Molecular-level understanding of nanomaterial interactions with bacterial cell surfaces can facilitate design of antimicrobial and antifouling surfaces and inform assessment of potential consequences of nanomaterial release into the environment. Here, we investigate the interaction of cationic nanoparticles with the main surface components of Gram-positive bacteria: peptidoglycan and teichoic acids. We employed intact cells and isolated cell walls from wild typeBacillus subtilisand two mutant strains differing in wall teichoic acid composition to investigate interaction with gold nanoparticles functionalized with cationic, branched polyethylenimine. We quantified nanoparticle association with intact cells by flow cytometry and determined sites of interaction by solid-state31P- and13C-NMR spectroscopy. We find that wall teichoic acid structure and composition were important determinants for the extent of interaction with cationic gold nanoparticles. The nanoparticles interacted more with wall teichoic acids from the wild type and mutant lacking glucose in its wall teichoic acids than those from the mutant having wall teichoic acids lacking alanine and exhibiting more restricted molecular motion. Our experimental evidence supports the interpretation that electrostatic forces contributed to nanoparticle-cell interactions and that the accessibility of negatively charged moieties in teichoic acid chains influences the degree of interaction. The approaches employed in this study can be applied to engineered nanomaterials differing in core composition, shape, or surface functional groups as well as to other types of bacteria to elucidate the influence of nanoparticle and cell surface properties on interactions with Gram-positive bacteria.
Bibliographical noteFunding Information:
This work was supported by the National Science Foundation under the Center for Sustainable Nanotechnology, CHE-1503408. The CSN is part of the Centers for Chemical Innovation Program. We thank Charlie Fry, Director of the University of Wisconsin-Madison Magnetic Resonance Facility, for help with the T1 relaxation measurements, Letitia Yao at the University of Minnesota NMR facility for help with the solution 31P-NMR experiments, and Michael Liou for help with statistical analysis. The National Magnetic Resonance Facility at Madison is supported by NIH grants P41 GM103399 (NIGMS) and P41GM66326 (NIGMS). Additional equipment was purchased with funds from the University of Wisconsin, NIH (RR02781, RR08438), NSF (DMB-8415048, OIA-9977486, BIR-9214394), and USDA. The Bruker AVANCE III 500 NMR spectrometer was supported by a UW2020 grant and a generous gi from Paul J. and Margaret M. Bender. The solution NMR conducted at University of Minnesota was supported by the Office of the Vice President of Research, College of Science and Engineering, and the Department of Chemistry at the University of Minnesota.