Synchrotron FTIR microspectroscopy of Escherichia coli at single-cell scale under silver-induced stress conditions.
The present work was focused on elucidating biochemical changes in the model bacterium Escherichia coli exposed to ionic silver mediated stress, at a single-cell scale. In order to achieve this, in situ synchrotron Fourier-transform infrared (sFTIR) microspectroscopy was performed, for the first time, on individual cells by attenuated total reflectance (ATR) combined with the use of zinc-selenide hemisphere for high spatial resolution. In a first part, the potential of the method was evaluated on bacteria subjected to a lethal 100 μM AgNO(3) concentration for 2 h compared to untreated 100 % viable cells. Differences in cell composition were assessed for the C-H stretching and protein spectral regions, indicating that the inhibitory action was targeted against both fatty acids and proteins. Transmission electron microscopy (TEM) confirmed morphological damages of the cell ultrastructure. The relevance of ATR-sFTIR microspectroscopy for highlighting the heterogeneity in Ag(+)-mediated effects within a given bacterial population was also pointed out. In a second part, cells were exposed to sub-lethal Ag(+) concentrations (<10 μM AgNO(3)) tested under "dynamic" growth mode: early addition vs. pulse in the mid-exponential phase, and compared to simultaneously batch-grown untreated bacteria or cells sampled just before the pulse, respectively. sFTIR microspectroscopy and TEM imaging were performed in close relation with growth kinetics characterization. No significant effect of the Ag(+) pulses was detected, in accordance with macrokinetics data. For early-treated cells, effects on fatty acid composition were shown, although no major alteration of protein secondary structure was noticed. These partial effects were consistent with TEM observations and growth kinetics.
Université de Toulouse, INSA, UPS, INPT, LISBP, Toulouse, France. claire.saulou@grignon.inra.fr
Claire
C
Saulou
Frédéric
F
Jamme
Laurence
L
Girbal
Claude
C
Maranges
Isabelle
I
Fourquaux
Muriel
M
Cocaign-Bousquet
Paul
P
Dumas
Muriel
M
Mercier-Bonin
D004926:Escherichia coli / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D012835:Silver Nitrate / Q000494:pharmacology*; D059010:Single-Cell Analysis / Q000379:methods*; D017550:Spectroscopy, Fourier Transform Infrared / Q000295:instrumentation / Q000379:methods*; D013312:Stress, Physiological / Q000187:drug effects; D017356:Synchrotrons
D012835:Silver Nitrate