Herrmann Moritz, Schneck Emanuel, Gutsmann Thomas, Brandenburg Klaus, Tanaka Motomu
Physical Chemistry of Biosystems, Institute of Physical Chemistry, University of Heidelberg, D69120 Heidelberg, Germany.
Soft Matter. 2015 Aug 14;11(30):6037-44. doi: 10.1039/c5sm01002k. Epub 2015 Jul 2.
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.
我们用细菌脂多糖（LPS Re和LPS Ra）单层建立了一个细菌膜模型，并通过使用与朗缪尔膜天平耦合的界面应力流变仪对其粘弹性特性进行了量化。在没有钙离子的情况下，LPS Re单层表现出纯粘性行为，而在存在Ca(2+)的情况下，相同的单层在压缩时经历了从粘性到弹性的转变。我们的结果首次证明，细菌外膜中的脂多糖在存在Ca(2+)的情况下可以形成二维弹性网络。与LPS Re单层不同，LPS Ra单层在存在和不存在Ca(2+)的情况下都表现出非常相似的流变转变，这表明即使在没有Ca(2+)的情况下，较长的糖链也可以形成二维物理凝胶。通过将单层暴露于抗菌肽鱼精蛋白，我们可以根据钙的存在直接监测细菌膜抗性的差异。
