Morphological responses of Legionella pneumophila biofilm to nanoparticle exposure

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

Acknowledgements

We would like to thank Luke Bury and Marie Capelle for their assistance in planktonic viability assays; Aaron Edgington, Dr JoAn Hudson, Donald Mulwee, and Dayton Cash for their expertise in TEM/SEM imaging at the Clemson University Electron Microscopy Lab; Dr Catherine Murphy's lab, specifically Stefano Boulos, Department of Chemistry, University of Illinois for the gold nanoparticle synthesis; the Jordan Hall Imaging Facility, Clemson University for use of confocal microscopy, and Clemson University for funding and support.

Declaration of interest : This research has been partially supported by grants R833886 and R834092 from the U.S. Environmental Protection Agency's Science to Achieve Results (STAR) program. The authors report no conflict of interest. The authors alone are responsible for the content and writing of the paper.