Bacterial lipopolysaccharides form physically cross-linked, two-dimensional gels in the presence of divalent cations.

Soft Matter 2015 Aug 2;11(30):6037-44. Epub 2015 Jul 2.

Physical Chemistry of Biosystems, Institute of Physical Chemistry, University of Heidelberg, D69120 Heidelberg, Germany.

We established a bacterial membrane model with monolayers of bacterial lipopolysaccharides (LPS Re and LPS Ra) and quantified their viscoelastic properties by using an interfacial stress rheometer coupled to a Langmuir film balance. LPS Re monolayers exhibited purely viscous behaviour in the absence of calcium ions, while the same monolayers underwent a viscous-to-elastic transition upon compression in the presence of Ca(2+). Our results demonstrated for the first time that LPSs in bacterial outer membranes can form two-dimensional elastic networks in the presence of Ca(2+). Different from LPS Re monolayers, the LPS Ra monolayers showed a very similar rheological transition both in the presence and absence of Ca(2+), suggesting that longer saccharide chains can form 2D physical gels even in the absence of Ca(2+). By exposure of the monolayers to the antimicrobial peptide protamine, we could directly monitor the differences in resistance of bacterial membranes according to the presence of calcium.

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http://dx.doi.org/10.1039/c5sm01002kDOI Listing
August 2015

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