kept pace with this emer- gence. While a significant increase in EHS research has occurred, our knowledge in this area is still insufficient to support a quantitative ecological risk assessment (Klaine et al. 2008). Further, ecotoxico- logical research on nanomaterials has relied predom- inantly on commonly used aquatic and terrestrial organisms and focused on standard exposure scenar- ios and effects endpoints developed for evaluating the impacts of solutes. One example is the focus on pelagic organisms to assess the toxicity of particles that may not have long residence times in the water column. Benthic organisms might be a more important nanotoxicological research need due to the anticipated longer exposure scenarios. Microbial biofilms cover almost all surfaces in aquatic ecosystems. These biofilms contain a rich diversity of prokaryotic and eukaryotic organisms and play an important role in nutrient cycling. How- ever, most toxicity evaluations with biofilms have focused on controlling their growth in man-made systems such as cooling towers and environmental control systems (e.g., Ricart et al. 2009; Bai et al. 2010). Recently, several studies have quantified the non-target impacts of soluble contaminants on bio- films. Lawrence et al. (2009) quantified the develop- ment of riverine biofilms in the presence of the antimicrobials triclosan and triclocarban. They quan- tified several changes in the exposed community including altered biofilm architecture, changes in species diversity and dominance, and an overall change from a community dominated by autotrophic processes to one dominated by heterotrophic pro- cesses. Tlili et al. (2008) examined the impacts of the herbicide diuron on biofilms during flooding Correspondence: Dr Tamara McNealy, Clemson University, Department of Biological Sciences, 132 Long Hall, Clemson, South Carolina 29634-0314, USA. Tel: +1 864 656 3058. Fax: +1 864 656 0435. E-mail: tmcneal@clemson.edu ISSN 1743-5390 print/ISSN 1743-5404 online Ó 2011 Informa UK, Ltd. DOI: 10.3109/17435390.2010.550696 Nanotoxicology Downloaded from informahealthcare.com by Professor Stephen Klaine on 11/06/11 For personal use only.