Graphene oxide (GO) is a promising
and remarkable nanomaterial that exhibits antimicrobial
activity due to its specific surface–interface interactions.
In the present work, for the first time, we have reported the antibacterial
activity of GO-coated surfaces prepared by two different methods (Hummers’
and improved, i.e., GOH and GOI) against bacterial
biofilm formation. The bacterial toxicity of the deposited GO-coated
surfaces was investigated for both Gram-negative (Escherichia
coli) and Gram-positive (Staphylococcus
aureus) models of bacteria. The mechanism of inhibition
is different on the coated surface than that in suspension, as determined
by measurement of the percentage inhibition of biofilm formation,
Ellman’s assay, and colony forming unit (CFU) studies. The
difference in the nature, degree of oxidative functionalities, and
size of the synthesized GO nanoparticles mitigates biofilm formation.
To better understand the antimicrobial mechanism of GO when coated
on surfaces, we were able to demonstrate that beside reactive oxygen
species-mediated oxidative stress, the physical properties of the
GO-coated substrate effectively inactivate bacterial cell proliferation,
which forms biofilms. Light and atomic force microscopy (AFM) images
display a higher inhibition in the proliferation of planktonic cells
in Gram-negative bacteria as compared to that in Gram-positive bacteria.
The existence of a smooth surface with fewer porous domains in GOI inhibits biofilm formation, as demonstrated by optical microscopy
and AFM images. The oxidative stress was found to be lower in the
coated surface as compared to that in the suspensions as the latter
enables exposure of both a large fraction of the active edges and
functionalities of the GO sheets. In suspension, GOH is
selective against S. aureus whereas
GOI showed inhibition toward E. coli. This study provides new insights to better understand the bactericidal
activity of GO-coated surfaces and contributes to the design of graphene-based
antimicrobial surface coatings, which will be valuable in biomedical
applications.
Bacterial cell division is a complex process brought about by the coordinated action of multiple proteins. Separation of daughter cells during the final stages of division involves cleavage of new cell wall laid down at the division septum. In E. coli, this process is governed by the action of N-acetylmuramoyl-L-alanine amidases AmiA/B/C, which are regulated by their LytM activators EnvC and NlpD. While much is known about the regulation of septum cleavage in E. coli, the mechanism of daughter cell separation is not clear in Caulobacter crescentus, a dimorphic crescent-shaped bacterium. In this work, we characterized the role of AmiC, the only annotated amidase in C. crescentus. AmiC from C. crescentus is functional in E. coli and restores cell separation defects seen in E. coli amidase mutants, suggesting that AmiC has septum splitting activity. The medial localization of AmiC was independent of DipM, an LytM domain-containing endopeptidase. Our results indicate that enzymatic activity is essential for medial recruitment of AmiC. Overexpression of AmiC causes cell separation defects and formation of chains. Finally, overexpression of AmiC in cells inhibited for cell division leads to lysis. Collectively, our findings reveal that regulation of daughter cell separation in C. crescentus differs from that of E. coli and can serve as a model system to study bacterial cytokinesis.
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