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PROBING BIOMECHANICAL CONSEQUENCES OF BACTERIAL ADHESION


n collaboration with Jerome Duval, biophysicist at the LCPME-LEM Nancy, we used multidisciplinary approaches to study the morphological, nanomechanical and electrohydrodynamic properties of well defined E. coli K-12 expresing various surface appendages (short and rigid Ag43 adhesins, longer and more flexible type 1 fimbriae and F pilus). Atomic force microscopy (AFM) and electrokinetics (electrophoresis) provided acces to key parameters, including membrane elasticity, turgor pressure, membrane permeability and charge or hydrophobicity distribution in bacterial envelop.

Our study investigated the biomechanical consequence of adhesion at a previously poorly explored scale and revealed the intimate relationship between surface adhesin  structure and flexibility and membrane elasticity and bacterial propensity to contract under hypertonic conditions.

• Francius, G. ; Poliakov, P. ; Merlin, J. ; Abe, Y. ; Ghigo, J.M. ; Merlin, C. ; Beloin, C. and J. Duval (2011) Bacterial surface appendages strongly impact on nanomechanical and electrokinetic properties of Escherichia coli cells subjected to osmotic stress. PLoS ONE 6(5):e20066


EARLY EVENTS OF BACTERIA:SURFACE INTERACTIONS

IThe molecular investigation of key events of biofilm formation in several bacterial models, including E. coli, showed that both initial interactions with abiotic surfaces and subsequent bacterial-bacterial interactions involve surface adhesive structures. These adhesins have been proposed to promote initial and mostly non-specific adhesion by overcoming antagonism between attracting and repulsing forces between the bacteria and the surface. Using approaches that develop on an hourly or dayly scale, bacterial irreversible attachment and biofilm formation was shown to be preceded by a reversible attachment step, in which most bacteria leave on-and-off the surface to join the planktonic phase. Although these studies underline the highly dynamic character of bacterial adhesion, many questions remain regarding the mechanisms and biophysics of surface adhesion because classical physico-chemical approaches handling equilibrium processes are not appropriate for satisfactorily describing the driving forces behind early steps of biofilm development.

In collaboration with Nelly Henry, biophysicist at the Institut Curie, we combined micrometric colloidal beads (as adhesion surfaces) and flow cytometry to develop a high-resolution analysis that reveals adhesin-dependent behavior in the very first steps of surface colonization by bacteria (see Figure). We performed a quantitative analysis of adhesion kinetics using several E. coli strains genetically engineered to produce well-characterized cell surface adhesins known to promote biofilm development. We revealed previously unknown adhesin-dependent behaviors, such as clear-cut differences in the very initial phases of surface colonization. We also demonstrated that initial adhesion correlates with almost instant surface property changes and that cell-to-cell association might serve as a surface colonization amplification mechanism. This study introduces an original approach to investigate the intricate relationships between the physico-chemistry of abiotic surfaces and bacterial adhesion.

• Beloin, C.; HouryA;, Froment , M. ; Ghigo J.M. and N. Henry. (2008). A short time scale colloidal system reveals early bacterial adhesion dynamics and adhesin-dependent behaviours. PLoS Biology 6(7): e167