Synchrotron Nano-FTIR Reveals Carbohydrate-Dependent Protein Conformational Changes at Bacterium-Nanoparticle Interfaces
Antimicrobial resistance motivates the development of approaches capable of probing nanoparticle-bacterium interactions with nanoscale sensitivity. Here, synchrotron infrared nano-spectroscopy (SINS) is applied to investigate interactions between carbohydrate-coated silica nanoparticles and the Gram-negative model bacterium Escherichia coli at the single-cell level. Silica nanoparticles (SiO2)…
The study explores the interactions between carbohydrate-coated silica nanoparticles and the Gram-negative bacterium Escherichia coli, employing synchrotron infrared nano-spectroscopy (SINS) at the single-cell level. The silica nanoparticles were coated with mannose, maltose, or trehalose, and their effects on bacterial envelope associations were investigated.
Correlative electron microscopy showed that carbohydrate-SiO2 coated nanoparticles were prominently associated with the bacterial envelope, specifically within the periplasmic region, unlike the bare SiO2 nanoparticles which showed no detectable association. SINS measurements, conducted directly on bacterial cells and at bacterium-nanoparticle interfaces, unveiled unique spectral signatures influenced by the type of coating.
The amide I band ratio, which reflects the relative contributions of -helical and beta-sheet protein secondary structures, was quantitatively analyzed. This analysis, coupled with position-based band-position assessment, helped characterize local spectral perturbations. The carbohydrate-SiO2 coating led to systematic changes in the I/I{beta} ratio, even at locations away from direct nanoparticle association sites, suggesting that the nanoparticles' influence extends beyond their direct contact points.
Further comparison between measurements taken on bacterial surfaces and at bacterium-nanoparticle interfaces revealed that the carbohydrate chemistry significantly modulated both the magnitude and spatial extent of the spectral perturbations. Among the tested carbohydrates, trehalose exhibited the most substantial interface-dependent shifts in the amide I band and a spectral component indicative of random-coil structures.
Overall, the findings illustrate that the surface chemistry of carbohydrates can modify nanoscale protein conformational changes at the nano-bio interface, underscoring the potential of SINS to discern chemically localized molecular responses at single-cell interfaces.
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