As more nanomaterials are used in consumer goods, there is an increased probability that they will end up in the environment and interact with organisms. Therefore, it is important to investigate how these nanoparticles interact with organisms in the environment, such as bacteria. Since nanoparticles often exhibit toxic effects by interacting with the surface of bacteria, the surface structures on bacteria should be considered. One surface structure, lipopolysaccharides (LPS), cover a significant portion of the Gram-negative bacterial surface, making it likely that they will interact with nanoparticles. LPS can be classified as either rough or smooth, with rough LPS having a lipid A and core saccharide region, and smooth LPS having a lipid A, core saccharide, and O-antigen region, which is a polysaccharide extension of the core saccharide region. Using Shewanella oneidensis MR-1, a Gram-negative bacterium exhibiting rough LPS, the binding of polyallylamine hydrochloride-wrapped gold nanoparticles (PAH AuNPs) to the bacterial surface was assessed in S. oneidensis MR-1 that had natural levels of LPS on their surface and compared to LPS-depleted S. oneidensis MR-1 using flow cytometry. The decreased binding observed when LPS was depleted indicates that LPS is a critical mediator of the nanoparticle-bacteria interaction. To explore more generally the role of LPS in mediating NP binding to bacteria, five Gram-negative bacterial species that express different LPS on their surface were chosen; this allows for a systematic look at the role of LPS in binding and ultimately in its role in predicting nanoparticle toxicity to bacteria. Flow cytometry was used to assess the binding of PAH AuNPs to the five bacterial species and the toxicity was investigated by determining the minimum bactericidal concentration of PAH AuNPs to the bacteria. Although flow cytometry results indicated that in general bacterial species with smooth LPS structures had increased nanoparticle binding, the toxicity results did not show the same trend. As a result, the toxicity cannot be predicted simply by the type of LPS structure and there must be more complex biological mechanisms that mask the effect of binding on toxicity.

Exploring the role of lipopolysaccharides in bacterial interactions with nanoparticles

255th National Meeting (2018)

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