1. The document investigates how surface properties of gold nanoparticles (AuNPs) functionalized with 3-mercaptopropylamine (MPNH2-AuNPs) interact with cell walls of different Bacillus subtilis mutant strains. 2. It finds that the tagE mutant strain, which is deficient in teichoic acid production, exhibited the highest percentage of cells bound to AuNPs. This suggests that teichoic acid is an important cell wall component in determining interactions with nanoparticles. 3. While cell surface charge measurements found no significant differences between mutant strains, the enhanced binding of AuNPs to tagE cells was not due to differences in surface charge. Instead,

1. 1 1 2 2 2 1
• This work was supported by the National Science Foundation under the
Center for Sustainable Nanotechnology, grant number CHE-1503408.
• Ariane Vartanian, Lisa Jacob and Prof. Cathy Murphy at University of
Illinois-Urbana
• Augsburg College URGO and McNair programs
• UMN Flow Core facility and Characterization Facilities
• Bacteria play various vital roles in the ecosystem, including nutrient cycling
and environmental remediation. At the bottom of the food chain, they also
become an important entry point for nanomaterials to potentially interact with
higher-trophic-level organisms.
Model bacterium, Bacillus subtilis allows us to :
• Identify mechanisms of nanomaterial toxicity mechanism to bacteria
• Investigate the importance of cell surface chemistry as well as NP surface
properties in NP-biological interactions.
Gram (-)Gram (+)
• AuNPs are functionalized with 3-mercaptopropylamine (MPNH2-AuNP).
Wall
Teichonic
acid
Peptidoglycan
Lipid bilayer
Using the two mutant strains of B. subtilis, the following questions can be
investigated:
• What components on WTA determine the interactions between cells and
NPs?
• Do the mutants exhibit different cell surface potentials?
• Are there differences in levels of NP toxicity to the mutants?
• Cell electrophoretic mobility were
measured to assess differences
in cell surface charges among
three strains.
• No significant differences were
observed.
• Elimination of D-alanine did not
appear to have a difference at a
macroscopic level.
• Modifications on WTA resulted in differences in interactions with NPs,
which suggests WTA is an important cell wall component to examine.
• The enhanced NP-binding to cell surfaces was not resulted from
differences in cell surface charges.
• Glucose-moieties found on WTA may be significant in providing steric
hindrance that reduces binding between cells and NPs.
• Perform force curve measurements to examine localized interactions of
nanoparticles with mutant bacterial cell walls.
• Computational modeling of WTA to examine interactions with NPs.
Bacillus subtilis
exposed to
MPNH2-AuNPs
tag E
S
B
4
9
1
ta
g
E
d
ltA
-4
-3
-2
-1
0
B . S u b tilis M u ta n t M o b ilitie s
Mobility
• Fluorescently labelled bacterial
cells pass through an
investigative beam and sorted
depending on fluorescence
emissions.
• Au-NP attached cells detected
by their strong side scattering
signals
• The percentage
differences in binding
between control and the
dltA with MPNH2-AuNPs
was negligible.
• Mutant tagE had the
highest percent of cells
bound to AuNPs.
8.9 + 3.0 nm
1 µm1 µm
S
B
4
9
1
-5
p
p
m
ta
g
E
-5
p
p
m
d
ltA
-5
p
p
m
0
2 0
4 0
6 0
%StainedCellswithAuNP
* * *
* * *
dlt A
200 nm
• Cells of varying
cultural densities
were grown for
calibration curve.
• NP-exposed cells
were grown and the
delays in growth
were fitted on
calibration curve.
Viability tests show no statistical
differences among mutants.
• Lipopolysaccharides on gram(-)
cell surfaces have been
demonstrated to be primary
sites for interactions with
MPNH2-AuNPs.
• What is the molecular-level
counter part on gram(+) cell
surfaces?
Feng, et. al., Chem. Sci., 2015, 5186.
Gunsolus, et al., Environ. Sci. Technol., 2015, 49, 10642.