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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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Electrophoretic mobility of the bacteria.Electrophoretic mobility versus KNO3 salt concentration as measured for E2152, E2146, E2302, and E2498 strains (indicated). Solution pH∼6.6.
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pone-0020066-g006: Electrophoretic mobility of the bacteria.Electrophoretic mobility versus KNO3 salt concentration as measured for E2152, E2146, E2302, and E2498 strains (indicated). Solution pH∼6.6.

Mentions: The dependence of the electrophoretic mobility µ on ionic strength is reported for the bacterial strains E2152, E2146, E2302 and E2498 in Fig 6. For all strains, µ is negative, as expected for biological particles [70], and decreases in absolute value upon increase of salt concentration, in agreement with enhanced screening of the charges embedded within the cell wall and/or surface appendage by ions present in the medium. The electrokinetic behavior of the cells is further typical of that for soft particles, as judged from the presence of an asymptotic plateau value for the electrophoretic mobility at sufficiently high ionic strengths [66], particularly evident when patterns depicted in Fig 6 are plotted according to a linear scale in ionic strength. Additionally, similarly to the nanomechanical features of bacteria reported above, the presence/absence and nature of the surface appendage impact notably the electrokinetic properties of the cells.


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)

Electrophoretic mobility of the bacteria.Electrophoretic mobility versus KNO3 salt concentration as measured for E2152, E2146, E2302, and E2498 strains (indicated). Solution pH∼6.6.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0020066-g006: Electrophoretic mobility of the bacteria.Electrophoretic mobility versus KNO3 salt concentration as measured for E2152, E2146, E2302, and E2498 strains (indicated). Solution pH∼6.6.
Mentions: The dependence of the electrophoretic mobility µ on ionic strength is reported for the bacterial strains E2152, E2146, E2302 and E2498 in Fig 6. For all strains, µ is negative, as expected for biological particles [70], and decreases in absolute value upon increase of salt concentration, in agreement with enhanced screening of the charges embedded within the cell wall and/or surface appendage by ions present in the medium. The electrokinetic behavior of the cells is further typical of that for soft particles, as judged from the presence of an asymptotic plateau value for the electrophoretic mobility at sufficiently high ionic strengths [66], particularly evident when patterns depicted in Fig 6 are plotted according to a linear scale in ionic strength. Additionally, similarly to the nanomechanical features of bacteria reported above, the presence/absence and nature of the surface appendage impact notably the electrokinetic properties of the cells.

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