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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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Bacterial morphology observed by AFM in air (contact mode).AFM height and deflection images (z-scale = 200 nm) recorded in air for E coli cells immobilized on a PEI-coated glass surface. a) E2152 b) E2146 c) E2302 d) E2498. The white arrows correspond to the thickness of a layer that surrounds the bacteria (see details in main text).
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pone-0020066-g002: Bacterial morphology observed by AFM in air (contact mode).AFM height and deflection images (z-scale = 200 nm) recorded in air for E coli cells immobilized on a PEI-coated glass surface. a) E2152 b) E2146 c) E2302 d) E2498. The white arrows correspond to the thickness of a layer that surrounds the bacteria (see details in main text).

Mentions: In order to correlate the presence or absence of surface appendages with their genetic and phenotypic characteristics, the four bacterial strains considered in this study were first imaged in air using AFM in contact mode. For that purpose, the bacteria-coated PEI surfaces were rinsed and gently dried with nitrogen. Additionally, while the resolution of the height images was limited due to the large curvature of the analyzed rod-shaped cells, deflection images were found to be significantly more sensitive to bacterial surface relief and morphological details, as shown in Fig 2.


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 air (contact mode).AFM height and deflection images (z-scale = 200 nm) recorded in air for E coli cells immobilized on a PEI-coated glass surface. a) E2152 b) E2146 c) E2302 d) E2498. The white arrows correspond to the thickness of a layer that surrounds the bacteria (see details in main text).
© Copyright Policy
Related In: Results  -  Collection

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

pone-0020066-g002: Bacterial morphology observed by AFM in air (contact mode).AFM height and deflection images (z-scale = 200 nm) recorded in air for E coli cells immobilized on a PEI-coated glass surface. a) E2152 b) E2146 c) E2302 d) E2498. The white arrows correspond to the thickness of a layer that surrounds the bacteria (see details in main text).
Mentions: In order to correlate the presence or absence of surface appendages with their genetic and phenotypic characteristics, the four bacterial strains considered in this study were first imaged in air using AFM in contact mode. For that purpose, the bacteria-coated PEI surfaces were rinsed and gently dried with nitrogen. Additionally, while the resolution of the height images was limited due to the large curvature of the analyzed rod-shaped cells, deflection images were found to be significantly more sensitive to bacterial surface relief and morphological details, as shown in Fig 2.

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