Improved model systems for bacterial membranes from differing species: Theimportance of varying composition in PE/PG/cardiolipin ternary mixtures

Abstract

Steady-state fluorescence anisotropy and dynamic light scattering (DLS) were used to determine the thermotropic properties of lipid systems that act as models for bacterial membranes of Yersinia kristensenii and Proteus mirabilis. Lipid proportions of PE:PG:CL of 0.60:0.20:0.20 and 0.80:0.15:0.05, were used in order to mimic these two membranes respectively. We observed that the introduction of cardiolipin (CL) as a third lipid component of any PE:PG mixture, changes the system's properties considerably. The results obtained by these two techniques show that the main transition temperatures obtained are undoubtedly CL-dependent. Additionally AFM experiments were performed and these results show that even at small concentration CL produces important changes not only in the membrane thermotropic properties, but also in the bilayer structure. In summary, we were able to compare how low and high CL concentration affect bacterial membrane model system properties which can provide a further explanation for the different antibiotic susceptibilities reported for Y. kristensenii and P. mirabilis.

Keywords::

• Antimicrobial
• bacterial membranes
• cardiolipin
• dynamic light scattering
• fluorescence anisotropy
• atomic force microscopy

Acknowledgements

Partial financial support for this work was provided by FCT PTDC/SAU-FAR/111414/2009. This work has also been supported by Fundaçãopara a Ciência e a Tecnologia through grant no. PEst-C/EQB/LA0006/2011. S. C. Lopes and C. Neves thank FCT for a SFRH/BPD/34262/2006 and SFRH/BD/61137/2009 fellowship, respectively.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.