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Bacterial surface appendages strongly impact nanomechanical and electrokinetic properties of Escherichia coli cells subjected to osmotic stress.

Francius G, Polyakov P, Merlin J, Abe Y, Ghigo JM, Merlin C, Beloin C, Duval JF - PLoS ONE (2011)

Bottom Line: Additionally, for a given surface appendage, the magnitude of the nanomechanical parameters decreases significantly when increasing bulk salt concentration.This effect is ascribed to a bacterial exoosmotic water loss resulting in a combined contraction of bacterial cytoplasm together with an electrostatically-driven shrinkage of the surface appendages.Altogether, AFM and electrokinetic results clearly demonstrate the intimate relationship between structure/flexibility and charge of bacterial envelope and propensity of bacterium and surface appendages to contract under hypertonic conditions.

View Article: PubMed Central - PubMed

Affiliation: Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, Nancy Université, CNRS UMR7564, Villers-lès-Nancy, France. gregory.francius@lcpme.cnrs-nancy.fr

ABSTRACT
The physicochemical properties and dynamics of bacterial envelope, play a major role in bacterial activity. In this study, the morphological, nanomechanical and electrohydrodynamic properties of Escherichia coli K-12 mutant cells were thoroughly investigated as a function of bulk medium ionic strength using atomic force microscopy (AFM) and electrokinetics (electrophoresis). Bacteria were differing according to genetic alterations controlling the production of different surface appendages (short and rigid Ag43 adhesins, longer and more flexible type 1 fimbriae and F pilus). From the analysis of the spatially resolved force curves, it is shown that cells elasticity and turgor pressure are not only depending on bulk salt concentration but also on the presence/absence and nature of surface appendage. In 1 mM KNO(3), cells without appendages or cells surrounded by Ag43 exhibit large Young moduli and turgor pressures (∼700-900 kPa and ∼100-300 kPa respectively). Under similar ionic strength condition, a dramatic ∼50% to ∼70% decrease of these nanomechanical parameters was evidenced for cells with appendages. Qualitatively, such dependence of nanomechanical behavior on surface organization remains when increasing medium salt content to 100 mM, even though, quantitatively, differences are marked to a much smaller extent. Additionally, for a given surface appendage, the magnitude of the nanomechanical parameters decreases significantly when increasing bulk salt concentration. This effect is ascribed to a bacterial exoosmotic water loss resulting in a combined contraction of bacterial cytoplasm together with an electrostatically-driven shrinkage of the surface appendages. The former process is demonstrated upon AFM analysis, while the latter, inaccessible upon AFM imaging, is inferred from electrophoretic data interpreted according to advanced soft particle electrokinetic theory. Altogether, AFM and electrokinetic results clearly demonstrate the intimate relationship between structure/flexibility and charge of bacterial envelope and propensity of bacterium and surface appendages to contract under hypertonic conditions.

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Related in: MedlinePlus

Bacterial morphology observed by AFM in aqueous medium (contact mode).AFM height and deflection images (z-scale = 2 µm and d-scale = 50 nm) recorded in 1 mM (left) and 100 mM (right) KNO3 aqueous solution for a single E. coli cell immobilized on a PEI-coated glass surface (z-scale = 2 µm and d-scale = 50 nm). a) E2152 b) E2146 c) E2302 d) E2498.
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pone-0020066-g003: Bacterial morphology observed by AFM in aqueous medium (contact mode).AFM height and deflection images (z-scale = 2 µm and d-scale = 50 nm) recorded in 1 mM (left) and 100 mM (right) KNO3 aqueous solution for a single E. coli cell immobilized on a PEI-coated glass surface (z-scale = 2 µm and d-scale = 50 nm). a) E2152 b) E2146 c) E2302 d) E2498.

Mentions: Following the previous findings, attempts were done to image the various bacteria in 1 mM and 100 mM KNO3 aqueous electrolyte so as to appreciate the dynamics of the above identified surface structures with varying salt medium content. Unfortunately, AFM technique used in contact mode turned to be inappropriate for imaging refined details pertaining to the bacterial surface ultrastructures of interest under wet conditions, as illustrated in Fig 3. This difficulty is imputed to the easy dislodging of the surface appendages by the AFM tip operating in fluid media according to contact mode, argument already mentioned by several authors [39], [97]. The required stress exerted by the tip on the bacterial structure for appropriate imaging of flexible F-pili or fimbriae filaments probably exceeds the forces responsible for their anchoring to the cell membrane and/or leads there to spatial displacement, thus rendering inefficient any surface scan for unraveling morphological details. Despite this limitation, images of bacteria as depicted in Fig 3 allow for retrieving quantitative morphological information for the bacteria as a whole, in particular their propensity to swell or shrink when changing salt concentration.


Bacterial surface appendages strongly impact nanomechanical and electrokinetic properties of Escherichia coli cells subjected to osmotic stress.

Francius G, Polyakov P, Merlin J, Abe Y, Ghigo JM, Merlin C, Beloin C, Duval JF - PLoS ONE (2011)

Bacterial morphology observed by AFM in aqueous medium (contact mode).AFM height and deflection images (z-scale = 2 µm and d-scale = 50 nm) recorded in 1 mM (left) and 100 mM (right) KNO3 aqueous solution for a single E. coli cell immobilized on a PEI-coated glass surface (z-scale = 2 µm and d-scale = 50 nm). a) E2152 b) E2146 c) E2302 d) E2498.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3105017&req=5

pone-0020066-g003: Bacterial morphology observed by AFM in aqueous medium (contact mode).AFM height and deflection images (z-scale = 2 µm and d-scale = 50 nm) recorded in 1 mM (left) and 100 mM (right) KNO3 aqueous solution for a single E. coli cell immobilized on a PEI-coated glass surface (z-scale = 2 µm and d-scale = 50 nm). a) E2152 b) E2146 c) E2302 d) E2498.
Mentions: Following the previous findings, attempts were done to image the various bacteria in 1 mM and 100 mM KNO3 aqueous electrolyte so as to appreciate the dynamics of the above identified surface structures with varying salt medium content. Unfortunately, AFM technique used in contact mode turned to be inappropriate for imaging refined details pertaining to the bacterial surface ultrastructures of interest under wet conditions, as illustrated in Fig 3. This difficulty is imputed to the easy dislodging of the surface appendages by the AFM tip operating in fluid media according to contact mode, argument already mentioned by several authors [39], [97]. The required stress exerted by the tip on the bacterial structure for appropriate imaging of flexible F-pili or fimbriae filaments probably exceeds the forces responsible for their anchoring to the cell membrane and/or leads there to spatial displacement, thus rendering inefficient any surface scan for unraveling morphological details. Despite this limitation, images of bacteria as depicted in Fig 3 allow for retrieving quantitative morphological information for the bacteria as a whole, in particular their propensity to swell or shrink when changing salt concentration.

Bottom Line: Additionally, for a given surface appendage, the magnitude of the nanomechanical parameters decreases significantly when increasing bulk salt concentration.This effect is ascribed to a bacterial exoosmotic water loss resulting in a combined contraction of bacterial cytoplasm together with an electrostatically-driven shrinkage of the surface appendages.Altogether, AFM and electrokinetic results clearly demonstrate the intimate relationship between structure/flexibility and charge of bacterial envelope and propensity of bacterium and surface appendages to contract under hypertonic conditions.

View Article: PubMed Central - PubMed

Affiliation: Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, Nancy Université, CNRS UMR7564, Villers-lès-Nancy, France. gregory.francius@lcpme.cnrs-nancy.fr

ABSTRACT
The physicochemical properties and dynamics of bacterial envelope, play a major role in bacterial activity. In this study, the morphological, nanomechanical and electrohydrodynamic properties of Escherichia coli K-12 mutant cells were thoroughly investigated as a function of bulk medium ionic strength using atomic force microscopy (AFM) and electrokinetics (electrophoresis). Bacteria were differing according to genetic alterations controlling the production of different surface appendages (short and rigid Ag43 adhesins, longer and more flexible type 1 fimbriae and F pilus). From the analysis of the spatially resolved force curves, it is shown that cells elasticity and turgor pressure are not only depending on bulk salt concentration but also on the presence/absence and nature of surface appendage. In 1 mM KNO(3), cells without appendages or cells surrounded by Ag43 exhibit large Young moduli and turgor pressures (∼700-900 kPa and ∼100-300 kPa respectively). Under similar ionic strength condition, a dramatic ∼50% to ∼70% decrease of these nanomechanical parameters was evidenced for cells with appendages. Qualitatively, such dependence of nanomechanical behavior on surface organization remains when increasing medium salt content to 100 mM, even though, quantitatively, differences are marked to a much smaller extent. Additionally, for a given surface appendage, the magnitude of the nanomechanical parameters decreases significantly when increasing bulk salt concentration. This effect is ascribed to a bacterial exoosmotic water loss resulting in a combined contraction of bacterial cytoplasm together with an electrostatically-driven shrinkage of the surface appendages. The former process is demonstrated upon AFM analysis, while the latter, inaccessible upon AFM imaging, is inferred from electrophoretic data interpreted according to advanced soft particle electrokinetic theory. Altogether, AFM and electrokinetic results clearly demonstrate the intimate relationship between structure/flexibility and charge of bacterial envelope and propensity of bacterium and surface appendages to contract under hypertonic conditions.

Show MeSH
Related in: MedlinePlus