Mechanistic Insight into the Effect of Polymer and NOM Coatings on Adhesion and Interactions between Nanoparticles and Bacteria

Engineered nanomaterials may be released to the environment and adversely affect the microbial community. Three generalized modes of interaction between NPs and bacteria that lead to observed toxicity are commonly described: physical contact between nanoparticles and cells (Type I), production of reactive oxygen species (ROS) (Type II), and release of toxic metal ions (Type III). Previous studies demonstrated that polymeric coatings and natural organic matter (NOM) may reduce antibacterial activities of nanoparticles. Thus, application of coatings is a mean to mitigate nanoparticle toxicity. However, coatings may have different effects depending on the mode of interaction between the NP and bacteria and the toxicity mechanism. The reasons for the different effects of coatings observed on nanoparticles having these different modes are still unclear. The primary objectives of this thesis are (i) to assess the effect that organic macromolecular coatings such as synthetic polymers and natural organic matter have on nanoparticle-microorganism interactions with type I, II, and III mode of action, and (ii) to determine the reasons for these effects. NZVI (type I), nano-TiO 2 (type II), and AgNPs (type III) were studied as representative nanoparticles. Poly(styrene sulfonate) (PSS), polyaspartate (PAP), humic acid, and carboxy methyl cellulose (sodium salt) (CMC) were used to coat nanoparticles. E. coli was exposed to bare and coated nanoparticles, and the bacterial concentration was determined at specific times using a plate counting technique. By observing different effects for the same coating on each type of nanoparticle, conclusions are made regarding iii the exact nature by which the adsorbed coatings (or in soluition) are affecting the observed growth inhibition of E. coli (toxicity).