Reproduction of fatty acid vesicles

Compartmentalization is an essential step for the origin of life to allow for the formation of more complex biotic building blocks. Possibly in early life preliminary compartments were formed out of prebiotic molecules, such as fatty acids. These molecules organize in bilayers at neutral pH and they show intriguing behavior with respect to self-reproduction of vesicles [1], in that fast addition of fatty acid at high pH to preexisting seed vesicles at neutral pH results in a fast formation of new vesicles with a size distribution that is closely related to that of the seed vesicles. The mechanism behind this so-called matrix effect is still a puzzle. One possibility would be that the fatty acids insert in the outer monolayer of the vesicle and that an excess of material in the outer leaflet with respect to the inner leaflet is then the driving force for budding and subsequent fission. In order to test this possible mechanism, we varied the rate of addition (insertion) of the new material. Slow addition would give the system time for movement of fatty acids from the outer leaflet to the inner leaflet and thus to remove this imbalance. Our results show that such a decrease of the addition rate indeed leads to growth of the vesicles instead of division, supporting our hypothesis. We also found, by including a fluorescent dye which is self-quenching at high concentrations, that during the fission process the content of the vesicles does not leak to the exterior. These observations agree well with results and predictions from coarse-grained molecular dynamics [2] and provide a plausible mechanism for the matrix effect [1].[1] Luisi et al. J. Phys. Chem. B 2008, 112, 14655-14664 [2] Markvoort et al., in preparation